Toneburst

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hamtech

Member
I am installing a remote head for.a mobile transceiver in my car and as i am unable to use a microphone whilst driving i Will be using aheadset, which is my problem. i need to be able to access the repeater near to where i live. This takes the form of a 1750hz tone burst lasting for about 2 seconds n to of the radio signal I have built a circuit using a 08m2 chip. It activates a tune sound for about 2 secs but i cannot get a tone close enough to open the repeater.

i am using a tune command tune pinc.2, 30,(d8/9) tried both.... . To generate a tone close to 1750hz. Is it possible to be more accurate as i. am 30 or so hz off frequency. i have tried sound command but cant getter any better.

I get a nice square wave out butthe wrong freqency, i pass square wave through a low pass filter to make it near sinusoidal. Just need a command to give me 1750' i cant seem to crack it. T hanks for your help in advance.
 
H

hamtech

Member
Srnet,
Thanks using the wizard got what i needed, my only problem is getting the repeater to respond - it doesnt.
However if i put a speaker on the output of the 8m2 on my breadboard it will with a mic connected to the radio open the repeater using the generated tone. When i get clever and use it in circuit it refuses to open the repeater.. I am mystified..
 
S

srnet

Senior Member
Could be to do with level, or harmonics.

The microphone may have a fairly effective and narrow filter on it for instance.

You would need to compare the two transmitted waveforms to check for any differences.
 
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Goeytex

Senior Member
My guess is harmonics caused by the sharp square wave.. You could possibly soften the edges of the signal with a low pass filter. If the level is too high then a voltage divider might solve that.

But, wouldn't a sine wave be better?

While it would be complicated to have a Picaxe generate a sine wave, a dual OP AMP can do a pretty good job of it. I have had pretty good luck doing a quadrature oscillator using an LM358.

http://www.ti.com/sc/docs/apps/msp/journal/aug2000/aug_07.pdf
 
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