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Author Topic: Resonance vs Noise  (Read 2188 times)
N4JTE
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Posts: 1157




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« on: January 12, 2012, 07:19:07 PM »

Never at a loss for a dumb question so here goes.
I use two element flattopped phased wire arrays on 40 and 80 and it seems like the noise level is centered on 7185 and 3942 where I optimixed.
I know noise is a signal etc, but having made some tests with 60 or so participants on two nets nobody has my unique tea kettle boiling on 80 or my 5-9 griddle on 40 some nights.
On 80 noise is gone when pointing east, more confusing. If I move far enough away freq wise, on either band things improve somewhat meaning differant kind of noise but not enought to write home or eham about.
Sooooooo, is a resonant antenna more prone to noise?
Tnx in advance,
Bob
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KB4QAA
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Posts: 2405




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« Reply #1 on: January 12, 2012, 08:24:23 PM »

An antenna with gain, will have gain on both signal AND noise.  Nature of the beast.  Now, if you have directionality, like with a dipole, you may lower noise from other directions.

Resonance by itself does not yield gain, either to noise or signal.
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N4JTE
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Posts: 1157




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« Reply #2 on: January 12, 2012, 08:35:31 PM »

rr think beam antenna, well aware of dipole properties, tnx
Bob
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WB6BYU
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Posts: 13331




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« Reply #3 on: January 12, 2012, 09:29:02 PM »

No.  Well...... hardly ever.


If your noise is strong in one direction and not in the other, I would suspect an interference
source in that direction.  There are lots of them in a modern house - I often test my 2m DF
receivers by locating our FAX machine.

With a very sharply resonant antenna you can hear the background noise come up as
you tune through the resonant point.  In fact, that is a common way to tune up a small
loop antenna - just peak it for maximum noise.  But that is band noise + signals, not
some sort of interference.  Noise, after all, is still an electromagnetic signal, and your
antenna can't differentiate between types thereof.  (Only those coming from different
directions due to the pattern.)

Now, it might be possible to achieve something like that if the RF amplifier in your
receiver was regenerative - for example, if the antenna tuning caused your receiver
front end to oscillate when it presented a specific impedance.  But that seems more
likely with a breadboard rig on the bench.


Of course the ultimate test is to use the 40m antenna to listen on 80m, or vice versa,
and see if you still hear the signals at the same frequencies.  Or just a whip antenna
or random wire.  They you'd know whether the noise is still there when the antenna is
not resonant.


But my guess is a noise source to the West, probably electronic equipment (but
possibly leakage from cable TV or network cables), and perhaps not too far away.
Might be time to build a small loop antenna and track it down.
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W8JI
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« Reply #4 on: January 13, 2012, 01:23:37 AM »

Resonance by itself does not impact ratio of signal-to-noise, but it certainly can impact sensitivity of the antenna.

Both bad noise and good signals will increase in the same proportion as an antenna is closer-matched to the receiver and feedline's impedance. The system becomes more sensitive to all external signals.

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