L MATCH ATU FOR QRP
by Sean 2E0BAX (Formerly
M3FVB)
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 the
antenna....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 it's 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. So in this project 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
pictures below 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,
yellow shaded area in diagram above. It just goes between
the S0239 and the switch and 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 are the two air variable 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 above
and as you can see, there are two S0239 sockets and yes, 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 internal view
above shows a lot of wires and ain't a pretty site just as the
outside does not 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 an SWR of 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 I'm
sorry to say this ATU is not for sale.
Phase 2, the
antenna, is not finished yet as of the time of this article 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............................................................to
be continued!
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