LF: MSF Is wrong

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

Last night, on another Group, G3PLX commented that his measurement of MSF timing showed an error and invited some others to check.

By feeding a GPS 1pps pulse into an SSB receiver on top of the wanted signal, then displaying the resulting output tuned for a 1kHz tone, the timing relationship between the MSF envelope and the UTC mark from GPS can be seen independently of any receiver introduced random delay.  I used my 5061 with its own PPS output offset by 20ms  to trigger the scope to observe and error.   Group delay in the SSB filter is, AFAIR from measurements made many years ago, around 1.6ms 

and...   sure enough ...   MSF is approximately 17ms 'fast' which is the figure Peter confirmed.

The two photos show the result looking at  MSF and the DFC77 signal respectively.  Scope display is 5ms per div.   I am 736km from Mainflingen, the DCF77 transmitter, which should result in a 2.45ms delay .  Depending upon how my IC746's  SSB filter treats an impulse,  it looks close enough for govt. work.  So that transmitter is correct.

MSF is clearly "wrong".   At least it's frequency is still spot on - or at least appears to be compared with my 5061A after a mere 1 hour phase check.

Andy  G4JNT

http://www.g4jnt.com/DropF/msf_timingerror_higherres.jpg

http://www.g4jnt.com/DropF/dcf77_timing_higherres.jpg

Andy  G4JNT

On 25 February 2016 at 07:39, 'Peter Martinez' Peter.Martinez@btinternet.com [rsgbtech] <rsgbtech@yahoogroups.com> wrote:

 

Andy:

Thanks for doing those checks. I deliberately didn't give my own
measurement result, to make sure we didn't influence each other's
interpretation, but your 18msec early agrees well with my estimate of
17msec. early. I did it by listening in the upper sideband. That gives me
similar clicks from both the GPS and the MSF keying edges. I measure the
time delay with a software scope since I no longer have a working real
scope - I would need ANOTHER scope in order to repair it!

This result surprised me because I am sure it has always been right before.
My first thought was that there was something wrong with my GPS (a Trimble
Palisade which I think you know), but I checked the timing from LORAN
(transmitted from the same site as MSF) and that showed the correct time
delay for the distance. You seem to get DCF77 exactly at the PPS pulse, and
so do I now. I seem to remember it was 4msec. late which is roughly what I
would expect. Maybe DCF77 is early by a few msec too.

I wonder why MSF is early? The Chinese time signal BPM on HF is always
early too but I can't remember the exact figure. Perhaps they are all
compensating for the delay through a particular receiver.

I am currently logging the phase of MSF against GPS to see how stable that
is, especially at night, although it should be pretty good here since it's
only 70km away.

73
Peter G3PLX

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Posted by: "Peter Martinez" <Peter.Martinez@btinternet.com>

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