Building a rubidium freqency standard at home - DIY

[Chipguy]

Hi !

Over a year back, Dave, Mike (mikeselectricstuff) and Gerry Sweeny were tinkering around with those FE-5xxx rubidium reference frequency generators. Recently I got into a project where I will nees something better than a usual 20 bucks TXCO i.e. the TXCO built into a frequency counter or generator.

So I decided to do the same thing Gerry Sweeny did and build a frequency standard.
For that purpose I obtained one of these



It's like an easy-to-use version of the FE-5xxx. Spectratime (Temex) LPRO.
It takes 24V in, and uses around 1.5A to warm up. For operation it takes around 0.6A.
The connector also has a 5V ref output, a frequency "adjust" input (+/-2.5 * 10 Exp -9), RxD and TxD (5V) which I don't use, a lock output (driven by the collector of a 2N2222 IIRC) and of course the RF output. The adjustment input on mine is deactivated by design and preset by a little trimmer on the interface board.

I wanted to have a nice looking unit the size of a Racal Dana 1999 counter or the size of any other popular half rack unit you can get these days. Gladly I got hold of one of these, a "Bopla" branded model called "Intertego" for free.



I also need some buffering and mains earth insulation for the output signal.
So I started researching the interwebz and found the page of a guy called Clint going by ham radio callsign KA7OEI.
Based on his circuit minus one LED transistor stage, the step down converter and the battery stuff I made a board with the same nice working buffer amplifier. So I save time to research an adequate OP-AMP myself

The circuit it is based on this project: http://www.ka7oei.com/10meg_rubidium1.html

The circuit I made:


And the board. It has been manufacturered by Jackaltac using the german PCB-Pool:


As you can see I had trouble with the Traco TEN 6W DC/DC converter.
This thing's input and output are so noisey that it can be measured at the output, around 100mV peak.
A frequency counter even picks it up with no source attached to the driver board.

As I have overestimated the power consumption I was able to use a small 2W DC/DC converter and I put some filters on the input and output (all salvaged parts from a broken Phihong wallwart PSU).
The transformer I used is actually made for SPDIF signal insulation (marketed as digital audio transformer) and it turned out to be perfect for 10 MHz.

Now I needed a power supply and came up with the idea of a high quality switching PSU.
So I got a TDK Lambda HWS50 PSU. They offer "lifetime" warranty (30 years in Germany) so they should be ok.

http://www.tdk-lambda.com/products/sps/ps_unit/hws/indexe.html

I also got a front panel, a base plate to mount everything on, and a rear panel.
I made them in Target and ordered them at the Panel-Pool http://www.panel-pool.com

Also, the remnants of broken PC power supplies can be quite useful, like the mains input filter.

Not that it really needs it, but I had this laying around...

So here is the finished built in pictures:

[David Hess]

That is very cool.

I am not surprised about the isolated DC/DC converter module.  I would not rely on an OEM module without evaluation.

I have read before that ethernet isolation transformers work well in this type of application.