Topband: Using shielded CAT5 data cable as feedline for active antenna; benefits of multi-turn K9AY loop/SAL/etc?
w8ji at w8ji.com
Sat Jan 2 23:19:23 EST 2016
> 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
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
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
If receive amplifier or system internal noise is helping set noise floor,
then it would help S/N.
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