More info about the Measures balanced tuner I built.
The Richard Measures 1990 article was followed for component values, the
choke / balun and layout.
1. PVC pipe
White, black has carbon, conductive. I pre-wound the coax to get the
correct pipe length, which ended up at about 12" on an outside diameter
of +/- 3 ½"
2. Coax
RG8X with solid dielectric. Obtained from Radio Works (no commercial
endorsement) The coax with foam may collapse. I started with 40' and
most was used as the winding. I had one PL259 connected by the coax
supplier.
3. For simplicity and individual adjustment of the rollers I eliminated
the motors, belts and gears. The reason I wanted individual roller
adjustment, my 234' dipole runs through trees which have leaves in the
summer and in the winter we have ice and heavy snow here in NH. My
concern was, I would have a antenna which at times could become
unbalanced and I wanted to be able to compensate for this condition.
4. I used the tuner on a wooden board for several months before
enclosing it in a wooden (Wine) box. I am sure the box, because of it's
original use, gives the rig more power. Once in the box, I installed
counter dials for ease of band changing.
5. The Measures design shows the capacitor being used either on the
roller input or output, depending which configuration gives the lowest
SWR. With my dipole 160-10 and my 20 meter 8JK, the tuner provides the
best match with the capacitor on the roller output.
6. I have temporally installed RF ammeters in each side of the feedline.
They read 1.75 RF amps, with key down, 800 watts DC input, on 40 meters.
I have not measured the other bands because the meters have not been
permanently installed. Frankly, I don't have a clue if 1.75 RF amps
means anything, but I think it just another way to ensure a balanced output.
7. QST April 2002, Pg 47 has another balanced tuner article, Feb 1990
was Measures article with pictures. The author of the April article, has
chose not to use the recommended capacitor value and the rollers he had
purchased for some other tuner project and I don't find where he stated
what their values they are. Point here is try to use the values which
Measures uses. I don't have the tech background most of you have so I
did not want to fiddle and diddle. There is an excellent picture of his
layout on page 50. I followed this layout, except I placed the choke,
perpendicular, in back of the rollers. I experimented with the choke
location and this was were it fit best for my enclosure. There was no
electrical effect if it was along side or in the rear of the rollers. I
even considered locating it at a remote location from the tuner.
8. I used Johnson Cat. No. 229-020-001 18uh rollers these have the
tapered output turns.
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