This page has information on some of the simple construction projects I have completed or, in some cases, am still working on.  These are station accessories every ham can should build, but just remember Byrne’s Law: In any electrical circuit, appliances and wiring will burn out to protect the fuses. Quick links Meter scales - techniques for re-labelling meters QRO baluns - high power 1:1 and 4:1 baluns for dipoles, loops, open-wire feeders etc. Mains voltmeter - a very simple yet handy project for a wet afternoon Bencher dust cover - another simple rainy-day project Kenwood radio-to-PC interface - a homebrew version of the IF232 Remote ATU - a long-term work-in-progress Rotator control box repair - large 4WD meets delicate Japanese electronics GS35b HF amplifier - another work-in-progress or ‘one day project’ Remote antenna switch - multiple antennas out in the field share the same low-loss feeder Manual antenna switch - a handy shack accessory, much cheaper to build than buy QRP rigs - homebrewing low power radios just for the sheer hell of it A ham’s workbench - where the above happens Keep notes - use a notebook, not just your logbook [There are other homebrew projects on this site too, including Elecraft rigs and antennas.] Access to the amateur bands is a privilege that comes with a purpose - ‘self training in radio communication’ as the old UK license used to say ... and maybe still does.  I shudder when I see the price of simple ham accessories and antennas made and sold commercially, especially when making your own is both instructive and fun.  Even better, I can often build better quality, longer lasting items than I can buy, for the simple stuff anyway.  After all, I’m just a hobbyist, not an electronics or engineering guru.  I don’t have an electronics degree but I’ve taught myself enough skills to get by, and making simple gadgets for the station or shack, or repairing things I’ve broken,  is the most enjoyable way of picking up new ones.   Meter scales I’ve used Letraset rub-down transfer letters to re-label old meter faces before but these days the computer makes a better job of it than I do.  Here are two suitable techniques: Tonne Software offers the nifty Meter program to create meter scales from scratch.  It’s a fiddly process to get the scales positioned and sized just right but sometimes that’s what it takes.  Even non-linear scales for SWR meters are possible. David G4FTC scans the old meter face on a flatbed scanner, adapts the image using a graphics editor, and prints it on a label to stick on the rear of the original face (in case he wants to go back to the original).  I guess you’d need to match the scanner and printer resolutions to get the size right but that’s a neat idea, David.  Tnx! Back to quick links QRO baluns In the US, it’s relatively easy to obtain QRO baluns but not so down here on The Far Side.  So, rather than pay an arm and a leg to obtain a commercial balun from W-land via airmail, I decided to have a go at making my own heavy-duty baluns capable of matching my amp’s output to various antennas.  The wonderful book  “Understanding, building, and using baluns and ununs - theory and practical designs for the experimenter” by the late Jerry Sevick W2FMI has been my inspiration and source of most of the ideas.  It’s a bit short on practical construction advice though and presents a confusing range of options including many designs lifted from the amateur literature and (mostly) systematically dismantled as a result of Jerry building and testing them (theory <> practice).  Lacking the ability myself to measure losses, impedance transformations, frequency response etc., I’m simply sticking to W2FMI’s preferred designs. The next step was to find a source of toroids.  Again, small toroids are sold in ZL but not the large ones (e.g. the FT240 with an outside diameter of 2.4”) suitable for QRO power levels.  On a recommendation I went to Amidon’s site and found all I need right there.  PDF scans of their spec sheets show the “K” material ferrite has a permeability of 290 and is good for LF toroids while the cheaper “61” material has a permeability of 125 and is fine for the higher HF bands.  They also sell Teflon tubing and Thermalize wire - although to be honest, I do just as well with coax inners.  Amidon’s prices are reasonable and delivery is quick and charged at their cost price. The first project was a wide-range 4:1 balun using a man-sized T400A2 iron powder toroid, designed to match balanced open wire feed to a normal unbalanced ATU.  I didn’t fancy paying extra for the copper wire and Teflon tubing suggested by W2FMI so I improvised, using the core from a spare length of RG58 coax which is more or less the same size and hence probably about the same impedance and voltage rating.  21 bifilar turns took the inner from about 5.6m of coax and the discarded coax shield will make earth straps for other projects. The toroid cost me US$30 + post from Amidon.  The nice grey gasket-sealed polycarbonate box came from Dick Smith, our local high street electronics supplier, for about US$15.  It’s better than a metal box in this application as there is no need for difficult-to-get HV feedthrough insulators on the balanced side.  At left are the parts laid out in kit form and the photo at right shows construction in progress.  Notice the 12” ruler under the kit: this toroid is 4” in diameter and needs a box at least 5” across to leave room for the windings. Next I built 1:1 LF baluns (chokes) using FT-240-K cores (US $18.50 ea + post) and more RG58 offcuts.  