Connecting an Ameritron ARB-704 PTT Relay Buffer to a FLEX-6000

Information provided by: Paul, W9AC

Amplifiers can damage a FLEX-6000 TX Relay line if the amplifier has too much relay control voltage, voltage spikes, or excessive current on the relay control line. Such damage often appears as "stuck" or "sticky" transmit relays in exciters or shorted transistors on transmit control lines. In most cases where the radio is damaged, the system transmits normally but the external amplifier stays locked in a "transmit" mode. This prevents receive signals from coming through the amplifier with normal levels whenever the amplifier is in the "ON" or "OPERATE" position.

The ARB-704 is compatible with all common radios and amplifiers even though radios and amplifiers do not have standardized keying voltages, accessory plugs, or wiring. This interface is designed to work with any amplifier/radio combination and is good "insurance" to protect your FLEX-6000 from damage regardless of the amplifier used.

Based on the ARB-704 manual, it would be connected as follows:

1) ARB-704 TX-SEND jumpers set for LOW SYSTEM;

2) ARB-704 J2 (Radio) connects to the Flex 6300 TX Relay KEY line;

3) ARB-704 J1 (AMP) line connects to the amplifier key line.

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  • 0
    Jay Terleski

    Most modern amplifiers are pulled up to 12V DC and key with a sink to ground level of 10ma or less. Will the Flex 6K series accept this? Please add some numbers for voltage and current to your article. The ARB has been found to add delay to modern amplifiers and can cause hot switching if the RF envelop is not delayed enough on rise time and fall time of the RF envelope. Please specify RF envelope specifications of the RF envelope from PTT as T0.

  • 0
    William (Bill) D. Furbish (N1EHM)

    I have the flex 6300 and the Amp is Ameritron 811H So, can I safely add the ARB 704 without changing anything in the radio.


  • 0
    Tim Ellison

    Bill - yes you can. You may need to tweak the TX Delay to compensate for the time it takes for the relay to close - maybe adding 10-20 ms

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