Topband: Topband Digest, Vol 240, Issue 23
Rune Øye
rune.e.oye at gmail.com
Sat Dec 24 05:33:16 EST 2022
RX loop at 3Y
Dear topbanders.
Reading todays topic on the reflector I thought I should jump in and
explain a bit. There are many reasons why we selected a RX loop for Bouvet.
· Space available at Cape Fie, this is the most difficult part.
· Diversity
· In band reception on 40 and 30m band.
The loop antenna is not a SALAD antenna but 4 x 1m square cross coupled
loops. The reason for 4 x loops was to overcome some thermal noise. Loops
are made of RG213 where I have used the screen of the RG213 as the element.
The LZ1AQ preamp mounted by the antenna has two functions in this setup.
1. Loop mode, typically for night-time use 160 to 40 meter band.
2. Vertical dipole mode 40 to 17meter daytime use.
3. Yes, it can be switched from the operator location / tent.
4. The LZ1AQ preamp is basically two preamps on one circuit board.
The loop will be pointed with the Null towards 160 and 80 meter antenna.
This will attenuate the 160/80m TX signal enough so you can RX on 160, 80,
and 40m with no signal ingress from other bands other than direct
harmonics.
The vertical dipole is mounted in the zero point or in front of the loop
and will be usable from 40m to 20/17m. A bit more output from the Vertical
dipole / preamp but spatial distance on those bands is good so no issue.
LOOP/VERT DIP>>preamp> Cat5>> DC Injector >> DX Engineering preamplifier >>
splitter.
The two PSU: 24V adjustable for the LZ1AQ preamp and the 12V PSU for the DX
- Engineering preamp, is HIFI linear PSU. I hope for minimal noise
ingress. Transmission line and switching is done using CAT5 cable.
Diversity reception.
RX loop to 160m TX antenna is around 350 to 400 meters, not a lot for
spatial reception on 160 but it is what it is. The Idea is to use the loop
together with the 160 and 80 TX antenna for Diversity.
The antenna was in use for 10 months at my location, not rural but not city
noise. I was working In-band from 160 to 17 meter with no issue. A few of
the expeditioners that have been to the rural places, claim they use the TX
antenna for RX. Yes, weather noise will always be the same but man made
noise should be minimal. I would love to bring an antenna with good
directivity for a few directions however, how on the planet are we going to
install that on the limited space we have.
Another issue is the weather on Bouvet that will keep us on the toes with
maintenance.
In case of “emergency”, I bring some BN202 cores and resistors in my
pocket. A 200–300-meter spare coax cable or CAT5 cable can always be
converted to a Bev antenna. The only direction for an Bev antenna could be
to the US west coast, not planned but you never know.
I am one of the team leaders for 3Y, responsible for “in the tent
equipment” and RX antenna. I have been working on this loop together with
LZ1AQ and hope this could give us some help on many bands. For the ones
that have tested in-band on an expedition, we all know that it doesn’t take
much ingress from a neighbouring band before it gets painful.
Thanks
Merry Xmas to all
73,
Rune LA7THA.
lør. 24. des. 2022 kl. 06:11 skrev <topband-request at contesting.com>:
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> Today's Topics:
>
> 1. Small Loop does not receive weak signal on 160m BOUVET RX
> SPOILER (JC)
> 2. Re: Small Loop does not receive weak signal on 160m BOUVET RX
> SPOILER (n4is at comcast.net)
> 3. Re: Small Loop does not receive weak signal on 160m BOUVET RX
> SPOILER (Wes)
> 4. Re: Small Loop does not receive weak signal on 160m BOUVET RX
> SPOILER (n4is at comcast.net)
> 5. Re: Small Loop does not receive weak signal on 160m BOUVET RX
> SPOILER (Jim Brown)
> 6. Re: Small Loop does not receive weak signal on 160m BOUVET RX
> SPOILER (n0tt1 at juno.com)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Fri, 23 Dec 2022 20:46:09 -0500
> From: "JC" <n4is at comcast.net>
> To: <topband at contesting.com>
> Subject: Topband: Small Loop does not receive weak signal on 160m
> BOUVET RX SPOILER
> Message-ID: <008c01d91739$856fed60$904fc820$@comcast.net>
> Content-Type: text/plain; charset="utf-8"
>
>
>
> Hi topband lovers
>
>
>
> Some friends contact me with deep concerns about the next Bouvet DX
> expedition receiver antenna called SALAD
>
>
>
> <
> http://www.lz1aq.signacor.com/docs/active-wideband-directional-antenna.php>
> Salad antenna
>
>
>
> I understand the concerns, Bouvet on 160m is a lifetime opportunity for
> most top-banders!
>
>
>
> When Doug NX4D, me N4IS and Dr Dallas started to try to understand the
> limitation of the new Waller Flag, the first big question was;
>
>
>
> How small a loop antenna can be to receive weak signal on 160, or MW?
>
>
>
> Dr. Dallas Lankford III (SK), measured the internal noise of a small loop.
> 15x15 FT on his quiet QTH, and wrote a paper with the derivation necessary
> to calculate the thermal noise of a small loop. The study most important
> point was:
>
>
>
> The sensitivity of small loop antennas can be limited by internally
> generated thermal noise which is a characteristic of the loop itself. Even
> amplifying the loop output with the lowest noise figure preamp available
> may not improve the loop sensitivity if manmade noise drops low enough
>
>
>
> The noise on Bouvet island will be very low, < -120 dBm at 500Hz, and for
> sure the internal thermal noise of the prosed RX antenna will limit the
> reception of weak signals on 160m, it may work on 80 and above, but for 160
> m, it will be a set up for failure.
>
>
>
> Why not a single, trustable beverage antenna over the ice or snow?? Or a
> proved K9AY or a DHDL??
>
>
>
> Below is the almost good transcript of the original pdf Flag Theory, for
> the long answer.
>
>
>
>
>
> 73?s
>
> JC
>
> N4IS
>
>
>
> Flag Theory
> Dallas Lankford, 1/31/09, rev. 9/9/09
>
>
> The derivation which follows is a variation of Belrose's classical
> derivation for ferrite rod loop antennas,
> ?Ferromagnetic Loop Aerials,? Wireless Engineer, February 1955, 41? 46.
>
>
> Some people who have not actually compared the signal output of a flag
> antenna to other small antennas have expressed their opinions to me that
> the signal output of a flag antenna has great attenuation compared to those
> other small antennas, such as loops and passive verticals. Their opinions
> are wrong. One should never express opinions which are based, say, on
> computer simulations alone, without actual measurements. The development
> below is based on physics (including Maxwell's equations), mathematics, and
> measurements.
>
>
> Measurements have confirmed that the flag signal to noise formula derived
> below is approximately correct despite EZNEC simulations to the contrary.
> For example, EZNEC simulation of a 15' square loop at 1 MHz predicts its
> gain is about +4 dbi, while on the other hand EZNEC simulation of a 15'
> square flag at 1 MHz predicts its gain is about ?46 dBi. But if you
> construct such a loop and such a flag and observe the signal strengths
> produced by them for daytime groundwave MW signals, you will find that the
> maximum loop and flag signal outputs are about equal. Although somewhat
> more difficult to judge, the nighttime sky wave MW signals are also about
> equal.
>
>
> Also, the signal to noise ratio formula below for flag arrays has been
> verified by manmade noise measurements in the 160 meter band using a
> smaller flag array than the MW flag array discussed below. Several years
> ago a similar signal to noise ratio formula for small un-tuned (broadband)
> loop antennas was verified at the low end of the NDB band.
>
>
> The signal voltage es in volts for a one turn loop of area A in meters and
> a signal of wavelength ? for a given radio wave is
>
>
>
> es = [2?A Es /?] COS(?)
>
>
>
> where Es is the signal strength in volts per meter and ? is the angle
> between the plane of the loop and the radio wave. It is well known that if
> an omnidirectional antenna, say a short whip, is attached to one of the
> output terminals of the loop and the phase difference between the loop and
> vertical and the amplitude of the whip are adjusted to produce a cardioid
> patten, then this occurs for a phase difference of 90 degrees and a whip
> amplitude equal to the amplitude of the loop, and the signal voltage in
> this case is
>
>
>
> es = [2?A Es /?] [1 + COS(?)]
>
> .
> Notice that the maximum signal voltage of the cardioid antenna is twice
> the maximum signal voltage of the loop (or vertical) alone.
>
> A flag antenna is a one turn loop antenna with a resistance of several
> hundred ohms inserted at some point into the one turn. With a rectangular
> turn, with the resistor appropriately placed and adjusted for the
> appropriate value, the flag antenna will generate a cardioid pattern. The
> exact mechanism by which this occurs is not given here. Nevertheless, based
> on measurements, the flag antenna signal voltage is approximately the same
> as the cardioid pattern given above. The difference between an actual flag
> and the cardioid pattern above is that an actual flag pattern is not a
> perfect cardioid for some cardioid geometries and resistors.
