Hi Regardless of the design, what ever filter you use will be sensitive to load. Hooking up a few dozen instruments to a standard line with BNC T's is unlikely to present 50 ohms to the filter. The more complex the filter, generally the more sensitive it will be ....
Bob -----Original Message----- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of ed breya Sent: Tuesday, December 13, 2011 12:07 PM To: time-nuts@febo.com Subject: [time-nuts] filtering a 10Mhz frequency standard? I reported a filter design I was working on back in November, using 10 base T LAN filter modules. The first experimental air-wired unit with two modules got to about -75 dBc at 30 MHz, rising to -65 dBc at 70 MHz. After building the same circuit with shielded compartments, it ran about -85 dBc flat over this range, but it should have been over 100. The weak link turned out to be the cross-talk within the modules themselves - there are two 17 MHz LPF sections in each, and I cascaded them all. Four separate modules cascaded, using only the Tx portion of each, should reach about 120 dBc rejection, with about 6 dB insertion loss. The original two-module circuit (or maybe even a single one) would probably suffice for most applications. I haven't yet impedance matched the 100 ohm differential filters to the 50 ohm cable environment - I'm thinking it may not even be necessary. If you have any old LAN cards, hubs, or routers around, you may already have some nice "free" LPFs for this purpose. The box to put them in (packaging cost) is another matter. Ed _______________________________________________ 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.