Modification of the FT-847 for Separate 144/432 Receive Antenna

A very useful modification to the Yaesu FT-847 is providing direct Antenna connections to the receiver on 144 and 432 MHz. This provides a no-fault way to connect tower-top preamps to the radio without risk of transmitting into them. Guenter Koellner, DL4MEA, documented the modification in 1998 on his website with several photos. I mostly copied his changes to the radio. I used square flange mounting sma connectors for my radio and soldered the RG-174 coax to the base of the pcb coax connectors and did not use the jumpers. The sma connectors were mounted to the vent openings on the rear of the radio. This required drilling only two small holes for the 2-56 mounting screws. I wired a surplus 6PST coax relay which selects six connections for my 144-MHz receiver. One returns to the radio to restore transceive operation thru the standard 144-MHz coax connector. Other selections are the eme preamp, satellite preamp, 2400-MHz down converter, and a 1420/144 MHz radio astronomy converter. The 432 antenna only goes to the satellite preamp, or restores for normal transceiver operation thru the regular 432-MHz antenna connector. I manually perform the change of connectors.

  • Diagram of FT-847 Rx Antenna modification
  • Photo

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