[RFI] Quidance on finding noise?

[Dave Cole]

Jim,
One of our local Old Timers, showed me a neat trick...  He took a milk 
carton, cut in half horizontally, then wrapped foil around the inside 
and outside of the milk carton.

This left a rather nice shielded cabinet for an HT to sit in, with just 
the antenna sticking out...  Now when you get close to the source you no 
longer have ingress via the plastic body of the HT...

73, and thanks,
Dave (NK7Z)
https://www.nk7z.net
ARRL Volunteer Examiner
ARRL Technical Specialist
ARRL Asst. Director, NW Division, Technical Resources

On 1/8/20 9:51 AM, Jim Brown wrote:
> 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
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