You Can Tune A Piano

I mentioned elsewhere about problems I had with my antenna tuner. While nobody asked, I figured it’s good writing practice to sit down and tell the story. Also, then it’s preserved for hysterical reasons. There’s also the fact that this stems from buying a new house and setting up everything in the ham shack all over again, which is a story that might deserve to be told, but at least right now that’ll be for another day.

Let’s assume for now that I’ve written the story about the new house and setting things back up, and you’ve taken that in. You’re probably left with the fact that I had to setup the old antenna at a new location, and the main takeaway is that if you buy one of these antennas now they say you should use 150′ of 400MAX. I think they said that before too, but at the time I got the antenna at the old house I know I purchased 75′ of coax to feed it. When I installed it there, I ran a sweeping arc from the antenna out into the back yard, then over towards the house and finally up into the antenna passthrough. I tried to pull that coax up when we moved, in part so maybe I could save it and in part so it wasn’t left in the ground, but after about 20′ or so of tugging and getting pissed off between how that was going and other reasons, I cut it off flush with the dirt, tucked it back in to the trench formed from pulling it up, and resigned myself to buying new when we moved. As it turns out that was probably not a horrible idea anyway, though I may have been able to use that 75′ run for another antenna I don’t think about it much.

At the new house, the antenna is around 20′ from the side of the house, and so I knew I’d be looking at a 25′ coax run to get there. Since one of the reasons for the long coax run was to “absorb” some of the losses from a mismatched antenna system, I wondered if putting a tuner right at the antenna would serve better. This way, instead of the tuner in the shack trying to match the coax+antenna, the coax would be matched to the transmitter anyway and the mismatched portion would be right at the antenna. I figured I might have less losses that way, and maybe a better performing antenna. Combined with actually putting down a decent amount of radials, which I mostly did, which again is another story.

So I picked up the kit from DX Engineering to modify the antenna for a remote tuner (MBVE-1UGBRT4), and rather than go with the smaller tuner I figured I’d spend the extra money now to prepare for eventually having an amplifier. At some point I might do that, especially if I want to do more SSB work. The installation was uneventful – you remove the 4:1 “unun” that sits at the base of the antenna and mount the tuner on there instead with a few other change – and once everything else was ready I prepared to use my new setup. Only I realized when I would transmit on some bands, notably 40m and 17m but occasionally on other bands, I could hear a hum in the shack. Alright, I’m getting RF back in here, what to do about it. Well between taking time to investigate, read up on things, and bad weather, it took me almost a year before I got to where I could start playing with ideas.

I started by picking up 10 snap-on ferrite beads to put on the coax. I figured five on each end might do the trick, and it did seem to make a slight difference, but not a lot. Next I picked up a 3″ ferrite toroid. See, at the feed point, I had about 5-6 turns of coax after it came out of the ground that was coiled up nicely and held together with velcro before going into the tuner, so I thought maybe if I just pass that through the ferrite it would make a difference. The answer pointed to “well, not really” so I took it back off. Turning back into the shack, one of the old RG-58A/U jumpers I had from the last house – which probably went from the tuner over to the antenna passthrough box – seemed like a good enough length to play with, so I used it to create a choke. Wound about 17 turns around it, spaced evenly around the toroid, and mounted that out there with a barrel connector coming off the feedline and then right into the tuner. That seemed to make quite a bit of difference now – having the 10 snap-on ferrites near the house side of the antenna passthrough box, and the 3″ toroid choke at the feedpoint. But it still wasn’t quite right, and I waited for warmer weather to finish testing.

It was around this time that I realized another problem which I half saw, but chalked up to RF getting into things it shouldn’t. When I would transmit with anywhere from about 75-85W of power – CW, not SSB this is – the tuner would seem to switch itself into bypass mode. You could see this by looking at the SWR meter on the Kenwood in the shack, as it would go from 1:1 to 3:1 or 5:1 or infinite depending on the band. No amount of power after that would make it work again, you would have to power cycle the tuner – turn the switch on the bias tee off and on again with a pause in between. I also noted that if my dual band radio, with its antenna maybe 20′ away from the HF vertical, sent out 50W on the 70cm band it would also trigger the tuner to go into bypass mode. I realized this when using the Gm mode on my Yaesu with my wife traveling around on a simplex frequency, and simultaneously trying to work FT8 stations – no matter what was going on at the time, if the Yaesu sent out that blip of RF, the tuner would bypass.

Finally the weather cooperated and I got out there again to play with things. I took the choke off the feedpoint and rewrapped the end of it, making around 26 turns I think when all was said and done and tighter to each other than I did before (I thought even spacing was better, I later found many articles that said the inside of the toroid should have no gaps between turns if possible). Mounted again, tested again, failed again. By now I’d had enough – I figured there’s enough information to warrant a return, and I had just a little over a month and a half before the end of the warranty period. So I reached out to MFJ to talk about a possible repair, and after a bit of runaround it’s on the way back to them now.

Meanwhile, I’m convinced the tuner is definitely a problem. The day I took it off the antenna, I dug out the unun that used to be at the feedpoint. I modified the wiring of things a little bit to accommodate the changes that had been made to get the tuner installed, and was able to mount the unun on the antenna with the existing feedline and choke going into it. Then I dug out the old MFJ-991 tuner that used to sit in the shack and wired that in where the bias tee had been put to inject 12V to the new tuner (which I won’t need if the new tuner isn’t there). Eventually I ordered a 4-pack of PL-259/SO-239 90-degree adapters to make the coax easier to deal with since 400MAX doesn’t bend easily, but even before that I was able to tune the antenna on all bands again. What’s more, there’s almost no discernible hum when I transmit on any frequency, AND I can push a full 100W on every frequency without the tuner freaking out anywhere. Since the remote tuner is supposed to be good for 600W, and I couldn’t even send 75W down the coax to it, I have a strong feeling something else is/was wrong with it. Hopefully MFJ finds out what and either repairs it or sends me a new one that doesn’t suffer from that problem.

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