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Need 12v during RX only (not TX)

Is there an output on the Flex 6600 that provides power only during RX? I see the ACC TX and RCA TX1, TX2, ... but they seem the "opposite" - they ground during TX.

I have a remote preamp that needs power during RX to activate the relays and amplifier. The 12v power must be off during TX to deactivate the relays and protect the amplifier.

If the Flex doesn't have this output, please make any suggestion for an easy way to provide a 12V power only during RX. Power needed is very low, less than 250 mA.

Thanks, Mark K6UFO

Best Answer

  • Geoff AB6BT
    Geoff AB6BT Member ✭✭✭
    Answer ✓

    Normally closed relay contact (as shown) powers preamp while in receive like this:


  • Geoff AB6BT
    Geoff AB6BT Member ✭✭✭
    edited July 7

    A simple solution would be to use an external 12 VDC supply and a relay with a fairly high DCR (low current requirement) The TX RCA jacks are speced at maximums of 40 VDC and 150 mA.

    So something like this:

    12VDC coil @ 30mA

    Edit: probably smart to add a reverse biased diode in parallel with the relay coil...

  • Erika - KØDD
    Erika - KØDD Member ✭✭✭

    Hi Mark, What You're referring to is what we in the VHF and UHF world refer to as a sequencer... I built my first one using relays only and it served me for many years flawlessly. I then bought a bunch of the Advanced Radio Research sequencers one for each band. I had scrapped out the mechanical sequencer years ago to get the parts back out. I took the little 2A AC control transformer that can be wired for 12 or 24 volts, wired it for 12v for this 6m preamp (but all my military surplus tower mount relays are 24vdc for 144, 222, 432) In went a diode bridge, a 50v computer style cap and a simple 12v 1amp regulator. Put it in a project box on one side and on the other all the control relays. An RCA connector on the back is the PTT lead triggering the sequencer I use a footswitch for that... Modern radios and transverters have sequencers built in. Triggering the PTT starts the action one section of each relay keys the next relay in order, most sequencers have 4 stages, but I pretty much needed only three. Tower relay to rcv, amplifier PTT for bias so it can make power, and the last relay keys the radio's PTT... you'd hit the footswitch and see each relay go click click click, pretty fast, let off the footswitch and verblap the relays all deenergize. Works good lasts long time. Erika DD

  • N5NHJ
    N5NHJ Member ✭✭✭

    ... and, if you like to get your hands dirty, here it is my Arduino project: 2 PTT in, 4 PTT out, 2 DC OUT or Reverse OUT.

    I8NHJ/Sequencerino: Arduino sequencer (github.com)

    73, Max N5NHJ

  • Mark Aaker K6UFO
    Mark Aaker K6UFO Member ✭✭

    Thanks for the suggestions, it appears the built-in TX1, TX2 connectors don't have the "12V during RX" capability, but can be programmed for delays. I didn't want to overlook a feature the radio might have. I will look into alternatives like the Normally Closed relay. Thanks, Mark K6UFO

  • Geoff AB6BT
    Geoff AB6BT Member ✭✭✭


    Yes, the TX RCA connectors are just either open drain or open collectors, if I recall correctly.

    I didn't elaborate on the relay idea but you could use the other pole connected to the the TX Inhibit input perhaps through an RC network to add a simple time delay to insure the premp is powered off prior to transmitting. I don't know the configuration of the TX Inhibit circuitry so I'm just speculating,

    The Normallly Open contact of the pole used to power the preamp could also be grounded so that line isn't floating.

    Just a couple ideas to think about and experiment with...

    Good luck with your project.

  • Mike-VA3MW
    Mike-VA3MW Administrator, FlexRadio Employee, Community Manager, Super Elmer, Moderator admin

    Hi Mark

    Why not use the USB Relays? You can control them to go on or off with a variety of triggers.

    There is no need to use the TX1-3 ports.

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