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
Download the new N1MM Logger+ at
<http://N1MM.hamdocs.com>. 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 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
_________________
Topband Reflector Archives - http://www.contesting.com/_topband
|