Total posts : 45366
[quote:9a7cf6f72a=”Ebacherville”]SO how does the rangemaster sync the signals for a wide area coverage.[/quote:9a7cf6f72a]
If two Part 15 AM systems broadcast on the same nominal frequency, and their coverage areas overlap, receivers in the overlap area will have a heterodyne (tone) in the program audio that is the difference frequency in hertz between the exact carrier frequencies of the two transmitters.
Program modulation also has to be phased correctly on each tx in the system. Otherwise the sidebands of the different transmitters in the system can tend to cancel each other, and create a lot of distortion in receivers.
Phase-locking the carriers onto the same frequency will eliminate the heterodyne, but will not affect another issue with this kind of system. Radiation from the nearby antennas will add in some directions, and cancel in other directions. This happens even when the txs are phase-locked, and is related to the lengths of the propagation paths in wavelengths from each receiver location back to each tx. If the signals arrive in phase, they add. If they are out of phase, they cancel.
This is a totally different issue from the heterodyne described above, and can result in fairly large geographic sectors with poor, or no signal. The Rangemaster approach does not appear to recognize this, at least from the info on their website (Keith Hamilton – pls correct me if I’m wrong).
Truly synchronizing two txs has been done in commercial radio (example WBZ, Boston), but elaborate means were used to be sure that the interference zones generated by the two phase-locked carriers were directed away from areas with high population. And trying to do that with more than two nearby txs would be very problematic.
Part 15-ers might get better coverage results by installing a very good ground system for a single radiator than by installing “sync-ed” txs. This refers to the resistance of the connection of whatever constitutes the ground system (radials, etc) to physical earth — not just using a larger gauge wire to connect to a cold water pipe, or whatever. Removing 10 or 20 ohms of resistance in the ground system can give a large improvement in radiation efficiency, due to the 1/10 of an ohm or so of radiation resistance for most Part 15 radiators.