[time-nuts] Notes on the Driscoll VHF Overtone Crystal (time-nuts Digest, Vol 65, Issue 114)

dk4xp at arcor.de dk4xp at arcor.de
Mon Dec 28 23:46:15 UTC 2009


> Von:     Magnus Lindahl <sm4rwi at telia.com>
> Do you have schematics, PCB-design etc. to share on your design with 3*
> BF862?

I will publish the results in Dubus. (www.dubus.org)
board size is 1.5 * 2.5 inch for oscillator, buffer, reference conditioner and PLL. 
No soldering without a  microscope, however. Lots of SSOP16, sot-336, 0603 & friends.

I wanted to make a VHF crystal oscillator that could be locked to a 10 MHz reference
and be used for the usual transverter designs. That required a locking grid of 
333 or 500 KHz. Furthermore, I wanted to avoid microcontrollers and other stuff
that had to be programmed. I wanted just normal stuff from Digi-Key and your
favorite crystal supplier. (Also, I wanted a nice clock source for state-of-the-Art 16 bit ADCs)

The fine locking grid has a devastating influence on the design. Either one compares
at 500 KHz, then locking to small error will take months, the pull-in range is ridiculous
(I don't want an oven for the 100MHz)  ----  or one compares to a harmonic of the 500 KHz,
then the phase comparator gain is ridiculous and the PLL kills the 100 MHz phase noise.

Probably I'll give in and stay with a 10 MHz grid. That will help hams who want to
multiply to 100 GHz and above.

I now have limited access to an Agilent signal source analyzer that does the three
cornered hat thing with cross correlation to 2 precision oscillators close to real time. 
I'm still stuck at -135 dB@ 100Hz @100 MHz, but without Rohde's limiter.
(only antiparallel Schottky across tank circuit and with BFG196 emitter follower)

I'll test w/o the follower and with the new limiter in week 1/2010

There are many things still to explore: thin film vs thick film resistors, influence of
emitter/source resistors, amplitude clamps, crystals, .......

regards, Gerhard   DK4XP


U.L.Rohde/David P. Newkirk: RF/Microwave Circuit Design For Wireless Applications,
page 762++
Wiley, ISBN 0-471-29818-2




More information about the time-nuts mailing list