You apparently have multiple line-wrap issues in your .asc file.
Try not putting everything in one line ;-) ...Jim Thompson
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I just tested it in a sample circuit, that new model is 1/3 the speed of the other model!
Envision grounded base with current source(s) to emitter. collector has 1k load with about 5mA bias current. Also substrate voltage at -8Vdc.
Roll off of old model approx 190MHz, new model 64.5MHz! significant differences there.
Plus has a bit more noise, if that's important.
You have no idea how long I waited to be able to finally say this, "I had no problems with it." ;)
Wow, yes, big difference. However the Ft of the CA3046 is meant to be around 300MHz, whereas the LM3046 is min 300, typical 550. I don't really know how much gain your test circuit was asking for, but they do say "DC to 120MHz" on the National data sheet... Maybe I'm asking too much to push to 150MHz, but surely not to 30?
That said, I was just playing with parallel R loading the tank, and it doesn't take much to drop the amplitude way down... it seems likely that my original problem was excessive tank loading.
Make it a bit more likely to start perhaps :P
-- Clifford Heath
I was taking signal off the tank because the signal level is 20dB better than at the emitter, while the spurious levels are the same.
I've switched the design to a tap off the inductor, which is still clean but much lower impedance (less tank load). I need to re-do the layout before retesting at a higher frequency, but all the symptoms I am seeing are explained by excess loading (or various sorts) on the tank.
I just got bitten yesterday by the very high Cbe of the 2N2222. 20pF indeed! I'll be more careful using those in future :)
Thanks everyone for your help.
Yes, fair enough. If you have a load with very high impedance (the gate of a very tiny fet perhaps) then taking the output from the large swing of the tank can give you the best phase noise floor at high offsets, but that load needs to be very high impedance. With a low impedance load it can stop it oscillating.
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