>
>
>
> In general a flag pattern will be
>
> es = [2?A Es /?] [1 + kCOS(?)]
>
>
>
> where k is a constant less than or equal to 1, say 0.90 for a ?poor? flag,
> to 0.99 or more for a ?good? flag. This has virtually no effect of the
> maximum signal pickup, but can have a significant effect on the null depth.
>
>
> 1- The thermal output noise voltage en for a loop is
>
>
>
> en = ?(4kTRB)
>
>
>
> where k (1.37 x 10^?23) is Boltzman's constant, T is the absolute
> temperature (taken as 290), (Belrose said:) R is the resistive component of
> the input impedance, (but also according to Belrose:) R = 2?fL where L is
> the loop inductance in Henrys, and B is the receiver bandwidth in Hertz.
>
>
>
> When the loop is rotated so that the signal is maximum, the signal to
> noise ratio is
>
>
>
> SNR = es/en = [2?A Es /?]/?(4kTRB) = [66Af/?(LB)]Es .
>
>
>
> The point of this formula is that the sensitivity of small loop antennas
> can be limited by internally generated thermal noise which is a
> characteristic of the loop itself. Even amplifying the loop output with the
> lowest noise figure preamp available may not improve the loop sensitivity
> if manmade noise drops low enough.
>
>
>
> Notice that on the one hand Belrose said R is the resistive component of
> the input impedance, but on the other hand R = 2?L. Well never mind. Based
> on personal on hands experience building small loops, I believe R = 2?L is
> approximately correct. What I believe Belrose meant is that R is the
> magnitude of the output impedance. For a flag antenna rotated so the signal
> is maximum, the signal to noise ratio is
>
>
>
> SNR = es/en = 2[2?A Es/?]/?(4kT?((2?fL)^2 + (Rflag)^2)B) =
> [322Af/?(?((2?fL)^2 + (Rflag)^2)B)]Es .
>
>
> Now let us calculate a SNR. Consider a flag 15' by 15' with inductance 24
> ?H at 1.0 MHz with 910 ohm flag
> resistor, and a bandwidth of B = 6000 Hz. Then A = 20.9 square meters and
> SNR = 2.86x10^6 Es . If Es is in
> microvolts, the SNR formula becomes SNR = 2.9 Es .
>
>
> Any phased array has loss (or in some cases gain) due to the phase
> difference of the signals from the two
> antennas which are combined to produce the nulls. This loss (or gain)
> depends on (1) the separation of the two
> antennas, (2) the arrival angle of the signal, and (3) the method used to
> phase the two flags. Let ? be the phase
> difference for a signal arriving at the two antennas. It can be shown by
> integrating the difference of the squares
> of the respective cosine functions that the amplitude A of the RMS voltage
> output of the combiner given RMS
> inputs with amplitudes e is equal to e?(1 ? COS( ?)) where e is the
> amplitude of the RMS signal, in other
> words,
> A=? 1
> 2??
> 0
> 2?
> 2 e2?cos?t??cos?t????2dt=e?2?1?cos???
>
>
> The gain or loss for a signal passing through the combiner due to their
> phase difference is thus ?(1 ? COS( ?)).
> Let us consider the best case, when the signal arrives from the maximum
> direction. For a spacing s between the
> centers of the flags, if the arrival angle is ?, then the distance d which
> determines the phase difference between
> the two signals is d = s COS(?). If s is given in feet, then the
> conversion of d to meters is d = s COS(?)/3.28.
>
>
> The reciprocal of the velocity of light 1/2.99x10^8 = 3.34 nS/meter is the
> time delay per meter of light (or radio
> waves) in air. So the phase difference of the two signals above in terms
> of time is T = 3.34 s COS(?)/3.28 nS
> when s is in meters. The phase difference in degrees is thus ? = 0.36Tf =
> 0.36 f x 3.34 s COS(?)/3.28 where f is
> the frequency of the signals in MHz. If additional delay T' is added
> (phase shift to generate nulls or to adjust the
> reception pattern), then the phase difference is ? = 0.36(T + T')f =
> 0.36f(T' + 3.34 s COS(?)/3.28) . If the
> additional delay is implemented with a length of coax L feet long with
> velocity factor VF, then the phase delay is
>
>
> ? = 0.37f(L/VF + s COS(?))
>
>
>
> where f is the frequency of the signal in MHz, s is in feet, L is in feet,
> and ? is the arrival angle.
>
>
> 2-
>
>
> In the case of the flag array above in the maximum direction there are two
> sources of delay, namely 60.6 feet of
> coax with velocity factor 0.70, and 100 feet of spacing between the two
> flag antennas. The phase delay at 1.0
> MHz for a 30 degree arrival angle is thus
>
>
> ? = 0.37 x 1.0 x (60.6/0.70 + 100 COS(30)) = 64.1 degrees.
>
>
> Thus the signal loss in the maximum direction at 30 degree arrival angle
> due to spacing and the phaser is
>
>
> ?(1 ? COS( 64.1)) = 0.75 or 20 log(0.75/2) = ?8.5 dB.
>
>
> Now comes the interesting part. What happens when we phase the WF array
> with dimensions and spacing given
> above? The flag thermal noise output doubles (two flags), and the flag
> signal output decreases (due to spacing
> and phaser loss), so the SNR is degraded by 14.5 dB to SNR = 0.55 Es .
>
>
>
> So a signal of 1.8 microvolts per meter is equivalent to the thermal noise
> floor of the flag array.
>
>
> On some occasions, when manmade noise drops to very low levels at my
> location, it appeared to fall below the
> thermal noise floor of the WF array. By that I mean that the
> characteristic ?sharp? manmade noise changed
> character to a ?smooth? hiss. To determine whether this was the case, I
> measured the manmade noise at my
> location for one of these low noise events at 1.83 MHz.
>
>
> To measure manmade noise at my location I converted one of the flags of my
> MW flag array to a loop. The loop was 15' by 15', or 20.9 square meters. I
> used my R-390A whose carrier (S) meter indicates signals as low as ?127
> dBm. The meter indication was 4 dB. Then I used an HP-8540B signal
> generator to determine the dBm value for 4 dB on the R-390A meter. It was
> ?122 dBm. Now the fun begins. The RDF of a loop for an arrival angle of 20
> degrees (the estimated wave tilt of manmade noise at 1.83 MHz) was 4 dB. So
> now manmade noise after factoring out the loop directionality was estimated
> as ?118 dBm.
>
>
>
> Field strength is open circuit voltage equivalent, which gives us ?112
> dBm. I measured MM noise on the R-390A with a 6 kHz BW. The conversion to
> 500 Hz is
>
>
>
> ?10 log(6000/500) = ?10.8,
>
>
>
> which gives us ?122.8 or ?123 dBm.
>
>
>
> The conversion to 500 Hz was necessary in order to be consistent with the
> SNR above which was calculated for a 500 Hz BW.
>
>
>
> The loop equation is es = 2?AEs/lambda = 0.41 Es, and 20 log(0.41) = ?7.7,
> rounded off to - 8, so we have -115 dBm, or 0.40 microvolts per meter for
> my lowest levels of manmade noise at 1.83 MHz in a 500 Hz bandwidth.
>
>
>
> This seemed impossibly low to me until I came across the ITU graph at
> right. Manmade noise at quiet rural locations may be even lower than 0.40
> microvolts per meter at 1.83 MHz. But what about the MW band? From the CCIR
> Report 322 we find that the manmade noise field strength on the average is
> about 10 dB higher at 1.0 MHz than 1.83 MHz, which would make it 1.26
> microvolts per meter at 1.0 MHz. Another 4 dB is added because of impedance
> mismatch between the R-390A and the loop, which brings manmade noise up to
> 2.0 microvolts per meter at 1.0 MHz. The RDF of one of these flags is about
> 7 dB, which lowers the manmade noise to 0.89 microvolts per meter.
> Observations in the 160 meter band do not seem to agree exactly with this
> analysis because flag thermal noise has never been heard on the MW flag
> array. But it would not surprise me at all if the flag array thermal noise
> floor were only a few dB below received minimum daytime manmade noise and
> that measurement error (for example, calib
> ration of my HP 8640B) accounts for the difference between measurement
> and theory. Also, observations with a flag array having flag areas half the
> size of the MW flag elements in the 160 meter band do confirm the signal to
> noise ratio formula; in this case, flag thermal noise does dominate minimum
> daytime manmade noise at my location (0.40 microvolts per meter field
> strength measured as described above.
