[time-nuts] WWVB d-psk-r down conversion method...
jimlux at earthlink.net
Wed Sep 24 00:23:15 EDT 2014
On 9/23/14, 10:11 AM, Alexander Pummer wrote:
> there is an interesting side effect with that phase modulation: in case
> the crystal filter is "narrow enough" --to use for the old AM format--
> the phase change creates an additional AM modulation, if you take in
> consideration that effect by the decoding the modulation, you could
> recover the time information "despite" of the presence of the PSK.....
> Question: as fare as I am informed there is no chip/system available to
> correctly decode the new signal form, what was the purpose of the whole
> modulation format change?
> The old AM format was happy with cca 200Hz bandwidth to recover the time
> information, which was utilized in many professional receivers, which
> used a crystal filter for 60kHz, for the PSK format the required
> bandwidth is at least five times wider, so crystal filter would be
> problematic and much more costly, the higher required bandwidth brings
> also more noise ....actually where is the advantage of the new
> modulation scheme?
These days I suspect nobody would use a crystal filter. You'd digitize
at some useful rate and implement your filter in software. The real
question would be how many bits do you need in the ADC and how fast do
you run it.
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