[hpsdr] Mercury Spurious Emissions

[Joe Martin K5SO]

On Sep 9, 2011, at 5:52 PM, Jeremy McDermond wrote:

> It seems as if Mercury is radiating spurious signals into the  
> antenna connector.  The symptom is showing up on 144.390 MHz.

Using my IC910 with a whip antenna a few feet from my HPSDR enclosure  
(Antec) I too can see a signal at about S3-S4 strength showing up at  
144.390 (or image thereof) when my three Mercs are running.  However,  
the signal is NOT being radiated from the Mercury antenna connector.   
In fact, when I directly connect the input of the IC-910 to the  
Mercury antenna connector the signal appearing at 144.390 MHz (or it's  
image, of course) actually goes away.  The emissions you are seeing  
are coming from the bus or the boards and not being output through the  
antenna connector, it seems.

That such VHF signals are present in the immediate vicinity of the  
HPSDR rig is not very surprising of course, no more so than similar  
type signals emanating from any bus-driven computer system, since the  
bus has relatively large amplitude square wave signals on it.   I was  
concerned that something was being radiated via the Mercury antenna  
connection, as was initially suggested...or at least I that's what I  
thought that's what the suggestion was.  Well, it isn't, in any case.

In this case it seems that standard, or perhaps elaborate, rf  
shielding techniques should be able to reduce the bus or board  
emissions to an acceptable level in the vicinity of the HPSDR rig, as  
has been already suggested.  Anyway, no wonder I didn't see much with  
the spectrum analyzer except for the 122.88MHz clock and it's  
harmonics when I connected directly to the BNC connector on Mercury  
earlier.  The problem you see isn't coming from there, clearly.

For your demos, in which folks may have handhelds right up next tot  
the HPSDR rig you may need to simply have a super shielded setup and  
not run with the covers off, but that hardly is conducive to showing  
people what the rig looks like.  At least I think you by now have a  
good idea what the issue actually is, right?

73,  Joe K5SO






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