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I bought a FE-5650A rubidium standard reference from eBay in the hope I can readily use it:

https://www.ebay.com/itm/142361240786

Unfortunately this is far from "reasily useable".

First and foremost, there is no RF connector (SMA, BNC, ...). Where is the 10 MHz output? (I hope it doesn't come out via the pin header, as it would result in significant interference

Second, the attached picture says there is a 9 pin connector:

enter image description here

However, there is only a 2x10=20 pin connector on my device. How to connect a simple 15V benchtop supply to this?

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    $\begingroup$ hm, the depicted "option 58" outputs a pulse-per-second signal, not 10 MHz as the ebay seller claims. $\endgroup$ Commented Jan 14, 2020 at 19:05
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    $\begingroup$ @MarcusMüller I think this is the solution (if you write an answer with this I can accept it). I wrote the seller and will be trying to return. $\endgroup$
    – divB
    Commented Jan 14, 2020 at 22:43

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There are a couple of different variants of these rubidium frequency standards.

FE-5650A Option 58 is what you have. It only has the 20-pin connector, no other connector, and some modifications are needed.

These devices do work, you can use them fairly easily, but if you want a 10 MHz analog output some modifications are needed.

http://www.leapsecond.com/museum/fei5650a/

The first step is to set up appropriate power supplies (+15V and +5V) with appropriate current, with the appropriate 20-pin Amphenol AMPMODU connector (annoying unusual connector to buy).

Read the link given above, which has pinouts and useful information.

Some people prefer to just desolder the original 20-pin connector, after taking the device apart, and solder new wires on.

There is also a 5-pin connector, hidden out of the way, which gives you the RS-232 TX/RX/GND connections. These are important so you can reconfigure the internal settings in the device's microcontroller program and change the output frequency. You'll need a computer connected to those test points.

There is an analog, sine-wave high frequency output from the frequency synthesiser - but it is not connected to an external connector on this version.

It goes into a fast comparator, becomes a square wave, and goes into a 23-bit digital counter, which divides down to the 1 Hz digital output present on the 20-pin connector.

In the default configuration, the frequency is 8.38860 MHz (2^23 Hz).

You can change the programming to give you a different frequency (say, 10 MHz) but then of course the 1 PPS output will not be accurate - it will be about 1.2 Hz.

You can easily modify the system with a "tap" off the internal coax cable (u.FL connector on the synthesiser board) and add a connector.

You may need to add some buffering, amplification or filtering, depending on your application, loading and what you have set the output frequency to.

There is a different version of the FE-5650 which is similar, but is a bit easier to deal with. It has a DE-9 connector and an SMA connector on the box, requires no modifications and uses a cheap, common DE-9 connection.

I believe this version outputs 10 MHz, but the disadvantage is there is no programmability. Easier to work with this in most cases - users who want to buy these rubidium standards but don't know which one to buy should probably buy this version.

Of course, if the seller gave you a description of oranges and delivered you apples, and didn't specify the correct variant names, you may discuss that with them.

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See http://www.leapsecond.com/museum/fei5650a/FE5650A-pin-out.gif for the pin out of option 58.

FE5650A pinout

http://www.leapsecond.com/museum/fei5650a/ supplies more detail.

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  • $\begingroup$ Thanks a lot, this is very useful! See the remark from Marcus Mueller: If you add that this device is actually NOT the frequency standard but only the 1pps option, I can also mark your answer as accept :) $\endgroup$
    – divB
    Commented Jan 15, 2020 at 2:35
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The datasheet that I found online has a picture of what looks like an F-connector on the same side as the multi-pin connector. That's where your output should be.

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    $\begingroup$ There isn't – look at the ebay photos! $\endgroup$ Commented Jan 14, 2020 at 18:53
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    $\begingroup$ The datasheet shows a connector. If the one that the OP bought doesn't have one, then it's probably been modified. In his or her shoes, I'd try to return it to the stock configuration by adding a connector. That does leave the question of where it should connect internally, which may be difficult to determine, but the buyer accepted the challenge when the purchase was made. Caveat emptor. $\endgroup$
    – rclocher3
    Commented Jan 14, 2020 at 19:35
  • $\begingroup$ The OP says that there is no RF connector of any type. $\endgroup$ Commented Jan 15, 2020 at 3:21
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This is an outstanding, highly detailed, "one-stop shop" reference about these devices.

http://www.leapsecond.com/u/parker/ParkerIntroRFS-PPCP.pdf

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  • $\begingroup$ Welcome @Luke and great information above in your other answer! Did you mean to post this (also very helpful) link separately? IMO it might be better off to edit it into your main answer. $\endgroup$ Commented Oct 10, 2022 at 22:52
  • $\begingroup$ It really would be best to add this to your existing answer, @luke. $\endgroup$
    – David Hoelzer
    Commented Oct 16, 2022 at 8:45

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