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    Amateur Radio

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  • Bruce H. McIntosh
    scotsman@afn.org
    Visit my work homepage
    Last revised Jun 10, 2017

    Invisible airwaves crackle with life
    Bright antennas bristle with the energy

    Amateur Radio

    The Great Antenna Project of 2016-2017


    Impetus

    Around about the time of the January 2016 VHF contest I got to contemplating the rather iffy state of my VHF antenna situation. Reported difficulties with my transmit audio led me to meter the 2m beam,and lo and behold the SWR was > 3.0 across the 2m band. In addition,that 15el 70cm antenna just isn't enough,especially since I only have 10W on transmit for that band. And finally,the really wet PT lumber with which I constructed the wooden tower is now,several years later,very badly warped.

    Inspiration and motivation coalesced in a few frenzied days of web surfing and perusing old magazines. I came away with a game plan for a wholesale rebuild of the VHF/UHF antenna farm. The overall plan is as follows:

    • Rebuild the wooden tower using the driest,straightest 2x4s I can find at GenericBigBoxStore™,with new features
      • Taller - 28' of wood structure as opposed to the current 20'
      • Straighter and more weather resistant - painted,kiln dried lumber
      • Hazer-esque "trolley" on which the antennas will mount
      • Rotator! No more "armstrong" rotator action in a pouring rain
    • Rebuild the 6m 4 element Yagi into a Larry Cebik "Route 66" 6 element OWA configuration on a 14' boom
      • Add another 6' to the boom
      • Add two more elements
    • Build a 9 element G0KSC LFA Yagi
    • Build an array of four 8 element Quagi beams for 70cm
    • Replace all feedlines with new LMR-400 UltraFlex using N connectors

    I've gotten orders off to Texas Towers and McMaster-Carr. Once the huge pile of tubing and rod stock shows up,down come the old antennas.

    Feedlines!

    It's a beautiful day,so I figured,"Why not get the feedlines into that freshly-buried conduit?" I recently connectorized three 30+' pieces of LMR-400UF,and picked up a 100' hunk of 8-wire rotator cable at Orlando Hamcation,for the once and future rotor install. I got the fishtape rammed through the pipe,and all the cables neatly laid out so they wouldn't tangle. I marked both ends of each cable (not that I've *ever* forgotten to do *that* before...).

    Then I bundled them all up in a plastic bag,duct-taped the bag to the fishtape,and started in on a back-and-forth,push-me-pull-you exercise to get the bundle down the pipe.

    I hit a couple of snags when things hung up on the joints between the conduit segments,but a little back-and-forth-ing got everything moving again.

    Finally the clump emerged from the other end.

    Some N to PL adapters and some right-angle PLs,and this lot's all done. When it's time to install the rotator,I'll break out the end of the 8-wire cable onto a barrier strip (to be replaced at the appropriate moment with a proper surge arrestor and ground). Time to button up the box.

    At the tower end,I wrapped the coax ends up good and tight in a plastic bag and coiled the tail of the rotator cable to keep it neat until I'm ready to put up the new wooden tower and the rotator.

    And just as a side note,I tracked down the fault in the existing above-ground run for the 2 meter Cheap Yagi. Water had gotten into one of the PLs,naturally,and soaked a few inches of the coax. It was just a few minutes' work to lop off about 6" and solder on a new PL. Oh yeah,I also got up on the roof and repaired the mount for the 2m vertical. Now to liberate a 2m FM rig from the garage.

    One crucial step was to clear the volume of space through which the newer,longer antennas would have to pass. I recruited my long-suffering tree-saw-weilding buddy Andy to shinny up a scary tall ladder and lop off a few of my neighbor's tree limbs that stuck out into my yard at the 30' or so level. Mission accomplished; now there's room for 16' long antenna booms.

    Six Meter Beam rebuild

    I took the 4el 6m beam down and rebuilt it into a 6el OWA beam a la Larry Cebik. It's a 14' long monster now.

    I got it up on the tower just as daylight was running out that day.

    New Two Meter Beam

    Soon as the rebuilt 6m beam was up,it was time to start the new 2m beam. First step was to splice together the two 8' boom sections,and get the holes for the element clams drilled. Had to stop for dinner after I got a few of the elements mounted.

    The antenna's all put together now,just sitting on the ground waiting for the new tower and "homebrew Hazer" to get built.

    New Wooden Tower and The "Homebrew 'Hazer'"

    I had a bunch of pictures but my phone's microSD card went Bravo Uniform the other day and ate several hundred photos,alas. What I've got so far is this: I half-lapped a pair each of 12' and 8' 2x4s,resulting in two 20' long 2x4s. I then lopped up another 2x4 into 3-1/2" long bits and screwed/glued them in between the long 2x4s every 18" or so. The end result is a little twisty,but not nearly as twisty as the existing tower! The other day I lugged it out of the garage,set it up on sawhorses,and gave it a good slathering of spar varnish for weatherproofing.

