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Author Topic: VFO Stability and PSK31  (Read 744 times)
KC8RFV
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« on: February 11, 2002, 04:30:32 PM »

Just built a soundcard interface for my Ten Tec Argosy.  I can receive and transmit ok - the problem is that my transmit frequency is ~100 hz down from my receive frequency such that I can't stay "locked on" to another station during a QSO.  I suspect VFO stability changing on transmit.  I probably am only now noticing it since I am using a mode with bandwidth of 30 Hz.  Can I do anything to fix it?  Are there other possibilities for the problem?  What do you all think - you never steer me wrong.
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W8CQD
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« Reply #1 on: February 11, 2002, 05:55:28 PM »

I don't know much about the Argosy, but I use a TS-520 which has tube finals.  I've found that that radio drifts quite badly unless I let it warm about for about a hour or so before using it.

Hope that helps!

73!

Scott/W8CQD
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NB6Z
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« Reply #2 on: February 11, 2002, 06:54:07 PM »

If you have a drift problem, there may be no good answer to that except to get a newwer model radio... If the problem is an actual off-set between the TX and RX frequency, you can solve that with your PSK31 program. Some programs (like the MixW and perhaps Digipan too) allow you to use the LOCK feature to unlock the TX and RX frequencies. You can set the offset by the needed amount, and this will give you normal operation as long as it does not drift...
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KF4HEY
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« Reply #3 on: February 11, 2002, 06:56:41 PM »

My Ten-Tec Omni C has Tx down 20Hz from Rx.  The "cure" for this is to use one of the PSK31 programs that has a selectable Tx offset.  I use WinPSK2.1 which has this facility.  Simply set the Tx offset to -100Hz and enable the NET and AFC functions.  It should work fine.  If you notice a little different offset in a QSO, simply change the offset setting until your turn overs are completely aligned.  

Note that you and the other guy aren't really aligned in radiated RF but the program has compensated at the audio frequency level.  Your signals will actually be out of alignment to other people watching your QSO because you are working a 100Hz split.  So remember not to start a QSO too close to someone on your down frequency side or you will overrun them with the offset.

Also let the rig warm up about 2-3 hours and it should be OK.

73,
Mike KF4HEY
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WB6BYU
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Posts: 13243




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« Reply #4 on: February 12, 2002, 05:00:20 PM »

Sounds like the RIT is enabled.  I know some of the early Ten-Tec
transceivers the control still had a small effect, even when it was
supposedly turned off. You should be able to adjust the RIT to
make up the difference.

Meanwhile, another ham here locally had the same problem with
a different transceiver.  I suppose it could have to do with RF
getting into the sound card and  upsetting the clock frequency on
the A to D converters.  (Try transmitting with the transmit power
backed down to nothing - if the problem remains, it probably is
not an RFI problem.)
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