[Antennaware] Antennaware Digest, Vol 117, Issue 1
Guy Olinger K2AV
k2av.guy at gmail.com
Tue Feb 5 11:36:53 EST 2019
The moderator (me) has no problems with this subject. I have no deputy
moderators, but will and have intervened if something gets out of hand.
This is a good discussion that I find interesting.
It appears that some content of the FAQ was rewritten without my
permission. Antenna design, pragmatic experience with same, how it performs
in various environments, what aspects improve performance are inseparably
intertwined with antenna modeling. One without the other is certain to
fail. If you do not know the weaknesses of NEC, including NEC4 related to
ground, modeling can generated physically unachievable essentially bogus
solutions.
Carry on gentlemen and 73,
Guy K2AV
On Tue, Feb 5, 2019 at 11:05 AM N4ZR <n4zr at comcast.net> wrote:
> Isn't this list intended primarily for antenna modeling topics? I think
> you're much more likely to get a responsive answer on Topband or Towertalk.
>
> 73, Pete N4ZR
> Check out the Reverse Beacon Network
> at <http://reversebeacon.net>, now
> spotting RTTY activity worldwide.
> For spots, please use your favorite
> "retail" DX cluster.
>
> On 2/5/2019 10:45 AM, Joe via Antennaware wrote:
> > Hey Ward, et al,
> > This is not related to the original topic but you mentioned BOG antennas
> and I have a question.Is installing a BOG near the ground system of an
> Inverted-L dangerous for a receiver? Separation between them would be about
> 1/8 wavelength, perhaps less, from the nearest radial.
> > In my situation, there would be radials and the BOG(s) in the same body
> of water. I have no clue how much RF current and voltage would be in there.
> > Thanks, Joe, K8MP
> >
> > -----Original Message-----
> > From: Ward Silver <hwardsil at gmail.com>
> > Cc: antennaware <antennaware at contesting.com>
> > Sent: Tue, Feb 5, 2019 09:57 AM
> > Subject: Re: [Antennaware] Antennaware Digest, Vol 117, Issue 1
> >
> >
> > I would suggest that you contact K9AY directly about the impedance
> mismatch
> > - k9ay at k9ay.com
> >
> > From my experience and in reviewing a lot of literature, unless the
> loop is
> > *really* small, preamplifier noise figure is not significant on the lower
> > HF and MF bands. I suppose it might be an issue for desktop rotatable
> > loops or "Beverage on Ground".
> >
> > 73, Ward N0AX
> >
> > On Tue, Feb 5, 2019 at 5:43 AM Andrew Ikin <andrew.ikin at btopenworld.com>
> > wrote:
> >
> >> Hello Ward,
> >>
> >> I think I need to rephrase my email. What I am trying to say is, a small
> >> terminated antenna e.g. a Flag or a Waller Flag is noise limited by the
> >> termination resistor. This is because the resistor has a 3dB noise
> figure.
> >> The antenna loss or low radiation resistance doesn't matter so much as
> this
> >> loss can be made up with an LNA. The issue is made worse because most
> >> practical
> >> designs have the matching transformer z that is the same as the
> termination
> >> resistor. Now if we use amplifier with high input z of say 30k Ohms;
> using
> >> chemandy.com Return loss and mismatch loss calculator
> >> the resistor noise is miss-matched to the amp. by approx. 10dB.
> >>
> >> Thus the antenna noise floor should be lower. However, I am assuming
> that
> >> the LNA has negligible noise when terminated with the antenna. This
> could
> >> be
> >> a design issue to get the noise figure down to less that 0.5dB!!!
> >>
> >> The example I gave using a high z amp. with the K9AY suggests that
> there is
> >> no loss in gain by using increasing the input z.
