Note that the "Extender" is Moto's name for a "Noise Blanker", which is the term that GE used.
The noise blanker (no matter who makes it) is an AM receiver (whose front end is parked on a (hopefully) quiet channel) whose IF is the same frequency as the main (FM) receiver IF. The AM IF's is inverted and injected into the FMs IF and the noise pulses cancel. At least that's the plan, and usually it works. So the noise pulses are cancelled at the IF frequency, long before they are demodulated. Some people say that the Moto Extenders don't work as well as GE's Noise Blanker circuit. Not having had a GE to play with, I can't speak to that as I don't have 1st hand experience. One person's whose opinion I respect has over 15 years of working on lowband GE and Motorola gear and he says that he'll take a Mastr II over a Micor any day as a 6m repeater receiver just from the NB design. He parks them on 51mhz and lets them run. When the NB (no matter who makes it) is working right it eliminates a LOT of the RF noise hash that is so prevalent on low band channels. It messes up when the AM front end hears noise that the FM doesn't, or when someone starts talking on the AM channel (the NB input). Moto recommends that the extender be parked a couple of MHz away from the main channel and most extender-equipped mobiles have an antenna splitter after the antenna relay so that it feeds both the FM and the AM front end. Low band repeaters come in single-receive antenna (no-noise-blanker) configurations, and some have an separate antenna input for the noise blanker. The extender sampling frequency needs to be a few mhz away from the desired frequency to guarantee that all that it picks up is wideband noise. This means that if you put a pass cavity tuned to the main receive channel in front of the splitter then the AM receiver will hear nothing (because the pass window is so narrow) and you effectively have no extender. This is the biggest argument for split site machines on 6. The same thing happens if you have a duplexer in place of the cavity in the above example. A low band duplexer has a narrow pass window so the repeaters with a single antenna port for both the main channel and for the NB have a situation where the NB never hears anything. I've seen one 6m repeater where they took a single-sited machine and split it. The old transmit antenna (on it's own feedline), and the two pass cavities were reused for the NB channel. The transmitter ended up a mile away with a 900 MHz cross-link. BTW in most cases you DON'T need a preamp on a 6m FM receiver!!! They already hear dot 25 or so and the effective sensitivity with the antenna connected will likely be in excess of 1uV at most sites just due to the atmospheric noise. Mike WA6ILQ At 03:50 PM 09/03/08, you wrote: >Actually it is your local coordination body that counts. I just >recently coordinated a new 6 Meter repeater for here on the Oregon >Coast. Our council, ORRC is coordinating 1.7 MHz splits here and has >been since 2003 or earlier. My pair is 52.93/51.23. I would not be >surprised to still find a couple repeaters left here in the state on >the old 1 MHz split as well. > >90 Feet of vertical separation, especially with a filter or two, >should work very well. Hopefully your Micor has the factory extender >option. That coupled with a low noise preamp (such as those made by >Angle Linear), should be a pretty good repeater. > >Good Luck, >Joe - WA7JAW
