FE Programmable Rubidium Oscillators - Page 1
Forum section: electronics / projects

author: Marc M.
author_rank: Regular Contributor
timestamp: March 14, 2013, 11:47:44 am
content: About 6 months back I purchased a Frequency Electronics FE-5680a Rubidium standards off fleabay from Nichegeek. When it arrived I was disappointed by its condition. It was still attached to the original PCB which they just cut around the unit with a saw. There were signs of water damage and corrosion to the board and unit. So the first thing I did was opened it up to look for internal damage and found the charred remains of a capacitor on the top board. I sent them photos and they sent a replacement unit at no cost and with no hassle. The replacement was in the same poor condition externally, but at least there was no signs of anything Chernobyled inside. These were advertised as the programmable variant, but I've had no luck with getting them to do anything other than output a very narrow (<10uS) 1 second pulse. The connections they listed are contradictary and don't appear to work. They were listed as follows:Pin Assignment1 +15v2 Ground3 Lock Indicator4 Not Used (but under notes they say "Applying +5v at pin4 does activate RFout at pin7")5 Ground6 1 pps output7 Not Used (but under notes they say "Applying +5v at pin5 does activate RFout at pin7")8 RS-232 RX9 RS-232 TXThe notation on Pin 7 referring to +5v on Pin 5 is incorrect because a quick check with a meter shows it's connected to ground on Pin 2. I know my 10mhz fixed output Rubidiums require +5v at pin 4 so that would make sense, but I still don't get any output at Pin 7 with +5v applied at Pin 4. I know there are a lot of variants of the 5680a (Why do they all use the same model #) but so far I've not come up with much about this one. I've posted a couple of pics of the inside and outside below.I'm wondering if anyone is familiar with this particular variant and if they've had any luck in getting them programmed and outputting RF at Pin 7? Any help or insight would be greatly appreciated.Marc -

author: grumpydoc
author_rank: Super Contributor
timestamp: March 14, 2013, 12:08:21 pm
content: Google is definitely your friend with the 5680 - there is a huge amount of information on t' 'net.http://www.ka7oei.com/10_MHz_Rubidium_FE-5680A.htmlis a good place to start as it describes the two main variants, plus some other links.I've been happy with mine - admittedly it did sulk when the 5V regulator died and fed 12V to the 5V pin but it seems to have survived that. I must run up the GPSDO though and check that it's still accurate (couldn't put a hair between them the last time I checked it).

author: olsenn
author_rank: Frequent Contributor
timestamp: March 14, 2013, 12:34:12 pm
content: I'm not sure about the whole RF output on pin 7, but I don't see how that would work well... atomic oscillators have horrible short-term stability; a cheap crystal oscillator and a small piece of dedicated circuitry would be much better for this.

author: grumpydoc
author_rank: Super Contributor
timestamp: March 14, 2013, 12:59:18 pm
content: It's not direct output from the rubidium oscillator - the variable ones use direct synthesis, the fixed 10MHz ones are a crystal oscillator disciplined by the rubidium oscillator (I think, they might be DDS as well, not 100% sure).

author: Marc M.
author_rank: Regular Contributor
timestamp: March 14, 2013, 02:10:06 pm
content: Quote from: grumpydoc on March 14, 2013, 12:08:21 pmGrumpydoc, thank you for the link. I have been to both KA7OEI's and ZL1PBU's pages. KA7OEI is specific to the fixed varients which I have working fine. ZL1PBU's page refers to the older programmable model with the printing on the case parallel to the long side of the case. As best as I've been able to determine, the one I have with the printing perpendicular to the long side is a newer and different variant. 2 of the 3 links are ZL1's page are dead, the third just deals with the Ruby software. There is a RF connector on the top board (bottom right in my pic) that has RF on it, but I measured that at 8.3886079 mhz, not the 10.00000000 I was expecting. I replaced the capacitor with a non-charcoal type in the original unit and got similar results.

author: bingo600
author_rank: Super Contributor
timestamp: March 14, 2013, 09:40:50 pm
content: Quote from: Marc M. on March 14, 2013, 02:10:06 pmDo you have a pic mcu on the board , far away from the db9 ?Then it might be the one here (he even mentions 8388608Hz) - witch can be set to 10Mhz by sending the correct dividerword to the pic (rs232) , then the pic programs the DDS chip to output 10Mhzhttp://www.qsl.net/zl1bpu/PROJ/Ruby4.htmYou're in luck ... Those usually costs a lot more than the fixed ones , and the output is taken from the RF PCB plug (solder a minicoax to it , and make a connector like seen herehttp://www.qsl.net/zl1bpu/PROJ/Ruby.htm/Bingo

author: Marc M.
author_rank: Regular Contributor
timestamp: March 15, 2013, 10:55:35 am
content: Many thanks to both Grumpydoc and Bingo600. I had prematurely discounted some of the links due to the very different package. I'm juggling 10 different things right now but had a few minutes of free time tonight so I dug into the links a bit further. Although their packages were different, the divider board was the same and I was successful in getting the RS-232 to connect and reprogram the divider. Ultimately, I want to use a micro-controller to set the output frequency for a stand alone precision frequency source.Thanks again for your help!Marc -