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“Question 1, if the slave units get their oscillator signal from the master, but the oscillator’s place in the AM circuit is BEFORE the modulator stage, how can the slaves sense the modulation from the master unit?”
Answer 1. The slave units, when being fed by a master oscillator with modulation, will not use their modulator portion of the circuit. You inject the master oscillator signal AFTER the modulator circuit of the slave unit.
/”Question 2, coaxial cable lengths become critical with high frequency signals, so how far apart can the slave and master be located?”
Answer 2. Since this kind of setup uses coaxes to send the master oscillator signal to the slave units, it does not matter how much signal level is traveling through that coax. Just make sure you do not use “leaky” coax, but regular shielded coax to feed the slave units. Separation of the units will depend on the local situation and ability to spread these things out, as well as budget considerations for the coax, and getting permissions to hang this coax and TX units where they are needed.
For example, if there is a section of the entire whole where the distance is considerable from one unit to the next, then you can use an amplifier to boost the master oscillator signal down the coax to the next unit, and if the signal is too much, simply attenuate it to properly drive the next slave unit without saturating it. Simple resistor networks can accomplish this.
Power for all of the units can originate at the master location by feeding the DC power down the coax and use that, along with DC isolation at each slave unit to separate the RF from the DC. So no need to string out another set of wires just for powering the slaves.
“Question 3, what kind of splitter is needed to drive more than one slave?”
Answer 3. The only time you would need a splitter is if your having to drive the coax that feeds the slaves with considerable RF power drive, like in the watts range. This will not be needed IMO. You can use simple coupling techniques like a pad resistor and a capacitor to couple from the coax into the slave unit. The pad resistor can serve two purposes here, attenuate the incoming master signal if needed, as well as provide proper loading characteristics before the oscillator signal is fed into the slave unit’s final.
As long as each slave unit is operating within the limits per 15.219 and 209, it does not matter what is going on inside the coax feeding each slave unit. It can have 10 watts or more on it. But as long as each slave unit is 100mW at their output, your fine.
A lot of college CC setups did this very thing when feeding multiple buildings and using one transmitter. LPB made custom splitters and attenuators for this type of setup. But the concept can also be applied for a multi 3 meter antenna setup spread out over a given area.
Think of it as your own little tv cable system, which works basically the same. Instead of having cables run into homes, each coupling point along the feed coax has a small 100mW unit and 3 meter stick. In tv cable, there are booster amplifiers along the main cable feed line to maintain signal levels along the entire length of that feed line. Inside each booster amp and drop box, are attenuators that can be selected and inserted into the signal path so that each residence is not over saturated with cable signal.
The same technique can be used for clustering 100mW transmitters from a master oscillator/modulator unit.