Topband: SDR Mythbusters - ADC Overload myths debunked...

[Tom W8JI]

>From Stu, K6TU

As with any technological change, there are many myths, past truths or part 
truths that get repeated endlessly and out of context by those frightened or 
challenged by the change.

 Software defined radios are no exception to this in the world of Ham Radio.

 Steve Hicks, N5AC and the VP of Engineering at FlexRadio has posted an 
excellent explanation and bust of the ADC overload myth on the FlexRadio 
community.  You don’t need to be registered on the community to read this 
excellent write up:>>>>>>

Regardless of the fact they cannot possibly overload, they overload here.

I don't understand his explanation at all.

We had ONE transmitter on while trying to receive. The ADC could not handle 
the level of one transmitter.  Because there was no in-band front end 
selectivity, the spacing did not matter.  We could not get the strong local 
signal outside a roofing filter.

With two transmitters on different non-synchronized frequencies, there will 
be periods of time when the voltages add. There will be periods when the 
voltages subtract. Anything following the summing point has to handle the 
random peaks, even an ADC.

The Flex we tried here, using it to listen while ONE transmitter was 
running, just went nuts. It was equally bad no matter what the spacing. At 
least with a radio with roofing filter, we could move the radio up or down 
band and use it.

73 Tom