Sharing antennas

Discussion in 'Software Defined Radio (SDR)' started by N0YPD, Nov 29, 2018.

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  1. N0YPD

    N0YPD Premium Subscriber QRZ Page

    Hello guys, I currently own an Icom 7410,and a new SDR,the rsp1a. I am hoping to share my main hf antennas with my SDR. I was looking at using the mfj-1708sdr,and hoping with this device i can still listen to both radios at the same time. Is this possible,if so how?
  2. N2UHC

    N2UHC Ham Member QRZ Page

    I've only split my random wire antenna among my HF receivers via a splitter I built, but I've never once attempted to split an antenna between a transceiver and a receiver. I'm too leery of putting 100W into my receivers. Unfortunately I don't know anything about the MFJ-1708SDR, so can't say if it's a good unit or not.
  3. AA5CT

    AA5CT Ham Member QRZ Page

    (1) Making a 'tap' post T/R relay inside the 7410 would be one solution ...

    The 'tap' would be to the RF line just after the transmit-receive relay inside the 7410 transceiver. This would assure that _no_ high-power transmit energy would ever be applied to the SDR.

    (2) Another approach would be to use an external 'tap' (i.e., signal splitter) *with* an external "T/R relay" (used to protect the splitter and SDR receiver) connected *to* the 7410's T/R logic-level signal line, with an appropriate relay coil driver/buffer circuit (a transistor or two) driving the relay in the "splitter".
  4. VE7BPB

    VE7BPB Ham Member QRZ Page

    The answer to your question is Yes.

    The How is answered in the MFJ docs, but suffice it to say it is very simple. Go for it.

    regards, Roy
  5. AA5CT

    AA5CT Ham Member QRZ Page

    Well, that is what the MFJ-1708SDR does - its an external T/R relay!

    From their website: Your transceiver and SDR unit share the same high-performance antenna system. This arrangement allows you to simultaneously watch and listen. Then, when you key up to transmit, the MFJ-1708SDR cuts off and grounds the SDR antenna line, ...
  6. K6RUV

    K6RUV Ham Member QRZ Page

    It works......
  7. KB4MB

    KB4MB Ham Member QRZ Page

    Correct. The new version puts both on receive and turns off the sdr when listening. There is a jumper if you only want the sdr to receive you can set. I like being able to switch back and forth between radios and dont notice much of a db drop having both connected.
  8. G0VKT

    G0VKT Ham Member QRZ Page

    I plan on buying an RSP1a soon to use along with my FT450D. I want to make a switch so the SDR can use the main antenna or a dedicated RX antenna. Auto grounding of the SDR on TX and a manual change for the SDR antenna.

    I mainly use FT8 and JS8. It would be good to compare the RX performance between the SDR and the 450.

    It should be fun working out a flexible switching system.



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