[ARC5] BC-453 drift

Sun Nov 5 11:20:07 EST 2017

Hi

The 453 does not have the selectivity to be a super duper weak signal CW radio. At least
the ones I have had always did a fine job of getting down to the atmospheric noise on
the frequencies they cover. Yes, that is in part a function of the amount of noise on those
bands …. It also is a function of antenna length. I rarely run < 50’ of wire on a radio down 
there. 

Bob

> On Nov 5, 2017, at 11:21 AM, K5MYJ <macklinbob at gmail.com> wrote:
> 
> Consider what this receiver was designed for. As a navigation receiver the amount of drift you are seeing did not matter.
>  
> This receiver is a poor choice as a weak signal receiver.
>  
> Bob Macklin
> K5MYJ
> Seattle, Wa.
> "Real Radios Glow In The Dark"
>> ----- Original Message -----
>> From: J Mcvey via ARC5 <mailto:arc5 at mailman.qth.net>
>> To: ARC-5 List <mailto:arc5 at mailman.qth.net>
>> Sent: Sunday, November 05, 2017 6:47 AM
>> Subject: Re: [ARC5] BC-453 drift
>> 
>> Thanks to all who have responded. It's not that I don't have access to good test equipment, it's just that I don't have that much at home where the radio is at the moment. It will go to my shop on Monday for further analysis.
>> 
>> However, I am a bit puzzled as to the "why" of the drift. The BFO is an "air variable" tuned LC . There is a 1000pf mica inside the can, but that is only a used as a bypass cap, not tuning. It checks out OK on ESR as well.
>> There isn't much to it to be defective!
>> An LC oscillator can be reasonably stable, because I have an ancient URM-25D that once warmed up, only moves a hertz or two, according to my freq counter.
>> My HP 8935 only goes down to 400KHZ , so for some MF and VLF , I actually use the URM-25D below 400HKZ..
>> 
>> I'll loosely Couple the freq counter into the oscillator and set it aside , checking for drift periodically.
>> One or the other or both are drifting, so that is what has to be determined first.
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> On Saturday, November 4, 2017, 11:48:46 AM EDT, J Mcvey via ARC5 <arc5 at mailman.qth.net <mailto: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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