Topband: 160 RX Loops

[Andy Ikin]

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.