[GPS_Standard] Requirements: a low jitter Sine to

[David Garnier]

Hi Zack,

Thank you for taking your time and answering my questions (even
if they were answered with questions!)   ;-)
I was trying to ask two broad questions, while trying to think out loud.

1) I recently got struck by lightning, lots of ham stuff got zapped... My
Motorola R1200a signal generators oven oscillator's power supply had
catastrophically failed.  (Lucky me, it looks like the rest of the 
generator survived.)

I have an extra Isotemp oscillator I was thinking of installing in 
there. I got
thinking about the "sine to square wave" circuit design I was going to use
then I began to wonder about jitter.  (The R1200a is actually a Systron
Donner 1702 and it's spectral purity is pretty bad.  SSB phase noise is
spec'ed ~103dBc @ 50 kHz offset at 1 Hz bandwidth.)

>The chip Bert uses is an LTC1485.  This is a Schmitt-trigger device, so I 
>imagine the jitter is fairly low.
>
>In another application, I was looking for a low phase-noise oscillator to 
>drive an Analog Devices AD9835 DDS chip.  Analog has an application note, 
>AN419, with just such a circuit.  It uses the MC10ELT21 chip as a low 
>phase-noise sine-to-TTL converter. Digi-Key stocks these. These chips are 
>good to at least 150 MHz!

I honestly didn't look at the LTC1485 that closely, (I am still fixing a 
couple things got fried,) *now*
I realize that part is 422 transceiver!  Hummm

Thanks for the lead on Analog Device App Note, I will look at the MC10ELT21.

> You will need a spectrum analyzer with the capability of looking at least 
> 145-150 dB below the carrier.

Actually that dynamic range isn't as bad as it sounds.  Last place I 
worked for had specially designed
crystal notch filters made by Netcom - for specific carrier frequencies 
of interest.  It made testing of
low noise 12 bit A/D receivers easier to implement in manufacturing.

>What are you going to use the circuit for?  I'm going to use it to either 
>phase-lock or directly synthesize LO's for microwave transverters for 24, 
>47, 76 GHz and up.

Jack, I'm still playing around on HF, I am a couple years behind you guys 
on getting on 10 GHz. One of these days neighbor we will actually make _
contact on the air_ instead of this medium.  ;-) Too much other stuff is 
getting in the way - like work.

Regards & 73's

Dave Garnier