are u not able to see 33pF and 22pF caps for positive feedback!Audioguru said:I don't see an oscillator because there is no positive feedback.
I see the output of an LM386 power amplifier trying to drive the dead short of the output of a 5V regulator that feeds 5V to two varactor diodes.
The extremely low impedances of the output of the power amplifier and the 5V regulator are shorting the varactor diodes.
The 9V regulator will not work unless its input is at least 10.5V or more.
The AC output impedance of the 5V regulator is a dead short. You are supposed to feed 5V through a series resistor to the vari-caps. The resistor prevents the shorting.aj_silverthunder said:http://www.flickr.com/photos/aj_silverthunder/4168982201/
how can the 5 volt short the two varicap diodes,the maximum voltage rating of BB139 is 30V!
No.aj_silverthunder said:if i add a 1k ohm resistor between the 7805 and the junction of the varactors. that will avoid shorting!am i right!
or can i increase the value of the resistor to 10K ohms .what do u say audio guru...
so then will i place a 56K inbetween 7805 and the varactor diodes!Audioguru said:No.aj_silverthunder said:if i add a 1k ohm resistor between the 7805 and the junction of the varactors. that will avoid shorting!am i right!
or can i increase the value of the resistor to 10K ohms .what do u say audio guru...
1k is far too low. The original circuit had 56k. it also had a 100k resistor from the audio source.
but if i will use 100K preset to lower the audio power from LM386!pranam77 said:As already mentioned by "Audioguru" the vari-cap diodes are connected to regulated 5v volts directly which will never work. Another point to be noted is that LM386 output which can drive a speaker, is directly connected for diode intersections which will over modulate the audio...Cheers
No.aj_silverthunder said:but if i will use 100K preset to lower the audio power from LM386!
and i can control the modulation level!
The cicruit requires just low level input, even directly from a condensor mic or with one stage of amplification will work fine. Why to amplify with LM386 and drop it with resistors again?...cheersaj_silverthunder said:but if i will use 100K preset to lower the audio power from LM386! and i can control the modulation level!
It is probably poor because the antenna connects directly to the oscillator and anything that moves toward the antenna or moves away will change the capacitance of the antenna and transistor which will change the frequency of the oscillator.aj_silverthunder said:tell me how is the frequency stability of the oscillator!
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