[Elecraft] [K1] VFO Drift Problem

[David Gilbert]

I'd also suspect the voltage regulator first, but another possibility is 
the varactor itself. Many years ago in another universe I was the 
product engineer for tuning diodes at a large U.S. semiconductor 
manufacturer. Varactors are simply reversed bias diodes with a junction 
profile optimized for a particular capacitance-versus-voltage curve.  
Accomplishing that inherently requires wafer processing that makes them 
less than ideal for other parameters, such as leakage.  Varactors are 
normally pretty stable, but as with anything else exceptions can occur.

I have a Kenwood TS-130V with an unstable varactor-tuned RIT as proof 
(culprit verified).

73,
Dave   AB7E



On 5/5/2011 7:19 AM, Don Wilhelm wrote:
>    Matt,
>
> I would first suspect the stability of the voltage regulators.  That VFO
> is tuned with a varactor, if the voltage changes, the frequency will
> change.  If that does not settle it down, I would wind L1 on a new core
> on the suspicion that the present one is more temperature sensitive than
> usual.
>
> 73,
> Don W3FPR
>
> On 5/5/2011 1:40 AM, Matt Scholz wrote:
>> Hi -
>>
>> I am trying to reduce my K1's VFO drift to an acceptable level. The VFO
>> frequency drifts up at a rate of about 30Hz/minute (after a 5 minute warm
>> up). Even after one hour, the drift is still about 15Hz/minute. This is
>> too much, obviously.
>>
>> I have been trouble shooting this with the help of Gary, AB7MY. So far I
>> have done the following:
>>
>> * Removed C2 to isolate D3 from the rest of the VFO circuit. No change.
>> * Replaced all three VFO poly caps (one at a time). See above.
>>
>> I was wondering if anybody had any ideas on how to further trouble-shoot
>> and resolve this issue...
>>
>> Thanks in advance and 73,
>>
>> -Matt / W6ZBA
>>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>