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Thursday, 1 January 2015
21.4 MHz VCO frequency modulated with 1 KHz
Testing -- first personal video upload to YouTube. (Content from 2013)
Hi Vasily, Nice schematic,as I see it's a series tuned colpitts oscillator.The two MV-209 varicap helps the stability of the circuit or with the 150μH choke are a kind filter? A question, I'm going to assembly soon,can you tell me how to apply AF signal? Thanks for your help and your time. Kostas,Greece.
Greetings and thanks! The 150 µH RFC exhibits high reactance (~ 20 k ohms) to the ~ 21.4 MHz carrier frequency to prevent the carrier signal from leaking into the modulator circuits. The 1 µF series C does the same --- this time 7.4 Meg ohms X ) Further, the 100K decoupling resistor serves the purpose; except it's for both RF + AF (has RF and AF bypass after it].
The swinging AF AC signal causes the varactor capacitance to vary and in tandem, this varies the deviation of the carrier frequency.
An op-amp mic amplifier with low output Z with a series output "build out" resistor such as 1K has worked for me. A transistor mic amp also worked fine in the "old days". Adjustable drive.
Hi Vasily,
ReplyDeleteNice schematic,as I see it's a series tuned colpitts oscillator.The two MV-209 varicap helps the stability of the circuit or with the 150μH choke are a kind filter?
A question,
I'm going to assembly soon,can you tell me how to apply AF signal?
Thanks for your help and your time.
Kostas,Greece.
Greetings and thanks!
ReplyDeleteThe 150 µH RFC exhibits high reactance (~ 20 k ohms) to the ~ 21.4 MHz carrier frequency to prevent the carrier signal from leaking into the modulator circuits. The 1 µF series C does the same --- this time 7.4 Meg ohms X )
Further, the 100K decoupling resistor serves the purpose; except it's for both RF + AF (has RF and AF bypass after it].
The swinging AF AC signal causes the varactor capacitance to vary and in tandem, this varies the deviation of the carrier frequency.
An op-amp mic amplifier with low output Z with a series output "build out" resistor such as 1K has worked for me. A transistor mic amp also worked fine in the "old days". Adjustable drive.
Best!
Todd