[Ground-station] 0 dBFS conventions?

[Derek Kozel]

At Ettus we use a sine wave with peaks at the rails.


On Sun, Jul 8, 2018, at 2:05 AM, Ground-Station wrote:
> It appears there are several conventions in digital communications for> measuring signal levels relative to the full scale of the A/D
> converter.> 
> Is there a de-facto standard definition of 0 dBFS in ham SDR work?
> 
> I'm currently using the convention that 0 dBFS corresponds to a
> rail-to-rail square wave (or full scale DC) in **both** the I and Q
> channels.> 
> I like this convention because it makes 0 dBFS exactly equal to the
> absolute largest signal possible. I'm not likely to encounter it in
> normal operation but I can conceive of an A/D being severely
> overdriven> by a malfunctioning AGC.
> 
> Another convention defines 0 dBFS as a sine wave with peaks at the
> rails. But then a square wave (if you could generate one) would
> be +3dBFS.> 
> Unlike the digital audio field where each channel is measured
> separately, I use a single level for the sum of the I and Q channel
> powers. I.e., if the I channel were a rail-to-rail square wave
> while the> Q channel was 0, this would be -3dBFS. A single carrier that is just
> starting to clip as it swings through the I and Q axes would be
> -6 dBFS.> You do have to be careful to include the factor of 2 when
> summing up the> squares of the samples in each channel.
> 
> But if there's a de-facto standard in ham SDR work, I'm willing to
> switch to it. Is there one?
> 
> Thanks, Phil
> 
> 
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