Ron, I don't think anyone was proposing putting the control RX 12.5 kHz away. I think the intent was not .5 channel away, but at least 1.5 channels away, or 37.5 kHz. Some sensitivity could be lost, and there may be a little desense moving off the transmitter side's notch, but may be workable for control.
Depending on who's on your adjacent pair, and how busy his repeater is, might it not be possible to go 25 kHz off, and each use the other's input frequency for control, simply with a different PL and different DTMF command structures? For that matter, could a very quiet 440 voice repeater with landline control be programmed with macros, accessible by landline or by DTMF on the input, that would spit out control codes for several other nearby repeaters on its output? Just have the control receivers at all the other repeaters listen to that machine's output, which would always be plenty strong enough to blast through marginal control receiver setups, intentional QRM, etc. Like a link hub, only used for control. (Or, both!) That might actually be a great use for some off-the-wall pair on 902 MHz or 1.2 GHz, a hub for both linking and control. Paul, AE4KR ----- Original Message ----- From: Ron Wright To: [email protected] Sent: Monday, May 12, 2008 7:34 AM Subject: RE: [Repeater-Builder] Re: Adding Control Receiver without Separate Antenna I would recommend not using a 12.5 kHz spacing freq in this case of a control receiever, a receiver that is only 12.5 kHz away from your regular repeater input. With typical good FM analog receivers these would both have overlapping passbands and an input signal on the repeater input would interfer with the control input. With som many using IC type DTMF decoders any interference, just over lapping distorted voice would hender the decoder decoding. A typical UHF duplexer would have a notch wide enough for a freq +/-25 kHz away. Know this is going to be another repeaters input, but with some research could find is close in distance to you. I have used control UHF freq that are 6.25 kHz spacing, but these were in the 446 range and on separate antenna. Just had access to this. I used this freq to give some added security. 73, ron, n9ee/r Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome. On Sun, May 11, 2008 at 10:24 PM, Laryn Lohman wrote: --- In Repeater-Builder@ yahoogroups. com, "John Transue" <[EMAIL PROTECTED] .> wrote: > > Laryn K8TVZ, > > So, if I understand, I should put a splitter after the pre-amp, and > the control frequency should be a split channel. Does this mean that I > use half way between two channels? Right, one of the 12.5 kc. in-between channels would be less likely to have something on them. > > Another question, who makes a good splitter, and how can I know I am > getting a good splitter? Well, I've seen 50 ohm splitters quite often at hamfests. I don't have a good brand name to point you to. I am, however, using a 75 ohm TV splitter. Purists will hate this, but especially, if you are after a preamp, I don't see this as a big deal. It works just fine here with no measured loss in repeater receiver sensitivity through the system. Use quality coax and fittings. I've found that RG142 works reasonably well with the TV splitters since it has a solid center conductor. If you are not using a preamp, then you really need to do things right, using a proper splitter, and still you may lose some sensitivity. Some of you are saying, where's the quality in that splitter scheme? Well, experimentally I've found it works well here, so after initial measurements showed me that things were still the same, I'll tend to stay with what works, but ready to ditch the whole thing if needed and go another route. Sometimes <quality> takes the form of performance, not looks or perfection. If system sensitivity had suffered it wouldn't be there for more than 15 minutes. Laryn K8TVZ
