The Trail-Tenna - New For April 2022
Owen Duffy in his excellent blog did a critique for a single core fairly low efficiency EFHW transformer. He left clues in the post about how to improve efficiency which I duly followed.
It was not hard. I changed the core(s) and windings and used a nanoVNA to measure then calculate estimated efficiency.
Then I experimented, made some decisions as to how it would be implemented, and so the Trail-Tenna was born.
Updated 21 April 202 2: see end
Why Do We Want A 50W Trail-Tenna?
Well my QRP+ 10W antenna is lovely but is not suitable for use much over about 10 watts of SSB. The core is quite light and even though it is very efficient, you can only push it so far before bad things happen (it gets too hot).
I wanted a 50W version. This is an ideal power for campers who may want just a little more output and have a bigger battery available.
For this extra power the core needs to be bigger and ideally have greater efficiency. Efficiency and core size are related, as well as core geometry and the windings and other things. So with some experimenting I settled on the designs shown in the pic above.
Fetures;
- 50W SSB suitable,
- Core efficiency of 95% (un-proven as yet),
- low weight and compact,
- No 1:1 balun included,
- 49:1,
- BNC connector,
- 40m/20m radiator and radial soldered on and supplied,
- 2 build-versions available;
- the “Sled Trail-Tenna” is light for occasional use,
- the “Pipe Trail-Tenna” is more robust.
“Sled” version using light weight antenna built on an open frame “L” bracket. See above, the top right image in the “L” bracket, not weather protected. Light duty wire makes it most suitable for occasional use.
“Pipe” mounted into 27mm OD pipe with 3D printed ends which is better protected from the weather, the ends permanently glued. Fitted with heavier duty wire designed to be more robust.
“A Winder” will be designed and printed for it, just to finish it off nicely and sized for the bosses zip-lock freezer bags in the kitchen.
Early Feelings
They are small, light, cute and capable. I like them.
The 50W suits my field activations when I take my FT897D and a car battery. I can also use it QRP with the IC703 just as well, and IC705 users can use it with digital modes better than the QRP+ version which is limited to 1 watt for digital.
The Sled version draws the eye. The Pipe looks more robust and functional.
I’m thinking this is an ideal antenna as a backup in the light version, and for general use in the more robust version.
They pack down to be compact and will sit nicely in zip lock bag in the side pocket of my Go bag.
= = More news after field tuning and testing = =
The love affair with this little matching transformer continues.
But there were some bumps in the road.
First of all I designed and printed a winder which was no great effort and I’m happy with.
But for the Pipe version two issues arose;
- It needs a lug so a rope can be put through it to support the unit from a pole or tree branch etc. After much experimenting it was designed and looks OK.
- The cable coming out the top of the unit for the radiator needs a cable clamp. How do you stop it being pushed back into the casing otherwise? This was elegantly solved also making the end result much better and giving improved weather sealing.
First field tests will be this weekend. Photos to follow.