[TenTec] Switching noise

[Hsu, Aaron]

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