[ARC5] BC-453 drift test

[Tom Lee]

Yes, WSPR is definitely more challenging!

The capacitors you changed -- I assume that a couple were part of the LO 
tank (say, C-8 and C-10 in the schematics I have). Is that right, or did 
changing others reduce the drift? I'm curious...

Tom

-- 
Prof. Thomas H. Lee
Allen Bldg., CIS-205
420 Via Palou Mall
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu
650-725-3383 (public fax; no confidential information, please)

On 1/10/2018 5:24 PM, J Mcvey wrote:
> The test was done at a more or less arbitrary frequency. The LO 
> started at 540Khz and ended up at 539.300Khz give or take a few hz.
> So, yes that would be about 0.13%.  However 700Hz and 1Hz/second  is a 
> big deal with WSPR! Once it settles down, I can decode WSPR, though.
> The radio stabilizes faster now that the caps were all replaced. It 
> used to take twice as long to get there. Going to give a try again 
> tonight.
>
>
>
>
> On Wednesday, January 10, 2018 7:48 PM, Tom Lee 
> <tomlee at ee.stanford.edu> wrote:
>
>
> Without knowing the LO frequency it's hard to give a precise answer, 
> but that warmup drift represents roughly a couple tenths of a percent 
> at midband. That sounds reasonable, as does the warmed-up drift. The 
> dropping in frequency during warmup is consistent with the inductor 
> and capacitor expanding as it heats up (L and C both increase under a 
> linear expansion), so it makes sense.
> -- 
> Prof. Thomas H. Lee
> Allen Bldg., CIS-205
> 420 Via Palou Mall
> Stanford University
> Stanford, CA 94305-4070
> http://www-smirc.stanford.edu <http://www-smirc.stanford.edu/>
> 650-725-3383 (public fax; no confidential information, please)
> On 1/10/2018 3:45 PM, J Mcvey via ARC5 wrote:
>> I recapped this radio and tested the LO drift afterwards.
>> Coupling the plate via 7pf cap and a x10 scope probe to a frequency 
>> counter, the results were as follows:
>> The LO dropped in frequency at a rate of about 1 HZ / second upon 
>> power up.
>> The drop rate slowed until it more or less stabilized an hour later 
>> 700 Hz lower than the start up
>> measurement.
>> Once at the bottom of the descent, it would sit and go up and down a 
>> couple of Hz in a very slow undulation.
>>
>> I guess this a normal warmup scenario? What say you?
>>
>>
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