FlexRadio 8400 – PTT click/pop even without amplifier

SM6YEC

I’m using a FlexRadio 8400 and notice a small audible “click/pop” sound every time I press the PTT. It happens even when no amplifier is connected, but it becomes more noticeable when I use my ACOM 600S with TX1 delay set to 25 ms.

I have checked:

• EQ, processor, and monitor are turned off
• No external devices except ACOM 600S
• TX1 is used correctly for PTT

Is this normal behavior with the Flex 8000 series? Could it be related to the internal relays or the audio chain?

Additional info:

• The ACOM 600S default TX delay is 15 ms, and using 20–25 ms is safe.
• The ALC input on the FlexRadio cannot be used for PTT; KEY IN on the ACOM is required.

73 Mattias SM6YEC

Mike-VA3MW

The radio does use Relay switching when going from RX to TX and back to RX. It is possible you are hearing those relays.

TX1 on the Radio is connected to KEY IN on the Amplifier.

ALC on a FlexRadio is a voltage input and should only be used with an ALC connection to an amplifier.

The Acom 600 has no ALC output.

The KEY OUT is not required, but could likely be interfaced with the RCA TX INHIBIT of the radio.

You may have to adjust the TX DELAY on the radio to keep the amplifier happy and to avoid HOT SWITCHING messages. Make sure the TX DELAY on PTT1 is more than 10ms. 25ms is a save value and should not impact any operations.

SM6YEC

Thanks Mike!

I have done everything exactly as you described.

Update:
Now I have the microphone and headphones connected directly to the radio, and the click/pop problem no longer occurs. Previously, I was using the SM7B through the RODECaster Pro and via the computer to the radio, which caused the issue to be heard on the air.

SM6YEC

SOLVED

When I lowered the microphone gain on the RODECaster, the problem disappeared.

73 Mattias