These were even easier to make with no need to strip off the coax outer cover and shield.  I use them to feed HF dipoles using RG58.  Ten turns of RG58 takes about 88cm of coax but I’ve found it’s best to just use the end of the feeder, running it through a cable gland into the box instead of using an SO239 and PL259. Be careful with those toroids!  The ferrite ones are more fragile than the iron powder ones and can be snapped by over-tightening the cable. I’m currently using one of the 1:1 baluns for a rotatable 17+30m band multidipole, made simply by connecting 2 normal dipoles in parallel with a common feed point, being the balun.  It seems to match quite  well, at least the SWR is low enough and I’m getting out OK on those bands.  [A third 12m dipole didn’t match at all well, possibly due to some weird resonance with the other 2 or due to the tribander beam a couple of metres above it.] The plastic box is not strong enough to use by itself as a dipole centre for long dipoles  so I normally use ceramic open wire spreaders, attached to the balun box using cable ties (two on the Mark I, four on the new improved Mk II) held in the boxes by jamming the cable tie heads into the box mounting holes from behind.  The antenna connectors use 5mm stainless steel bolts and wingnuts for convenience.  The bolts and SO239 (if used) are sealed with superglue which is liquid enough to flow into the tiny gaps and goes rock hard, preventing them from moving even under intense pressure.  The same goes for any fingers that stray into the glue ... It takes a bit of work to make neat holes in the polycarbonate boxes for SO239 sockets or cable glands.  First I drill a 13mm hole using the largest drill I have, then a tapered hand reamer to enlarge it, and finish off with a circular file and (for the round sockets) a small flat file to flatten one side of the hole to match the flat on the socket.  This flat, along with the superglue, stops the socket from turning while tightening the PL259 on the coax downlead.  By the way, I always cover plugs used outside with a layer of self-amalgamating tape to avoid corrosion and stop water getting into the coax, topped off with a further layer of insulating tape to cut down on UV damage from the very bright NZ sunshine. The toroids are held in place in the boxes using offcuts of high density foam cut to size from an old gardening kneeling pad.  The rated efficiency of these toroidal baluns (around 98-99%) shouldn’t cause any problems with overheating even at QRO levels, but I check them occasionally for heat damage and moisture ingress.  One advantage of constantly experimenting with new antennas is that there are plenty of opportunities to check the connections! Lately, I’ve been making 75 ohm 1:1 baluns for my fullwave loops.  I simply wind a few turns of the 75R matching line around a toroid inside a box at the loop’s feedpoint.  Dead simple and works nicely.  [To be honest, they are working at an impedance close to 100 ohms according to the theory, but are absolutely fine in practice.  My loops always outperform my dipoles.  YMMV.] One curious result to report: one of my usual 50R 1:1 choke/baluns created a noticeable impedance mismatch for the club’s 10m Yagi.  Possibly some sort of self-resonance effect?  I must remember to check out my baluns on the bands they are designed for in future using an antenna analyser and resistor in place of the antenna ... which reminds me I need to dig out some 50R and 100R carbon resistors from my junk box and put them in the antenna analyser carry-bag. Back to quick links Mains voltmeter I have keyers, ATUs, filters, computers and all sorts of measuring gizmos, some of it homebrew, some not.  I built a crude wooden box (right) for an AC voltmeter to keep an eye on the mains and discover exactly why the lights flicker when I key the amp and go very dim every so often (left). Key to this project was finding this fabulous old 4” 300-degree movement AC voltmeter, made in Auckland and liberated to the appreciative amateur market from a demolished NZ power station.  Then it was simply a case of knocking the electronics together one idle afternoon.   Back to quick links A $10 dust cover for the Bencher paddle I love my Benchers.  I’ve tried various other paddles from time to time but, for whatever reason, the Bencher iambic paddles suit my fist better than the rest. The only slight drawback to them is that they collect dust.  Aside from looking less shiny, the dust sometimes shorts out the contacts at the very close spacing that I prefer.  It’s easy enough to clean the contacts by carefully sliding a plain piece of paper through the gap but it always worries me that I’m slowly eroding the thin gold-flashed contacts. The answer is a dust cover: Thanks to a suggestion from my pal Lee ZL2AL, I made this fetching lime green creation from a plastic box sold as a desktop holder for square pads of notepaper.  By coincidence, the box is almost exactly the same size as the Bencher base, although too high, and it has a cutout that might have been made to fit over the paddles.  All it took was a bit of careful and patient work with a junior hacksaw to cut the box in half, followed by smoothing and straightening the edges with a fine file and emery paper.  