MFJ-1708B jumpers 3 and 4

Discussion in 'Software Defined Radio (SDR)' started by K1VW, Aug 2, 2020.

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  1. K1VW

    K1VW Premium Subscriber QRZ Page

    I expect this has been discussed, and I looked for an existing thread and didn’t find one. I feel sure other people have been down this path.

    On my MFJ-1708B, the antenna connection goes to only the SDR on receive and XCVR on transmit, it doesn’t split the receive signal. I stared at the schematic... yup that’s how it is set up to be. There are spots on the circuit board for jumpers 3 and 4, not used. JP4 would be a straight split, I tried it temporarily and yes it splits. The schematic shows JP 3 with a pair of resistors R11 and R12. My board doesn’t have those resisters but I presume the idea is 9 ohms would send more signal to the SDR, less to the XCVR.

    So who has experimented with this and what have you decided? Just use JP4 with a simple split? Or use resistors as shown, and what values? My xcvr is IC-7100 and SDR is SDRplay SDRduo.

  2. K1VW

    K1VW Premium Subscriber QRZ Page

    PS: when there is no power, or when you transmit, the relays switch to the NC Normally Closed position shown in the diagram. That’s the failsafe for loss of power. When it is powered and receiving, everything switches to NO normally open position and the SDR is enabled. Without JP3 or JP4 there is no receive path to XCVR.

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