I've done three 15 MHz to 10 MHz conversions now, an RFTGm-II-Rb, RFTG-m-XO, and an RFTGm-II-XO. So I'll mention the quick and dirty mod that worked. The circuit boards are virtually identical between all three.
I pulled the 15 MHz metal cased filter out. Backtrack from the +23dBm 15 MHz output, thru the buffer amplifier, and you'll run into the metal bandpass filter. I used an oscilloscope to find the 10 MHz output on the OCXO. Using a 470pf ceramic monolithic capacitor I ac coupled off a sample of the RF via a small coaxial cable. Then route it over to a resistive power divider into the missing filter's output socket. The resistive divider is a very small 1K ohm 10turn pot in series with the coax center conductor. I used a 51 ohm from the filter output to ground to form the other part of the divider and help terminate the buffer amp input. This allows all the level alarm circuitry or whatever is under the daughter board to continue functioning. The potentiometer is adjusted to drive the output buffer amp to +23 dBm at 10 MHz output just like it was with 15 MHz originally. I also have the original 15 MHz passive external distribution divider for the system. So the +23 dbm drives the splitter to give six 10 MHz outputs at +9 dBm each. It's an interesting divider. I'll have to take it apart sometime. It has two inputs to allow the Rubidium RFTGm-II-Rb unit's output to become the backup source. When the XO output fails it's muted, and the Rb takes over as online source. By the way I modified the RFTGm-II-Rb the same way to use the buffer amp to output 10 MHz from the LPRO. The associated boards are identical between the Rb and the XO, just stuffed with different parts. In fact there's a spot for the GPS receiver, its just missing parts. Maybe when I learn a lot more about the loop constants and how they interact I'll get ambitious and try grafting the LPRO into the XO system to see if that results in a GPS locked Rb. My RFTGm-II-Rb however still has problems. Thanks to the help of several on the time-nuts list, I did get both units functioning redundantly again after the lightning damage several years ago. But after about six or eight hours the Rb side turns itself off. I'm thinking a DC-DC converter is probably overheating inside and shutting down. Over the next month I hope to open it up and confirm that. I may just use an external power supply and remove the suspect 5v dc-dc converter as a test of the theory. Always hard to test a thermal problem when the only way to do it is to open the box confining the heat. 73, Charles Osborne, K4CSO ----- Original Message ----- From: "Bo Granlund" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Sunday, April 13, 2008 4:08 PM Subject: [time-nuts] Lucent RFTG-m-XO 15MHz -> 10MHz > Hi everybody, > > Sorry for asking this kind of stupid question, but I've tried to do my best > with google and it hasn't revealed a lot of decisive results. > > The thing is, I have a Lucent RFTG-m-XO that outputs 1PPS and 15MHz signal. > I was wondering, how do you go ahead and convert the 15MHz output to a > 10MHz output? What kind of equipment do I need in between there to make > this happen? > > I'm really sorry, because I do realize this is a really stupid question, but > I'm kindof out of ideas, and I'm more of a software guy than an electronics > guy. :) > > Oh, there is a 10MHz input to the RFTG-m-XO. What is the purpose of this > input? > > kind regards, > Bo Granlund > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
