Topband: Non-resonant receive antennas

Milt -- N5IA n5ia at zia-connection.com
Thu Dec 18 09:55:55 EST 2014 

Jim,

If the arrival angle of the signals is high, then definitely the low dipole 
will perform stupendously.

At XZ0A in 2000 we were having trouble the first few evenings receiving 
signals at our sunset and for a couple of hours afterwards.  The Beverage RX 
antennas were working very effectively after that time period, for the 
entire night time.

Our conclusion was that the signals were arriving not only skewed (what 
signals we were hearing were best on the VK/ZL Beverage and not the direct 
path on the JA/NA Beverage) but also high arrival angle.

I installed a full sized dipole at 20' AGL, suspended by bamboo poles at the 
center (centered on the helicopter landing zone as we suspected the Myanmar 
Generals were not going to come visit us) and terminated in the jungle on 
either side of the helo landing spot.

The dipole was oriented east/west, broadside to the N/S.

Immediately at the start of that day's Topband operation the NA signals came 
right up out of the noise floor shortly before sunset.  Q5 copy signals on 
the dipole were barely discernable while listening on the VK/ZL Beverage.

For 3 weeks we enjoyed this RX signal capability during the early evening 
time period.

BUT, when it was time for the signal path to change it did so within a 5 
minute period every night.  It was like someone was disconnecting one 
antenna and connecting the other, so dramatic was the switch of RX path from 
skewed, high arrival angle to direct path, much lower arrival angle over a 
period of a few short minutes.  It was like clock work each evening.

The low dipole RX antenna allowed an XZ0A 160 M contact to be entered in 
hundreds of NA log books which most likely would have never happened without 
it.

My personal experience with low (10' AGL), full sized (1/4 WL) horizontal 
loops at my home station is they work very well for high arrival angle 
signals but are nearly deaf to low angle signals.

Good luck, and YMMV.  The low dipole is a specialty RX antenna.  And you can 
never have too many RX antennas.

If anyone would like to see photos of the low dipole at XZ0A, send me a 
direct request.

73 de Milt, N5IA



-----Original Message----- 
From: James Rodenkirch
Sent: Thursday, December 18, 2014 7:26 AM
To: Top Band Contesting
Subject: Topband: Non-resonant receive antennas

I noticed JC's comment below about a low dipole as a receiving antenna.

Did I interpret that correctly?  I've read of a Dipole on the ground as a 
low noise receive antenna for 160 but.........can a non resonant dipole 
installed at low heights be better, as a receive antenna, than a vertical or 
L antenna? How about a non-resonant dipole, say, two feet above ground, at a 
length of 100 feet? Would you feed it with coax or figure out the Zo at 160 
and use a suitably wound xfmr to match to 50 ohms???

Just athinkin' of ways to use available low horizontal space, albeit the 
available space is insufficient for a beverage.

Thoughts???  72, Jim Rodenkirch K9JWV



> From: n4is at comcast.net
> To: jkaufmann at alum.mit.edu; topband at contesting.com
> Date: Wed, 17 Dec 2014 23:11:10 -0500
> Subject: Re: Topband: 8 circle: DXE vs Hi-Z
>
> Hi guys
>
> Polarization does play a lot on 160m for two reasons. I can say that 
> because
> I am using my HWF (two horizontal flags end fire) since 2009. The first 
> one
> is local man made noise that propagate only vertical due the attenuation 
> on
> the horizontal component near the ground. And Second the DX signal always
> come in both polarization.
> The result form the two reasons is an optimized signal to noise ration 
> using
> horizontal polarization.
>
> I have both WF with the same RDF, during SR or SS there is almost no sky
> noise coming from the back because of the darkness, however local man made
> noise comes from any direction, especially if you live in a city lot like 
> I
> do. Most of the time the noise is coming at the same direction you want to
> hear the DX, and if you add power line noise the situation deteriorates a
> lot for the VWF due vertical polarization. Using my HWF I normally get 10 
> dB
> better SNR than my VWF that has the same RDF and same aperture of 74 
> degree
> measures, I can turn the antenna and measure it, they are not optimized 
> for
> best F/B, I optimized them for maximum rejection of local man made noise.
>
> The HWF is not a dipole. The two phased loops take of angle us 40 degree 
> and
> there is a huge attenuation for signals above 60 degree. Low dipole is a
> huge issue if the dipole is resonant, it will interact with all other
> receiver antennas and will destroy directivity of all of them, if you want
> to use a low dipole make it not resonant. Gain in not important so it  can
> be short as a 30 m dipole and still will hear the same way. Another issue
> with low dipoles is the amount of energy absorbed from the TX antenna. If
> you connect a power meter and a 50 ohms load o the low dipole and transmit
> KW on the TX antenna, you can measure several WATTS at the low dipole . 
> You
> can burn you front end with a low resonant dipole.
>
> Adding to all that there is another very interesting observation from my
> last 5 year using a high RDF horizontal RX antenna, when the TX signal
> refract on the ionosphere the signal split in two waves, that was very 
> well
> explained by K9LA. What I observed is that these two waves does propagate 
> in
> different directions. I normally receive VK6 near my SR with better SNR
> horizontal from 210 degree SSW and with better SNR from 280 degree 
> vertical.
> Sometimes the horizontal peak is 20 minutes before the vertical peak that 
> is
> most of the time at my SR.
>
> 73's
> N4IS
> JC
>
>
>
>
>
>
>
>
> -----Original Message-----
> From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of John
> Kaufmann
> Sent: Wednesday, December 17, 2014 8:59 PM
> To: topband at contesting.com
> Subject: Re: Topband: 8 circle: DXE vs Hi-Z
>
> Good points about polarization.  If the signals and/or noise are polarized
> predominantly in one state, then RDF may not be a good predictor of SNR
> performance, particularly if the antenna receives predominantly in an
> orthogonal polarization.  On the other hand, if the polarization state of
> the signals and noise evolve randomly with no preference for any one 
> state,
> which is often assumed for skywave signals, then RDF will be--on 
> average--a
> good receiving metric, subject to the previous stated qualifications about
> the spatial distribution of the received noise.  However, some of the past
> discussions on this reflector about preferential polarization of skywave
> signals on 160 may call into question the assumption of randomly polarized
> signals.
>
> 73, John W1FV
>
>
> -----Original Message-----
> From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of Richard
> (Rick) Karlquist
> Sent: Wednesday, December 17, 2014 3:19 PM
> To: Lee K7TJR; 'Terry Posey'; 'John Kaufmann'; topband at contesting.com
> Subject: Re: Topband: 8 circle: DXE vs Hi-Z
>
> All this discussion about RDF overlooks the issue of polarization.  If you
> make an array of verticals with a certain RDF (assuming noise comes from 
> all
> directions uniformly), the array will be better than an individual 
> vertical
> by the RDF factor.  However, what I have found is that a horizontally
> polarized antenna, such as a low dipole frequently receives considerably
> better than a vertical.  In that case, you would be better off using an
> array of low dipoles.  The reason why horizontal polarization can be 
> better
> is that the horizontal component of terrestrial based noise is highly
> attenuated over distance as a ground wave.
>
> Rick N6RK
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