>
>
>
>
>
>
>
>
>
> -------------- next part --------------
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>
> ------------------------------
>
> Message: 2
> Date: Fri, 23 Dec 2022 17:59:50 -0500
> From: <n4is at comcast.net>
> To: <topband at contesting.com>
> Subject: Re: Topband: Small Loop does not receive weak signal on 160m
> BOUVET RX SPOILER
> Message-ID: <007c01d91722$44a262c0$cde72840$@comcast.net>
> Content-Type: text/plain; charset="UTF-8"
>
> Doug NX4D asked me to add his comments,
>
> Hey JC and Topbanders, This is meant as a suggestion, not a criticism.
>
> The reason I sounded an alarm to JC was the concern that the proposed
> SALAD/ LZ1AQ 160m receive loops by the upcoming Bouvet DXpedition/ 3Y0J
> are much too small for receiving weak signals on 160m. With the current
> poor 160m condx, it would be a shame for them to go to all this trouble and
> expense, then not be able to pull in medium to weaker sigs with the loops.
> I would suggest the loop(s) be at least 10 ft (3m) diameter.
>
> >From experience I found that my original WF with small phased loops could
> not hear the weakest sigs others around me were hearing, due to being
> thermal noise limited. The solution was to make the loops much larger, by
> which I could then hear all sigs very well.
>
> 73/ NX4D
>
>
>
> ------------------------------
>
> Message: 3
> Date: Fri, 23 Dec 2022 19:45:28 -0700
> From: Wes <wes_n7ws at triconet.org>
> To: topband at contesting.com
> Subject: Re: Topband: Small Loop does not receive weak signal on 160m
> BOUVET RX SPOILER
> Message-ID: <c09bb4e3-60d6-402c-48e8-e903a539b9e8 at triconet.org>
> Content-Type: text/plain; charset=UTF-8; format=flowed
>
> All interesting.? But let me ask (and standby for flames) what is wrong
> with
> them simply listening on the TX antenna?
>
> I know, I know, conventional wisdom says that you can't possibly work 160
> DX
> without a separate RX antenna.? I'll confess that I am a little pistol and
> will
> never be on the TB Honor Roll, but I got on the band just to add another
> DXCC
> band to my collection (now nine).? I'm now at 144 confirmed, running just
> 500W
> and a 55' inverted-L on both TX and RX. Generally speaking I hear better
> that I
> get out.
>
> Looking at my chances of working 3Y the optimum time is their sunrise
> (~3:30Z)
> when I am in complete darkness and straight across the terminator. They
> will
> have the sunlit ocean to their rear and the S. American landmass toward
> me.?
> Maybe someone can enlighten me, but I fail to see how a directional
> antenna will
> improve the SNR of my signal at their end.
>
> Wes? N7WS
>
>
> On 12/23/2022 6:46 PM, JC wrote:
> > Hi topband lovers
> >
> >
> >
> > Some friends contact me with deep concerns about the next Bouvet DX
> expedition receiver antenna called SALAD
> >
> >
> >
> > <
> http://www.lz1aq.signacor.com/docs/active-wideband-directional-antenna.php>
> Salad antenna
> >
> >
> >
> > I understand the concerns, Bouvet on 160m is a lifetime opportunity for
> most top-banders!
> >
> >
> >
> > When Doug NX4D, me N4IS and Dr Dallas started to try to understand the
> limitation of the new Waller Flag, the first big question was;
> >
> >
> >
> > How small a loop antenna can be to receive weak signal on 160, or MW?
> >
> >
> >
> > Dr. Dallas Lankford III (SK), measured the internal noise of a small
> loop. 15x15 FT on his quiet QTH, and wrote a paper with the derivation
> necessary to calculate the thermal noise of a small loop. The study most
> important point was:
> >
> >
> >
> > The sensitivity of small loop antennas can be limited by internally
> generated thermal noise which is a characteristic of the loop itself. Even
> amplifying the loop output with the lowest noise figure preamp available
> may not improve the loop sensitivity if manmade noise drops low enough
> >
> >
> >
> > The noise on Bouvet island will be very low, < -120 dBm at 500Hz, and
> for sure the internal thermal noise of the prosed RX antenna will limit the
> reception of weak signals on 160m, it may work on 80 and above, but for 160
> m, it will be a set up for failure.
> >
> >
> >
> > Why not a single, trustable beverage antenna over the ice or snow?? Or a
> proved K9AY or a DHDL??
> >
> >
> >
> > Below is the almost good transcript of the original pdf Flag Theory, for
> the long answer.
> >
> >
> >
> >
> >
> > 73?s
> >
> > JC
> >
> > N4IS
> >
> >
> >
> > Flag Theory
> > Dallas Lankford, 1/31/09, rev. 9/9/09
> >
> >
> > The derivation which follows is a variation of Belrose's classical
> derivation for ferrite rod loop antennas,
> > ?Ferromagnetic Loop Aerials,? Wireless Engineer, February 1955, 41? 46.
> >
> >
> > Some people who have not actually compared the signal output of a flag
> antenna to other small antennas have expressed their opinions to me that
> the signal output of a flag antenna has great attenuation compared to those
> other small antennas, such as loops and passive verticals. Their opinions
> are wrong. One should never express opinions which are based, say, on
> computer simulations alone, without actual measurements. The development
> below is based on physics (including Maxwell's equations), mathematics, and
> measurements.
> >
> >
> > Measurements have confirmed that the flag signal to noise formula
> derived below is approximately correct despite EZNEC simulations to the
> contrary. For example, EZNEC simulation of a 15' square loop at 1 MHz
> predicts its gain is about +4 dbi, while on the other hand EZNEC simulation
> of a 15' square flag at 1 MHz predicts its gain is about ?46 dBi. But if
> you construct such a loop and such a flag and observe the signal strengths
> produced by them for daytime groundwave MW signals, you will find that the
> maximum loop and flag signal outputs are about equal. Although somewhat
> more difficult to judge, the nighttime sky wave MW signals are also about
> equal.
> >
> >
> > Also, the signal to noise ratio formula below for flag arrays has been
> verified by manmade noise measurements in the 160 meter band using a
> smaller flag array than the MW flag array discussed below. Several years
> ago a similar signal to noise ratio formula for small un-tuned (broadband)
> loop antennas was verified at the low end of the NDB band.
> >
> >
> > The signal voltage es in volts for a one turn loop of area A in meters
> and a signal of wavelength ? for a given radio wave is
> >
> >
> >
> > es = [2?A Es /?] COS(?)
> >
> >
> >
> > where Es is the signal strength in volts per meter and ? is the angle
> between the plane of the loop and the radio wave. It is well known that if
> an omnidirectional antenna, say a short whip, is attached to one of the
> output terminals of the loop and the phase difference between the loop and
> vertical and the amplitude of the whip are adjusted to produce a cardioid
> patten, then this occurs for a phase difference of 90 degrees and a whip
> amplitude equal to the amplitude of the loop, and the signal voltage in
> this case is
> >
> >
> >
> > es = [2?A Es /?] [1 + COS(?)]
> >
> > .
> > Notice that the maximum signal voltage of the cardioid antenna is twice
> the maximum signal voltage of the loop (or vertical) alone.
> >
> > A flag antenna is a one turn loop antenna with a resistance of several
> hundred ohms inserted at some point into the one turn. With a rectangular
> turn, with the resistor appropriately placed and adjusted for the
> appropriate value, the flag antenna will generate a cardioid pattern. The
> exact mechanism by which this occurs is not given here. Nevertheless, based
> on measurements, the flag antenna signal voltage is approximately the same
> as the cardioid pattern given above. The difference between an actual flag
> and the cardioid pattern above is that an actual flag pattern is not a
> perfect cardioid for some cardioid geometries and resistors.
> >
> >
> >
> > In general a flag pattern will be
> >
> > es = [2?A Es /?] [1 + kCOS(?)]
> >
> >
> >
> > where k is a constant less than or equal to 1, say 0.90 for a ?poor?
> flag, to 0.99 or more for a ?good? flag. This has virtually no effect of
> the maximum signal pickup, but can have a significant effect on the null
> depth.
> >
> >
> > 1- The thermal output noise voltage en for a loop is
> >
> >
> >
> > en = ?(4kTRB)
> >
> >
> >
> > where k (1.37 x 10^?23) is Boltzman's constant, T is the absolute
> temperature (taken as 290), (Belrose said:) R is the resistive component of
> the input impedance, (but also according to Belrose:) R = 2?fL where L is
> the loop inductance in Henrys, and B is the receiver bandwidth in Hertz.
> >
> >
> >
> > When the loop is rotated so that the signal is maximum, the signal to
> noise ratio is
> >
> >
> >
> > SNR = es/en = [2?A Es /?]/?(4kTRB) = [66Af/?(LB)]Es .
> >
> >
> >
> > The point of this formula is that the sensitivity of small loop antennas
> can be limited by internally generated thermal noise which is a
> characteristic of the loop itself. Even amplifying the loop output with the
> lowest noise figure preamp available may not improve the loop sensitivity
> if manmade noise drops low enough.
