Somewhere in the grand eloquence of the InterWebs there is already a record of my having put the station first in a spare bedroom with antennas in the attic, then moving all that to a converted outhouse and finally, moving it all back into a spare bedroom with antennas hosed up with remote switches &c back out in the former outhouse. So them details you can find elsewhere, if you're interested.
Yeah, I know: I am imagining that I actually have a readership, another narcissism to which we are all drawn in these days of instant FaceBook fame & all those book reviews we do for Amazon.
But the story continues with the final addition of a remote control Z-match that will handle the crap spewed by my HF radios and a rehabilitated SB200 amp. And the story of the amp is almost as boring as this tale, so I'll deal with that later.
Suffice it to say that I have taken the Z-match circuit that I first cribbed from the InterWebs maybe
ten years back and modified the part sizes so I could run 500W through it. The first two Z-matches were designed for QRP, since I was whacked about that at the time. For QRO – which was 100W max for some time – I used either an SG-239 or an LDG auto tuner (I went through two of 'em), an Elecraft T1 autotuner (only blew on of those up) and the AH4 that hoses up to the Icom radios.
The low power QRO tuners worked really well. I found the SG-239 to be the most easy to use, mainly 'cause it's set up for the user/owner to dream up the distances between the tuner and the rest of the radio stuff, along with advice on a tune/lock/reset doodad for real and serious remote control. The LDGs were interesting 'cause they're made to do interesting things for power levels under 20W. Same-same the T1, although it's not as easily remoted. But in the end, if I was going to run more than 100W (or under 20 with the Elecraft & one of the LDG tuners), I needed something a bit more husky.
Making the decision began with the T1 dying on me at the beach vacation complex. Took me a couple minutes to finally determine that I was off the air with that box.
Lucky for me, I had dragged along my rather arcane lookin' home-brew Z-match.
This was an obvious learning moment.
For all the nice things you can say about an automatic antenna tuner, QRO or not, you're still stuck dealing with a machine the controls of which are not exactly in your paws. If the automatic parts of the tuner are controlled by some AI thingie in the box, it can make up its mind a bit far from what you'd even be willing to try. And if the AI thingie in the box quits, you have a nice circuit board with a bunch of useless parts on it. You're off the air.
Now any manual antenna tuner demands an operator with paws. And most of the time, such antenna tuners have husky enough parts to at least let you know when you've reached the design limits by arcing across capacitor plates or between turns on a coil. And of all the tuner designs that I've messed with, the Z-match beats all the other knob-twistin', coil-switchin', variable efficiency boxes by more than a marginal distance.
Two knobs, most of the time, take care of all your needs.
Thus the decision to figure out how to build a QRO Z-match, with QRO meaning anything up to and maybe even a bit past 500W.
The way this station is set up, I have two runs of about 75 ft in double-shielded Ethernet coax taken from service at the university from which I retired. The two runs, along with a big pile of confusing control cables, go from the pipe chase that heads the upstairs bathroom bathtub/shower to the former outhouse & part-time ham radio shack.
Out in the shack I have built two boxes containing what are called either toggle-relays or ratchet-relays. The coils on these beasts trip a ratchet kind of like a on/off/on pushbutton. One pulse they close alternate contacts. Another pulse and they go back to what they were before the first pulse. Thus they do not need constant voltage & current to stay in whatever switched state I want. I discovered, after I bought what I thought was a reasonable number from Roger's digs
, that they're rare little beasties and they're very expensive. That and the kind I have don't seem to exist any more. Bummer.
At least I have enough of 'em to make a six-hole antenna switch for the HF antennas and a four-holer for the VHF/UHF antennas. (And yes, I know switching HF is a whole bunch less fussy as VHF/UHF. Gimme some credit for at least trying. And no, I don't do moon-bounce of run QRO stuff on VHF/UHF. What I can hear is good enough for me.)
So with this switching system, I can pick out either fixed-frequency antennas, such as the 4BTV I got for Christmas or the 30m/17m vertical that I made out of beat up CB vertical parts and some hardware from DX Engineering
. And for the tunable beasts, well, that's why I have all those extra control cables running out there.
I tune the tower as a shunt-fed vertical on 75m. Works pretty good too. Consistent good reports from the Late Nite Radio/Old Hippies on the Air
gang. I originally hoped to switch it between two shunt lines for 40m and 75m but I found the relay chosen (one of those then-inexpensive toggle relays) turned into carbon powder running more than 100W. Lesson thus learned has tempted me to build a motor-driven doodad to switch those load lines. Ain't gotten that far yet. The tower, however, has its limits.
It doesn't do 60m or 160m or any of the other bands that are interesting in these days of low sunspot counts.
For that I need an old friend antenna: the open-wire-fed, balanced feed dipole lash-up that was my antenna of choice (my choice or not) for many of the first couple decades I wasted money on the air. And when we put up the tower last summer – we being KD8HCV, non-ham Dale Goubeaux, a few admonitions from my youngest and with my wife biting her nails – I made sure to put a yard-arm and pulley at the top of it with which I could haul up any antenna wires I wanted.
