Topband: Using shielded CAT5 data cable as feedline for active antenna; benefits of multi-turn K9AY loop/SAL/etc?
Pete Smith N4ZR
n4zr at contesting.com
Sun Jan 3 12:01:18 EST 2016
I should have been clearer - all his work is with small loops, typically
1 meter diameter. My interest was in the possibility of improving the
performance of my omnidirectional active Skimmer antenna, currently a
Clifton Labs 8-ft vertical. Since some of his antennas favor horizontal
polarization, according to his writeups, my thought was that perhaps
combining vertical and horizontal polarization might yield a net
improvement in SNR.
73, Pete N4ZR
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On 1/2/2016 11:19 PM, Tom W8JI wrote:
>> 2. He cites experimental data showing that coplanar crossed loops
>> and multi-turn quad loops both offer very significant improvement in
>> the recovered signalcompared with a single loop. See
>> to check whether I got this right. Anyway, it occurred to me to ask
>> if anyone has ever tried multiturn K9AY, SAL or flag/pennant
>> receiving antennas, and did you see something similar?
> Be careful in what you might think the data means. The measurements
> are for an unmatched system, and apply to broadband untuned loops with
> "low impedance" loads.
> In a case like that, the parallel wires reduce the impedance primarily
> by reducing reactance. It is no different than a thicker conductor,
> which would reduce reactance and increase current in the simple circuit.
> This does not necessarily mean the loop would have a higher SNR, that
> would depend on how the amplifier "likes" the lower impedance and if
> external noise is limiting the system.
> It does not mean more directivity. An even larger improvement in
> sensitivity would come from cancelling reactance.
> If a small terminated loop had increased conductor size it would have
> more sensitivity, which means increased signal and noise pickup,
> because the termination and source resistances would decrease.
> You can see this effect by modeling an EWE antenna, or any small
> loop. As the conductor is made thicker the optimum termination
> resistance decreases. This increases sensitivity, because radiation
> resistance remains the same and loss resistances decrease. You can
> pick up a few dB in sensitivity in certain cases.
> If the amplifier or receive system is affecting S/N in a significant
> manner, it would improve S/N. If external noise is the significant
> factor in sensitivity, then it would pretty much do nothing.
> This effect occurs in all sorts of lossy antennas. For example, if you
> paralleled two close-spaced Beverages (making them act like a single
> very wide conductor) sensitivity increases. This does not mean S/N
> ratio increases, because signal and noise from the antenna would
> increase at the same rate. It just means the level of signal and noise
> from the antenna is a bit higher.
> If receive amplifier or system internal noise is helping set noise
> floor, then it would help S/N.
> 73 Tom
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