The AM Forum

I just got an MFJ-993B autotuner and will try it out soon. It's rated 300W which should be enough for AM on the the TS-430 or the DSB900DX. Sure I have a couple manual tuners, but I also have very funky antennas, and Antron A-99 (10M vertical that also is tunable to 40M with tuner) and a 40FT piece of wire, end-fed.
I hope the autotuner will let me switch between the antennas more quickly and I hope it's manual adjustments will let me set the tuning in cases where the tuner  "gives up" due to SWR above 2.5 or so. I shouldn't be able to hurt it with a 100W radio.
Has anyone use one of these and what kind of experience was it?

How about automatic tuners in general?

Hi Pat,

A couple of years ago, when I put together my second floor studio B slopbucket station, I installed an SGC-239 auto-tuner in the basement to handle the remote tuning chores for my 160 meter antenna. I could control on/off functions and also do a tuning reset remotely from the upstairs station. The tuner did all the matching without any other intervention from me. It worked amazingly well and allowed me to move anywhere on the 160 meter, 75 meter, 60 meter, and 40 meter band. I found that it was necessary to "train" it by finding a spot on each band where the tuner could successfully find a match, and then moving in roughly 10 kc steps up and down the band, to let it figure out a match and store the data. It was very cool being able to simply dial up a frequency and then be able to operate there after half a second or so. I did run some low power (15 watts) AM with the setup and it worked out fine.

I got so spoiled that when I added a linear in studio B I ended up buying a Palstar AT-Auto (differential T-match configuration with a roller inductor) and I'm enjoying the same convenience with that at the KW level. I installed the Palstar right in the upstairs station and ended up mounting a balun outside the window on a ground mounted 20 foot length of TV mast. I run coax (about 20 feet of LMR-400) from the tuner, through a window bulkhead, to the balun and it works great from 160 - 40 meters.

From what I have heard, the 993B is light-years ahead of the SGC-239 in its abilities and is much faster than the Palstar at finding a match. I expect that you will really enjoy the convenience!

73,

Rob W1AEX

Hi Rob,

You are right! Now that I have tried it out - it can match almost anything, and I have some really crappy antennas! The "noise poof" 40FT end fed wire hanging 8FT above ground is a challenge because 15-20FT is insde the lab, hung from the ceiling by insulators, and 40FT is outdoors. I talked with a 100W slopbox to XE1L in Mexico city on this before BTW. This has always been very tricky/sharp to tune with the roller inductor manual tuner except on 40M. Don't ask me how, but I tuned it on 20M where it is closer to 1/2 wave and I could never get this to work with the roller box due to arcing. I don't expect it was efficient but it did tune. The success might have been because I used the tuner's internal 1:4 balun and grounded one end while letting the HV end fed the wire. It's been hit and miss with MFJ's productes here in the bunker of doom, but for the money on this one I am very pleased. And, when I switched to the coax-fed vertical rod on 40M (The antron is a 10/11 meter antenna but It works with a tuner on 40M OK), the tuner clicked right over, and that was great because now I can tell which antenna will be better almost immediately.