> >
> >
> >
> > Notice that on the one hand Belrose said R is the resistive component of
> the input impedance, but on the other hand R = 2?L. Well never mind. Based
> on personal on hands experience building small loops, I believe R = 2?L is
> approximately correct. What I believe Belrose meant is that R is the
> magnitude of the output impedance. For a flag antenna rotated so the signal
> is maximum, the signal to noise ratio is
> >
> >
> >
> > SNR = es/en = 2[2?A Es/?]/?(4kT?((2?fL)^2 + (Rflag)^2)B) =
> [322Af/?(?((2?fL)^2 + (Rflag)^2)B)]Es .
> >
> >
> > Now let us calculate a SNR. Consider a flag 15' by 15' with inductance
> 24 ?H at 1.0 MHz with 910 ohm flag
> > resistor, and a bandwidth of B = 6000 Hz. Then A = 20.9 square meters
> and SNR = 2.86x10^6 Es . If Es is in
> > microvolts, the SNR formula becomes SNR = 2.9 Es .
> >
> >
> > Any phased array has loss (or in some cases gain) due to the phase
> difference of the signals from the two
> > antennas which are combined to produce the nulls. This loss (or gain)
> depends on (1) the separation of the two
> > antennas, (2) the arrival angle of the signal, and (3) the method used
> to phase the two flags. Let ? be the phase
> > difference for a signal arriving at the two antennas. It can be shown by
> integrating the difference of the squares
> > of the respective cosine functions that the amplitude A of the RMS
> voltage output of the combiner given RMS
> > inputs with amplitudes e is equal to e?(1 ? COS( ?)) where e is the
> amplitude of the RMS signal, in other
> > words,
> > A=? 1
> > 2??
> > 0
> > 2?
> > 2 e2?cos?t??cos?t????2dt=e?2?1?cos???
> >
> >
> > The gain or loss for a signal passing through the combiner due to their
> phase difference is thus ?(1 ? COS( ?)).
> > Let us consider the best case, when the signal arrives from the maximum
> direction. For a spacing s between the
> > centers of the flags, if the arrival angle is ?, then the distance d
> which determines the phase difference between
> > the two signals is d = s COS(?). If s is given in feet, then the
> conversion of d to meters is d = s COS(?)/3.28.
> >
> >
> > The reciprocal of the velocity of light 1/2.99x10^8 = 3.34 nS/meter is
> the time delay per meter of light (or radio
> > waves) in air. So the phase difference of the two signals above in terms
> of time is T = 3.34 s COS(?)/3.28 nS
> > when s is in meters. The phase difference in degrees is thus ? = 0.36Tf
> = 0.36 f x 3.34 s COS(?)/3.28 where f is
> > the frequency of the signals in MHz. If additional delay T' is added
> (phase shift to generate nulls or to adjust the
> > reception pattern), then the phase difference is ? = 0.36(T + T')f =
> 0.36f(T' + 3.34 s COS(?)/3.28) . If the
> > additional delay is implemented with a length of coax L feet long with
> velocity factor VF, then the phase delay is
> >
> >
> > ? = 0.37f(L/VF + s COS(?))
> >
> >
> >
> > where f is the frequency of the signal in MHz, s is in feet, L is in
> feet, and ? is the arrival angle.
> >
> >
> > 2-
> >
> >
> > In the case of the flag array above in the maximum direction there are
> two sources of delay, namely 60.6 feet of
> > coax with velocity factor 0.70, and 100 feet of spacing between the two
> flag antennas. The phase delay at 1.0
> > MHz for a 30 degree arrival angle is thus
> >
> >
> > ? = 0.37 x 1.0 x (60.6/0.70 + 100 COS(30)) = 64.1 degrees.
> >
> >
> > Thus the signal loss in the maximum direction at 30 degree arrival angle
> due to spacing and the phaser is
> >
> >
> > ?(1 ? COS( 64.1)) = 0.75 or 20 log(0.75/2) = ?8.5 dB.
> >
> >
> > Now comes the interesting part. What happens when we phase the WF array
> with dimensions and spacing given
> > above? The flag thermal noise output doubles (two flags), and the flag
> signal output decreases (due to spacing
> > and phaser loss), so the SNR is degraded by 14.5 dB to SNR = 0.55 Es .
> >
> >
> >
> > So a signal of 1.8 microvolts per meter is equivalent to the thermal
> noise floor of the flag array.
> >
> >
> > On some occasions, when manmade noise drops to very low levels at my
> location, it appeared to fall below the
> > thermal noise floor of the WF array. By that I mean that the
> characteristic ?sharp? manmade noise changed
> > character to a ?smooth? hiss. To determine whether this was the case, I
> measured the manmade noise at my
> > location for one of these low noise events at 1.83 MHz.
> >
> >
> > To measure manmade noise at my location I converted one of the flags of
> my MW flag array to a loop. The loop was 15' by 15', or 20.9 square meters.
> I used my R-390A whose carrier (S) meter indicates signals as low as ?127
> dBm. The meter indication was 4 dB. Then I used an HP-8540B signal
> generator to determine the dBm value for 4 dB on the R-390A meter. It was
> ?122 dBm. Now the fun begins. The RDF of a loop for an arrival angle of 20
> degrees (the estimated wave tilt of manmade noise at 1.83 MHz) was 4 dB. So
> now manmade noise after factoring out the loop directionality was estimated
> as ?118 dBm.
> >
> >
> >
> > Field strength is open circuit voltage equivalent, which gives us ?112
> dBm. I measured MM noise on the R-390A with a 6 kHz BW. The conversion to
> 500 Hz is
> >
> >
> >
> > ?10 log(6000/500) = ?10.8,
> >
> >
> >
> > which gives us ?122.8 or ?123 dBm.
> >
> >
> >
> > The conversion to 500 Hz was necessary in order to be consistent with
> the SNR above which was calculated for a 500 Hz BW.
> >
> >
> >
> > The loop equation is es = 2?AEs/lambda = 0.41 Es, and 20 log(0.41) =
> ?7.7, rounded off to - 8, so we have -115 dBm, or 0.40 microvolts per meter
> for my lowest levels of manmade noise at 1.83 MHz in a 500 Hz bandwidth.
> >
> >
> >
> > This seemed impossibly low to me until I came across the ITU graph at
> right. Manmade noise at quiet rural locations may be even lower than 0.40
> microvolts per meter at 1.83 MHz. But what about the MW band? From the CCIR
> Report 322 we find that the manmade noise field strength on the average is
> about 10 dB higher at 1.0 MHz than 1.83 MHz, which would make it 1.26
> microvolts per meter at 1.0 MHz. Another 4 dB is added because of impedance
> mismatch between the R-390A and the loop, which brings manmade noise up to
> 2.0 microvolts per meter at 1.0 MHz. The RDF of one of these flags is about
> 7 dB, which lowers the manmade noise to 0.89 microvolts per meter.
> Observations in the 160 meter band do not seem to agree exactly with this
> analysis because flag thermal noise has never been heard on the MW flag
> array. But it would not surprise me at all if the flag array thermal noise
> floor were only a few dB below received minimum daytime manmade noise and
> that measurement error (for example, cal
> ibration of my HP 8640B) accounts for the difference between measurement
> and theory. Also, observations with a flag array having flag areas half the
> size of the MW flag elements in the 160 meter band do confirm the signal to
> noise ratio formula; in this case, flag thermal noise does dominate minimum
> daytime manmade noise at my location (0.40 microvolts per meter field
> strength measured as described above.
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> > _________________
> > Searchable Archives:http://www.contesting.com/_topband - Topband
> Reflector
>
>
> ------------------------------
>
> Message: 4
> Date: Fri, 23 Dec 2022 23:12:27 -0500
> From: <n4is at comcast.net>
> To: "'Wes'" <wes_n7ws at triconet.org>, <topband at contesting.com>
> Subject: Re: Topband: Small Loop does not receive weak signal on 160m
> BOUVET RX SPOILER
> Message-ID: <000401d9174d$f1ac6cb0$d5054610$@comcast.net>
> Content-Type: text/plain; charset="utf-8"
>
> Wes
>
> I missed the second question. How a receiving antenna can help on your
> signal there. The RX antenna is good as the directivity or RDF. Based on my
> measurements and extensive experiments with the Waller Flag, for 1 db
> improve in RDF you can get 2db or more on signal to noise ratio aiming at
> the signal, plus de rejection on side and back nulls. You can check more
> about this on my webinar at WWROF
>
>
> https://wwrof.org/webinar-archive/high-performance-rx-antennas-for-a-small-lot/
>
> I measured 2db over 100 tests or more, including using WSJT SN readings.
> It is a practical result, not just computer simulation.
