Hi Alberto,
What an interesting experiment !
Do we have any idea about the internal workings of the "inexpensive", Conrad
clock ?
I was wondering if it contained some logic circuits, or even a
microcontroller, to derive the 1Hz pulse from the transmitted signal, and
whether there chould be any gradual change in the output caused by the
varying delay across the logic gates in the clock.
I'm thinking of the sort of delay you get between the input and output of an
invertor when it changes state.
This delay could be supply voltage dependant, although you seem to have
ruled out temperature variations with the climatic control in your nice cozy
shack !
73
Hugh M0WYE
----- Original Message -----
From: "Alberto di Bene" <[email protected]>
To: "LF Mailing List" <[email protected]>
Sent: Tuesday, March 09, 2004 11:57 AM
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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