Uploaded November 2022 | Updated September 2026, 1 hour ago
Antenna tuning unit (ATU) is one of the most used accessories in Ham Radio. There is plenty of various automatic antenna tuners but manual ATU’s are indispensable when it comes to a back-up need or there is no way to provide the automatic tuner with the external power supply as the battery power is scarce on that POTA or SOTA activation.
This universal mini ATU is redesigned from an old Zetagi MM27 CB antenna matcher which I discovered in my junk-box. It is still possible to buy one new off the internet. The variable capacitors are the most valued part in this CB matcher, Zetagi states they could stand 100W of power. Well, I did try 45W and it was ok. I’m not so sure about 100W though, :). Probably, with a bit bigger toroid inductor in this my design it could be fine. The rotary switch of this size might be the most difficult part to find. Again, lucky me, it all was in my junk-box… That’s why we like visiting flee-markets and rallies, don’t we?
I was inspired by the article in my favorite ham radio magazine SPRAT , issue Nr 108, Autumn 2001.
Please leave your comments, questions or suggestions in the comments section. Please consider subscribing and help this channel grow. Thank you!
73! Linas LY2H
Antenna tuning unit (ATU) is one of the most used accessories in Ham Radio. There is plenty of various automatic antenna tuners but manual ATU’s are indispensable when it comes to a back-up need or there is no way to provide the automatic tuner with the external power supply as the battery power is scarce on that POTA or SOTA activation.
This universal mini ATU is redesigned from an old Zetagi MM27 CB antenna matcher which I discovered in my junk-box. It is still possible to buy one new off the internet. The variable capacitors are the most valued part in this CB matcher, Zetagi states they could stand 100W of power. Well, I did try 45W and it was ok. I’m not so sure about 100W though, :). Probably, with a bit bigger toroid inductor in this my design it could be fine. The rotary switch of this size might be the most difficult part to find. Again, lucky me, it all was in my junk-box… That’s why we like visiting flee-markets and rallies, don’t we?
I was inspired by the article in my favorite ham radio magazine SPRAT , issue Nr 108, Autumn 2001.
Please leave your comments, questions or suggestions in the comments section. Please consider subscribing and help this channel grow. Thank you!
73! Linas LY2H