>
> With a good RX antenna 11 to 12 dB RDF you can work 150 counties on 160
> any 12 month period. I did it for 10 years. Using a Waller Flag, Doug
> NX4D, worked 314 on 160m from a 1/5 acre lot. All CW.
>
> I started with a vertical WF on 2003, and an Horizontal Waller Flag in
> 2010, the noise here in my city lot is very high now, and my Vertical
> Waller Flag is down because the HWF does not see the vertical manmade
> noise, so I have no noise on the HWF. I worked in the last 10 year close to
> 300 countries on 160m, only CW, and I am now at 305, however I heard over
> 320 countries down here in South Florida from a city lot. The VWF can dig
> signals on CW 10 db below noise and my HWF can dig 20 db bellow noise, when
> you compare with the TX antenna. I can measure that as well, with 2
> instances on WSJT on my radio two identical receivers, a signal -20 SNR on
> the vertical shows a 0 db on the HWF.
>
> More information about the HWF here >
>
> https://wwrof.org/webinar-archive/n4is-waller-flag-construction/
>
> You can download the presentation too, Doug and I do not provide any
> additional support or question anymore, we spent hundred of hours on it and
> few people listened us.
>
> So, conclusion a RX antenna can dig you signal out of the noise.
>
> 73's
> JC
> N4IS
>
>
>
>
> -----Original Message-----
> From: Topband <topband-bounces+n4is=comcast.net at contesting.com> On Behalf
> Of Wes
> Sent: Friday, December 23, 2022 9:45 PM
> To: topband at contesting.com
> Subject: Re: Topband: Small Loop does not receive weak signal on 160m
> BOUVET RX SPOILER
>
> All interesting. But let me ask (and standby for flames) what is wrong
> with them simply listening on the TX antenna?
>
> I know, I know, conventional wisdom says that you can't possibly work 160
> DX without a separate RX antenna. I'll confess that I am a little pistol
> and will never be on the TB Honor Roll, but I got on the band just to add
> another DXCC band to my collection (now nine). I'm now at 144 confirmed,
> running just 500W and a 55' inverted-L on both TX and RX. Generally
> speaking I hear better that I get out.
>
> Looking at my chances of working 3Y the optimum time is their sunrise
> (~3:30Z) when I am in complete darkness and straight across the terminator.
> They will have the sunlit ocean to their rear and the S. American landmass
> toward me. Maybe someone can enlighten me, but I fail to see how a
> directional antenna will improve the SNR of my signal at their end.
>
> Wes N7WS
>
>
> On 12/23/2022 6:46 PM, JC wrote:
> > Hi topband lovers
> >
> >
> >
> > Some friends contact me with deep concerns about the next Bouvet DX
> > expedition receiver antenna called SALAD
> >
> >
> >
> >
> > <http://www.lz1aq.signacor.com/docs/active-wideband-directional-antenn
> > a.php> Salad antenna
> >
> >
> >
> > I understand the concerns, Bouvet on 160m is a lifetime opportunity for
> most top-banders!
> >
> >
> >
> > When Doug NX4D, me N4IS and Dr Dallas started to try to understand the
> > limitation of the new Waller Flag, the first big question was;
> >
> >
> >
> > How small a loop antenna can be to receive weak signal on 160, or MW?
> >
> >
> >
> > Dr. Dallas Lankford III (SK), measured the internal noise of a small
> loop. 15x15 FT on his quiet QTH, and wrote a paper with the derivation
> necessary to calculate the thermal noise of a small loop. The study most
> important point was:
> >
> >
> >
> > The sensitivity of small loop antennas can be limited by internally
> > generated thermal noise which is a characteristic of the loop itself.
> > Even amplifying the loop output with the lowest noise figure preamp
> > available may not improve the loop sensitivity if manmade noise drops
> > low enough
> >
> >
> >
> > The noise on Bouvet island will be very low, < -120 dBm at 500Hz, and
> for sure the internal thermal noise of the prosed RX antenna will limit the
> reception of weak signals on 160m, it may work on 80 and above, but for 160
> m, it will be a set up for failure.
> >
> >
> >
> > Why not a single, trustable beverage antenna over the ice or snow?? Or a
> proved K9AY or a DHDL??
> >
> >
> >
> > Below is the almost good transcript of the original pdf Flag Theory, for
> the long answer.
> >
> >
> >
> >
> >
> > 73?s
> >
> > JC
> >
> > N4IS
> >
> >
> >
> > Flag Theory
> > Dallas Lankford, 1/31/09, rev. 9/9/09
> >
> >
> > The derivation which follows is a variation of Belrose's classical
> > derivation for ferrite rod loop antennas, ?Ferromagnetic Loop Aerials,?
> Wireless Engineer, February 1955, 41? 46.
> >
> >
> > Some people who have not actually compared the signal output of a flag
> antenna to other small antennas have expressed their opinions to me that
> the signal output of a flag antenna has great attenuation compared to those
> other small antennas, such as loops and passive verticals. Their opinions
> are wrong. One should never express opinions which are based, say, on
> computer simulations alone, without actual measurements. The development
> below is based on physics (including Maxwell's equations), mathematics, and
> measurements.
> >
> >
> > Measurements have confirmed that the flag signal to noise formula
> derived below is approximately correct despite EZNEC simulations to the
> contrary. For example, EZNEC simulation of a 15' square loop at 1 MHz
> predicts its gain is about +4 dbi, while on the other hand EZNEC simulation
> of a 15' square flag at 1 MHz predicts its gain is about ?46 dBi. But if
> you construct such a loop and such a flag and observe the signal strengths
> produced by them for daytime groundwave MW signals, you will find that the
> maximum loop and flag signal outputs are about equal. Although somewhat
> more difficult to judge, the nighttime sky wave MW signals are also about
> equal.
> >
> >
> > Also, the signal to noise ratio formula below for flag arrays has been
> verified by manmade noise measurements in the 160 meter band using a
> smaller flag array than the MW flag array discussed below. Several years
> ago a similar signal to noise ratio formula for small un-tuned (broadband)
> loop antennas was verified at the low end of the NDB band.
> >
> >
> > The signal voltage es in volts for a one turn loop of area A in meters
> > and a signal of wavelength ? for a given radio wave is
> >
> >
> >
> > es = [2?A Es /?] COS(?)
> >
> >
> >
> > where Es is the signal strength in volts per meter and ? is the angle
> > between the plane of the loop and the radio wave. It is well known
> > that if an omnidirectional antenna, say a short whip, is attached to
> > one of the output terminals of the loop and the phase difference
> > between the loop and vertical and the amplitude of the whip are
> > adjusted to produce a cardioid patten, then this occurs for a phase
> > difference of 90 degrees and a whip amplitude equal to the amplitude
> > of the loop, and the signal voltage in this case is
> >
> >
> >
> > es = [2?A Es /?] [1 + COS(?)]
> >
> > .
> > Notice that the maximum signal voltage of the cardioid antenna is twice
> the maximum signal voltage of the loop (or vertical) alone.
> >
> > A flag antenna is a one turn loop antenna with a resistance of several
> hundred ohms inserted at some point into the one turn. With a rectangular
> turn, with the resistor appropriately placed and adjusted for the
> appropriate value, the flag antenna will generate a cardioid pattern. The
> exact mechanism by which this occurs is not given here. Nevertheless, based
> on measurements, the flag antenna signal voltage is approximately the same
> as the cardioid pattern given above. The difference between an actual flag
> and the cardioid pattern above is that an actual flag pattern is not a
> perfect cardioid for some cardioid geometries and resistors.
> >
> >
> >
> > In general a flag pattern will be
> >
> > es = [2?A Es /?] [1 + kCOS(?)]
> >
> >
> >
> > where k is a constant less than or equal to 1, say 0.90 for a ?poor?
> flag, to 0.99 or more for a ?good? flag. This has virtually no effect of
> the maximum signal pickup, but can have a significant effect on the null
> depth.
> >
> >
> > 1- The thermal output noise voltage en for a loop is
> >
> >
> >
> > en = ?(4kTRB)
> >
> >
> >
> > where k (1.37 x 10^?23) is Boltzman's constant, T is the absolute
> temperature (taken as 290), (Belrose said:) R is the resistive component of
> the input impedance, (but also according to Belrose:) R = 2?fL where L is
> the loop inductance in Henrys, and B is the receiver bandwidth in Hertz.
> >
> >
> >
> > When the loop is rotated so that the signal is maximum, the signal to
> > noise ratio is
> >
> >
> >
> > SNR = es/en = [2?A Es /?]/?(4kTRB) = [66Af/?(LB)]Es .
> >
> >
> >
> > The point of this formula is that the sensitivity of small loop antennas
> can be limited by internally generated thermal noise which is a
> characteristic of the loop itself. Even amplifying the loop output with the
> lowest noise figure preamp available may not improve the loop sensitivity
> if manmade noise drops low enough.
