[time-nuts] WWVB d-psk-r down conversion method
csteinmetz at yandex.com
Mon Sep 22 19:56:28 EDT 2014
>One of the methods suggested for working with the wwvb psk is down
>converting to a lower frequency. When experimenting with NAA I had built a
>24 Khz receiver that down converted that signal to a 100 Hz base band.
>It was a minor effort to shift it to 60 Khz by changing the LO.
> * * *
>for 100 Hz the LO must be at 60.1 or 59.9 Khz. Or synthesize it etc.
> * * *
>Not sure there is a real need to lock the LO at all.
I'm not sure I understand how this helps.
I thought the point of removing the PSK was to reconstitute a version
of the original unmodulated carrier, so it can be used to discipline
an oscillator at some convenient frequency (the PSK needs to be
removed because it upsets the PLL phase detector). That works (in
theory) with a TRF receiver, because the received carrier IS the tx
carrier that is locked to a standard at the transmitter (modified by
the propagation delay and delay variation, and then by
doubling/squaring). But once you convert the received frequency by
using a LO (or BFO, whichever you want to call it), the recovered
carrier frequency is dependent on BOTH the tx frequency AND the
LO/BFO frequency. You have lost the link to the tx frequency standard.
Am I misunderstanding the goal of the exercise?
More information about the time-nuts