[RFI] Quidance on finding noise?

[Jim Brown]

On 1/8/2020 4:46 AM, Don Kirk wrote:
>   I do agree that looking at the audio
> signature ahead of time is useful to help decide if the noise looks like
> power line type noise as that provides a clue about my 136 MHz AM tracking
> equipment being useful or not.

The most important "signature" is often the RF spectrum with waterfall, 
because it provides clues as to the nature of the noise source -- is it 
generated by arcing (nearly always power line equipment) or 
power-controlled electronics, which are not. In general, power control 
electronics (variable speed motors, switch-mode power supplies) are LF 
square waves from free-running oscillators. Their harmonics extend to 
high HF, but rarely beyond 6M. You can't chase this stuff at VHF or UHF.

By contrast, the power line noise that we have been chasing all our 
lives is ARCING of some equipment that is part of the electrical power 
distribution system, and it IS best chased at VHF/UHF. Certainly at HF 
with loops as a start, but VHF/UHF to zero in on the source.

Another important point. Resonant antennas like Yagis have their 
well-defined directional ONLY on the bands for which they were designed. 
The directivity of a 2M Yagi is only predictable on 2M, a 432 Yagi only 
on that band.

A trick I learned during Fox hunts with our local Chicago area club is 
that a talkie can be made "half-space" directional by holding it very 
close to your body; I once won a 2M Fox Hunt with only a TH-F6A, a duck, 
that trick, and then removing the duck when I got close.

73, Jim K9YC