> >
> >
> >
> > Notice that on the one hand Belrose said R is the resistive component
> > of the input impedance, but on the other hand R = 2?L. Well never
> > mind. Based on personal on hands experience building small loops, I
> > believe R = 2?L is approximately correct. What I believe Belrose meant
> > is that R is the magnitude of the output impedance. For a flag antenna
> > rotated so the signal is maximum, the signal to noise ratio is
> >
> >
> >
> > SNR = es/en = 2[2?A Es/?]/?(4kT?((2?fL)^2 + (Rflag)^2)B) =
> [322Af/?(?((2?fL)^2 + (Rflag)^2)B)]Es .
> >
> >
> > Now let us calculate a SNR. Consider a flag 15' by 15' with inductance
> > 24 ?H at 1.0 MHz with 910 ohm flag resistor, and a bandwidth of B =
> > 6000 Hz. Then A = 20.9 square meters and SNR = 2.86x10^6 Es . If Es is
> in microvolts, the SNR formula becomes SNR = 2.9 Es .
> >
> >
> > Any phased array has loss (or in some cases gain) due to the phase
> > difference of the signals from the two antennas which are combined to
> > produce the nulls. This loss (or gain) depends on (1) the separation
> > of the two antennas, (2) the arrival angle of the signal, and (3) the
> > method used to phase the two flags. Let ? be the phase difference for
> > a signal arriving at the two antennas. It can be shown by integrating
> > the difference of the squares of the respective cosine functions that
> > the amplitude A of the RMS voltage output of the combiner given RMS
> > inputs with amplitudes e is equal to e?(1 ? COS( ?)) where e is the
> > amplitude of the RMS signal, in other words, A=? 1 2??
> > 0
> > 2?
> > 2 e2?cos?t??cos?t????2dt=e?2?1?cos???
> >
> >
> > The gain or loss for a signal passing through the combiner due to their
> phase difference is thus ?(1 ? COS( ?)).
> > Let us consider the best case, when the signal arrives from the
> > maximum direction. For a spacing s between the centers of the flags,
> > if the arrival angle is ?, then the distance d which determines the
> phase difference between the two signals is d = s COS(?). If s is given in
> feet, then the conversion of d to meters is d = s COS(?)/3.28.
> >
> >
> > The reciprocal of the velocity of light 1/2.99x10^8 = 3.34 nS/meter is
> > the time delay per meter of light (or radio
> > waves) in air. So the phase difference of the two signals above in
> > terms of time is T = 3.34 s COS(?)/3.28 nS when s is in meters. The
> > phase difference in degrees is thus ? = 0.36Tf = 0.36 f x 3.34 s
> > COS(?)/3.28 where f is the frequency of the signals in MHz. If
> > additional delay T' is added (phase shift to generate nulls or to
> > adjust the reception pattern), then the phase difference is ? = 0.36(T
> > + T')f = 0.36f(T' + 3.34 s COS(?)/3.28) . If the additional delay is
> > implemented with a length of coax L feet long with velocity factor VF,
> > then the phase delay is
> >
> >
> > ? = 0.37f(L/VF + s COS(?))
> >
> >
> >
> > where f is the frequency of the signal in MHz, s is in feet, L is in
> feet, and ? is the arrival angle.
> >
> >
> > 2-
> >
> >
> > In the case of the flag array above in the maximum direction there are
> > two sources of delay, namely 60.6 feet of coax with velocity factor
> > 0.70, and 100 feet of spacing between the two flag antennas. The phase
> > delay at 1.0 MHz for a 30 degree arrival angle is thus
> >
> >
> > ? = 0.37 x 1.0 x (60.6/0.70 + 100 COS(30)) = 64.1 degrees.
> >
> >
> > Thus the signal loss in the maximum direction at 30 degree arrival
> > angle due to spacing and the phaser is
> >
> >
> > ?(1 ? COS( 64.1)) = 0.75 or 20 log(0.75/2) = ?8.5 dB.
> >
> >
> > Now comes the interesting part. What happens when we phase the WF
> > array with dimensions and spacing given above? The flag thermal noise
> > output doubles (two flags), and the flag signal output decreases (due to
> spacing and phaser loss), so the SNR is degraded by 14.5 dB to SNR = 0.55
> Es .
> >
> >
> >
> > So a signal of 1.8 microvolts per meter is equivalent to the thermal
> noise floor of the flag array.
> >
> >
> > On some occasions, when manmade noise drops to very low levels at my
> > location, it appeared to fall below the thermal noise floor of the WF
> > array. By that I mean that the characteristic ?sharp? manmade noise
> > changed character to a ?smooth? hiss. To determine whether this was the
> case, I measured the manmade noise at my location for one of these low
> noise events at 1.83 MHz.
> >
> >
> > To measure manmade noise at my location I converted one of the flags of
> my MW flag array to a loop. The loop was 15' by 15', or 20.9 square meters.
> I used my R-390A whose carrier (S) meter indicates signals as low as ?127
> dBm. The meter indication was 4 dB. Then I used an HP-8540B signal
> generator to determine the dBm value for 4 dB on the R-390A meter. It was
> ?122 dBm. Now the fun begins. The RDF of a loop for an arrival angle of 20
> degrees (the estimated wave tilt of manmade noise at 1.83 MHz) was 4 dB. So
> now manmade noise after factoring out the loop directionality was estimated
> as ?118 dBm.
> >
> >
> >
> > Field strength is open circuit voltage equivalent, which gives us ?112
> > dBm. I measured MM noise on the R-390A with a 6 kHz BW. The conversion
> > to 500 Hz is
> >
> >
> >
> > ?10 log(6000/500) = ?10.8,
> >
> >
> >
> > which gives us ?122.8 or ?123 dBm.
> >
> >
> >
> > The conversion to 500 Hz was necessary in order to be consistent with
> the SNR above which was calculated for a 500 Hz BW.
> >
> >
> >
> > The loop equation is es = 2?AEs/lambda = 0.41 Es, and 20 log(0.41) =
> ?7.7, rounded off to - 8, so we have -115 dBm, or 0.40 microvolts per meter
> for my lowest levels of manmade noise at 1.83 MHz in a 500 Hz bandwidth.
> >
> >
> >
> > This seemed impossibly low to me until I came across the ITU graph at
> right. Manmade noise at quiet rural locations may be even lower than 0.40
> microvolts per meter at 1.83 MHz. But what about the MW band? From the CCIR
> Report 322 we find that the manmade noise field strength on the average is
> about 10 dB higher at 1.0 MHz than 1.83 MHz, which would make it 1.26
> microvolts per meter at 1.0 MHz. Another 4 dB is added because of impedance
> mismatch between the R-390A and the loop, which brings manmade noise up to
> 2.0 microvolts per meter at 1.0 MHz. The RDF of one of these flags is about
> 7 dB, which lowers the manmade noise to 0.89 microvolts per meter.
> Observations in the 160 meter band do not seem to agree exactly with this
> analysis because flag thermal noise has never been heard on the MW flag
> array. But it would not surprise me at all if the flag array thermal noise
> floor were only a few dB below received minimum daytime manmade noise and
> that measurement error (for example, cal
> ibration of my HP 8640B) accounts for the difference between measurement
> and theory. Also, observations with a flag array having flag areas half the
> size of the MW flag elements in the 160 meter band do confirm the signal to
> noise ratio formula; in this case, flag thermal noise does dominate minimum
> daytime manmade noise at my location (0.40 microvolts per meter field
> strength measured as described above.
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> > _________________
> > Searchable Archives:http://www.contesting.com/_topband - Topband
> > Reflector
>
> _________________
> Searchable Archives: http://www.contesting.com/_topband - Topband
> Reflector
>
>
>
> ------------------------------
>
> Message: 5
> Date: Fri, 23 Dec 2022 20:34:56 -0800
> From: Jim Brown <jim at audiosystemsgroup.com>
> To: topband at contesting.com
> Subject: Re: Topband: Small Loop does not receive weak signal on 160m
> BOUVET RX SPOILER
> Message-ID:
> <fa7fb9a5-e630-63f1-388f-d0cc1ef364b3 at audiosystemsgroup.com>
> Content-Type: text/plain; charset=UTF-8; format=flowed
>
> On 12/23/2022 8:12 PM, n4is at comcast.net wrote:
> > I missed the second question.
>
> I understand Wes's point quite well. I have friends who operate 6M from
> very remote places where there is no local noise to light up rare grids.
> They're rare because no one lives there to create noise.
>
> The vast majority of active hams are surrounded by a LOT of noise
> generated by electronics in their own homes and those of their
> neighbors, as well from power lines, street lighting, and other sources.
> WE are the ones who most need serious RX antennas (and also to devote
> our energies to killing as much as possible of our noise at the source).
>
> The difference in local noise between what WE hear and what the DX hears
> can easily be 20 dB.
