--- In [email protected], "Bob A" <[EMAIL PROTECTED]> wrote: > 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?
Capping, in this case, normally means removing the loop and put a covering over the opening. Also, to get the deepest, sharpest notch use the lowest insertion loss setting on the can. This will make a great Notch cavity. By the way, the can in this cinfiguration is a tunable open quarter wave stub. By coaxial theory, that means, what ever frequency that the "stub" is tuned for looks to be a short at that frequency...oh the same stub, if shorted, would appear to be open at the same frequency. > > 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/
