Tuna Tunah II QRP Antenna Tuner

2018-08-14 The comments below were again verified today when I set up my 35 ft wire and gave it a try using the tuna tunah ii. It tuned 40, 30 and 20, 17, 15, 10 and 6 meters and I had a short but solid QSO on 20 meters with it. I was unable to get it to tune 80 meters.

2018-07-25 As I have been playing with the 35 ft end fed wire antenna I've gained some experience with both the Tuna Tunah II and the EMTECH ZM-2 tuners. Both work well, each with it's strengths and weaknesses in this particular situation. The main strength of the Tuna Tunah is the range of impedances it can deal with. A consequent weakness is that it is somewhat cumbersome to tune given the many switches involved. On balance I believe that weakness is overshadowed by its strength. I talk about my experience with the ZM-2 on that page.

From what I am learning while using this tuner it is quite versatile and can handle a surprising range of antenna impedances. It takes a little patience and persistence to find the right combination of switches but I have yet to find anything it won't tune!

If you compare the photo at left with the official photo QRPme's website you'll notice that I replaced the provided RCA connectors for transmitter and antenna with BNC connectors. I don't have any coaxial cables with RCA connectors on them so they were a major inconvenience. Not sure why the manufacture used them as they are rare in ham radio for antenna connections especially.

I also added, then removed the switch to the right of the mounting screw. It switched in an additional 220pf of capacitance but I never found a situation where I needed it so have since removed it.

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Yesterday I took it and my portable setup consisting of a Yaesu FT-817nd, 35 ft stealth antenna and Wonderpole to a nearby forest preserve and set everything up. When I turned on the radio it was obvious that no antenna was attached. That is when I discovered in my careless packing everything I had broken the tune/operate switch so nothing was connected! Of course I had nothing with me to repair it so no contacts, even though when I bypassed the tuner and tied the antenna directly to the radio there were quite a few strong signals on the bands. But SWR made operating impossible.

I've contacted QRPme to see if I can buy the switch from them but in the meantime I removed the remnants of the old one and using jumpers connected it in the operate mode for now. The FT-817 indicates SWR so I can operate without it.

While I had it apart I decided to make another change I've wanted to do for some time. The Tuna can is about 1/4 inch taller than it needs to be which makes the thing a bit awkward to use and to pack. In my portable bag it is the tallest thing in there which in part contributed to the broken switch.

Jumpers temporarily replacing the broken tune/operate switch.

Cut down tuna can next to an unopened can showing the 1/4 inch reduced height and one of the pop rivets holding the cut off top portion in place.

Finally, with lots of fussing, I managed to force the top part inside the bottom part of the can and used a couple very small aluminum pop rivets to keep it in place. I'm pretty happy with the results. Now the circuit board is one inch above the bottom rather than 1-1/4 inches which makes it fit much more conveniently in my portable package. Now if those were just short handled switches.... :-)

So I cut it down about 1/4 inch. The result next to a standard (unopende!) tuna can is shown at left. Much more elegant, wouldn't you agree?

I considered various approaches to cut the can so I could keep the top lip part into which the circuit board fits perfectly. In the end, I carefully marked a line 1/4 inch down from the top all around the can and used my Harbor Freight tool with a cutting disk to carefully cut along the line.

Harbor Freight tool I used to cut the tuna can.