Eric, thanks for the valuable info. I initially budgeted for the 1556 duplexer and noticed this afternoon that it only goes down to 148 Mhz. So I called Telewave and they didn't have a listing on the 1456 that's why I asked abt the 4 cavity duplexer. the sales guy started giving me some story about a custom build getting up to the $3-4K range that didn't make sense to me. I'll call back and see what's up, he did sound rather young and inexperienced on the phone. Do you mind saying what you paid for the TPRD1456 (or email privately if you like).
John/N4SJW --- In [email protected], Eric Lemmon <[EMAIL PROTECTED]> wrote: > John, > > I used CommShop to come up with the minimum required duplexer isolation > for a 2m transmitter putting out 50 watts, and a receiver of 0.35 uV > sensitivity 600 kHz away. The answer was 87.2 dB. > > Bear in mind that computer programs like CommShop that calculate > duplexer isolation have to make many assumptions, including the response > characteristics of a typical receiver and the spurious harmonics of a > typical transmitter. For example, a MICOR Sensitron receiver is far > superior to the majority of synthesized mobile radio receivers, and a > tube-based GE MASTR PA is much quieter than the majority of solid- state > PAs. Nevertheless, I don't think the TPRD1454 duplexer is a good > choice. > > For a few hundred bucks more, Telewave will sell you the TPRD1456 > duplexer, which has six cavities and better than 95 dB of isolation. I > just bought a TPRD1456 duplexer directly from Telewave for a new 2m > repeater I'm putting up, and I measured it with my network analyzer > right after it arrived. The insertion loss was -2.1 to -2.3 dB, and the > isolation was -104 to -108 dB. These are very good numbers, and will > ensure that my 100 watt MICOR repeater will have zero desense. > > Most duplexer manufacturers will agree that a duplexer with six 5" > cavities will almost always out-perform a duplexer with four 8" > cavities. However, when you have a Decibel Products or RFS/Celwave > duplexer with four 8" copper cavities that are silver-plated, you're > talking high performance and big bucks! The Telewave cavities are > similar in quality and performance to the now-defunct WACOM products. > > Bottom Line: Go for a minimum of 90 dB of isolation. > > 73, Eric Lemmon WB6FLY > > johnmichaelwelton wrote: > > > > Need to get several 2M duplexers for a hospital project. The Telewave > > TPRD1454 (4 cavity, 5 in) provide 77dB isolation (~$750). I'll be > > using 40-50 watt Mitrek's into DB220 or DB224 antennas. Is the 77dB > > going to be a headache = should I spend an extra 1.5 to 2K per > > duplexer for better isolation or will Telewaves work reasonably well? > > I need 4 so price does matter. > > > > thanks, > > > > John/N4SJW > > > > > > Yahoo! Groups Links > > > > > > > > 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/
