PUFF Screen Grab of VHF Oscillator is it ok

[Kevin]

http://homepage.eircom.net/~doylekevin/fmtx.JPG

Hi all,
I put a screen grab of a VHF oscillator I am designing, onto my web-space
for you to look at.

I'm also using Cotter W. Sayer "Complete Wireless Design" book but there
isn't any pictures or explainations of what should appear on the smith chart
for a stable oscillator.

Can someone tell me if my design looks ok and what values of S11,21,12,22 I
should have.

Cheers,
Kevin.

 

[Kevin]

Hi Bill,
Thank you very much for your great reply.
I'll try to re-gig my circuit a bit.

Q.
Is it better to go with a lo current design?
One of the models uses 5v for Vce and 15mA for Ic.

Cheers,
Kevin.
"billcalley" <billcalley@yahoo.com> wrote in message
news:1118644371.346739.42430@g44g2000cwa.googlegroups.com...

Hi Kevin,

S22 should be closer to S11, whether it be 50 ohms or at some other
common value -- or your simulated open-loop gain results will be
inaccurate. And you must also plot your phase, which must be at or
near zero degrees at your peak S21 gain. And for maximum loaded Q --
and it looks like you are already doing this -- keep 'c' (the
series inductor) high in value, and 'd' (the series capacitor) low
in value (the narrower the S21 slope the higher the Q). And your
biasing resistor 'h' is too low in value (unless you have a high
current or low Vcc oscillator); but if you have calculated that that is
the bias you want, then you will have to add a choke (an RFC) in series
with the resistor, as well as a decoupling cap between the battery and
the RFC, to stop the RF from entering the supply.

Best,

Bill