WB2MIC Homebrew Monster Xmatch 
   
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 
Rotors and stators cut from two sheets of steel using tin snips.  1/4"  threaded rod.  The spacers between all plates, front and back are all 1/4" hex nuts.  There are 122 hex nuts in each of the two capacitors I built.   I used the article, "Build Your Own Transmitting Air Variable Capacitors!" by David Hammack N4DFP and the fine plans by DL5DBM, Anwar von Sroka 
#2
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.
#3
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  
#4
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.
#5
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.
#6
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.
#7
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
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. 
#9
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.

#10
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.

  
73, Jozef Hand-Boniakowski WB2MIC