[600MRG] Buying "NOS" line filters?

[Paul N1BUG FN55mf]

Few easy answers Dave. The only interference I can do anything about is
that generated in my own home. I'm finding some of those by the obvious
route... turning off circuit breakers and unplugging things. I pretty
much have it down to things in the ham shack now. I know the computer is
a problem, hopefully to be solved with the new filter in a few days. I
think I might have one other source in here somewhere but haven't
isolated it yet. I have to be careful what I unplug... if I remove power
to a USB or audio device Windows freaks out, re-enumerates everything
and all my receiving software goes down for the count! I hate Windows!
I'm going to try to use an old, tired laptop to check with the shack
circuit breakers off - or better yet with the main breaker off.

When I kill all the sources in my home the only other recourse I have is
directional antennas or noise nulling systems. That will be phase two.

Just when I had hope, yesterday two "new"? sources of interference came
on and haven't let up since! These are most likely not in my home,
unfortunately, although there is room for doubt on one of them. I'm not
sure they are new. I think I have seen them before and they tend to be
relentless for a few days, then gone for a week. I can't figure out what
would produce that pattern.

At least with a line filter now on the refrigerator I don't have long
periods of 10 to 15 dB reduction in S/N on both bands due to that broad
crap masking everything.

If I were going out tracking "external" noise I would probably try a
small multi-turn non-resonant loop. I have one about about 18 inches in
diameter that I used about 12 years ago hunting power line noise - along
with various VHF and UHF hand held yagis. The small loop worked well on
160m but would probably need more turns at 630m or below. As I recall
the null was pretty sharp, which was helpful.

Paul N1BUG



On 1/13/2025 8:52 AM, Dave Riley wrote:
> When we get near the bottom of our noise QRN interference then it comes
> time to see the ether noise and at 630m there is a LOT of noise here. I
> can depend on a differential of antenna noise on 630m when short/no
> shorting of the antenna port averages around 9-12 db ..
> The question now is how to isolate the various sources of noise.. Do I
> use a small loop or an E probe?
> Have been using SDRplay for some time and it seems as good as a spectrum
> analyzer.
> I can get rid of some noise that has nothing to do with the sigs inside
> of 630m and the SDR is sure help to find the sources..
> What to do??
>
>
>> On 1/13/2025 7:34:33 AM, Paul N1BUG FN55mf <paul at n1bug.com> wrote:
>>
>> Thanks Tom. Your knowledge is always appreciated.
>>
>> I've ordered one to try.
>>
>> 73,
>> Paul
>>
>>
>>
>> On 1/12/2025 1:37 PM, Tom W8JI wrote:
>> > Transient abuse or lighting damage might be an issue with used filters.
>> > Physical damage might be a concern, but you could see that.
>> >
>> > Given the high quality parts used in power line filters I wouldn't
>> worry
>> > a bit about age or handling issues.
>> >
>> > 73 Tom
>> >
>> > On 1/12/2025 5:02 AM, Paul N1BUG FN55mf wrote:
>> >> Does anyone have thoughts on possible risks of buying new, old
>> stock AC
>> >> line filters on eBay? I am tempted as I see some good deals but I
>> wonder
>> >> about aging of high value capacitors (1.5 uF, .47 uF). I also wonder
>> >> about possible damage from dropping or sudden impact since they
>> probably
>> >> use ferrite for high value inductors (47 mH). These filters that have
>> >> good performance at LF and into VLF are very different in terms of
>> parts
>> >> values, size and weight from the ones I have experience with at HF,
>> VHF
>> >> and UHF frequencies. The more I think about it, the more I think
>> paying
>> >> almost twice as much at Digi-Key or Mouser is probably wise.
>> >>
>> >> 73,
>> >> Paul N1BUG
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