[Elecraft] Velleman Power Supply

[Jim Wiley]

Well, it turns out I was somewhat in error regarding the RFI potential 
of the small Velleman PSSMV7U power supply I described a couple of days 
ago.  It does have some RFI, but oddly enough, only in a few spots.  I 
have been experimenting with various filters to see if it can be tamed, 
and I think this will eventually be successful,  but there is still some 
work to be done.   Of course, if all you are using it for is a battery 
charger, and running the rig off the gel-cell (charger off) when 
operating, this won't be a problem. It will easily charge the battery 
(from flat) in about 5 or 6 hours, less of course if the battery is not 
completely discharged.


 The RFI from my unit is almost  non-existent on the 160 meter band, and 
very low on 20 meters and higher bands. It is worst on 40 and 30 
meters.  There are a couple of spots on 80 that are bothered, but most 
of the band is clear.  The RFI sounds like a raspy sweep in frequency, 
or an odd sort of repetitive clicking, at about 2 second intervals, 
depending on where you are listening, and moves across a small portion 
of the band at a variable rate, depending on how much current is being 
drawn.  In most cases, atmospheric noise from the antenna is enough to 
mask the RFI, but in a few spots it can be heard clearly.  Other than a 
few bad spots, the RFI is gentle enough that I can easily hear through 
it, and in fact for a while didn't recognize it for what it was.


Sorry to be the bearer of bad news, as it initially appeared that this 
small unit would be perfect.  Oh well.  If I am successful in building 
an in-line filter (between the power supply and the K2), I will pass on 
the specs.  So far, I have tried a simple L section filter consisting of 
about 25 turns on a FT-50-43 core plus a 0.22 uF cap, and that 
definitely helped, but didn't result in complete quieting of the RFI.  I 
will experiment further to see if I can do better.  It may also take 
putting the power supply inside a small metal enclosure and/or using a 
grounded AC cord - which I would like to avoid if I can, as shielding 
would make the system larger and heavier.  I need to fire up the 
spectrum analyzer and do some sniffing to see if the RFI is conducted or 
radiated, or both.


- 73
Jim, KL7CC