> >>
> >> 73
> >>
> >> Andrew G8LUG
> >>
> >> -----Original Message-----
> >> From: Ward Silver
> >> Sent: Monday, February 4, 2019 7:50 PM
> >> To: antennaware at contesting.com
> >> Subject: Re: [Antennaware] Antennaware Digest, Vol 117, Issue 1
> >>
> >> A flux-coupled transformer with separate windings provides galvanic
> >> isolation between the feed line shield's outer surface and the loop.
> >> Coupling from the loop to the feed line can upset the pattern and couple
> >> noise on the feed line into the antenna.
> >>
> >> It is also a good idea to add a choke of several thousand ohms on the
> feed
> >> line at the antenna to prevent common-mode current on the outside of the
> >> feed line shield from getting into the cable and becoming
> differential-mode
> >> signals. Same concern at the receiving end although most receivers are
> >> well-shielded.
> >>
> >> 73, Ward N0AX
> >>
> >> On Mon, Feb 4, 2019 at 11:00 AM <antennaware-request at contesting.com>
> >> wrote:
> >>
> >>> Send Antennaware mailing list submissions to
> >>> antennaware at contesting.com
> >>>
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> >>> than "Re: Contents of Antennaware digest..."
> >>>
> >>>
> >>> Today's Topics:
> >>>
> >>> 1. Fw: source impedance of resistor terminated antennas (Andrew
> Ikin)
> >>>
> >>>
> >>> ----------------------------------------------------------------------
> >>>
> >>> Message: 1
> >>> Date: Sun, 3 Feb 2019 23:04:32 -0000
> >>> From: "Andrew Ikin" <andrew.ikin at btopenworld.com>
> >>> To: <antennaware at contesting.com>
> >>> Subject: [Antennaware] Fw: source impedance of resistor terminated
> >>> antennas
> >>> Message-ID: <2E4939776E6344ECB4242B584629630C at DESKTOPCPQEP29>
> >>> Content-Type: text/plain; charset="UTF-8"
> >>>
> >>>
> >>>
> >>> From: Andrew Ikin
> >>> Sent: Sunday, February 3, 2019 10:38 PM
> >>> To: antennaware at contesting.com
> >>> Subject: source impedance of resistor terminated antennas
> >>>
> >>> Is there any reason why most resistor terminated antennas like the K9AY
> >>> and the Flag use a matching transformer to the Rx feed line that has
> the
> >>> same impedance as the termination resistance. The reason for the
> question
> >>> is, such antennas have a ideal match to the 3dB noise generated by the
> >>> termination resistor and this resistor has no radiation resistance.
> >> Hence,
> >>> for antennas like a small size Flag, the performance could be limited
> by
> >>> the resistor noise.
> >>>
> >>> However, if the antenna is connected to a high zin amp., then the
> >> resistor
> >>> noise should be reduced by the miss-match and if the amp. noise figure
> is
> >>> very low, then it may be possible improve the antenna performance?
> >>>
> >>> Winding the clock back 20 years I noticed that the K9AY Rx matching
> >>> transformer could be replaced by a high zin amp. with a voltage gain
> of
> >>> 11dB. The overall gain increase compared to using 9:1 z transformer was
> >>> 20dB. This increase in gain is what would be expected (11dB amp. plus
> 9dB
> >>> by replacing the 9:1 transformer). Thus, the antenna gain compared to
> one
> >>> without the amp. had not been degraded by using high zin amp.. However,
> >>> then I didn?t consider the effect of resistor noise, but this wouldn?t
> be
> >>> an issue with the K9AY.
> >>>
> >>> Is there something else I need to consider?
> >>>
> >>> 73
> >>>
> >>> Andrew Ikin
> >>> G8LUG
> >>>
> >>> ------------------------------
> >>>
> >>> Subject: Digest Footer
> >>>
> >>> _______________________________________________
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> >>> Antennaware at contesting.com
> >>> http://lists.contesting.com/mailman/listinfo/antennaware
> >>>
> >>>
> >>> ------------------------------
> >>>
> >>> End of Antennaware Digest, Vol 117, Issue 1
> >>> *******************************************
> >>>
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