>
> What Wes may be missing is that the DX may be hearing stations from
> multiple directions, callers from areas with easy prop to them may be
> MUCH stronger than callers from areas that must be worked under exactly
> the right conditions and for rather short time windows, and that those
> loud callers may have a tendency to not stop calling. :) THAT'S where
> serious RX antennas can help at the DX location.
>
> And as both Wes and I have observed, great system engineering involves
> devising systems to solve specific problems. One size never fits all.
>
> 73, Jim K9YC
>
>
> ------------------------------
>
> Message: 6
> Date: Fri, 23 Dec 2022 23:03:36 -0600
> From: <n0tt1 at juno.com>
> To: wes_n7ws at triconet.org,topband at contesting.com
> Subject: Re: Topband: Small Loop does not receive weak signal on 160m
> BOUVET RX SPOILER
> Message-ID: <AABT4PCM7AJXGZKA at smtpout03.vgs.untd.com>
> Content-Type: text/plain; charset=utf-8
>
> I was one of the 160m ops at "nearby" FT5XO. I can tell you that when
> the
> WX was good the TX antennas worked very well for receiving. When the
> WX turned bad, such as during the snow storm we worked through, the 160m
> TX antennas
> were very noisy....just as noisy as those anywhere on the planet.
>
> Don't get me started about those awful 160m fishing buoy transmitters!!
>
> 73,
> Charlie, N0TT
>
> On Fri, 23 Dec 2022 19:45:28 -0700 Wes <wes_n7ws at triconet.org> writes:
> > All interesting. But let me ask (and standby for flames) what is
> > wrong with
> > them simply listening on the TX antenna?
> >
> > I know, I know, conventional wisdom says that you can't possibly
> > work 160 DX
> > without a separate RX antenna. I'll confess that I am a little
> > pistol and will
> > never be on the TB Honor Roll, but I got on the band just to add
> > another DXCC
> > band to my collection (now nine). I'm now at 144 confirmed,
> > running just 500W
> > and a 55' inverted-L on both TX and RX. Generally speaking I hear
> > better that I
> > get out.
> >
> > Looking at my chances of working 3Y the optimum time is their
> > sunrise (~3:30Z)
> > when I am in complete darkness and straight across the terminator.
> > They will
> > have the sunlit ocean to their rear and the S. American landmass
> > toward me.
> > Maybe someone can enlighten me, but I fail to see how a directional
> > antenna will
> > improve the SNR of my signal at their end.
> >
> > Wes N7WS
> >
> >
> > On 12/23/2022 6:46 PM, JC wrote:
> > > Hi topband lovers
> > >
> > >
> > >
> > > Some friends contact me with deep concerns about the next Bouvet
> > DX expedition receiver antenna called SALAD
> > >
> > >
> > >
> > >
> >
> <http://www.lz1aq.signacor.com/docs/active-wideband-directional-antenna.p
> hp
> <http://www.lz1aq.signacor.com/docs/active-wideband-directional-antenna.php>>
>
> > Salad antenna
> > >
> > >
> > >
> > > I understand the concerns, Bouvet on 160m is a lifetime
> > opportunity for most top-banders!
> > >
> > >
> > >
> > > When Doug NX4D, me N4IS and Dr Dallas started to try to understand
> > the limitation of the new Waller Flag, the first big question was;
> > >
> > >
> > >
> > > How small a loop antenna can be to receive weak signal on 160, or
> > MW?
> > >
> > >
> > >
> > > Dr. Dallas Lankford III (SK), measured the internal noise of a
> > small loop. 15x15 FT on his quiet QTH, and wrote a paper with the
> > derivation necessary to calculate the thermal noise of a small loop.
> > The study most important point was:
> > >
> > >
> > >
> > > The sensitivity of small loop antennas can be limited by internally
> > generated thermal noise which is a characteristic of the loop
> > itself. Even amplifying the loop output with the lowest noise figure
> > preamp available may not improve the loop sensitivity if manmade
> > noise drops low enough
> > >
> > >
> > >
> > > The noise on Bouvet island will be very low, < -120 dBm at 500Hz,
> > and for sure the internal thermal noise of the prosed RX antenna
> > will limit the reception of weak signals on 160m, it may work on 80
> > and above, but for 160 m, it will be a set up for failure.
> > >
> > >
> > >
> > > Why not a single, trustable beverage antenna over the ice or
> > snow?? Or a proved K9AY or a DHDL??
> > >
> > >
> > >
> > > Below is the almost good transcript of the original pdf Flag
> > Theory, for the long answer.
> > >
> > >
> > >
> > >
> > >
> > > 73?s
> > >
> > > JC
> > >
> > > N4IS
> > >
> > >
> > >
> > > Flag Theory
> > > Dallas Lankford, 1/31/09, rev. 9/9/09
> > >
> > >
> > > The derivation which follows is a variation of Belrose's classical
> > derivation for ferrite rod loop antennas,
> > > ?Ferromagnetic Loop Aerials,? Wireless Engineer, February
> > 1955, 41? 46.
> > >
> > >
> > > Some people who have not actually compared the signal output of a
> > flag antenna to other small antennas have expressed their opinions
> > to me that the signal output of a flag antenna has great attenuation
> > compared to those other small antennas, such as loops and passive
> > verticals. Their opinions are wrong. One should never express
> > opinions which are based, say, on computer simulations alone,
> > without actual measurements. The development below is based on
> > physics (including Maxwell's equations), mathematics, and
> > measurements.
> > >
> > >
> > > Measurements have confirmed that the flag signal to noise formula
> > derived below is approximately correct despite EZNEC simulations to
> > the contrary. For example, EZNEC simulation of a 15' square loop at
> > 1 MHz predicts its gain is about +4 dbi, while on the other hand
> > EZNEC simulation of a 15' square flag at 1 MHz predicts its gain is
> > about ?46 dBi. But if you construct such a loop and such a flag
> > and observe the signal strengths produced by them for daytime
> > groundwave MW signals, you will find that the maximum loop and flag
> > signal outputs are about equal. Although somewhat more difficult to
> > judge, the nighttime sky wave MW signals are also about equal.
> > >
> > >
> > > Also, the signal to noise ratio formula below for flag arrays has
> > been verified by manmade noise measurements in the 160 meter band
> > using a smaller flag array than the MW flag array discussed below.
> > Several years ago a similar signal to noise ratio formula for small
> > un-tuned (broadband) loop antennas was verified at the low end of
> > the NDB band.
> > >
> > >
> > > The signal voltage es in volts for a one turn loop of area A in
> > meters and a signal of wavelength ? for a given radio wave is
> > >
> > >
> > >
> > > es = [2pA Es /?] COS(?)
> > >
> > >
> > >
> > > where Es is the signal strength in volts per meter and ? is the
> > angle between the plane of the loop and the radio wave. It is well
> > known that if an omnidirectional antenna, say a short whip, is
> > attached to one of the output terminals of the loop and the phase
> > difference between the loop and vertical and the amplitude of the
> > whip are adjusted to produce a cardioid patten, then this occurs for
> > a phase difference of 90 degrees and a whip amplitude equal to the
> > amplitude of the loop, and the signal voltage in this case is
> > >
> > >
> > >
> > > es = [2pA Es /?] [1 + COS(?)]
> > >
> > > .
> > > Notice that the maximum signal voltage of the cardioid antenna is
> > twice the maximum signal voltage of the loop (or vertical) alone.
> > >
> > > A flag antenna is a one turn loop antenna with a resistance of
> > several hundred ohms inserted at some point into the one turn. With
> > a rectangular turn, with the resistor appropriately placed and
> > adjusted for the appropriate value, the flag antenna will generate a
> > cardioid pattern. The exact mechanism by which this occurs is not
> > given here. Nevertheless, based on measurements, the flag antenna
> > signal voltage is approximately the same as the cardioid pattern
> > given above. The difference between an actual flag and the cardioid
> > pattern above is that an actual flag pattern is not a perfect
> > cardioid for some cardioid geometries and resistors.
> > >
> > >
> > >
> > > In general a flag pattern will be
> > >
> > > es = [2pA Es /?] [1 + kCOS(?)]
> > >
> > >
> > >
> > > where k is a constant less than or equal to 1, say 0.90 for a
> > ?poor? flag, to 0.99 or more for a ?good? flag. This has
> > virtually no effect of the maximum signal pickup, but can have a
> > significant effect on the null depth.
> > >
> > >
> > > 1- The thermal output noise voltage en for a loop is
> > >
> > >
> > >
> > > en = v(4kTRB)
> > >
> > >
> > >
> > > where k (1.37 x 10^?23) is Boltzman's constant, T is the
> > absolute temperature (taken as 290), (Belrose said:) R is the
> > resistive component of the input impedance, (but also according to
> > Belrose:) R = 2pfL where L is the loop inductance in Henrys, and B
> > is the receiver bandwidth in Hertz.
