Buzz on Tx, only on 10 meters

Jeff - AK0DX

I am getting a buzz from my new 6300 on 10 meters when I transmit over 40 watts. It sounds like 60 Hz relay chatter. All the other bands are ok. Same symptoms with the antenna tuner on or off, into a dummy load or not. If I keep it below 40 watts I can run my amplifier without any problems which leads me to believe it is not a RFI issue. Power supply is a 35 amp Samtec. Any clues?

Steve W6SDM

I would look for RF.  It could be coming in before the amp on a specific band.  I had a similar problem that I fixed with ferrites and changing some random wire lengths.

Jeff - AK0DX

Thanks Steve, I will try that. The power light also turns red during the event.

Steve W6SDM

That's correct.  Your power light should always turn red when you transmit.

Tim - W4TME

I don't like the sound of this (no pun intended). So I have changed this post to a problem topic and converted this topic to a support HelpDesk ticket (http://helpdesk.flexradio.com) for expedited issue resolution.  If anyone else is experiencing an issue similar to this one, please submit a HelpDesk support ticket for issue resolution.

Steve W6SDM

By the way... I just loaded up my 6300 to several settings over 40 watts out and couldn't reproduce the problem - with or without the amp.

Jeff - AK0DX

Resolved

I removed all the cables except for the CAT5, Power, and Coax connected directly to a Dummy load. The problem went away. Then I added the system cables back in one at a time to find the culprit. I isolated it down to an RCS-4 antenna switch. I used it on the input side of the amp to switch between different radios. Replaced the switch and the problem went away.  RFI was the problem, but no need to add ferrites. This was the first time I tried the rig on 10 meters. Thanks for the suggestion Steve and Tim please feel free to close the ticket. I tested all the bands with no issues.

Steve W6SDM

I am glad you found the problem, Jeff.  RFI can be frustrating to track down.  All it needs is a length of wire to become resonant and the ever-present RF finds its way into the system.  I had problems with RFI and ground loops as I put my station together and had to play detective like you did. 

MFJ sells a device called the MFJ-805 RFI Detector, which can be clamped onto cables to determine if there is any RF resonating on them.  I haven't had to use mine in a while, but whenever I add something to the station or move something around, there is always that possibility.