[time-nuts] Near-perfect chip for Loran-C frequency receiver

[Kasper Pedersen]

Bruce Griffiths wrote:
> Your original loop antenna should have a lower phase tempco 
> (particularly if a lower TCE coil former than a plastic lid is used) 
> than any ferrite antenna, particularly so if the antenna is resonated.
> Quartzlock have abandoned the use of ferrite antennas and substituted a 
> balanced shielded loop antenna for this reason for their VLF phase 
> tracking receivers.
>   

When I built a DCF77-DO (selective I/Q front end, the rest a software 
radio in an AVR), I ran into this problem of phase tempco. A loop was 
better, but it was unhandy, and I still had phase drift in the 
amplifiers, filters and mixer propagation delay.
My fix was to have a tiny transmitter loop near the antenna (just the 
feeder cable termination resistor). Once in a while the microcontroller 
generates a 77.519kHz carrier, gets a phase measurement using the same 
frontend and I/Q mixer, and uses this for compensation.
DCF77 does wiggle quite a bit at dawn, plus there is the occasional 1us 
phase adjustments at the transmitter end.

http://n1.taur.dk/dcf/    (~100km NNW of PHK)

I recall having seen better than this with Loran?

/Kasper Pedersen