Updated: May 5, 2022
It's been some time since I made a batch of tiny EFHW using a 3D printed case and to be honest I wish I never made them.
The cost/time to printing the case added to the fiddly-ness of the assembly made it an unpleasant experience. However, they did work as very light weight QRP antenna transformers.
You can see below, when I added the transformer to my resonant wire at home the SWR was very good on the amateur bands.
So, I plugged in my Yeasu 817ND (now replaced) and decided to do a little low power 2w FT8, this was only after making some voice contacts SSB10w.
The results were promising. With this in mind I decided to revisit the idea at a later date.
Step forward a couple of years.
About a month ago I decided to re-visit these little transformers for two reasons. Firstly for QRP Radio Amateurs and also for SWL (myself included) who wanted an external antenna for HF reception which works and is cheap.
I designed and ordered PCB's with the idea of selling these as kits for people to make.
So here it is!!!!!! Inc. error T50-44 not T50-43.
This is very easy to build.
As for the specification. 12w SSB - lower I used 2w FT8 no problem.
As for how small this is.
A massive 26 grams and you can lose 4 of them if you don't use a wing nut and use a normal nut.
Bigger than a pound coin actual size is 90mm long, 28mm wide and 15mm deep. I could shave a little of the width and length. However, I want to retain the strain relief and cable tie holes (if needed).
I tested it last night using a NanoVNA with a 3.2k capacitor between earth and the antenna and the response is very good from 7mhz to 25mhz, good 80m and 12-10m bands. With a resonant wire this is a very usable transformer.
I will put this on the shop soon, the kit should will come in under £10....
If you fancy making a 3D printed enclosure yourself here is the link.