[ARC5] BC-453 drift

[Bob kb8tq]

Hi

I’d step back a bit and look at what’s in the radio. Have there been any repairs done?
Did parts get swapped out as part of the repairs? Putting a Y5V cap where an NPO / 
mica used to be will create all sorts of “fun” issues. Equally a mica that has a cracked
package will do odd things on and on forever. Same thing applies to a coil that took a 
blow in some previous life. 

The simple answer on the BFO vs LO is (as mentioned elsewhere) to inject a stable 
signal into the IF. In this day and age, a square wave off a sound card might be an 
adequately good signal to do the job. Just pick the right harmonic and go. 

Bob



> On Nov 4, 2017, at 11:43 AM, J Mcvey via ARC5 <arc5 at mailman.qth.net> wrote:
> 
> Still trying to get a handle on the drift problem.
> I disconnected the lower bleeder/bias resistor (R23) and installed a Zener stack that added up to 109V.
> 
> The radio sound OK on CW, but has an almost imperceptible slow drift to higher audio frequency on the WJST-x 
> waterfall. It's more pronounced on WJST-x because the waterfall is very slow, so it shows the drift over time better.
> Doesn't look bad on FL digi, but if you notice where you start and where you are in 10 minutes, there is quite a spread.
> 
> In 15 minutes it went from 1050 Hz to almost 1400 HZ and doesn't seem to be slowing down.
> I used a beacon with a reasonably strong signal to do the tracking.
> I zero-beated the signal at 1050 then watched the drift. When I turned the BFO off, the audio was still at 1050.
> The beacon is AM , so I guess the IF's would still be broad enough to compensate for the front end drift?
> If the BW is say, 1000 HZ, a 400 hz shift in the LO should start degrading the signal-right? The signal sounds steady and when I fiddled with the tuning , It could not make it batter than it already  was. I think the bigger issue may be the BFO.
> I'm trying figure out if it's the BFO or the LO- or both...but it ain't easy!
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