MFJ-971 portable ATU modification

Unlike the posts of the past few days, which have been sat as drafts for several weeks and I’ve just tidied up and pressed send, today’s offering is hot off the press.

Several months ago the guru suggested investing in a portable ATU capable of QRP work, specifically the MFJ-971.


After waiting patiently for a few weeks, one popped up on eBay and I managed to get it for less than 50% of a new one, so happy days.

Then he hit me with the “you’ll need to mod it” line. What? Why? How?

No worries, a very kind sole, also playing in the “share the knowledge game” had been there before and had posted all that needed to be known here.

For my work, all I need at the moment is the bypass switch.

So today, faced with the prospect of more episodes of The Blacklist (which is very good watching) I made the conscious effort to be both practical and creative and donned multiple layers and ventured out into the garage.

I’m not saying anything, but there’s more chance of seeing Monty and Mabel in our garden today than in a John Lewis store! It’s freezing.

Now, when this thing arrived it had obviously been loved and looked after by it’s previous owner. It arrived in it’s original packaging which is huge, wrapped in a protective film. And now I was about to set to work on it? It didn’t seem right.

When I sprung the case, the whole thing smelt of a solidly built item designed by people who care about all things radio and want it to last. It could probably withstand a nuclear war!

The fact the manual consists of 3 pages of letter sized paper typed on a typewriter in Courier font, single line spaced with no diagrams shows these are the kind of people who will shoot you without hesitation for blaspheming at anything radio related.

Forwards and onwards! My biggest worry was drilling the case as it’s a nice unit and a drill slip would have pained me for ever and a day. Thankfully that went without a hitch and the DPDT switch was installed.



With the unit in front of me, the blog notes from M0UKD made a lot more sense.  The one thing I was warned of, was the need for the biggest soldering iron tip available. Advice well worth every penny as the wires in this thing just suck the heat up. I tried to desolder the antenna capacitor and transmitter capacitor leads but gave up and gently trimmed them in the end. It’s worth cleaning up the attachment points as the flux or resin from the manufacturing process didn’t give the easiest surface to work with.

I soldered four 3″ fly leads to my switch and soldiered on. In about 15 minutes, all done. A quick whip round with the DVM to make sure everything was where it should be and we were finished.



And now, with the case back on its ready for action. As others have commented, it’s a shame the bypass switch isn’t there as a factory fit, but like most things in life, you can’t have everything.

Besides, there’s fun to be had taking things apart and making them do things they were’t designed to do!