Saturday, March 14, 2015

Building 10 MHz OCXO


As part of my experimenting with building a double conversion up-converter I'm working on building a 10 MHz OCXO for the first LO.  I'm using a 3.3vdc LDO voltage regulator to power the OCXO.  This regulator is really simple to setup.  And aside from the IC itself it just takes two small ceramic capacitors to be stable.  When built the little DC-DC converter takes up less space than a US quarter.  The downside of this device is HEAT.  If input to the IC is > 10vdc it gets pretty hot trying to bring it output down to 3.3v.  So I'm limiting the input to 10vdc.

I'll probably eventually require this using an LM117 as those can take up to 40vdc input and run output as low as 1.25vdc (+-).  The way I've used them in the past I added a potentiometer and some resistors and caps to create variable voltage output.  But these devices can also just run a static voltage output by using a fixed resistor and some caps.  

The trouble with just about any of these is disapation of heat.  The process of dropping 13.8vdc to 3.3vdc if not done properly can generate enough heat to burn your finger when touching the device or heatsink.  So there's a balance that needs to be made.

ANYWAY...Here's a photo of the 10 MHz OCXO with the LDO Regulator onboard. 



Here's a shot of the LM117 variable supply I'm using to drop 13.8vdc to 10vdc which then drops to 3.3vdc that feeds the OCXO.


This is not the final configuration, this is just a test setup to verify the Variable Frequency adjustment of the OCXO using a voltage divider resistor network.  See the adjustable 1k Ohm Pot for that.