    Now it's time to come up with the "Homebrew 'Hazer'". It'll be a "sleeve" of 1/2" pressure treated plywood that will slide up and down on the tower. A pair of brackets on one side will hold a rotator and a thrust bearing. I'll rig it with pulleys and rope so I can raise and lower it to work on the antennas without having to tilt the tower over.

    Fast forward to spring of 2017. The Homebrew Hazer has come along nicely. It worked out to a piece of plywood,several heavy duty shelf brackets,some 2x6,and a few lengths of galvanized pipe. Here's an early mockup of how it'll look.

    After everything's cut and fitted,it's time to blue-and-screw the blocks that hold the "bearings" (1" pipe with cpvc pipe covering). Several VERY long screws run through the blocks for mechanical reinforcement.

    Ran a quick check to make sure my math was right and that the 2x4 tower will fit through the thing.

    After a couple coats of spar varnish for weatherproofing,I mounted the Yaesu thrust bearing on the top shelf. The "Homebrew Hazer" is now done,and ready to mount the rotator.

    Rotator overhaul

    Some time ago I started overhauling my two ancient CDE rotators. The one that got selected for this project is still in need of some TLC,including a new position potentiometer and a locking plug to replace the badly corroded screw terminals. First step was to take the thing back apart,at which point some carelessness on my part drove home the point one online commentator made:

    "There are two classes of people: those who have spent ages on their hands and knees chasing ball bearings all over the place,and those who have not taken apart a CDE rotator."

    Sure enough,one of those plastic bearing retainers got away from me,and greasy steel balls went everywhere. Anyhow,I got the thing disassembled and got all the stray balls tracked down.

    With painstaking care I nipped off each lead,attached a pin,and inserted it into the new locking connector. Not bad,if I do say so myself!

    After I replaced the busted position pot on top of the motor unit,I went to start putting it back together again. That's when I realized I didn't remember how the fool gearbox was arranged. Argh! But first,the new connector is too bulky to fit through the hole in the base sideways,so I had to file a couple clearance notches to get the thing on there.

    Now it's onto the gearing... after a bunch of trial and error I finally glommed onto how it all fits together. Here's the stacking order (watch out for all the bushings and bearing washers, or you'll be taking it apart and putting it back together again like I did!).

    After some further jiggery-pokery (Obscure Dr. Who reference) to get the ring gear lined up just so,on went the motor assembly. Note the shiny new positioning pot.

    Added in some more lithium grease (owing to losses from cleaning off all the runaway balls),got it put back together,and pulled it off the work stand. No rattling noises,so nothing came loose durning assemmbly (sigh of relief).

    Last step was to mount the rebuilt rotator to the "Homebrew Hazer" and test-fit a piece of mast to make sure stuff'll line up. Looks pretty good! I'll need to come up with some way of shimming the 1" TV mast to get it centered on the rotator.

    Now all I need is a break in the weather before the June VHF contest this weekend!

    Saturday dawned bright and sunny,though it will rain by afternoon. Let's get busy! First up is to snake a hunk of rotator cable from the entry point around the office/hamshack to where the rotator goes,and get it all hooked up.

    Next,cart the Homebrew Hazer outside and temporarily hook up the rotator just to see if it works.

    And lo and behold,it does!

    At long last,it all goes up in the air!

    The weather still held through the morning and into the afternoon,though lord lord was it HOT out there. The old tower tipped over for the last time,and the antennas were dismounted. Then off came the old tower and on went the new one.

    A trial tip-up at this point revealed that the thing was a tad too top-heavy,and just a shade too tall. The Sawzall and spar varnish were brought into play to shorten and weatherproof the situation.

    The post itself was just a tad twisted,so the tower took a bit of persuasion to slide into position.

    The Homebrew Hazer was mounted to the tower and the rotator turned to "face" west. 10' of mast went through the thust bearing and along with some shims to center it was clamped to the rotator.

    The antennas were mounted to the mast and reconnected to their feedlines,and the whole operation hauled by main force up to operating position. Then it was determined that the 6m beam wasn't high enough to clear the top of the tower,so there ensued a couple of iterations of lower it all,adjust positions of the antennas,then haul it all up again. With the temp and humidity both in the 90s,it was NOT fun!

    At long last,with the mondo storm system rolling in double-time,everything was hauled up and into position. The rotator was brought into play and this time the 6m beam cleared the tower on its way around to north. Hot diggity! No more running outside in the rain to "armstrong" the antennas around! The Great Antenna Projecte is done... for now... I do still have the new 70cm antennas to work on,but that'll wait until fall.

    Further updates as events warrant...

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