Rick, N6PE wrote:
Hi all,
With high local line noise, is a TUNED LOOP or non-resonant RX loop a better
option?
I've seen blogs that shielding a loop really doesn't do much.
Comments?
Rick, I guess there are two noise issues here. First is conducted power-line
noise, this flows along the feeder screen and either gets into the antennas
RF return path to ground or re-radiates the noise direct to the antenna.
Second is the antennas susceptibility to radiated Electric Field noise
within the Near Field of the antenna. This can be a particular problem in a
urban RF environment below 4MHz.
Conducted power-line noise can be reduced by using a simple 1:1 feeder
isolation transformer or a high inductance common mode choke close to the
Rx. Or by using an antenna with a low capacitance matching transformer e.g.
a Flag antenna. However it is important to note that terminated loop
antennas ( Flag, EWE, K9AY ), Vertical and Active Whip antennas are
susceptible to locally radiated E-Field noise.
One antenna that does have very high immunity to conducted power-line and
locally radiated E-Field noise is a low impedance Balanced Broadband loop
antenna. Also some well designed tuned loop antennas afford similar
immunity.
I have conducted noise immunity tests with screened and unscreened
Balanced Broadband loops and I have not been able to measure any difference
in their noise immunity. Notwithstanding, loop screening is necessary for
a tuned loop if it is not perfectly balanced.
One disadvantage with the Balanced Broadband loop is the lack of directivity
other than the figure of eight pattern. This can be remedied by a end-fire
array of two loops. This will provide higher directivity than a Flag with
very high noise immunity.
73
Andrew Ikin.
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160 meters is a serious band, it should be treated with respect. - TF4M
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