Re: Sunday Herald yesterday

On 3 May, 10:03, "DAB is the Betamax of digital radio" <dab.is@dead>
wrote:
Richard Evans wrote:
DAB is the Betamax of digital radio wrote:
Richard Evans wrote:

Hence the DRM+ receiver base would not necessarily be starting from
scratch.

True, although DRM+ receivers could do with narrower RF bandpass
filters than would be used for FM.

I was thinking of filters defined in software. Don't many receivers
already use software filters.

It's best to use the correct bandwidth RF filter prior to the ADC, because
the noise power is proportional to bandwidth, so if you use a filter meant
for FM you'd be reducing the SNR and the sensitivity.

Presumably the IF would go through some sort of filter, and then be
digitised, so that software can do the rest of the work. So couldn't
they just define a filter in software for 50khz or 100khz, depedning
upon which mode of DRM+ is being used.

I'm sure they would do that, but the damage has been done if they let in too
much noise prior to sampling.

Surely as long as the analogue filter acts below the Nyquist limit of
the digital sampling, any subsequent digital filtering will remove
noise as or more effectively as an analogue filter of the same
bandwidth would have done?

It may be slightly inefficient to run a system at full sample rate
(and hence bandwidth) in modes where you subsequently filter out most
of the bandwidth and probably downsample too, but it would certainly
work. It is the basis of most audio ADC design!

Cheers,
David.

.

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