[Boatanchors] Switching Power Supply hash

[N4ue@aol.com]

Carl, K4ZRD, sells a system for cooling our old tube type radios. There has 
been some concern and discussion regarding the possibility of hash causing 
interference on HF.
To preface this discussion, I must state that Carl is a very good friend and 
neighbor! I have assisted him with some minor details with these power 
supplies.
Yes, switching power supplies do indeed produce some hash and spurs. However, 
some are MUCH worse than others!!I  I discovered this, after putting together 
a CW QRP operating position for 40 Meters. The radios used here for that, 
consist of a Collins 75A-4 and a Vectronics QRP Xmitter (what a combination, 
eh?).......

I will not bore all of you who are not interested in the details, but if you 
e-mail me direct, I will forward you a Word document with all the numbers. 

Here is a brief synopsis:

Equipment used:
Icom 756PRO, Preamp 2 engaged, 2.4 KhZ SSB filter engaged (hey, it will be a 
boatanchor, someday)

Frequencys covered:
160M through 6M

Equipment tested:
Two each of K4ZRD power supplies
Two each of Compaq brand power supplies

Test methodology:

Attempt 'worst case scenario' coupling between power supply output and 
UNSHIELDED antenna wire to the PRO.
Why did I do this? Because at the present, I only have long wire antennas 
(towers still in the yard) and this is how I discovered the noise on my 75A-4.

Results:
I can honestly state that the brand of power supply Carl uses, is excellent 
and as testified by actual owners, is clean. The Compaq is another case, 
however.....

Thanks for the time.

ron

N4UE