| WB2MIC Homebrew
Monster Xmatch |
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| The homebrew bug
bit me in the backside and I just had to build something. Not
being completely satisfied with the MFJ941D so-called "antenna
tuner", I decided to build a better Xmatch. Damn.
Those variable capacitors are expensive! Being a thrifty sort of
fellow, I decided to try my luck at making my own variable capacitors,
coils, insulators, the works. This page is a testament to the
determination that drives hams (a.k.a amateur radio) operators. Any
of the images below (about 320 X 240) can be clicked on for a larger
version (approximately 640 X 480). Photo #7, the finished Xmatch
minus the knobs has a link to
even a bigger image. |
| #1 |
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| #2 |
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Both front and back plates are 1/4' Plexiglas.
The capacitor on the left is only the rotor (bottom) assembly. I learned my lesson quick. Don't
individually cut the stator semi-circles using tin snips one at a
time. Instead, make a 2 rotor-sized square template.
Use a hole
saw in the middle. After the square is cut out, cut
through the middle of the square splitting the hole and then round the edges with a file. |
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| #3 |
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Another view of the completed, and,
yet
to be finished capacitor. Initially, the capacitor was to
have 9 rotor plates and 8 stator plates. It wound up being
17 stator & 16 rotor plates. I was inspired by the
CO2KK article, "Arnie
Coro's 'Easy-to-Build' PI Network Tuner" from Radio Havana Cuba "DXers Unlimited" website. I decided my
Xmatch would be a pi-network circuit. |
| PI Network An |
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| #4 |
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With the two variable capacitors
completed, on to the inductor, i.e., coil. I did some
reading on the Q of coils and settled on the dimensions. I
used a 2-1/2" o.d. white PVC pipe cut to 10" in
length. Two homemade stand-off insulators would support the coil. |
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| #5 |
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I drilled 2 sets of holes near each
other at both ends of the coil. One is for the #10 wire on
the coil. The other is for he 52 end-to-end 1/4 in plastic ties
used as
spacers. |
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| #6 |
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The ends of the ties are snipped
off. In this photo the coil is not evenly spaced yet.
On the bottom of the coil at each end are two 1" PVC pipe end
caps fastened with brass screws, nuts and washers. The end
cap is 1/3 of the stand-off insulator. |
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| #7 |
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Here is the completed pi-network Monster
Xmatch. You can see the stand-of insulator in front made
from two 1" end caps and a short 2" piece of 1" PC
pipe. The base is veneered particle board. The tap is
an alligator clip lead. The
stand-off output in the back is the antenna output. |
| Click above for bigger image. The full (big) size
image is here. |
| #8 |
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I couldn't wait to get some knobs to test the tuner
out so I put a hack saw to a 2-1/2" PVC pipe. A pair of
1/4" hex nuts quickly produced the two "deluxe"
circumvolution protuberances gauges ("knobs"). The Monster Xmatch sits
on a book shelf. |
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Finally, decent knobs from a hamfest. These
two black knobs came from the Sept 13, Ballston Spa NY
hamfest. Also notice that I rewound the spaces between the
inductor wire turns with colored plastic ties instead of all (look
above) white ties. This allows for easier clap reclipping by
keeping track of the location by color for each band.
The main hamshack uses an Icom IC756 Pro III with a Palstar
AT1500CV. See: 2008
Station.
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| Some final thoughts. Looking back,
I would use the thinner aluminum sheets instead of steel. Aluminum
would no be so hard on the
hands. The Monster Xmatch has been tested on 40 meters where
the 10th tap on the coil and 20% capacitance on both capacitors provides
maximum power transfer with 1:1 match for the transmitter. The
Monster Xmatch works very well and unlike the MFJ941D the settings do not require
readjusting during longer transmission as a result of heating low grade components.
The Monster Xmatch total construction cost was $44.20 which includes the
cost of a pair of good quality circular tin snips. There is much
satisfaction in getting a piece of gear working. The Monster
Xmatch especially so. On to the next
project. Send questions and/or comments to jozef@metaphoria.org
or to wb2mic@arrl.net
Monster Xmatch completed 05/14/05. Knobs, colored ties
09/14/08. Page last modified 11/30/09.
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| 73, Jozef Hand-Boniakowski WB2MIC |
