AM Sync guidelines   
These instructions are intended for use by a technician. The AM1000 units are synchronized by a standard RS485 interface. The limit on length for the interface is about 2000 feet. Amplifiers can be used for longer cable lengths. First rotate the board with the components up, with the (2) 7 pin terminal blocks to the left and the (1) 3 pin terminal block to the right (See Figure 1).

INITIAL SETUP:
Place a shunt in J7 if the unit is the last slave in a daisy chain
SETTING UP MASTER:
Locate J9. Place a shunt in the “SEND” position (left). Be sure that there is no shunt in J7. All of these jumpers are located to the right of the bottom heatsink. The master has the crystal.

SETTING UP SLAVE
 Locate J9. Place a shunt in the (slave) position, pins 2&3 (right). If this is the last slave in the (Figure 2) daisy chain configuration you can place a shunt in J7. This will add a 220 ohm termination. All of these jumpers are located to the right of the bottom heatsink.  

CABLING (Figure 2) Daisy chain
The AM1000 has 2 terminal blocks to make cabling easier. The transmitters are connected together in a daisy chain.   The power and audio coming from the studio go to either of the (2) 7 pin terminal blocks of the master. Then the remaining 7 pin terminal block is cabled to the first slave, matching all signals. The (power + and -) of the Master goes to the (power + and -) of the first slave. Important: make sure the “+” and “-“connections are correct, the same for the (audio + and -) and (S + and -) connections.  For long runs of wire you can use an individual local power supply for each transmitter because of the voltage drop. Be sure to use twisted pair cable, Category five 24 gauge cable works well. You can use standard telephone cable to synchronize the transmitters but that won’t work as well as cable intended for RS485 use. Individually Shielded twisted pair cable is an even better choice. Connect the shield to the GND (ground) connection on the terminal block.  Connect the shield at only one end of the cable. 

FIRST TUNE MASTER
Turn all slaves off (locate on/off switch to left of board). Follow instructions in the main tuning instruction manual to tune master. Once the Master is operating disable the Master output by removing the coil tap select shunt J6. These jumpers are located near the large coil. This will disable the RF signal but still allow the sync signal to be sent to the Slave. Return this shunt to its original position after tuning slaves. Turn on each slave on and tune up each Slave as normal, one at a time.

PREPARE FOR FINAL TUNING
Final tuning needs to be done with some sort of field strength indication. It is important to note that hooking a voltmeter to the transmitter power amp voltage (red and black) tuning method will not work when more then one transmitter is on. It has to be a field strength indicator of some sort. The further away the indicator the better. A scope with a length of wire on the input will suffice. Or simply use a voltmeter set to the lowest AC range. Spread the leads out. Of course a field strength meter or a selective frequency meter approx. 1000ft away is best. Use Walkie Talkie’s or a cell phone to communicate. 

FINAL TUNING 
Turn all units on. The carriers are synced now and won’t heterodyne, but to prevent the transmitters from canceling  you need to synchronize the phase. If the phases are not properly synchronized it is possible that the slaves may actually cancel the masters’ signal resulting in signal dead spots.  To adjust the phase there are 2 jumpers on the board that delay the signal phase by a jumper selectable time period. The job is to find the position of J10 and/or J5 (PHASE DELAY) (Positions 1-12 on the jumpers) on each slave that will synchronize the carrier. If you use J5 leave the J10 jumper in the number 6 position. If the U6 and U4 chips are not installed then moving J10 or J5 will stop the unit from working (there may be a permanent wire soldered in J10 and J5). If you can’t seem to get anywhere try reversing the S+ and S- inputs to the slave. This will reverse the signal 180 degrees and you can start from there. You can also adjust the phase delay on the Master unit using J10 and J5.  When the slave signal is fully delayed (J5 on Position 12 and J10 on Position 6) the delay is approximately 300 degrees. The step is about 15 degrees. Be sure your audio polarity is correct, + to + and – to -.  Do a final tune on each transmitter watching your RF field strength indicator.  You are watching the field strength indicator to indicate when the transmitters are in phase and are not canceling.
NOTES
Total maximum spacing from the Master to the final Slave is 2000 feet (standard RS485 rules apply) unless you are using an amplifier. Each transmitter can have its own separate power supply. There is no limit on the audio line length since it is 600 ohm, (telephone line) Impedance. All the “A” terminals on Figures 2  go to a grounding rod in the earth for lightning protection.  The idea is to place the units around a large building/shopping mall and connect the sync so there is no heterodyne and adjust phase so there is no phase cancellation or flutter. Be sure the audio is in phase (+ to + and – to –) or you can get some cancellation. If you are driving many transmitters with a long balanced pair you may need to match the audio impedance properly. For example two 600 ohm audio loads in parallel would equal 300 ohms, this 300 ohm load would need to be matched to a 600 ohm output.
Figure 1

Figure 2
Serial (daisy chain)

Figure 3 wire connections

 

As of the writing of this document the FCC rules for clustering (multiple transmitters) are nonexistent, we know of no rules against multiple transmitters and have been told by FCC agents that they have no objections to it. We have been told by the FCC enforcement bureau that multiple transmitters placed around a shopping mall or other large building for example would be legal. Systems using multiple transmitters (for example along a highway) have been around for many years. But until multiple transmitters is addressed by FCC rules we can’t guarantee that the FCC will not object to it. Rangemaster Transmitters Inc. sells its’ transmitters to comply with FCC rules.

Here is a response from the FCC concerning the matter in 2006:

Response: 
If the transmitter was certified under Section 15.219 of our Rules and is an unlicensed AM transmitter, there is no limit on the number of transmitters that may be installed and no minimum distance at which they may be spaced.

The RangeMaster was originally designed to be a "highway transmitter", used to cover a highway with an AM band signal. A transmitter is placed every 1/10 or so down the highway, and the transmitter carriers and audio is synced by wire. This achieves continuous coverage of the highway. However the transmitters are not intended to be installed very close to each other, for example inches apart. Installing the unit like this is a violation of the rules.
The idea is to space them far enough apart to achieve continuous coverage without exceeding the field strength that would emanate from one transmitter (in the area of that transmitter). If you are unsure what this means please call us.

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