Miniature tuner for end fed half wave antenna

I said good bye to my military backpack. I used it too hard, weight was to much for it, and quality was not good enough. In most cases I take many things with me up to the mountains. Small survival pack can grow so big quickly when a tuner, few more battery pack, or few extra meters of wire (and so on...) should be carried. 

I decided to put a lightweight and small setup together. The old Ft-817 can not be lighter, also LI-PO batteries are the lightest options, but my tuner is not the smallest no matter how good it is working. My favourite setup is a fishing pole and tuner combo antenna. I wanted to create something smaller than that. 

One of my friends Gabor HA7MAC told me about the idea of using a transformer with a cap at the coax side with half wave radiating element. Gabor is a top bloke and also fanatic QRPer. If he says something I will listen, because there is always something to learn... The original idea is from PD7MAA. The source of the circuit can be found here: http://pa-11019.blogspot.hu/2012/04/149-transformer-for-endfed-antennas-35.html 

I had some FT-243-like toroids and started the test on a rainy afternoon. 

Finally I decided to use a smaller core, but it is still well enough for QRP usage.

This is a recycle project, only used parts are in the box. The cap is changed to a vinyl variable one, and a small tuning aid with a led is also built in. You can find the description of it below. It is switchable of course not to eat too much from the QRP power.

 Size matters... as you can see it is really small. Smaller than a cigarette box.

Banana plugs are used as connectors for CP and the radiating element. 

The switch on the right side is to disconnect the tuning indicator from the line. 

I prefer using counterpoise even with a single wire antenna. It makes the system stable and easy to tune. There is a set of radial wires for my vertical setup with banana plugs at the wires' ends, therefore I didn't have to make CP wire kit for this project.

Using is easy. Just connect the half wave wire to the ant banana socket and twist the cap for best SWR on the radio, or the brightest light on led.  

As you can see, inside is not over-sophisticated. The white stuff on the core is plumber tape. Hot glue can help to keep things on their place. Germanium diodes are made in Hungary in the mid of 70's, variable cap is a cheap Chinese one from a small broadcast receiver.

The transformer is a bit tricky. PD7MAA describes every details of it. In nutshell, there are two times seven turn, plus two more with twisted wires at the feed. The end goes to GND, while the twisted to the input. 

One has to be careful not to touch the output of the transformer while transmitting! It can burn your finger even at QRP level. 

On air tests? I need some time to test, compare and I will share my experiences later. My plan is to compare half wave end fed, norcal-like doublet with speaker cable, norcal-like doublet with professional symmetric feedline, doublet with 1 to 4 transformer 5m vertical with my L-match tuner, with tuner+unun and one of my mate's ZM-2 tuner. The goal is to find the smallest and the most effective antenna for QRP prtable use.

I will use swr meter, analyser, and field strength meter with live on air tests of course. 

Are you curious? Come back later! :)

Update:

I have tested many antennas comparing tuners, transformers etc... 
This one works. It just does the job. What you need to take care is the proper length of the counterpoise, the antenna height and the sloping angle. Honestly a quarter wave length vertical, or random wire antenna of course with radials performs just as well as the half wave one, with difference hardly noticeable. An "L" match tuner is a bit bulkier of course, but practically it is easier to work with it when operating qrp portable.
The half wave antenna with this tiny tuning unit is very useful, when one has a favourite place with fairly the same conditions all the time, same height, angle and so on. In this case big tuners can't beat the mini half wave coupler. 
In case of a weekend house or camp house I would prefer building a big matching box with large coils made of silver coated wire to reduce losses.
Anyway, It was good experience and great fun playing with it. I am sure I will take it with me to places where high watchtowers or trees are surely waiting for me...