I then cut up the cut-off section of box to make four corners that overlap the base to hold it in place, sticking them on with UHU clear glue. The tabs are a tight fit across the width but have a bit of leeway front and back. If you try this at home, hunt around the local stationery stores for a box that doesn’t have four big cutout holes in the base, or be prepared to cut and stick a piece of plastic in place to cover up the holes.  Mine is a “Durable” brand box with no holes, costing about $10 including its stack of notepaper. Back to quick links Kenwood radio to computer interface The boring grey diecast box here is my version of an IF232C Kenwood radio to PC interface for my old TS850’s.  It uses a MAX232 chip to convert between 12V RS232 and 5V Kenwood standards.  I didn’t bother with opto -isolators - no need.   That construction project was finally completed in 2005 but started about 5 to 10 years previous.  The RS232 connector on the right is a commercial USB to RS232 convertor because the PC doesn’t have an RS232 serial port.  At last I can log frequencies directly from the radio and avoid some of my contest logging screwups, I hope! My K3 has the RS232 port option fitted, but I’m still using the same cheap USB-RS232 converter from Duck Smuth, our local Tandy-equivalent.  FWIW my advice, contrary to dire warnings elsewhere, is not to fret about the particular chipset your USB-RS232 converter uses: buy a try cheap one and just see if it works.  If not, buy another ... Back to quick links Remote control ATU I picked up a pair of big motorised vacuum capacitors at a radio rally in North London several years ago, and a couple of big motorised roller-coasters too. I'm hoping to finish a remote controlled (manually-tuned) QRO ATU .... if only I can find the time to build it! So far, I've managed to get the roller-coaster stepper motor drive working, and I've started to figure out how to control the vacuum cap (10-1000pF variable plus 3 x 500pF fixed caps with RF relays in series). Unfortunately , the vacuum cap units are earthed through the cap chassis so for a balanced feeder I’ll probably need to leave the chassis floating (a technique I've used for years).  I may go for the dual-balanced ATU design published by AG6K in QST Mar 1990, using an air-core balun instead of lossy ferrite.  Anyone out there fancy designing an auto ATU with PICs? As you can tell, that’s an unfinished project. Back to quick links Ouch!  Large 4WD meets small Daiwa rotator control box OK, it’s not exactly a construction project - more of a reconstruction. This mess is the result of someone who shall remain nameless deciding to drive the car across the field when I was assembling a new beam and rotator ready for CQ WW CW 2006.  The rotator control box was “hidden” in the long grass under a tree and while I worked on the pole 20m away, that ‘someone’ drove out to the field to bring me a beer.  Very nice.  But then the ‘someone’ drove off the track and back directly across the grass to the house with a sickening crunch as she passed the tree.  She didn’t even notice the new speed bump in the lawn, or the irate radio ham jumping up and down in her ‘lipstick mirror’. The wheel crossed the front left hand side of the box, crushing the indicator panel and case.  First job after we’d collected the pieces and I’d calmed down was to disassemble the box and assess the internal damage.... The rotational indicator is basically clockwork: a series of gears, driven by a small electric motor, turns the pointer and a potentiometer gives positional feedback to the electronics, a simple Wheatstone bridge circuit.  With all the main bits out of the box, the front panel was buckled and above you can clearly see the bent drive shaft for the indicator/pointer.  So, with pointy-nose pliers in hand and nothing to lose by having a go, I disassembled the gear box, straightened the shaft and reassembled it.  The motor didn’t work due to its wires being sheared inside the end cap near the commutator so some precision shaping with a scalpel and soldering iron was called for.  Amazingly enough, it worked! After reassembling the innards, I painstakingly rebuilt the plastic box using superglue and a hot glue gun to tack the fragments back together, and turned it upside-down so the worst bits don’t show quite so much.  I used clear sticky film to hold the cracked bits of the perspex front panel in place rather than replacing it because it would be too hard to re-draw the compass bearing outer circle by hand.  Anyway, the cracked panel tells a story. The repair cost me a day’s labour in the shack and workshop, and with no rotator there was no way to turn the HF beam for CQ WW CW 2006, so I had a go at 40m single-band instead ... and made a record Oceania score. During 2007, I bought a shiny new control box for a Yaesu rotator that I’m planning to convert to work the Daiwa, hopefully with a bit more oomph too since there is a fair bit of voltage drop on the long rotator control cable at present (even using heavy duty “trailer cable”).  That’s another “one day project” (as in I’ll get around to  it one day). Meanwhile, I’ve fitted 4 x 12V white LEDs (a dollar a piece from Dick Smiths, NZ’s equivalent of Radio Shack or Maplin) behind the display of the old control box in place of the temporary incandescent bulb which burnt a big brown blob into the Pacific Ocean (and they say global warming is a myth!).  The LEDs are powered off the 12-0-12v transformer taps with 2 diodes and no smoothing capacitor.  The old control box really is a junker but still it refuses to die! Now all I have to do is remember to fit the beam pointing the right way ... yup, you guessed it ... Back to quick links A “one day” project - a GS35b HF amplifier I’ve been collecting bits to build an HF amp to replace the LK550 - one day.  