On 4/1/2016 1:25 PM, [email protected] wrote:
Hi Jim, A properly constructed loop antenna absolutely requires a preamp.
Yes, but usually the preamp function built into the radio is sufficient.
If your loop is operating correctly it will be omni-directional for skywave signals and it will have an extremely deep null for an unwanted signal propagated to your antenna from one local vertically polarized interference source. A well constructed loop should have a null depth of 60-80 dB and a null beamwidth of just a few degrees. A very rigid mechanical mount is required to keep the deep null pointed directly at your interference source.
It is easy to model a loop on NEC, and the results I have seen do not predict anything like 60 to 80 dB nulling. With a circumference of 20 to 40 feet on 160 meters, the null is only 10 or 15 dB deep.
A properly constructed loop should be transformer matched to keep the loop balanced and both the coaxial cable and power cable must be exceptionally well isolated from the loop.
Exactly right
A low noise figure high gain preamp is essential.
I've tried that on my loops, and all it does is make the S-meter move more. No audible difference.
Frank W3LPL
73 Rick N6RK _________________ Topband Reflector Archives - http://www.contesting.com/_topband
