RadioBanter - View Single Post

July 14th 04, 05:09 PM

In article ,
says...
OH, for Pete's sake. Loops are sensitive to the H vector. Wires receive
the E vector. Most near field noise tends to be predominantly E field.
But, that seems to only be effective up to 3 or 4 MHz, due to the wavelength
factor, i. e. the near field shrinks as you go higher in frequency. Fully
formed far field wavefronts of noise sources will be just like wanted
signals, and unless some polarization difference is available, then
directivity is the only way to improve S/N. Only in special circumstances
can you see much improvement above 5 MHz due to near field/far field
differentiation.

But, my point was that no improvement in S/N was reported in the original
post.

True; I didn't report it but it is there. Typically at most
frequencies the desired signal is reduced 1 to 2 S-units with respect to
the whip antenna (strong ones) or my high long wire weaker signal...156
feet AWG 16 up 45 feet fed off center w/ a 4:1 balun) but the noise
level is reduced by anywhere from 3 to 6 S-units...a very! worthwhile
tradeoff. Exact quantitative measurements are not possible on the
Sat800 RCVR because you can't turn off the AGC. My understanding of why
the shielded loop performs this way is that near field noise is
cancelled while far field signal is only attenuated by some factor
relating to capture area. In my temporary rooftop mount I was unable to
easily check out the effect of broadside null.

Only a decrease of noise accompanied by a decrease in signal. No
relative comparison offered. Are we supposed to *assume* that the signals
went down due to time of day, while the noise went down because it is a
loop? Maybe the opposite is true? Not enough data to prove either.

--
Crazy George
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