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Suitable oscillator for 53KHz stereo MPX input in FM transmitter

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Willen

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Hi,
Searching about 3 years I got very nice solution by Dick Cappels (member here too) and going to make this stereo encoder for FM transmitter. He used simple colpitts oscillator which has 1nF base capacitor to ground. Some people worry about this capacitor because upper frequency of 53KHz MPX might be cut down. Mr. Dick played with it but he got nice channel separation. Increasing the cap value, he got R is being decreased.

So I am feeling to use another type of oscillator (maybe Hartly?) which will accept whole 53KHz MPX without any error and which will modulate FM nicely without noises. I simulated a circuit too- what about it? Any improvement? My another main problem is 'Modulation Factor' because I cannot see effectiveness of MPX modulation to carrier. 'Carrier factor' is fine in simulation.

(I have collected four another circuits too, will attached here but as a #2 post because using cell phone I cannot upload two photos at the same time.)
 

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  • Stereo OScillator.GIF
    Stereo OScillator.GIF
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Last edited:
And here I collected some oscillator too. I want to be engage with simple one and really nice one. If my OP simulated oscillator is completely nice then I will make that one.

I think oscillator here (#2-ABCD) all are almost same. B looks like powerful, isn't it? Probably all are same in the case of 53KHz acceptance but again main factor is effectiveness/quality of modulation, isn't it? Thank you!
 

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  • OSC collection.GIF
    OSC collection.GIF
    62.1 KB · Views: 156
My FM transmitter uses only 470pF for the C4 in the similar FM transmitter circuit from Dick Cappel where he used 1000pF.
Then the 53khz is not attenuated much. If the output impedance of the stereo encoder is also reduced maybe with audio opamps then the response at 53kHz will be perfect.
 
I built a version of dick's circuit too, only I dont have a avr programmer so I used a pic with a simple program, the pic even uses its built in rc osc, it works fine, it would have to drift quite a way to notice the difference.
 
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