[RFI] Mystery noise

[David Eckhardt]

It was aimed at the lower HF frequencies.  Measured to perform well there
on the HP 8753C.  It worked quite well.  The interference from multiple
SMPSs within the unit registered S-8 to S-9 before choke installation.
After installation, no movement on the IC-7300 meter which is 3 dB / S-Unit
and S-0 at -100 dBm (wish we hadn't lost 27 dB of S-Meter indications to
-127 dBm as with the old Collins "Standard").  I can still detect a bit of
the interference, but usually sky noise overrides that.

Dave - WØLEV



On Fri, Aug 13, 2021 at 7:01 PM Jim Brown <jim at audiosystemsgroup.com> wrote:

> On 8/13/2021 11:04 AM, David Eckhardt wrote:
> > But, I have a rather monstrous common mode choke on the new
> > refrigerator/freezer power cord.
>
> Remember that effective common mode chokes work by exhibiting a low Q
> (broadband) resonance, so should be tuned (wound) to the range where
> suppression is needed.
>
> > At least that was accessible unlike
> > the clothes washer/dryer and dish washer, and a few additional SMPS's in
> > other appliances.
> >
> > And.....if I get serious about a specific radio astronomy associated
> > project, only the computer serving that project is on.  All others are
> > off and the internet is OFF, including the wireless router. Not just
> > OFF, but denied AC power!
>
> A lot of our network infrastructure can be suppressed by choking
> connecting wiring, including, but not limited to, their power, coax from
> CATV internet and CAT5 between modem and router. DSL is a more difficult
> kettle of fish, as the service cable can radiate. Noise from their SMPSs
> can be eliminated by replacing them with suitably rated linear supplies.
> I go a step further by using the linear supplies to float-charge sealed
> lead-acid batteries.  I do the same with outboard video monitors. Mine
> were purchased about five years ago when Samsung and several other
> vendors were using 14VDC, and work fine in the 12-14 range.
>
> I've used nothing but Thinkpads since about 2005. They're pretty good
> for RFI, although I recall one vintage that was nasty on 2M. Running
> with only their built-in screen and a wireless mouse eliminates more
> wiring that could radiate. I always choke PSU wiring and cables to
> external monitors.
>
> 73, Jim K9YC
>
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-- 
*Dave - WØLEV*
*Just Let Darwin Work*