[sdiy] Black Magic oscillator cans

[Magnus Danielson]

From: Tim Ressel <madhun2001 at yahoo.com>
Subject: Re: [sdiy] Black Magic oscillator cans
Date: Sun, 20 Jul 2003 16:32:33 -0700 (PDT)

> Hey all,
> 
> Thanks for all the responses. What a group! Now that I
> think about it, It's kinda hard to tune a crystal so
> your gear is in tune with someone else's. Maybe its
> time for an adjustable oscillator. Someone mentioned
> an LC oscillator. I think I have an adjustable cap
> somewhere.
> 
> Thanks all!

I think you should be able to make do by using a 4046 and a pair of dividers.

The 4046 (or at least any of its 74HC/HCT variants (4046, 7046 and 9046) is
able to spit out the 2.00024 MHz you want. Now, you need two dividers to do
the reference-frequency. If you take a 11 MHz crystal oscillator, divide it by
12500 and then have the output of the 4046 divided by 2273 and then toss these
into the phase-detector of the 4046. The loop-filter should be a wide-bandwidth
filter, but recall that the reference frequency is just 880 Hz.
If you have a CPLD or FPGA in the neightborhood, then the frequency divider
stuff is quickly done. If you do them in CMOS you might need to do some
fiddling.

However, if you have a TOG on the output of this 4046 anyway, I suspect
greatly that you get the 880 Hz output anyway, so that divider-chain is for
free. And the 12500 is 5 * 5 * 5 * 10 * 10 so you should be able to use several
small dividers of your choice in many different combinations.

Another method is to build a LC-based oscillator with a varicap diode. However,
the same booring divider-setup is needed for the PLL if you intend to hit the
same frequency.... LC-based oscillators isn't bad when you put them under
frequency/phase-locking.

Cheers,
Magnus