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LF: Re: Ionospheric doppler ?

To: [email protected]
Subject: LF: Re: Ionospheric doppler ?
From: "Marek SQ5BPM" <[email protected]>
Date: Tue, 9 Mar 2004 18:29:08 +0100
References: <[email protected]>
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Hello Group,

  I made yesterday an interesting experiment and would like to know
your opinions about it.
Hello Alberto and all,

I think that the accuracy will never be sufficient for this kind of
measurement. Remember about the frequency you are using for synchronization,
77500 Hz, so you'll never get much better accuracy than 1 / 77500 Hz = ca.
129 uS. Accuracy like this is only achieved by expensive receivers using the
phase component of the signal (I've read something about 50 uS). This
probably cannot be achieved with simple receivers that detect the moment of
the DCF pulse start/stop. The narrower is the bandwidth of the receiver, the
more difficult it is to tell exactly the moment the pulse actually started
and little _amplitude_ variations can influence the detector, probably much
more than phase changes. On the other hand - the wider is the bandwidth of
the receiver, the more noise it picks up and it gets more difficult not to
be disturbed by the noise itself...

I think however that phase variations could be measured by checking for
changes of phase of the signal carrier itself, at worst downconverted with a
mixer and phase-drift-free BFO. You would have to cope then with
phase-encoded data however...

Excuse me if I am wrong somewhere above.

73! Marek SQ5BPM

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