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GQ beat note.

A

Anonymous

Guest
Hi,
I've recently built a timing module for my GQ that plugs into the decade counter socket after its removal. It has a 12F PIC driving another counter on the module, so that some timing is selectable and is not all sequential to the clock.
With the reject control, I can alter the delay between 7us and 15us. By depressing one push button, the reject control will now alter the pulse width from between 40us and 80us, and by pressing another push button the reject control alters the sample width between 7us and 15us.
While experimenting with various settings I
 
Hi Kev,
The only thing on the board that could beat with the pulse/sample frequencies is the audio generator. This circuit is suffiently decoupled so that there is no obvious breakthrough or interaction, but there could be a low level effect. How it could enhance weak signals though, is not clear. Perhaps you could program the PIC to generate the audio chopping square wave so that it is synchronous, and see what happens.
Eric.
 
Hi Eric,
Good thought, thanks for that. My chopper is running at about 560Hz and the strange audio band occurs around the 14us delay region, this would mean it would have to be an 11th or 13th harmonic causing the (positive) distortion?
If I try a chopping frequency of 700 to 900 hertz it should move the band up around the 10us delay region, I'll let you know how I get on.
However, it seems that this may be peculiar to my unit since nobody else seems to have noticed it, judging by the lack of comments anyway.
I wonder if the de-coupling cap has dried out on my unit, I think you used an electrolytic on the chopper?
Cheers
Kev.
 
Hi Kev,
I am glad to hear you got your circuit working. Sounds like it is working great. That is a good thing.
Now, as to your problem, I am hoping you can provide a few more details as to when this particular condition exists. By this I mean, does it happen at a certain pulse width and if so, what is that width. Does the delay have to be at a certain setting also? In other words, do two or more conditions have to occur to produce the odd results, and if so, just what are those conditons, specifically.
I have run into a few strange things over time but have had most disappear as improvements were made. One thing that still exists is something like a tone beating when the delay and pulse width are long, which I suspect is caused by a drop in battery voltage during the pulse on time, which is producing a beat with the audio.
I just built a regulator into a new battery pack and now I need to see if the problem minimizes. I am now trying LI Ion batteries and regulating the 14.4V down to about 12V. This battery pack is lighter than my standard 10 pack of NiMh's.
Reg
 
Hi Reg,
Nice to hear from you, was a little worried you hadn't contributed.
I will answer your questions soon, I'm doing surgery on GQ at present, it's all disembowelled, and I've been crook, had some days in bed.
It's not a problem with the GQ, I want to enhance this effect if I can. It does occur at later reject times, I'll get back to you later.
Cheers
Kev.
 
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