Hi All
I'am having some probs with a if amp that uses a mc3372 chip.

There is a crystal osc on pin1 and pin2, i'am trying to read the
frequency of the oscillator to make sure that it is 10.245Mhz.

I used a 10x probe on my counter and read 10,24258Mhz on pin 1,
(base of internal transistor), but on pin 2 (emitter of internal transistor)
i get 10.695Mhz but it is jumping around, up to 10.815Mhz, it's all over
the place.
Anyone got any hints as to what might be wrong ?.

Regards
Howard

 

Hello,

Are you currently using the decoupling capacitors as given in the datasheet schematics?
There are always a 10 μF and a 0.1 μF accross the powersupply to ground.

Bertus

 

Hi
This amp\detector is the one from QRP 2m FM Transceiver PP-002m
http://www.ariroma.it/docs/projects/pp_002m.pdf

I have built it from L4 up to and including the audio amp, as you can see
that there is only a 100nF on the in\output of ic 8 (LM7805) but no 10 μF
accross the power supply to ground.

Howard

 

Hello,

I think that using the probe on the oscillator, will put a load to it.
The probe capacitance will influence the frequency.

Bertus