[Skimmertalk] [RBN-OPS] What causes audio images with QS1Rs?

[Pete Smith N4ZR]

Hi Rick - I've been in contact with Phil and he has been very 
responsive.  He says that clipping at the ADC would not produce images 
of the sort that appear equidistant from the center frequency, mimicking 
the behavior of a quadrature detector/sound card RX.

It's an interesting idea to ask the QS1R guys who have this problem to 
use a fairly strong signal source and the SDRMAXV software to see if an 
image appears where you'dexpect. In one case I recall clearly, the 
images all tracked back to a center frequency of 7045.5, which I presume 
squares with the 91 KHz that CW Skimmer covers in 96-KHz mode.


73, Pete N4ZR
Check out the Reverse Beacon Network at
http://reversebeacon.net,
blog at reversebeacon.blogspot.com.
For spots, please go to your favorite
ARC V6 or VE7CC DX cluster node.

On 2/23/2013 6:07 PM, Rick Kiessig wrote:
>
>
> Have you looked at the signals with SDRMAX V, both zoomed-in and in 
> the wideband display?
>
> Any chance it could be related to interference / front-end overload 
> from broadcast stations? With my setup, I was seeing wideband noise 
> and spurious spots from B/C stations before I installed a B/C filter.
>
> With SDRMAX V running, do you see the clipping light come on? The 
> Skimmer FPG A code doesn't light up the clip light in the same way, so 
> you'll get more accurate info while running SDRMAX V.
>
> You might also ping Phil N8VB and/or the QS1R reflector. Phil's 
> support has generally been excellent.
>
> 73, Rick ZL2HAM
>
> *From:*RBN-OPS at yahoogroups.com [mailto:RBN-OPS at yahoogroups.com] *On 
> Behalf Of *Pete Smith N4ZR
> *Sent:* Sunday, February 24, 2013 10:30 AM
> *To:* RBN-OPS at yahoogroups.com; Skimmertalk at contesting.com
> *Subject:* [RBN-OPS] What causes audio images with QS1Rs?
>
>
>
> During the ARRL CW contest, we had two Skimmers using the QS1R/Skimmer 
> Server combination that each produced many false spots, with the 
> "signature" commonly associated with Skimmers using simple SDRs, ones 
> which rely on a co mputer sound card for A/D conversion.  That is, the 
> two spots are spaced equidistant from the receiver's center frequency, 
> one is significantly stronger than the other, and they arrive at the 
> server typically within the same second.
>
> We're having no luck isolating what is different about those 
> particular systems.  So far we've ruled out inadequate power supplies, 
> and the idea of excessive gain before the receiver doesn't look 
> promising.  Does anyone have any theories we can explore?  I'll be 
> glad to provide the data in Excel format for anyone who wants it.
>
> Thanks in advance!
>
> -- 
>   
> 73, Pete N4ZR
> Check out the Reverse Beacon Network at
> http://reversebeacon.net,
> blog at reversebeacon.blogspot.com.
> For spots, please go to your favorite
> ARC V6 or VE7CC DX cluster node.
>
>
>
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