Thanks Skipp and Paul for input so far- I suspected that this would be a bit marginal. However, we're only running 40 watts, and the rx selectivity seems pretty good. It's an older Motorola, and it has 4 small cavity filters at the input of the rx inside the box. Running 600 kHz split with 2 antennas now, and I can find spots for the rx antenna in which the system works OK for local communications.
To Skipp's question, the old cavities have tee connectors attached direct to the ports, and they are all SO-239. With cascaded hybrid ring pass filters on the rx, and just a notch can teed into the tx side set to rx frequency, maybe it'll go. Paul, when you say "capping" the other port, do you mean shorting it or leaving open, or with stub or what? And, if these old cans are single port, no shunt Ls or Cs, does this mean they will notch as-is or will they need external help? -----Original Message----- From: [email protected] [mailto:[EMAIL PROTECTED] On Behalf Of Paul Kelley Sent: Friday, August 12, 2005 7:28 PM To: [email protected] Subject: Re: [Repeater-Builder] Duplexer Configuration Question > No piston trimmer that I can see, unless it's inside the > can across the loop. I was thinking of cracking one open > to find out. Anyway, though, it would have to be > adjustable to peak up the cavity, so why would they hide > it in there? No, they wouldn't be hidden inside. Just checking. > On the ring duplexer, it supposedly just inverts the > notch of the can into an equally sharp bandpass....by > making a steep cut away from the rx frequency, it should > hold off the tx to some extent....right? Well, it'll keep the transmitter carrier out of the receiver, at least to a degree. But you also need to knock down the noise generated by the transmitter on the receive frequency. If this is to be a 600 kHz split system, you probably need to attenuate that noise 60 dB or so... perhaps less, probably more, depending on the particular transmitter, receiver, etc. With cavities only on the RX side you'll have no protection from the noise and a LOT of desense. > As I said, I have one additional can now, with two ports in/out, so > I'll throw that one in the tx lead to make a 3-can setup. If this > sounds all wet, please let me in on the right answer. If you mean just inserting a pass cavity into the TX lead, it won't give you nearly enough protection from the noise on your RX freq. I'd suggest making another hybrid ring for the TX side with this cavity used as a notch cavity. Most pass cavities work fine as a notch by capping one connector and just using the other. A hybrid ring duplexer with two cavities on the RX and one on the TX just might do it, although it'll be a bit marginal on the TX side. As I understand it, you'll need to construct 3 rings, one for each cavity. Hopefully someone with real experience with the hybrid ring will jump in here and help you out! Paul, N1BUG Yahoo! Groups Links -- No virus found in this incoming message. Checked by AVG Anti-Virus. Version: 7.0.338 / Virus Database: 267.10.8/71 - Release Date: 8/12/2005 -- No virus found in this outgoing message. Checked by AVG Anti-Virus. Version: 7.0.338 / Virus Database: 267.10.8/71 - Release Date: 8/12/2005 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/
