TX / RX Switch for SDR share antenna with transceiver

Discussion in 'Software Defined Radio (SDR)' started by VE4AJM, Jun 24, 2020.

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  1. VE4AJM

    VE4AJM Ham Member QRZ Page

    What do you recommend for a tx / receive switch for use on a transceiver to share an antenna with an SDR dongle? The MFJ seems to be unavailable at the moment, and there are somewhat mixed reviews and quality control problems reported.
     
  2. KC2RGW

    KC2RGW Premium Subscriber QRZ Page

    I used a Dow-key relay wired off my foot switch for a while. Worked well.
     
    VE4AJM likes this.
  3. KC2RGW

    KC2RGW Premium Subscriber QRZ Page

    Just an added tip, if the SDR and software doesn't have audio muting built in on TX, (a lot now do, SDRUno, SDRConsole do it, and maybe even HDSDR) the Dow Key relays have versions with open frame relays on the body, so you have TX and RX coaxial so-239 or N and then an open frame relay with four or so contacts. I made a breakout box with a ribbon cable that would open the audio line (in my case the audio feed to computer speakers) so it would mute audio upon TX so you don't get feedback when you are talking.

    The one down side to a TX/RX switch vs using an IF tap or RX Antenna out on a rig, is that the AGC "bounces" as you go between TX and RX. So after TX there is a half second or so "bounce" as the AGC re-aligns again and the audio levels on RX. If you are in a group that does fairly quick break-in style chatting on SSB, it gets a bit tedious.
     
    VE4AJM likes this.
  4. N0YPD

    N0YPD Premium Subscriber QRZ Page

    I have been using the MFJ t/r switch,and it's doing fine trouble free for a year or so now.
     
    VE4AJM likes this.
  5. VE4AJM

    VE4AJM Ham Member QRZ Page

    It must be popular, because its sold out every place I tried to get one. All the big US and Canadian retailers are out of stock. Even MFJ doesn't have any on their website.
     
  6. VE4AJM

    VE4AJM Ham Member QRZ Page

  7. KC2RGW

    KC2RGW Premium Subscriber QRZ Page

    What rig are you using as the TX?
     
  8. VE4AJM

    VE4AJM Ham Member QRZ Page

    It's an old tube transceiver, a Hallicrafters sr-150.
     
  9. VE4AJM

    VE4AJM Ham Member QRZ Page

    So I bought and received the one listed on ebay above. It seems well made. I have tried it and it functions well. I also hooked it in and then bypassed it to see what effect it was having on the signal strength to my receiver. It appear to lower the signal by about 2/3 of an S unit for an S5 signal. Certainly with spitting the signal, there is expected to be some reduction in signal strength. I will report later if I find anything wrong with this unit.

    I used my RTL SRD. net unit this weekend to scan the band, and found it amazingly helpful in locating SSB signals on the 20 meter band. I have never worked so much DX in my life, and without a doubt I would not have been able to find all the stations I did without having an SDR generated panorama of the band. It's a great sidekick to an older rig.
     
  10. KK4NSF

    KK4NSF Ham Member QRZ Page

    me too! The MFJ switch works perfectly with my TS-440 / SDRplay set-up.... plus it didn't break the bank.
     

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