QRP in the Driftless

Homebrew EFHW from scratch

I have been thinking about making a couple of minimalist EFHW antennas with SMA connections for use with the (tr)uSDX. After weeks and weeks of out-of-stock conditions for my preferred kit, I ordered up some parts and started to make one from scratch. Starting with an FT50-43 toroid core, I wound the 49:1 unun:

3 turns primary, 20 turns secondary, using 26 gauge magnet wire.

The SMA connector on the (tr)uSDX seems to be well supported by the case, and reasonably sturdy, but to protect it further I bought some 6 inch SMA jumper cables and cut one in half to make a flexible input connection. RG-316 fits neatly in the two 1/8″ holes I drilled to form a strain relief:

100 pf 1kv capacitor across the input.

I bought a bunch of prototyping boards of various sizes years ago at a hamfest and I am slowly using them up, one by one. Having this one saved a lot of time and effort!

Parts all in place. I used some fast-curing J-B Weld epoxy to mount the terminal block for some extra strength.
The completed wiring, in my usual kind-of-messy point-to-point style. I am so glad of the PTFE insulation used in RG-316; if I had used RG-174 with polyethylene insulation it would surely have melted and shorted out!
Cut roughly to desired shape with big diagonal cutters, now off to the basement to finish the job:
Less than a minute with the belt sander smoothed the edges and rounded off the corners, now it’s ready for some glue-lined heatshrink tubing. I have been using the radiant heat from the electric cooktop for shrinking tubing lately; though slow, it feels easier than getting one of the heat guns out.

I’m planning on using the (tr)uSDX as the primary test instrument, running it at low power from the USB connector. Watch for the report soon!

Found on the bench, later, a few leftovers; enough perfboard to make another one, and a label that I meant to put on the board before shrinking on the tubing. I was in a hurry to finish it up, and forgot!

I hope you found this interesting; if you have any questions or comments feel free to post them below, or email me. Thanks for visiting driftlessqrp!

Posted

in

by

Admim

Tags:

, ,

Comments

Leave a Reply

Your email address will not be published. Required fields are marked *