> > >
> > >
> > >
> > > When the loop is rotated so that the signal is maximum, the signal
> > to noise ratio is
> > >
> > >
> > >
> > > SNR = es/en = [2pA Es /?]/v(4kTRB) = [66Af/v(LB)]Es .
> > >
> > >
> > >
> > > The point of this formula is that the sensitivity of small loop
> > antennas can be limited by internally generated thermal noise which
> > is a characteristic of the loop itself. Even amplifying the loop
> > output with the lowest noise figure preamp available may not improve
> > the loop sensitivity if manmade noise drops low enough.
> > >
> > >
> > >
> > > Notice that on the one hand Belrose said R is the resistive
> > component of the input impedance, but on the other hand R = 2pL.
> > Well never mind. Based on personal on hands experience building
> > small loops, I believe R = 2pL is approximately correct. What I
> > believe Belrose meant is that R is the magnitude of the output
> > impedance. For a flag antenna rotated so the signal is maximum, the
> > signal to noise ratio is
> > >
> > >
> > >
> > > SNR = es/en = 2[2pA Es/?]/v(4kTv((2pfL)^2 + (Rflag)^2)B) =
> > [322Af/v(v((2pfL)^2 + (Rflag)^2)B)]Es .
> > >
> > >
> > > Now let us calculate a SNR. Consider a flag 15' by 15' with
> > inductance 24 ?H at 1.0 MHz with 910 ohm flag
> > > resistor, and a bandwidth of B = 6000 Hz. Then A = 20.9 square
> > meters and SNR = 2.86x10^6 Es . If Es is in
> > > microvolts, the SNR formula becomes SNR = 2.9 Es .
> > >
> > >
> > > Any phased array has loss (or in some cases gain) due to the phase
> > difference of the signals from the two
> > > antennas which are combined to produce the nulls. This loss (or
> > gain) depends on (1) the separation of the two
> > > antennas, (2) the arrival angle of the signal, and (3) the method
> > used to phase the two flags. Let f be the phase
> > > difference for a signal arriving at the two antennas. It can be
> > shown by integrating the difference of the squares
> > > of the respective cosine functions that the amplitude A of the RMS
> > voltage output of the combiner given RMS
> > > inputs with amplitudes e is equal to ev(1 ? COS( f)) where e
> > is the amplitude of the RMS signal, in other
> > > words,
> > > A=? 1
> > > 2p?
> > > 0
> > > 2p
> > > 2 e2?cos?t?-cos?t?f??2dt=e?2?1-cos?f?
> > >
> > >
> > > The gain or loss for a signal passing through the combiner due to
> > their phase difference is thus v(1 ? COS( f)).
> > > Let us consider the best case, when the signal arrives from the
> > maximum direction. For a spacing s between the
> > > centers of the flags, if the arrival angle is a, then the
> > distance d which determines the phase difference between
> > > the two signals is d = s COS(a). If s is given in feet, then the
> > conversion of d to meters is d = s COS(a)/3.28.
> > >
> > >
> > > The reciprocal of the velocity of light 1/2.99x10^8 = 3.34
> > nS/meter is the time delay per meter of light (or radio
> > > waves) in air. So the phase difference of the two signals above in
> > terms of time is T = 3.34 s COS(a)/3.28 nS
> > > when s is in meters. The phase difference in degrees is thus f =
> > 0.36Tf = 0.36 f x 3.34 s COS(a)/3.28 where f is
> > > the frequency of the signals in MHz. If additional delay T' is
> > added (phase shift to generate nulls or to adjust the
> > > reception pattern), then the phase difference is f = 0.36(T +
> > T')f = 0.36f(T' + 3.34 s COS(a)/3.28) . If the
> > > additional delay is implemented with a length of coax L feet long
> > with velocity factor VF, then the phase delay is
> > >
> > >
> > > f = 0.37f(L/VF + s COS(a))
> > >
> > >
> > >
> > > where f is the frequency of the signal in MHz, s is in feet, L is
> > in feet, and a is the arrival angle.
> > >
> > >
> > > 2-
> > >
> > >
> > > In the case of the flag array above in the maximum direction there
> > are two sources of delay, namely 60.6 feet of
> > > coax with velocity factor 0.70, and 100 feet of spacing between
> > the two flag antennas. The phase delay at 1.0
> > > MHz for a 30 degree arrival angle is thus
> > >
> > >
> > > f = 0.37 x 1.0 x (60.6/0.70 + 100 COS(30)) = 64.1 degrees.
> > >
> > >
> > > Thus the signal loss in the maximum direction at 30 degree arrival
> > angle due to spacing and the phaser is
> > >
> > >
> > > v(1 ? COS( 64.1)) = 0.75 or 20 log(0.75/2) = ?8.5 dB.
> > >
> > >
> > > Now comes the interesting part. What happens when we phase the WF
> > array with dimensions and spacing given
> > > above? The flag thermal noise output doubles (two flags), and the
> > flag signal output decreases (due to spacing
> > > and phaser loss), so the SNR is degraded by 14.5 dB to SNR = 0.55
> > Es .
> > >
> > >
> > >
> > > So a signal of 1.8 microvolts per meter is equivalent to the
> > thermal noise floor of the flag array.
> > >
> > >
> > > On some occasions, when manmade noise drops to very low levels at
> > my location, it appeared to fall below the
> > > thermal noise floor of the WF array. By that I mean that the
> > characteristic ?sharp? manmade noise changed
> > > character to a ?smooth? hiss. To determine whether this was
> > the case, I measured the manmade noise at my
> > > location for one of these low noise events at 1.83 MHz.
> > >
> > >
> > > To measure manmade noise at my location I converted one of the
> > flags of my MW flag array to a loop. The loop was 15' by 15', or
> > 20.9 square meters. I used my R-390A whose carrier (S) meter
> > indicates signals as low as ?127 dBm. The meter indication was 4
> > dB. Then I used an HP-8540B signal generator to determine the dBm
> > value for 4 dB on the R-390A meter. It was ?122 dBm. Now the fun
> > begins. The RDF of a loop for an arrival angle of 20 degrees (the
> > estimated wave tilt of manmade noise at 1.83 MHz) was 4 dB. So now
> > manmade noise after factoring out the loop directionality was
> > estimated as ?118 dBm.
> > >
> > >
> > >
> > > Field strength is open circuit voltage equivalent, which gives us
> > ?112 dBm. I measured MM noise on the R-390A with a 6 kHz BW. The
> > conversion to 500 Hz is
> > >
> > >
> > >
> > > ?10 log(6000/500) = ?10.8,
> > >
> > >
> > >
> > > which gives us ?122.8 or ?123 dBm.
> > >
> > >
> > >
> > > The conversion to 500 Hz was necessary in order to be consistent
> > with the SNR above which was calculated for a 500 Hz BW.
> > >
> > >
> > >
> > > The loop equation is es = 2pAEs/lambda = 0.41 Es, and 20
> > log(0.41) = ?7.7, rounded off to - 8, so we have -115 dBm, or 0.40
> > microvolts per meter for my lowest levels of manmade noise at 1.83
> > MHz in a 500 Hz bandwidth.
> > >
> > >
> > >
> > > This seemed impossibly low to me until I came across the ITU graph
> > at right. Manmade noise at quiet rural locations may be even lower
> > than 0.40 microvolts per meter at 1.83 MHz. But what about the MW
> > band? From the CCIR Report 322 we find that the manmade noise field
> > strength on the average is about 10 dB higher at 1.0 MHz than 1.83
> > MHz, which would make it 1.26 microvolts per meter at 1.0 MHz.
> > Another 4 dB is added because of impedance mismatch between the
> > R-390A and the loop, which brings manmade noise up to 2.0 microvolts
> > per meter at 1.0 MHz. The RDF of one of these flags is about 7 dB,
> > which lowers the manmade noise to 0.89 microvolts per meter.
> > Observations in the 160 meter band do not seem to agree exactly with
> > this analysis because flag thermal noise has never been heard on the
> > MW flag array. But it would not surprise me at all if the flag array
> > thermal noise floor were only a few dB below received minimum
> > daytime manmade noise and that measurement error (for example,
> > calibration of my HP 8640B) accounts for the difference between
> > measurement and theory. Also, observations with a flag array having
> > flag areas half the size of the MW flag elements in the 160 meter
> > band do confirm the signal to noise ratio formula; in this case,
> > flag thermal noise does dominate minimum daytime manmade noise at my
> > location (0.40 microvolts per meter field strength measured as
> > described above.
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > > _________________
> > > Searchable Archives:http://www.contesting.com/_topband - Topband
> > Reflector
> >
> > _________________
> > Searchable Archives: http://www.contesting.com/_topband - Topband
> > Reflector
> >
>
>
>
> ------------------------------
>
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>
> End of Topband Digest, Vol 240, Issue 23
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