[RFI] National RF HFDF Vector Gun Update

Paul Christensen w9ac at arrl.net
Sun Jul 10 13:53:48 PDT 2011

> With the Vector Gun, I have been able to pinpoint 2 noisy switching
> power supplies that produce RFI primarily in the 10 MHz range...

Frank, nice report and much appreciated...

One limitation of the National  that it is only specified to work down to 10 
MHz.  I had seen this unit before but stopped short of a purchase due to 
this limitation.  I have had many instances of SMPS noise where it is only 
prevalent between 160m and 80m and no trace of noise whatsoever at higher HF 
frequencies.  In fact, nearly all the HF SMPS noise sources I've encountered 
in my neighborhood have all produced noise under 6 MHz.

Any idea to the frequency limitation?  I suspect it is the size of the 
antenna loop needed at the lower HF frequencies.  Also, how sharp is tuning? 
Broadly sharp is fine -- but not too sharp that one cannot make out the 
peaks and valleys on a pandapter when using an SDR receiver connected to the 
RDF antenna.

Paul, W9AC

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