At 1/17/2006 12:17 PM, you wrote: >For best performance you will need in the order of 120db isolation >between TX and RX.
While more isolation is always better, 120 dB is a bit of overkill in most instances. 90-100 dB is a more reasonable value. > It generally takes a duplexer with 6 cans 3 on each >side with a band pass, band reject mode of operation. 6 cans with >notch only will not make the grade. Notch only cavities are fine so long as your repeater isn't co-located with other comm. equipment. If it is, a BpBr duplexer probably isn't enough; you should have a true pass cavity on the TX to keep other TXs from entering your TX & mixing, causing interference. Same goes for the RX. BpBr duplexers do help a bit with in-band rejection & generally have better isolation specs than notch-only cans, but offer no isolation once you get over 50-100 MHz away from their operating frequency. And you do need the out-of-band rejection on a preamp, as many well-designed preamps are inherently broadband & will actually perform well at twice the design frequency! > Then do not go overboard on the >gain. Stay with something in the order of 7-10db with under 1 db noise >figure. Depending on the RX, 7-10 dB may not be quite enough. A 0.4 uV RX with 7 dB of low-noise gain in front of it will only drop down to 0.18 uV - still room for improvement. Some of the better preamps available are designed specifically for moderate gain (~16 dB) to prevent overload problems. See http://www.anglelinear.com for more info. Bob NO6B Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
