John, a couple of comments... Duplex is the ability to talk and listen, send and receive, simultaneously, nothing more.
In telephones, the technical challenge was to amplify baseband audio in both directions over long circuits without creating feedback, which required keeping the two audio paths separate using hybrid transformers and other techniques in the network. In RF repeaters, the transmitter and receiver have inherently separate audio paths; the challenge here was operating them both at the same time without RF interference. Early systems used separate sites, separate antennas, and eventually cavity tuned circuits configured as "duplexers." At the risk of confusing this further, a repeater, which is duplex in the RF realm, also absolutely has two independent audio paths. When it IDs, that audio is only on the output. When it times out, the user is suddenly only on the input. The controller is normally programmed to feed input audio, mixed with audio from the controller and other sources, to the output, but the hardware has the capability to transmit audio content completely different from what's on the input. In fact, if the controller runs an audio delay, the incoming and outgoing audio streams are never the same. Many repeaters have a local mic which can be used by a technician at the site. It feeds only the transmitter, independent of the receive audio path. I used the term "bidirectional" to refer to the crossband mobile's function of being able to repeat from either band to the other. (The equivalent on a 2M machine would be one which could use either of its frequencies as an input, and output on the other. There are some link scenarios where this could have application, but it has lots of drawbacks.) I intentionally defeat this capability to remain legal, since I have no way to put my callsign on any transmissions coming from the car back to me on UHF. 73, Paul AE4KR ----- Original Message ----- From: John Barrett To: [email protected] Sent: Thursday, November 08, 2007 9:35 PM Subject: RE: [Repeater-Builder] Part 97 question reference to Repeater control A repeater is NOT full duplex.. it is not simultaneously processing completely separate audio streams in and out.. it is processing the SAME audio in and out. There is only ONE audio path - full duplex requires TWO. Telephones accomplish this by modulating both audio signals on a common "carrier" (the DC power provided by the telco), modems do it by using different tone frequencies for send and receive.. essentially half duplex, but coerced into being full duplex by the behavior of the telephone line. The modems accomplish this by negotiating which modem will use which frequencies (hence all the V## protocols.. they define how the modems negotiate) A repeater is NOT bidirectional - audio streams flow in only one direction, from sender to reciever From this point of view the repeater is a filter in a half duplex link. The only reason a repeater uses 2 frequencies is because you cannot transmit on the same frequency as you receive.. Full duplex direct (non-repeater) RF links require 2 frequencies.. one transmit for user A, and one transmit for user B.. this is a true example of full duplex.. both streams are completely independent, and have no influence on the other except through "processing" at the end points, human, computer, or otherwise. You could accomplish an apparent full duplex repeater link in RF using 3 frequencies. 2 for input, one for output, and mix the inputs. The only problem is the 2 users have to agree which input they will use (oooo shades of modem negotiation here !!). a Party Line, or Conference Call would require one input per user.. In each of these cases, all users listen to the same output. ------------------------------------------------------------------------------ From: [email protected] [mailto:[EMAIL PROTECTED] On Behalf Of MCH Sent: Thursday, November 08, 2007 10:28 PM To: [email protected] Subject: Re: [Repeater-Builder] Part 97 question reference to Repeater control Simplex: One frequency - you can either TX or RX, but not both. Half Duplex - Two frequencies - you can either TX or RX, but not both. Your TX frequency is different than your RX frequency. Full Duplex - Two frequencies - you can RX and TX at the same time. A repeater is Full Duplex operation. It can RX and TX at the same time. Bi Directional means you can come in on one frequency and go out the second, or come IN the second and go OUT the first. Joe M. Nate Duehr wrote: > > On Nov 8, 2007, at 2:34 PM, Paul Plack wrote: > > > Manufacturers sometimes market features on new radios without regard > > to Part 97. I have an Alinco DR570T, one of the first, if not THE > > first, dual-band mobile to feature full duplex crossband repeat. As > > designed, it's crossband repeat function was clearly not legal. > > From your description (and knowing the radio) you mean "bi- > directional" (but not at the same time), not "full-duplex" (which > means you can go both directions through it at the same time). > > I'm seeing the term "full-duplex" misused more and more in regards to > dual-banders in cross-band repeat mode... did someone publish an > article with this less-than-accurate terminology again somewhere? :-) > > -- > Nate Duehr, WY0X > [EMAIL PROTECTED] > > > Yahoo! Groups Links > > >
