Re: LF: More Phase plots

[Andy Talbot <andy.g4jnt@gmail.com>]

It was Peter who told me about the offset, and I wondered if I could also see it - rekindling my interest in coherent LF reception  (and many hours of VB programming to update the receiver display software) !

I just looked at the central 100kHz spectral line.  If you filter the signal narrow enough it appears very clearly

Are you implying it is a function of the imbalance, because I've always assumed its just "there"

The attached spectral plot is with a lower decimation applied, so showing several Hz either side. The 7.5Hz (or whatever) spikes due to the PRI are there.

Andy

On 31 March 2018 at 10:52, Markus Vester <markusvester@aol.com> wrote:

Hi Andy, LF,

the frequency offset on the Loran signal has been present since Friday (Mar 24). It showed up as a rainbow pattern on my monitor
http://df6nm.bplaced.net/LoranView/LoranGrabber.htm
and was immediately confirmed by Peter G3PLX, who then communicated the problem to the ooperators. It looks like the frequency offset is alternating between exactly +1ppb and -1ppb, as if a digital timing control unit were going rail-to-rail while attempting to to lock to the proper time.

Peter had discovered a similar phase-drift fault already in August 2016. This was later fixed, but has left a permanent timing error on the master pulsegroup (on LoranView the trace is slightly left of it's.slot)

Andy did you actually undo the Loran pulse phasecodes for your measurement, or simply look at the 100.000 kHz spectral line which results from the unbalance of the phasecode scheme (ratio of 11 to 7 positive to negative pulses for master, 10 to 6 for secondary) ? 

Best 73,
Markus (DF6NM)

-----Ursprüngliche Mitteilung-----
Von: Andy Talbot <andy.g4jnt@gmail.com>
An: LineOne <rsgb_lf_group@blacksheep.org>; rsgb_lf_group <rsgb_lf_group@yahoogroups.co.uk>
Verschickt: Sa, 31. Mrz 2018 9:40
Betreff: LF: More Phase plots

While I'm still on a roll with high stability off-air monitoring, here is a plot of the one remaining 100kHz  transmission, from Anthorn, taken overnight.  

http://www.g4jnt.com/DropF/clipboard_201803310831.png

It has been reported by a few amateurs that this is exhibiting a 1 PPB frequency error, and that is clearly visible on my plot.  The rest of the wobbles are multipath.   Although a pulsed signal, when filtered to a narrow-enough bandwidth a stable spectral line at [exactly] 100kHz appears.

There is some quite spectacular fading

Andy  G4JNT