Building a rubidium freqency standard at home - DIY - Page 1
Forum section: electronics / projects

author: Chipguy
author_rank: Unknown
timestamp: July 26, 2014, 04:06:40 pm
content: 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 theseIt'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 myselfThe circuit it is based on this project:http://www.ka7oei.com/10meg_rubidium1.htmlThe 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.htmlI 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-Poolhttp://www.panel-pool.comAlso, 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:

author: David Hess
author_rank: Super Contributor
timestamp: July 28, 2014, 03:57:15 am
content: 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.