At 02:35 PM 4/13/2005, Bill VanAlstyne, W5WVO wrote:
>I've read in a couple places lately -- maybe in ads, not sure -- that
>creating an "effective RF ground" (whatever that would imply at the
>wavelength in question) can reduce received noise in the antenna circuit,
>even when an "RF ground" isn't necessary for antenna current return, such as
>when driving a correctly-tuned balanced antenna. Is this true? I work a lot
>of 6M SSB/CW, and man-made QRN is often the limiting factor on receiving
>weak sigs. My 5-el homebrew yagi presents a virtually pure-resistive 50 ohms
>load at 50.125, according to my 259B. Wouldn't expect any improvement on the
>transmit side. But would my receive noise floor really drop if I put down a
>counterpoise under my carpet near the rig? Or outside? If so, why? I don't
>see it. Please enlighten me as to how antenna currents developed by noise
>sources could be reduced with an "RF ground". Given that the antenna,
>feedline, and radio are perfectly matched to each other at 50 ohms, where
>would these currents be flowing, and how would an "RF ground" reduce them?
>
>Bill / W5WVO
>New Mexico / DM65
>_______________________________________________
I could see where creating a single point ground, or a big ground plane
under your shack, might reduce the possibility of ground loops (or wiring
loops in general) that could pick up local noise and conduct it into the
inside of your radio (i.e. on the power wires?)
Here's an experiment.. Put a dummy load on the receiver input (or at the
antenna feed point). Does the noise still exist? If so, it's not getting
in through the antenna, so it must be coming in on wires, cables,
radiation, etc. In such a case, changing the grounding system might help.
Fooling with a PCR1000 indoors running off a laptop, I've found all sorts
of interesting phenomena and noise sources. Switching which outlets
various wall warts are plugged into results in striking differences in
received noise (both on a whip at the PCR1000 and outside antennas,
although obviously, more so on the former) Clearly, the new breed of
switcher based wallwarts aren't the most quiet devices in the
world. Laptop displays also seem to be big noise emitters (maybe the
inverter for the fluorescent backlight?)
By the way, the noisiest RF device I have is one of those pods designed to
read and control the OBD-II diagnostic port in a car. No FCC sticker on it
(perhaps it fits in an exempt category.. clearly it's faster than 9kHz
clock rate?) but it radiates enough to disrupt FM radio reception in the
car, to say nothing of killing HF radio anywhere near it.
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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