Re: Yo! RF dudes!

On Sat, 07 Apr 2007 15:55:57 GMT, Joerg
<notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx> wrote:

Mike Monett wrote:

Joerg <notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx> wrote:

>> So there's lots to look at that might help.

> Ulrich Rohde's book "Communications Receivers" is one that I find
> indispensable for such noise critical jobs. If it just didn't have
> such an ugly green cover after the dust cover fell apart.

Aha - an expert! I've done some work in start/stop oscillators for
data recovery in hard disk drives. How do you like this 50MHz
version? The oscillator amplitude is set by the R2 which sets the
current source in the emitter. The initial amplitude is set by the
R1 from the collector of Q1 to ground.

The constant current source gives very low loading on the tank and
helps stabilize the oscillator amplitude, much like Rohde's bias
stabilization patent. It also helps align the emitter current pulse
to the peak of the base sine wave in accordance with Hamijiri and
Lee. So it helps meet several different requirements at the same
time.


I can't load a SPICE file on this PC. It's the "grunt work" computer.
Can you post a schematic?

However, I am not an expert on gated oscillators. Although we had to
design some low noise ones for ultrasound machines but this was mostly
done in the digital domain. Really fast clocks, so the amount of "scoot"
was quite modest and could be handled with an adjustable phase shifter
in the nsec range. I used to do that with SD5400 arrays so when they
were orphaned by the mainstream mfgs it was like losing an old friend. Sigh.

We have one product that uses a 600 MHz gated oscillator, using a
coaxial ceramic resonator and a mmic.

Speaking of MMICS, Mini-Circuits has switched vendors again, and, one
again, the ERA series is screwed.

John

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