Thursday, February 19, 2015

100 Mhz OCXO 200ppb For Home Brew Upconverter

I still have some work to do on this.  The closest (bottom left) (pin 1) large pad get +1.15-2.15vdc via resistor network voltage divider that bridges over from the large pad behind it  (pin 14) that is the +3.3vdc Power Supply pin.

The SMA is the 100Mhz @ 200ppb output from the OCXO which comes off pin 8.

The resistor network I was talking about is a voltage divider in the standard configuration of R1 and R2 except that I've slightly modified it to include a 1-turn 1000 Ohm Potentiometer which should allow fine tuning the OCXO by as much as -500hz and +500hz.  Hopefully this won't be needed much as that the point of having the OCXO to start with, but it simplifies retouching tuning quite a bit and seemed simple enough to add (as long as my design holds up!).

There will be a KNOB on the front of this which allows easy access for tuning the OCXO to mate up with the signals on the 9 Mhz output of the FTDX-5000.  INSTEAD OF having to go into HDSDR software's option menu and extio menu to adjust things (WHICH DRIVES ME NUTS!).

I hadn't realized that I had to provide a Vcc for pin 1 initially, and at first when I discovered this I didn't really like the idea.  Still not sure I do frankly, BUT since it adds a feature I hadn't thought of to start with I figured why not make it something I can make use of, instead of simply setting pin 1's voltage to 1.65vdc which SHOULD place the OCXO at 0pmm/0hz offset from 100 Mhz.

This "feature" provides a much as 1 full Khz adjustment (I think, according to the doc's I've read).