F3WT <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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Thank you , Bob!
73 and season's greetings to all.
Pierre - F3WT
Le 21 déc. 05 à 00:36, Robert Donnell a écrit :
I feel like the two-filters in the transceivers was a continuation
of the theme of the 2A/2B receivers, where changing sidebands was
actually moving the filter response, with respect to the BFO.
You've all probably seen some of the rigs from other makers, with a
single filter and analog VFO. When you changed sidebands, you had
to either use a different tuning mark, or recalibrate against the
100 kHz crystal, to account for the carrier being shifted about 3
kHz between upper sideband and lower sideband. With Drake rigs
this was not necessary, since the carrier oscillator stayed put.
The first Drake transceiver I owned was a TR-3, and I felt like the
dual filters gave the radio an upscale flavor, in addition to the
potential for improved frequency stability in the local oscillator,
because the only time it changed frequency was when it was shifted
into the passband for CW transmission. Shifting the carrier
frequency instead of using (and switching) a second crystal was
undoubtedly a cost saving measure, probably to offset the cost of a
second filter, and perhaps to save from having to build potentially
less-reliable or less-stable real-time crystal switching.
Also, shifting the VFO, to compensate for shifting the carrier
oscillator, would have been virtually impossible to make track over
the full range of the VFO, without having a second slug-tuned
inductor to either swap between, for sideband changes, or to offset
the VFO the proper amount at all points in the tuning range, when
the alternate sideband was selected. That sounds like my idea of a
technician's nightmare. I'm betting just getting one slug-tuned
inductor to track a 12% frequency range change with linear
frequency change vs. slug insertion was not trivial to learn how to
do.
In any event, I thought the dual-filter arrangement more elegant
than the alternative.
73, Bob, KD7NM
---------- Original Message ----------------------------------
From: F3WT <[EMAIL PROTECTED]>
Date: Tue, 20 Dec 2005 22:26:05 +0100
F3WT <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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Hi Garey,
Very clear explanation below!
I have a related question I was wondering about for a while:
Why were TR4s - and others by he way - designed with 2 sideband
filters and 1 Xtal ( 9MHz ) rather than todays set of 1
sidebandfilter and 2 Xtals (SSB) or 3 including CW?
Was it a problem then shifting VFO without loosing stability?
73, Pierre - F3WT
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