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Re: Topband: ADC Overload

To: "'topband'" <topband@contesting.com>
Subject: Re: Topband: ADC Overload
From: "Paul Christensen" <w9ac@arrl.net>
Date: Mon, 12 Oct 2015 15:08:00 -0400
List-post: <topband@contesting.com">mailto:topband@contesting.com>
>"The favorable SDR averaging doesn't apply when the RF voltage at the receiver 
>input is dominated by one huge signal, and if that signal exceeds the 
>capability of the ADC in the radio, overload can definitely occur. So, 
>although I believe that nearly all manufacturers will soon migrate to superior 
>SDR technology, the "big gun" multi-multi contesters may want to hang onto 
>their old Yaesu/ Icom/Kenwood transceivers (or else use bandpass filters on 
>the inputs of their SDR rigs)!
73, Jim W8ZR"

Nice explanation of CLT in this context, Jim.   So, as you and Tom point out, 
1, 2 or 3 extremely strong stations falling within the wideband SDR input can, 
and does cause severe OL effects in our SDR receivers.  

Then what if we *deliberately* inject hundreds, if not thousands of discrete RF 
carriers into our SDR receivers from say...an internal RF carrier or noise 
generator, mixed with the desired RF signal to mitigate OL caused by a few 
strong carriers?  It would be interesting to see the math and note what, if any 
reasonable limits apply, even if the amount of OL protection is small but there 
nonetheless.  If this is a viable form of OL mitigation, then by now, someone 
must have already addressed this, possibly in an academic or IEEE paper?

Paul, W9AC

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