Topband: Using shielded CAT5 data cable as feedline for active antenna; benefits of multi-turn K9AY loop/SAL/etc?

[Pete Smith N4ZR]

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 
>> <http://www.lz1aq.signacor.com/docs/experimental-comparison-v10.pdf> 
>> 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
>