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Flex radios in an in-band configuration

Varistor Member ✭✭
edited November 2019 in FLEX-6000 Signature Series
First, happy holidays to all! Hope everyone is enjoying the wonderful season.

Second, my question is aimed at contesters with real hands on M/n experience. Speculations can be helpful, but at least must understand the use case and its implications.

So I am in the process of building a bunch of in-band radio switching boxes to be used in M/n contesting environments. In a very simple example, imagine you have two radios- Radio A and Radio B- that share the same amplifier and TX antenna. They may (likely) or may not (unlikely) have a separate RX antenna.

When Radio A starts TXing, the box switches A's antenna output to the amp's input, switches Radio B to the RX antenna, and finally sends a PTT to the amp. Things work the same way if Radio B starts TXing and the box locks Radio B if both radios attempt to TX at the same time.

So my question is how do I send a TX Inhibit signal to a Flex? Before you respond "let the logger do interlocking", please consider the following:

1) Some contests do require hardware interlocks
2) The logger cannot handle SSB where I can simply press the PTT on the mike and cause the radio to TX (or grab the paddle and start CWing away).

Yaesu and Electraft radios have TX Inhibit inputs. Kenwood and Icom do not, but even if using them there is the solution to have all controls signals (e.g., CW, mike, FSK, etc.) go into the controller and have the controller disable the inputs for one radio when the other one is TXing.

By the way, this use case is not just limited to M/n; it applies to SO2R as well where you don't want to have two signals at the same time.

Every now and then the question of using Flex in contesting comes up. In order to have Flex radios show up at major and winning stations, it is critical to have a solution for interlocking across two or more radios. You may want to watch the TK0C YouTube videos showing how 6 guys do M/2; their use of multiple rigs is a great example of maximizing what's allowed in M/2. These have 1 x Run and 2 x S&P radios PER BAND.


  • Mack
    Mack Member ✭✭✭
    edited March 2019
    Flex radios have built in hardware interlock capability that achieves your goal. The new 6600 radios have built in contest bandpass filters. 

  • Ria
    Ria Member ✭✭
    edited November 2019
    There are two ways to do TX inhibit and interlocks. Hardware as Mack mentioned with the “TX REQ” input and software. PGXL is a good example of a software implementation. I use it SO2R. Ria N2RJ
  • Varistor
    Varistor Member ✭✭
    edited December 2017
    It took me a while to find the TX REQ input as I didn't realize it's on the accessory port. Thank you!
  • Ria
    Ria Member ✭✭
    edited December 2017

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