6600M transmitter stops intermittently on CW

  • 4
  • Problem
  • Updated 3 months ago
  • In Progress
My 6600M running the latest version of V 3.x software started exhibiting intermittent transmit failures during the SKCC WES CW contest yesterday.  Specifically, I would be sending and during a dash (key down, transmitter transmitting) the RF output from the 6600M would drop to zero.  Letting the key up and then pressing it down again to sent the next character caused the transmitter to come back on.  However, as long as I held the key down, the RF would stay off.

My setup is a 6600M driving an Ameritron ALS 1306 amp driving a dipole.  I have a tuner between the amp and the antenna but it is usually in bypass.  

There is an EA4TX remote antenna switch and a logging PC connected to the 6600M via  USB cables.  Neither the switch nor the PC seem to be doing anything when the problem occurs. 

The 6600M is limited to 50 watts output and I have measured that with a separate meter. It's built-in ATU is in bypass, no ALC connection or other feedback to the 6600M is present, the SWR between the 6600M and the amp is about 1.1:1.  SWR to the antenna is 1.3:1.  No measurable common mode current in the shack.  The ambient temp in the shack is about 68F and the 6600M air vents are completely clear and power is steady.  No alarms, lights or error messages appear.

The problem is hard to trap because it occurs only every several hundred characters and the 6600M keeps the amp keyed on so its "transmit light" stays on, just no RF comes out of the 6600M.  It does not matter whether or not the amp is on.  I observed the problem on 20m and 40m bands.  Others weren't tested.

Although it is not very new, the last thing added to the shack is the EA4TX switch and it connects to the 6600M via a USB cable.

I would like some help fixing this because people say I'm missing the occasional letter.
Jaimie "Jim" Charlton   AD0AB
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James Charlton

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Posted 3 months ago

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Tim - W4TME, Customer Experience Manager

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Official Response
This is defect G7759 and it is currently being investigated by the software team.  At this time the workaround is to stop sending and allow the radio to transition to RX and then start resending.