Re: [Repeater-Builder] Re: Mobile Duplexers

[Kevin Custer]

"skipp025" wrote: Hi Jim, I really don't want to argue with you, but it can be done and I've done it numerous times. It all comes down to a number game (the specs) and a reasonable approach. no6b wrote: I'd like to see the specs on what you've come up with. A key advantage of the 2.5 MHz split that I use is that at that spacing the G.E. RX front end has significant rejection: over 40 dB at the TX freq., so it can work with as little at 40 dB of duplexer rejection at the TX freq. 40 dB of rejection of the transmitter power may be enough to make it duplex, but I doubt 40 dB would be enough rejection of the transmitter sideband noise number. A 5 watt signal is +37 dBm.  *Typical* transmitter sideband noise with a good radio set is likely -90 to -100 dB below the carrier at 2.5 mHz spacing.  Many receivers intended for repeater service will hear a signal at -125 dBm. +37 minus 90 is negative 53 dBm.  Now take -125 and subtract -53, and the duplexer will have to provide 62 to 72 dB of isolation.  Now, use a PLL exciter and your right at that -40 number for both. Kevin Custer 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 the Yahoo! Terms of Service.