Separate Transmit and Receive Antennas Produce Audio Distortion (possible RF feedback?)

Jim Bryce W5HFS

Separate Transmit and Receive Antennas -- Distortion: Beta v1.0.5; Flex 6700; Win 7. In the last day or so since I installed Beta v1.0.5 I've received several reports that my audio is distorted, and I've received several that it's beautiful. Just now I discovered the what I believe to be the variable. When I am using my Tennadyne T-6 to both receive and transmit on ANT1 I get great audio reports. When I use my Tennadyne to transmit on ANT1 and use my Pixel RF PRO-1B magnetic loop antenna to receive on RXA I get terrible audio reports. I can switch back and forth between the two states to demonstrate this. I had not experienced this before, but I am not sure that it is a function of the new software or was there all along, and I was not often using the loop. It may be a problem in the new software. It may be necessary to use the loop amplifier's ability to be switched off during transmit. I am not using a power amplifier; my impression has been the switching off would only be needed, if at all, with power amplifier and then only to protect the loop's amplifier and, possibly, the receiver's frontend.

Dave-N9CHM

I've been using 2 PRO-1B loops with my 6500 (1.0.5 software) for the last several days with no audio distortion problems. I do use an amplifier, running 1000-1200W on 40 & 75M and I use the relay switch for both loops as suggested to protect the LNA in the loops. I would try running an RCA phone patch cable between the radio and the relay in the loop to ground the loop/LNA on transmit. I suspect that is the problem.

Jim Bryce W5HFS

Dave's answer confirms my suspicion of the solution. The Pixel's optional switch off provides a fix for this environment. I suggest additional testing by Flex, because many other configurations may lack such an option. I've noticed that when I have the Pixel connected through RXA on other bands I can continue to observe those bands during transmission. I do not at this time know if that type of operation is also potentially a source of distortion.

Dave-N9CHM

I haven't been able to make the observations you're had since I ground the loops on TX and I only have a single SCU. However, even before I had the FLEX, I always ran my low band RX antennas through a front end saver, which also grounds the RX antennas on TX. As a matter of fact, I run the RX out from the loops into my FES before going into the 6500. So I have 2X the protection on the FLEX's front end! It only seems prudent with the cost of the radio, and I'd hate to fry the FLEX's front end!

Jim Bryce W5HFS

Dave: Thanks for the ideas. What are the particulars of your "Front End Saver"? I

Dave-N9CHM

I've been using the FES made by KD9SV for years. The only place I know to order one is http://www.radio-ware.com/ You can read the details there.

K1UO Larry

Array Solutions also has a good FES. No connection..just passing along the info. It is highly recommended that one ,of some type , be used on the RX only ports before feeding external RX antennas directly into the Flex.