Antenna Tuner w/ Intermittent Problems

Jerry W2TXB

I have a 6700 and v3.3.33.10471 SSDR that have been working well since the last update... at least until very recently. Twice during the past week or so, when I selected "TUNE" or "ATU", the tuner does not tune a known good antenna correctly. When the tuning is deselected or completed, there is no received signal until I shut down and restart the SSDR and the 6700; this includes disconnecting the DC power from the 6700 for a few minutes.\

This is a very intermittent problem and (so far) difficult to duplicate, but I wonder if anybody else has experienced this. Is it a known glitch that is being addressed in the next SSDR update?

Mike-VA3MW

Just some thoughts.

Often, this can be related to RFI or an intermittent antenna connection at some point between the end of the coax and the actual antenna.

If it was me, I would hook up an antenna analyzer and put it in a mode that is constantly reading SWR and other values and see if they start to jump around.

The other test is to get 2 dummy loads and hook them up in parallel and see if you get a 2:1 SWR and if the tuner will reliably tune the 25ohm load.

I would say to roll back to 3.3.32 or the previous version, but since it is a 6700, you can't do that.

At the moment, I don't think it is the software since the tuner software wasn't touched in the update. I have not seen others report the problem as well. Usually when it is a software problem, lots of people mention it.

Jerry W2TXB

I dug out my dummy load and have it ready for the next time the problem this occurs (if it does). In the meantime, I inspected the antenna (124.5' end-fed wire with LDG 9:1 balun that has worked perfectly since it was installed) and all appears as it should.

Mike-VA3MW

Do you have an analyzer that you can read the complex impedances at the end of the LDG for the frequencies you are having issues? You might be on the edge of the tuner range for the 6700 which is only a 3:1 ATU. The radio ATU is only designed to extend the range of an already resonant antenna.

They are not the same as an external ATU which has a much bigger tuning range.

This is why having an analyzer helps to tell the story.

Jerry W2TXB

I suspect there may be a problem with high reflected power with the end-fed; I also have a multi-band dipole that the analyzeron the input of the balun indicates is slightly better, although it is also not resonant in any of the Amateur bands. I have no accurate means of measuring at the output of the balun. Will try an external tuner, although the internal tuner display indicates a very low SWR.

Mike-VA3MW

It would help if you had one. You could find a NanoVNA on eBay (or even Amazon) for about $50 that should help tell the story. They are actually pretty good.