A new paddle with no moving parts

I have had a KX2 transceiver for some time now and it has become my “go to” SOTA radio. It came with an Elecraft Precision Keyer Paddle KXPD2. I quickly became familiar with the paddle, but occasionally had problems with it. I am still not sure with one of the issues relating to intermittent paddle operation – perhaps I was getting some grit which interfered with the mechanical operation.

I had previously used a capacitive touch paddle with my FT-817. I had purchased a kit, assembled it and mounted it in a plastic case. It worked fine until I was on a summit one day and it started drizzling…… Operation became very odd very quickly with moisture about in the air, even if not on the paddle. I reverted to a mechanical paddle with the FT-817.

Another problem that I had with the Elecraft unit was the mounting screws became loose, resulting in contact posts moving and thus the paddle became unusable. The first time this occurred, I disassembled the paddle once I was at home and re-tightened the screws. But the problem recurred. I then used a small amount of Loctite on the two screws and reassembled the unit. All has been fine since, apart from the occasional intermittent contact issue.

I had read the article in the February 2019 issue of QST magazine on a paddle based on pressure sensors with interest. I took no action at the time, but was very interested when I saw an article on a variant developed by David VK3IL – see David’s blog.

After reading David’s blog, I made contact inquiring if he had a spare pcb left, knowing that even a prototype board order usually results in the buyer receiving several boards.  A few days later, a parcel arrived in the post – a pcb plus a kit of the required parts. Many thanks David! Others should note that David DOES NOT provide or sell kits. I was simply lucky that he was willing to share a kit with me from the extra items that he had on hand due to minimum order quantities with many suppliers.

I soon had the paddle assembled and tried it out. Success – it worked first time, despite my sloppy effort in soldering the tiny SMD diodes to the board. I then needed to consider how to mount the pcb assembly so that it was usable. I had seen David’s blog photos, with a layer of heatshrink tubing over the assembly, but that did not feel “right” in my hand.

I had a thought and tried something out. The thought worked with the first attempt, but the assembly could be a little longer to better sit in my hand. So after using my first attempt on a few summits, I cut away the material and started a new variation.

Material

The assembled pressure sensitive paddle, including a suitable length of audio cable with a 3.5 mm stereo plug. (I cut a short length from a purchased stereo – stereo lead that was to hand).
2 pieces of “closed cell foam” cut from a cheap hiking sleeping mat.
A  short length of heat shrink tubing.

Assembly

Simply cut the foam to the required size. The size will partly depend on the size of your hand.
Place one piece of foam on each side of the pcb assembly, then slip the heatshrink over the “sandwich”. Use a hot air gun to shrink the tubing onto the sandwich. Done. You should get the idea from the image below. The sandwich area is about the width of my palm.

Use

Simply plug the paddle into the paddle jack on the KX2. When I want to send, I pick up the paddle with my left hand, brace that hand against a table or my body and “squeeze” using my right hand. Works flawlessly to date, apart from the operator errors!

I am still a little slow with CW, operating at around 10-12 wpm.

Thanks for a great bit of kit David!

I works so well that I removed the Elecraft paddle from the radio. Now I really should devise a method of covering the case opening where the paddle connected to the radio.

KX2_Paddle

The pressure sensor based paddle and the KX2

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