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You referenced 2 ground mounted transmitters co-phased with each other as a combined system, whereas I described elevated ungrounded transmitters on the the same frequency each outside of each others range, working indepentently… There would be a dead zone between them, therefore no concern of sync or phase.
Below is a NEC calculation of the groundwave field on 1700 kHz radiated by a single, elevated, ungrounded, Part 15 AM transmit system for the other conditions shown.
If a field intensity of 500 uV/m from transmitter A operating alone produced a relatively noise-free signal in an AM receiver located along Butler Avenue, fields added by operation of transmitter B (same specs) would have to be at least 10 dB weaker than that 500 uV/m field in order to have ~tolerable interference to transmitter A in the receiver output.
The chart shows that a 500 uV/m field is produced about 370 meters away from transmitter A. Interference on the same frequency would have to be less than 158 uV/m for a protection ratio of 10 dB or more to transmitter A, at that distance.
The chart shows that transmitter B (same specs as A) produces a 158 uV/m field at a distance of about 1 km.
The bottom line here is that for this set of conditions, transmitters A&B would have be located 1.37 km apart along Butler Avenue, and each would have ~acceptable performance along Butler Avenue for a horizontal distance of 370 meters toward the other transmitter.
There would be a zone about 0.63 km wide centered midway between the two transmitters where mutual interference could be a problem.
This analysis does not consider the effects of non-synchronous carrier frequencies and modulation timing/polarity.
If another transmitter spacing would be better I can check that.
Hopefully this will provide information that can help.