sa602

Hi,

I am trying to use SA602 to design a mixer/osc mainly because it is readily available and popular. The main problem I have is the oscillator design. The data sheet does not have much information on how to design the oscillator. My goal is to design 150MHz LO using LC as a VCO. The data sheet only has examples for particular frequencies.

I've designed LC osc using transistor before, but it requires knowledge of the gm of the transistor. The design process was to determine the negative resistance of the transistor plus the two caps on Base/Emitter and Emitter to ground. Since the SA602 doesn't have info on the gm of the oscillator transistor, I cannot calculate the values for these two caps.

I figure that this part is very popular, so there must be a lot of engineers having experience with it. Any help on the design will be appreciated.

Andy

perhaps an article copy as published in Elektor electronics Jan92 might throw some light
copy is attached.

This is wonderful! Thanks a lot.

In the article the two capacitors C1 and C2 values are given in equation 2 and 3. It mentions that it is for crystal oscillator up to 20MHz. When I calculate the values for 150MHz, they turn out to be 8pF to 80pF respectively. I wonder if these values are good at 150MHz because the stray capacitance may affect the startup of the oscillation. Anyway, I'm going to pick up a few of the SA602 tomorrow and breadboard it.

Is there any more suggestions?

Andy

generally RF circuits at and above 50MHz, better to solder on rf type copper board than breadboard. All the best.

You are right. Thanks for the reminder. When I said breadboard I actually meant getting my exacto knife to cut traces in the copper clad board. I've just picked up the SA602 in SMT package.

Is there any other suggestions on the oscillator design in SA602? I was reading the book "Experimental Methods in Rf Design" and there is a circuit using SA602. In that circuit, however, the two capacitor across B/E and E/GND are the same value (680pF). That puzzles me because it contradicts the equation from Joseph Carr's paper. I cannot remember what the frequency is in that circuit. Let me read it again tonight.

Thanks,

Andy

I need a simple remote control for 50 meter distance.