Hi Jim:
Thanks for the note. Let's see if I can describe to you what I
see. After even a short transmission of, say, 5 seconds, running
something like 5W, the frequency of the received PSK-31 signal slowly
moves to the left on the waterfall display of my MixW program traveling
about the width of a typical PSK-31 signal in about 2-3 seconds. There
seems to be no greater frequency shift running 50W for periods up to 1
minute duration. I am not sure if my TX frequency is varying. I can't
tell by ear at this point on another receiver. I have a frequency
counter, and can measure the TX frequency on CW if that will provide any
insight. The PS should have no voltage sag at this low power level. I
use it for other projects. It is a commercial switching supply SEC
1223. Since I didn't really suspect the PS, I haven't as yet done any
measurements. on it. I certainly appreciate any assistance you can
provide.
Brian K7RE
Jim Lux wrote:
> At 12:22 PM 12/31/2006, Brian Kassel wrote:
>
>> Hi Ross:
>>
>> As I had mentioned in 2 messages to Tim:
>>
>> "I also got a reply from Ken, N9VV. He basically agrees with you, and
>> I gladly accept the turn on drift, no problem. I stand informed and
>> educated by you both, thanks!
>>
>> What does bother me though is the drift that occurs for about 2
>> seconds after going from TX to RX. This same amount of drift happens no
>> matter what power level is run, and no matter for what time period the
>> transmission occurs. Makes for tough operating in a digital mode
>> contest, which is my main operation here. I have never seen this
>> mentioned on the Flex reflector. Owing to the fact that the drift
>> amount and time to stabilize remains the same, it doesn't seem like any
>> temperature related phenomena. If this is inherent to normal operation
>> of the SDR-1000, then it would appear that either the K2WS mod, or the
>> GPS mod may be in order. I really want to be sure though before I spend
>> the big bucks, that there is no other alternative. "
>>
>> " I should have mentioned before that I did indeed test with the AFC on
>> and off in both sound card programs (MixW and Digipan), no difference in
>> the drift was seen in any case, still a few tens of Hz. "
>>
>> So even accepting the short initial turn on, I am still saddled with
>> the TX-RX drift. Also, I am not totally sure that going with the K2WS
>> or GPS mod, the TX-RX drift will be cured. Still open for any ideas!
>
>
>
> Something weird is going on. There shouldn't be that much change in
> the frequency just changing from Tx to Rx and back. Is your power
> supply voltage varying (although, I think the XO runs off a regulated
> 5V)? Is the frequency change a "step" change or a slow drift to a new
> steady state (where slow is a couple seconds)..
>
> My SDR1000s (old ones, no thermistors) drift on initial power up, but
> are rock steady shifting between Tx and Rx.
>
>
>
>
> James Lux, P.E.
> Spacecraft Radio Frequency Subsystems Group
> Flight Communications Systems Section
> Jet Propulsion Laboratory, Mail Stop 161-213
> 4800 Oak Grove Drive
> Pasadena CA 91109
> tel: (818)354-2075
> fax: (818)393-6875
>
>
>
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