There used to be Linear Translators that were land based. There was one around the Pittsburgh area. I'm sure somewhere there are a few left, but they are few and far between.
Joe M. Rod Lane wrote: > > I would hate to see your insightful comment missed. I haven't seen > anyone else pick up on the part of your message about the linear > transponder. If someone wants to pass many different modes through a > repeater, you can't do better than a transponder. I've been on the > transmitting and receiving end of them for years with the satellite > world, and we haven't had to wholesale change out them with the change > from FM video to digital modes. They just work. > > Not being an expert on designing them, my understanding of the process > is as follows. > > On a block level, they're much simpler than they seem. Take a tightly > bandpass filtered IF from just about any quality radio, AGC it really > well, frequency convert it to the desired output frequency, run it > through a LINEAR power chain, and you now have the transponder. A > simple RF envelope detector can act as the "squelch" so that the > output power chain isn't constantly running to amplify ambient noise > that wanders into the system's input bandpass. > > The only other challenge is to be able to ID the repeater. A simple > MCW oscillator somewhere in the chain, either at the IF frequency or > output fundamental, and you're legal. FM, D-Star, P25, AM, CW, SSB > and virtually any mode that'll stay within the bandpass of the IF will > go through unimpeded ( and undistorted.) One possible minor down side > is that the user's radio needs to be somewhat on-frequency. If they > come in 1 KHz low, they go out 1 KHz low. In theory, it's not the > repeater owner's problem, but can be noticed on the output. > > I remember someone a few years back doing mods on a standard repeater > amplifier to "linearlize" it for ATV and SSB with some bias network > additions. As long as the PA is reasonably linear, slight distortions > in the linearity curve shouldn't create huge issues except with modes > like QAM or other modes with serious amplitude-dependent requirements. > > I wish I had the time. Being an RF guy, not a software type, it > sounds like a great project. > > 73 de N1FNE > > --- In Repeater-Builder@yahoogroups.com, Kris Kirby <[EMAIL PROTECTED]> wrote: > > > > On Tue, 24 Apr 2007, Steve Bosshard (NU5D) wrote: > > > Took a couple of antique GE Phoenix SX mobile radios. Programmed for > > > 442.0/ 447.0. With TOT. Carrier Squelch - Took Receiver Un Squelched > > > lead to PTT thru a one transistor keying transistor. > > > > > > Took VOL / SQ Hi and ran it thru a single common emitter stage - > > > bipolar amp and applied the collector output to the high side of the > > > TX deviation control and set for +/- 1 Khz TXD. Did have to bypass > > > the emitter leg of the single stage amp and wallah - DSTAR Repeater - > > > sort of. Maybe P25 repeater too? Simple - really do need to > > > regenerate the data signal and key on detected data with a CCD > chip to > > > give the preamble tone time to get thru. > > > > Excellent work Mr. Bosshard. This is one of the things that I've wanted > > to explore with D-Star but haven't had the time. This approach also > > works for most other modes based on FM (9600 BPS packet, Motorola DES, > > etc.). > > > > Truly, to support multiple modes or technologies, we need only look at > > the world of linear transponders for a clue -- there's really not much > > of a point in having too much of a radio there when you're just > > repeating in the input RF. > > > > -- > > Kris Kirby <[EMAIL PROTECTED]> > > "The illegal we do immediately. The unconstitutional takes > > a bit longer." -- Henry Kissinger > > > > > Yahoo! Groups Links > > >
