L MATCH ATU FOR QRP

This is phase one of my portable qrp setup where i will be operating from the car in the local hills using the FT 817.

Phase two is....well that is soon but before i finish the antenna i wanted something to match it with, something that will match 160m - 10m. I already own a very good ATU but its big with a built in SWR meter and its commercial so its time for something smaller and being used for qrp i decided to have a go and build one myself.

My construction skills are limited but i will have a go and enjoy the experimentation side of the hobby very much, so here i have to use readily available materials and my small collection of tools with lots of imagination.

The L match is designed for the matching of random and long wires and should not be mounted in a metallic box/case, i used a small plastic food container which was the most expensive part of the project. That set me back one pound for 3 or 33.3p for one! The coil was formed around a small length waste water pipe (off cut) and the variable capacitors were robbed from a CB swr meter and matcher...thanks Bernard G3SHF.

Heres the circuit and the picture is provided with permission by VK3YE be sure to check his site out he writes articles and enjoys his QRP, click this link to go there http://www.alphalink.com.au/~parkerp/

I made a slight change to the original circuit by adding an extra capacitor to the TX side, it just goes between the S0239 and this allows more bands to be matched.

The top view shows the controls which are Left to Right: The inductor tapping switch (thanks to ROY at work who donated this item and will cost me a pint of cider!) which is requiring a knob at this moment and i have the sore fingers to prove it!

Moving to the Right is the two v/caps with the red markers and sitting above and below these caps is two studs one for the antenna and the lower one for the earth. I use leads fitted with croc clips to attach to the studs...cheap, simple, easy and its low power.

Heres a side view and as you can see there is two S0329 sockets and i know this atu is for matching long wires however this adds more options and i have found i can match a length coax with a PL259 on it and nothing on the other end. That drooping of the S0239's is caused by the shape of the container, its a design feature HI.

The guts shows a lot of wires and aint a pretty site just as the outside dont resemble an ATU but it WORKS and for me thats all that counts. Spending lots of time playing around with this hooked up to the radio i found it matches almost anything under 3:1 from 160m all the way up to 2m! To me thats a bargain at just over 33p ( oh yes the pint of cider Roy) and im sorry to say this ATU is not for sale.

Phase 2 is not finished yet and could be another week or two away at the most if not a lot sooner, as i intend to be portable from my car i need to make something for the antenna which will............................................................

 

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