ProScan III Antenna Compatibility

Dear Valued MRC Customer,

With the anticipated increase in ENG antenna replacements in the U.S. as part of the Nextel/BAS Frequency Reallocation program, MRC is issuing this technical bulletin to assist customers who currently have ProScan or ProScan II ENG antennas and are going to replace these with ProScan III antennas.

Caution- Do NOT connect an antenna controller that is configured for a ProScan/ProScan II to a ProScan III antenna. Damage to the antenna and/or the controller will likely result. Likewise, do NOT connect a controller that is configured for a ProScan III to a ProScan/ProScan II antenna.

The ProScan III incorporates a serial data bus to control the antenna feed. This RS485 data bus uses pins “C” and “D” on the 26P circular connector for the data transmission. These pins formally were used for Horizontal and Right Circular polarity switching in the ProScan/ProScan II antennas (contact closure to ground arrangement). If the antenna is connected to a controller that is not equipped with the RS485 data bus, an accidental switch to one of these polarizations could cause 24 volts DC to pass through the RS485 wiring. This would damage the RS485 UART devices in the antenna controller and on the antenna relay board.

Do not connect an antenna controller that is designed to operate an UltraScan, MicroScan, Ellipse or Sectorscan antenna to a ProScan III antenna. The RS485 data bus could be damaged as described above.

Caution- Check the feed voltage to the antenna at the back of the antenna controller before making the final connection to the antenna. The feed voltage should be approximately 24-30 volts.

Some broadcasters with tall towers (>2000’) had changed the feed voltage from their antenna controllers to operate the older antennas on 48-52 volts. This was necessary because active devices used in these older antennas required a greater current draw.

The ProScan III requires a nominal 24-volt feed voltage to operate properly. A feed voltage above 32 volts will damage the antenna internal power supply and distribution boards. The ProScan III active devices draw much less current than previous designs.

If possible, MRC recommends that the installation personnel also check the feed voltage at the end of the control cable BEFORE attaching the cable to the antenna to ensure 24-30 volts. To check the voltage, place a DC multimeter between pin (the + feed voltage) and pin X or Y (grounds). If the feed voltage is above 32 volts, correct the feed voltage before attaching the control cable to the antenna.

If our customers can please keep these bulletins in mind when they are specifying, replacing or upgrading equipment on their ENG/Central Receive sites, it will ensure money saved, less downtime and a quicker BAS transition.

If you have any questions, please call your sales rep or MRC tech support at 1-800-490-5700 (press 4) or email at