Hello, As part of our Dstar/Analog testing (see the thread posted several months ago) we modified a Mastr II repeater to transmit, alternately, Dstar and analog signals: For analog, we used the radio's phase modulator and for Dstar, we used the direct-FM on the compensation line. In our opinion, the Mastr II produced a better-quality signal than the IC-91AD, mostly because it didn't suffer from the "PLL Bounce" problem that the direct-FM modulated Icom radios have (e.g. associated with the PLL trying to track the low-frequency components of the modulation.)
Modulation of the Dstar baseband signal was quite trivial: Application of the baseband to the temperature compensation line. This is a technique that we'd used years ago when we put a bunch of Mastr Exec II's on 9600 baud packet - although Dstar is easier to manage in some ways as it operates at half the symbol rate and much lower deviation. While we haven't seriously considered putting up a "Mastr II" based repeater of any sort, we did think about what it would take to do so: - Maintain frequency/temperature compensation. Adding the modulation shouldn't affect the compensation line. In most cases, this line doesn't really change voltage unless there are some temperature extremes involved. If it does, however, the amount of deviation could change slightly as the V/F ratio changes. Presuming that one wishes to maintain frequency stability in excess of what the standard compensation method offers (e.g. better than a "5C" or even a modified "2C) it would be easy to add a very simple crystal oven, heating the crystal/oscillator to only slightly above the expected maximum ambient: This would solve the V/F problem and likely yield more than adequate frequency stability. Another possibility would be to lock to an external reference, such as an ovenized oscillator or a GPS reference (which I have done on an analog, multi-repeater UHF synchronous/voting system using Mastr II's.) As the voltage changes, however, the change in deviation available should also be compensated - but the majority of this change could be accommodated with a simple thermistor-based compensator using an op amp - if the temperature swing wasn't excessive. - From what we observed, the linearity of the this modulation is perfectly acceptable on a High-band VHF Mastr II - and should even be a bit better on a UHF version. (For 9600 baud packet, this was a bit more critical, but that was with about 4 times the deviation.) - The greatest challenge will be the modification of the receiver, as it will be necessary to narrow the IF if one wishes to take advantage of the closer channel spacing possibilities afforded by Dstar. There are (apparently) "narrowbanding" kits for many commercial radios in which the IF filtering is replaced to accommodate the 12.5 kHz analog channel spacing - a bandwidth that *may* be appropriate for the Dstar spacing in some parts of the country (e.g. 12.5 kHz or more.) Whether or not such retrofits are available specifically for the Mastr II, I have not checked, but I have refit a Master II with standard 10.7 MHz IF crystal filters (which *are* readily available in a variety of different bandwidths - and for fairly low cost) and had excellent result for 9600 baud packet (with the appropriate change in LO frequency, of course) and have little doubt that, if appropriately aligned, it should also work for something like Dstar. Based on our experience with the 9600 baud retrofits, making it pass data with minimal distortion of the receive waveform would probably involve more effort and finesse than the "standard" method of tuning a Mastr II (e.g. voltmeters and signal generators) as more-careful attention must be paid to the flatness of the passband! The final hurdle would be to be able to demodulate, process, and remodulate the baseband data in the manner appropriate to Dstar repeater operation, but I believe that this has already been done by others. 73, Clint KA7OEI > > hi all, > > i heard about some modif that could be done on Master 2 repeater so it > would be possible to operate them > > with dstar,anyone knowes something about it??? > > there should be a kind of board that would be added at the M2 so it > would be possible to linked it on the network !!!!!!!!! > > is it possible???? > > have you heard of it > > > > thanks for the help > > i maybe interested to modify one of my M2 into Dstar and become one of > the few in The Province on Dstar > > gervais ve2ckn >
