Efratom FRS - first step into timenuttery

[capt bullshot]

So I've got myself an Efratom FRS Rubidium,
just to discover it loses lock after maybe 20 minutes on the first try.

There's quite a bit of information on this unit around here and the web, so I found the manual and some other papers regarding their repair. I managed to repair (or rather re-adjust the drive level of the frequency multiplying step recovery diode) the unit.

Here's a report of what I did to bring it back to lock:
http://wunderkis.de/efratom-frs/

So what to do next? I'd like to check its absolute accurary and how far has the rubidium frequency drifted over time, I think a GPSDO is the next stop on my way to a timenut ...

[DC1MC]

Cool, should I send you my GPSDO, to have something to compare with , both of them, the Efratom and the True Position are collecting dust here due to some miserable circumstances.

Btw, how dos the signal look at the LOCK output when is locked and when not, I want to put a blue LED in the connector shell to be on when locked, this is a really ferocious mod 

 Cheers,
 DC1MC

[capt bullshot]

Btw, how dos the signal look at the LOCK output when is locked and when not, I want to put a blue LED in the connector shell to be on when locked, this is a really ferocious mod 

My units lock output goes to logic low when the lock is achieved, and logic high while unlocked. If you want to connect a LED from this output to a positive supply, you'll have to limit this supply to about 5V, a simple resistor to 24V won't do the job due to the internal circuitry of that output.

[DC1MC]

Btw, how dos the signal look at the LOCK output when is locked and when not, I want to put a blue LED in the connector shell to be on when locked, this is a really ferocious mod 

My units lock output goes to logic low when the lock is achieved, and logic high while unlocked. If you want to connect a LED from this output to a positive supply, you'll have to limit this supply to about 5V, a simple resistor to 24V won't do the job due to the internal circuitry of that output.

I wanted anyway to use a bipolar there, now I hope to do it with a pnp and 2 resistors.

 Cheers,
 DC1MC

[capt bullshot]

I wanted anyway to use a bipolar there, now I hope to do it with a pnp and 2 resistors.

Check the circuit in the manual, this output is just a npn switching to ground, but clamped with a zener diode. So it can sink enough current to drive a LED, but the voltage must not go above 5V.

You should get away with a simple circuit like that

[DC1MC]

Nice, I think I have dome 5V1 somewhere, this is even better as long as the Zener holds .

 DC1MC

[SoundTech-LG]

So I've got myself an Efratom FRS Rubidium,
just to discover it loses lock after maybe 20 minutes on the first try.

There's quite a bit of information on this unit around here and the web, so I found the manual and some other papers regarding their repair. I managed to repair (or rather re-adjust the drive level of the frequency multiplying step recovery diode) the unit.

Here's a report of what I did to bring it back to lock:
http://wunderkis.de/efratom-frs/


Wow! Just Wow!!!  Great article, teardown, repair, adjustment and info!
Good Job!


So what to do next? I'd like to check its absolute accurary and how far has the rubidium frequency drifted over time, I think a GPSDO is the next stop on my way to a timenut ...

[Dr. Frank]

Good repair description ..  .. for the case that my own FRS will stop operation.

Next step would be to mount the Rb standard on an appropriate heat sink, if not already done, otherwise you'll reduce its lifetime.

Calibrating the standard against a GPSDO would be the next step, by using an appropriate T.I. counter with 1ns resolution at least, and monitoring the phase difference over hours using TimeLab, that would be my proposal.

Frank

[capt bullshot]

I've updated my repair report due to some experience that I made with the units over time, adding this here just for the records:

http://wunderkis.de/efratom-frs/#update