At which point we get back to the QRO Z-match.
High power RF, I learned many times over the four decades I've been doing this – requires lots of space or expensive vacuum. Capacitors that work great for 5W or 20W have a tendency to arc and melt when pressed past their design limits.
Which is why I was sooo damn happy to find a split-stator, dual-gang 40-475pF capacitor in Roger's stash for only $40-odd bucks. That made things very easy.
If you look at the schemo above, you'll note that the frequency-dependent part of the Z-match's transformer requires a dual-gang set up. Try finding one of those. I did for a long time and figured I'd just end up putting two Ten Tec 400pF high-voltage variables on the same shaft or ganged with a toothed belt. The discovery at Roger's made that shopwork project unnecessary.
Which left only the coil, something that I didn't feel like building more than maybe twice on a good day with no Ls in it. So I bought some time back a 4-inch diameter toroid of #2 material.
I went with the #2 'cause I figured my main intention was to get 160m through maybe 15 and that'd be good enough. If I'd wanted to be fussy, I'd have used a toroid of #6 material, which is more suited for tuning between 60m and maybe even 6m. I know this 'cause my two QRP Z-matches use the #6 material and they's just super good. Wanting to have 160m meant I'd have to go with #2, which, obviously, I did.
Which left only the gauge of wire to consider. And having just resurrected a much-abused SB200, I'd learned that wire sizes under #12 are like asking for trouble. So I went to PowerWerx's
webpage and ordered a chunk of #10 wire.
And when the wire arrived, I discovered something: winding #10 wire is like trying to straighten coat hanger wire. And yet, after a couple hours of consideration, I managed to get the core wound
with the #10, layered with fiberglass tape and the secondary – for which I only had a bit of #12 – on taped up.
I've never been good at estimating how much energy it takes to do things, which means that I'm not good at estimating what's gonna happen to various parts when they're stuffed with lots of energy. So when I stuck the finished Z-match out under the tower & hosed it up to the pitiful remnants of earlier open wire projects, I didn't expect to see the system fail so quickly.
When I hauled the box back inside and opened the beast up, my nose told me something was up.
I let all the smoke out.
Well, if not all
the smoke, at least a fair batch of it.
And I'd burned the enamel off the windings in a couple places. Which meant that my investment in #10 magnet wire had, one might say, gone up in smoke.
My back up was a chunk of #10 multi-strand wire in a Teflon jacket. More hard to wind stuff.
So I tore off the magnet wire, rewrapped the core and rewound the Teflon over where the smoked stuff had been. I wound the first 10 or so turns close, twisted in the tap, wound the next six or seven open, so the secondary could lay between 'em with space to not burn up again, and then wound the last ten or so turns a bit less than close-wound until I had the previously used 27 turns on the core.
Then it was “back in the box, bitch” and off to try it out.
I found that the Teflon wire, by dint of its being insulated, even close-wound makes more inductance than the enamel, which had been nominally spaced out across the coil. So I could tune the antenna through to about 1.2 MHz, way past 160m. So I took off a few turns at the top and tried again. Got to 1.650 MHz with that. So I hauled the box back in, took two turns off the bottom and suddenly I was good.
The lowest frequency I could hit was about 1.75 MHz. The highest? Well into 6m. And where once tuning 20m had been seriously problematic, now it was just a tad closer to not too frustrating.
With that, I'm done with it.
If you've looked at the pictures, you might be wondering what I used to box this beast up. Answer's simple: PVC. The body of the box is a 10” chunk of high pressure PVC pipe salvaged from a university project. The end pieces – well, the entire innards – is chunks of PVC sheet
that I bought from Small Parts.com
. I used a saber saw to cut out the disks that form the end panels and the mounting surface for the two drive motors. A table saw cut the main chassis down the width to slide into the pipe. And the end of the pipe sealed shut was cut slightly larger than necessary, chamfered around the edge to slide into the pipe with reasonable force and then glued into place with good ol' fashioned PVC glue. Some of the innards is reinformed with pieces of PVC sheet either screwed into place of glued there.
The motors came from Hong Kong. I found 'em on the Virtual Village
. One is a 2 RPM motor (driving the frequency tuned part) and the other is a 4 RPM (input capacitor; it's a bit too fast on some bands). I cobbled together a PCB to control the motor direction
through a relay. Got three boards made inexpensively at ExpressPCB.com, which gave me a direction control motor for the shunt feed to the tower as well.
All together, I'm happy with the way this beast works. Yes, it's huge, all things considered, and it does resemble the remote tuners that I saw and used with the WRT2 transmitters on the USS Saratoga (may she rust in peace) nearly 40 years ago. The final installation will come this spring, when the snow is gone and I can finally get out to the garage to torture pieces of angle metal to build a X-frame cradle for the beast. Gonna lash it down between the tower and the wall of the shed. And put up some legitimate open-wire feed. Then it'll be even more kick-ass. And come next winter, I'll have no excuse to avoid the 160m contests.
If only I could figure out how to pay for a 160m amp . . .