On a military satcom program in the mid 80's that I worked on, we used a 10 MHz crystal filter with about a 100 Hz BW to reduce phase noise of our Rb source. Regards - Mike
Mike B. Feher, N4FS 89 Arnold Blvd. Howell, NJ 07731 732-886-5960 -----Original Message----- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Leigh L. Klotz, Jr WA5ZNU Sent: Wednesday, June 23, 2010 12:54 AM To: time nuts Subject: [time-nuts] FRS-C TTL / sine outboard filter question At the local flea market, I picked up what appears to be an Efratom FRS-C. It is marked "TTL" internally. It has the passive connector board, but not the active board with the 15 MHz synthesizer on it. Mine is marked "TTL" internally. The service manual has a chart showing the differences between the sine and TTL options, and I converted it to the sine version by changing a jumper to a resistor and populating an LC filter with 10uH and 100pF (~5 MHz). I also terminated the RF connection on the connector board with a 47 ohm resistor to ground. The output now doesn't have the tremendous overshoot it used to have, but it's also not very sinusoidal. That's not surprising given the simplicity of the on-board filter. Instead of a multi-stage LC filter, I wondered about a crystal ladder filter: since the output frequency is fixed, the high Q and low cost of the crystal filter might be an advantage, but I wasn't sure about how effective xtal ladder filters are at suppressing harmonics, as each individual crystals would have odd overtone responses, so it might not be a good plan. Does anyone have practical experience with a filter topology for cleaning up the output of the FRS-C at 10 MHz? Leigh. P.S. Just so that I can be topical, note that the FRS-C has a C-field adjustment 0-5V input, so I could use it as the reference oscillator for a TPLL. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
