Hallo lowfers.
On 22-May-02 hamilton mal wrote:
----- Original Message -----
From: Vernall
To: [email protected]
Sent: Sunday, May 19, 2002 10:40 PM
Subject: LF: Re: pegelmesser
Mal,
The frequency stability of any selective level meter with a VFO for a local
oscillator makes them suspect for staying tuned within a fraction of a Hz for
long periods. The digital display on a Siemens D2019 I have merely counts
the VFO (with a constant 100 kHz offset to give passband centre frequency)
and numbers actually change with VFO warmup. The display is to 10 Hz, so it
can not be used for pre-setting to a QRSS signal that is expected to be below
the noise and therefore impractical to try tuning by "ear". As well, the BFO
is a free-running RC oscillator so the recovered audio can have further drift
of centre frequency.
I agree but some WG selective level meter are provided by an external local
oscillator input, to be used when the instrument is coupled with companion
generator. If you know the IF frequency you can order an appropriate Xtal
and build an XFO for 136 kHz.
There are some selective level meters with master oscillator arrangements
for tuning and demodulation, and can have fractional Hz stability.
In saying the obvious, selective level meters are primarily intended for
determining signal levels.
Hello Bob
Look for a pegelmesser with phased locked loop oscillators, synthisized etc
the same as mine and you will find they make a great LF receiver, especially
the models with the 20 hz filters.
Even the free running osc type are useful if kept switched on all the time
and inside the house with a fairly constant temperature and not outside in
the bicycle shed!!
I do not have any trouble resolving and keeping signals within the 20 hz
bandwidth for hours at a time. I especially like the W&G SPM-12, with the 10
khz IF output. I built an external product det, audio stage and it works
extremely well, very sensitive and the filters are well suited to LF work.
Another W&G very useful is SPM-15, synthetized, 3100 and 25 Hz filter, with
generator in the same case but useless without a low-pass or tuned filter
bitween the antenna and SPM.
73 de Mal/G3KEV
Bob ZL2CA
73 de Claudio
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Claudio Pozzi http://www.qsl.net/ik2pii happy Linux user
E-Mail: Claudio <[email protected]> <[email protected]>
Date: 22-May-02 Time: 18:59:11
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