After refurbishing the 137 kHz preamp, I'm back on LF - Rx only -
The wideband 455 kHz ceramic filter has been replaced by a 600 Hz
mechanical filter, mainly to improve the RX's dynamic.
I don't know if it is any better yet ...
The frequency chirp is noticeable on the night capture. Hope you
can get rid of it soon.
The Loran-C lines are best received during the day due to a lower
band noise. They give a precise idea of the overall stability.
73 and HTH
Michel - f5wk
Le dimanche 2 juin 2013 à 16:07:53, Jcraig écrivait :
Hi Stefan, Markus and Group,
Thanks for looking Stefan. The ERP was down until the second Decca
module was switched in at 2330 bringing the output power from 150 to
450 watts (3.2 amps to the aerial.) After this the signs appeared on
the DF6NM grabber.
Thanks to Markus for the detailed report. The next steps are to reduce
the 0.02 Hz chirp, frequency offset and phase glitches. I am grateful
for your finding these and providing a progress report.
The breadboard comprises an Oscilloquartz 8663 10 MHz DOCXO which feeds an
AD9851 clocked at 60 MHz. The dds programming and keying is done with
an arduino. The DOXCO is calibrated against WWV by averaging out the
diurnal ionospheric doppler shifts over a period of a week.
I think the offset could be improved by setting the DDS to 13.777 MHz
and dividing by 100 and the phase glitches/chirps could be reduced by
using a better power supply for the DOCOXO. Bumps can be seen in the
spectrum of the DOCXO at 10 MHz which are presumably due to the
heaters being switched on and off and causing supply voltage
Thanks also to Vern who is still running his grabber with strong signals
being copied during the day. I'll leave the TX on until tomorrow ~1000
73 and tnx agn
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