Hi
Interesting thoughts. I would have to check the handbook at home.
It is also a problem with overload, and this could be solved partly
adding an AGC to the ADD-ON unit. Depends on the IF level how
complicated it would be.
Perhaps it is not worth, but it is always worth investigating into
when documents are good. SO42P is my favourite device for productdetector/mixer.
SPM-3 is another interesting unit, but I believe the selectivity
is based on LC-filters, and it really is too broad. Have kept a few for possible
interest for 136kc activity in Norway.
73
Jan-Martin
LA8AK (JO38XC)
-----Original message-----
From: Alan Melia [mailto:[email protected]]
Hi all, yes the output from most of these things is the "IF"( and so is from
a carefully designed defined-gain amplifier), there is an Option for the
SPM-12 which is an SSB demodulator. Several LF users have build add-ons to
the standard SPM-12, which has a 10kHz output. It should be possible to use
a chip like the NE602/612 to make a simple demod even at audio frequencies
plus a filter for the image. A relatively simple single pi-section LP filter
with a rejection notch at the image frequency should be adequate for
confortable listening. I did work out the details for the SPM-3 (1.5kHz)
but never built it.
If you want something more sophisticated Zetek have launched a chip with a
mixer and (external component) configurable filter module in it, which is
available from Farnell I believe.....this has a maximum operating frequency
of 600kHz so could even be used as the basis of a simple receiver on 136k.
It was covered in one of the mags (possibly EW) sometime in the last 12
months. I have details somewhere.
Whilst it could work for strong signals, I have my doubts that a divider
chip would be much use with weak signals and lots of noise. Dividers are
used in Bat Detectors, but mixer versions are much better......the bat
conservationists are finding that soundcard DSP programs, like Spectrogram,
are helping them to identify individual bats !! I suppose that is the sort
of thing Robert originally wrote it for !!
Cheers de Alan G3NYK
[email protected]
-----Original Message-----
From: [email protected] <[email protected]>
To: [email protected] <[email protected]>
Date: 04 November 2002 08:14
Subject: LF: Siemens D2006 Selective Level Meter/Pelelmesser
Hi
Does somebody know if it is possible to change the pitch?
It has 80Hz as well as 3100Hz bandwidth, but the pitch is ca
1000Hz and not too pleasant to listen to, would rather prefer 500Hz
73,
Jan_Martin
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