I remember a couple of years ago, I bought a new HT and was checking it's
non-ham band receive. I discovered some very local interference on VHF and
traced it to the wall wart for my TenTec Rx320! It was audible 25 feet away.
73,
Mark
----- Original Message -----
From: "Hsu, Aaron" <aaron.hsu@unistudios.com>
To: <tentec@contesting.com>
Sent: Monday, March 10, 2003 17:41 PM
Subject: [TenTec] Switching noise
> I often hear from others that they don't hear the "hash" from the
switching
> power supply (SPS) they own. In thinking about it, I remember that I
lived
> with switching noise for a couple of years not knowing that it was hash
> generated by the SPS that powered my laptop computer. It was only one day
> when I had the SPS unplugged from the wall that I notice the bands were
> quieter. Living in the greater Los Angeles area, I had always attributed
> the noise to atmospheric, industrial, or nearby CB sources when, in fact,
it
> was locally generated! I now knew *exactly* what SPS hash sounded like
and
> how to ID a noisy power supply.
>
> I wonder how many people really know how to identify "hash" from
background
> noise as they often sound alike (at least to me). For those of you who
have
> never heard SPS "hash", in my experience, it is just as if the noise floor
> of the radio was raised for a couple (or few) S-units. No distinctive
type
> of sound, just white noise. This would repeat every xKHz where x was some
> multiple of the switching frequency of the SPS. For example, on 20
meters,
> it might be quiet on 14.200 and as you tuned up the band, the noise floor
> would get louder until it peaked 14.210 and then it would fade back to
> "normal" by 14.220 and repeat when it got to 14.260, peaked at .270, back
to
> normal at .280, etc. In really bad SPS's, the peaks hit S9+. Sometimes
> there's a "buzz-saw" type noise. Sometimes, you can even hear your
computer
> "talking" to you in digital hash. I use to be amused by this in my
> Commodore 64 days.
>
> Another thing occured to me...with the number of electronic "gadgets" now
> sold (along with proliferation of their SPS "wall warts"), I wonder how
much
> the RF noise floor has risen compared to say, 20 years ago? It would be
> interesting if someone had measurements of the atmospheric noise floor at
> 14.200 from say, 10, 20, and 30 years ago just to compare. More so, I'd
> like to see a NF comparison at 10MHz and 100MHz where ethernet currently
> resides (so-to-speak). How many new hams don't know that the S3 level
> noise/hash they're hearing on their radio is not normal and is caused by
the
> brand new SPS powering the rig? To the average newbie, It's a brand new
> power supply - brand new things can't possibly generate noise. So, they
go
> on thinking it's normal and just live with it.
>
> So it seems that switching noise is subject to one's perception of what
> noise sounds like. If a person has always had an S3 noise floor or noise
> every few KHz, they might be use to it and not know better. Also, we live
> in a world full of SPS units and just that, in and of itself, may be
raising
> the "ambient" noise floor on earth. Any thoughts or comments?
>
> 73,
>
> - Aaron, NN6O
>
>
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