Garey Barrell <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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Craig -
I'm still not clear if you are referring to the transmitted signal or
the sidetone.
First off, the CW signal is NOT generated by an audio tone, as in the
32S-1. I can also assure you that this is NOT normal operation for the
TR-7. It isn't as stable as a TCXO controlled synthesizer, but it also
doesn't have the phase noise associated with this type of frequency
control system. I have used the TR-7 on PSK-31, which is probably the
most demanding mode we have with regard to frequency stability, with no
problem AFTER about a 15 minute warm-up.
You might first try exercising the sidetone frequency adjust trimmer
C1136, accessible through the headphone jack. This cap trims the 5.645
BFO crystal oscillator, and a little corrosion could possibly cause a
problem.
All frequencies involved in frequency control in the TR-7 are generated
by three crystal controlled oscillators AND the PTO. Obviously, any of
these can demonstrate instability in the event of a component failure.
The most common source of frequency instability I have found in the TR-7
is U1001, a CMOS (4016) analog switch IC on the PBT/Reference board. DC
control voltages that control the MODE shifting and PBT (by shifting the
13.695 MHz VCXO) are switched through this IC, and the failure mode is a
varying "ON" resistance in the switches. Likewise, the RIT functions
are similarly controlled by U1, a 4016 on the "parent" board.
Let us know what you find!
73, Garey - K4OAH
Atlanta
Drake C-Line Service Manual
<http://www.k4oah.com>
Craig Roberts wrote:
Craig Roberts <[EMAIL PROTECTED]> made an utterance to the
drakelist gang
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I should clarify my earlier message The CW problem doesn't seem to be
a frequency instability as much as a tone instability. Received
frequencies are stable. My readout is stable. The CW tone, however,
is not. Activating the PBT makes it drop in frequency dramatically.
So does switching to sideband mode, then back. It's gotta be a leaky
oscillator cap somewhere -- but where?? I'm totally unfamiliar with
this rig.
Thanks again,
Craig
W3CRR
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