Usually these radio controlled clocks only check the time every few hours or
when they are turned on. Normally the 1 pulse per second is just derived
from the internal oscillator and I would expectyou to see the few
parts-per-million drift of that, with a sudden correction from 'time to
time'
The fact that you were seeing a slowly changing varions plus / minus is
surprising.
I can observe doppler shift on MSF and DCF, but this is very pronounced at
dawn and dusk - a few parts in 10^-9 over tens of minutes, which is less
than the 80 - 120ns on 1 second you saw
Andy G4JNT
-----Original Message-----
From: Alberto di Bene [mailto:[email protected]]
Sent: 2004 March 09 11:58
To: LF Mailing List
Subject: LF: Ionospheric doppler ?
Hello Group,
I made yesterday an interesting experiment and would like to know your
opinions about it.
Waiting for the weather to become such to allow me to go on my roof
to install there a GPS antenna, in the meantime I started to play with an
inexpensive radio-controlled clock, made by Conrad, bought a few years
ago at the Friedrichshafen Messe in Germany, which receives the DCF-77
signal.
This clock has an output meant to drive an external electro-mechanical
hand clock, and on this output there is, of course, an 1pps pulse.
I have an HP-5328B Counter, with a 10811 OCXO which is always (24/7) on.
My shack is in the basement, with a constant temperature of 21 Celsius,
no drafts,
so any variations in the measured frequency or time is real, and not an
artifact
of the counter.
The 5328 has a sort of reciprocal counting feature, where you can use an
external signal as a gate for an internal 100 MHz oscillator, phase
locked to
the OCXO. In addition you can prescale the external signal.
So what I did was to prescale by ten the 1pps signal from the clock,
then used
this 10 second interval to count the internal 100 MHz oscillator, giving
a resolution
of 1 ns. If everything were perfect, I should have obtained a count of
exactly 10^9.
What I measured was a value that differed from the ideal by an amount slowly
changing with time, ranging from -80 ns to + 120 ns. The count was very
consistent from period to period, showing no short term random jitter.
In one case I measured a variation of about 100 ns in a time lapse of
roughly
one hour.
I am by no means an expert in propagations and ionospheric effects, so
my question
is : are the values I measured compatible with what is known about
ionospheric doppler ?
If not, what else could be an explanation of that slow change ? I would
tend to exclude,
for the reasons reported above, an artifact of the HP counter.
Thanks for any explanations
73 Alberto I2PHD
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