Thanks to another ZL ham, I have a chassis, a GS35b valve and a little pile of circuit boards and components, most of which are usable.  I’ve even found a suitable fan to cool the beast, thanks to stalking our ZL equivalent of eBay for long enough.   I bought this meaty HV transformer from someone who bought and dismantled several 5kW commercial transmitters from an airport radio installation: it weighs about 90kg and now sits on its own furniture-removal trolley base, capable of carrying 200 kg allegedly (though it is bowed already!).  Should be good for a few kV at an amp or more, at full smoke.  The oil-filled paper capacitors sitting next to it will do a few µF at a few kV and may be built in the transformer box along with the rectifiers, soft start, control relays and meter for a self-contained PSU.  Well maybe - a string of modern HV electrolytics will give much more regulation I’m sure. The bars currently laid on top of the transformer will hopefully be enough to lift it: I need to build a strong case with an angle-iron frame.  It will hold the shack floor down most of the time but may go /P for contests.  Eventually.  Provided I can lift it into the back of the car anyway.  ... Meanwhile I am thorughly impressed with my KPA500 from Elecraft. Back to quick links   Remote antenna switch Having multiple antennas out in the field is great for diversity and flexibility but linking each one back to the shack with high-quality coax feeder is both expensive and awkward.  I much prefer to use remote-controlled antenna switches at the far end of the main feeders, selecting antennas with a small switch beside the rig. For the Mark 1 remote switch I used heavy duty (high current) open frame 12V relays with big contacts and decent change-over air gaps.  Although not designed for RF switching, these worked OK ... at least until water got into the box and they corroded away.  The SWR was reasonable up to 10m. The Mark 2 switch design uses vacuum relays from Russia and is great.  Rainwater got into that box too (spot the systematic failure mode!) and corroded the coils on two of the relays, since replaced.  The relay boxes now sit up on bricks inside plastic containers to (hopefully) keep them out of the wet. I recently rebuilt the Mark 1 switch with five more vacuum relays - the 6th relay has very narrow contact spacing so I’ve kept it aside to use as a TX-RX change-over relay in the new amp as I believe it will be a fast switcher. Both switches use an identical control system, so the boxes are interchangeable.  Relays are selected simply by applying +24V or -24V (relative to the common ground) to one of three wires in a separate control cable.  I decided not to use the coax as a signalling line for fear of having to isolate the control circuitry from QRO HF, and to avoid any chance of introducing nonlinearity that might create sproggies on receive. Back to quick links Manual antenna switch This is a surprisingly useful little gadget if, like me, you enjoy trying out different antennas and comparing their performance.  It sure beats plugging and unplugging antennas from the rig all the time and it’s easy to make, and cheaper even than the flimsy rubbish often sold to/by hams. Parts required: A strong metal box - diecast aluminium boxes are good. A good switch - about 3 to 6 ways, single pole, ideally a strong, high-voltage ceramic type for longevity and if you will be running more than say 100W. SO239 sockets - one per switch position plus one more for the input (unless you prefer to use a coax tail with a PL259 connector - that’s not a bad idea as it reduces one connector pair and cuts about 0.1dB of loss).  If you are into UHF, use N-type sockets instead and standardise your whole station on N-types.  Given the choice, use good quality Teflon -insulated sockets with a square metal mounting flange and 4 fixing bolt holes rather than the round type with a large round nut, as the latter tend to work themselves loose over time. Nuts and bolts to fix the SO239 sockets and, perhaps, the switch (depending on its design).  If you have a sizeable junk box, you may find enough similar ones for the project but it’s probably worth buying sufficient new ones as they are cheap enough and look better. Enamel spray paint. Sticky labels. Assembly instructions: Paint your box, unless you like that minimalist grey utilitarian look.  You can do it later but then you’ll have to dismantle or paint around the fixtures - it’s easier to do it now.  Car paint or Hammerite work well for me.  Spray cans avoid the need to clearn your brushes but you need to build up thin layers slowly to avoid unsightly runs.  Let it dry for at least a day or two. Mark the positions of the antenna connectors and switch on the box.  Use a ruler to get them lined up nicely.  When you’ve decided where to drill, make small indents with a centre punch (an automatic centre punch is a worthwhile investment).  Double check that you have marked all the holes in the right places before you start drilling. Drill the holes.  If you are under 16, get mummy to help.  Always use good quality high speed steel drill bits intended for cutting metal - cheap drill bits are both a bad investment and a safety hazard.  Wear safety specs and other safety gear if you anticipate becoming an old ham.  If you don’t have a large enough drill bit for the SO239s, ream out the largest holes you can drill using a hand reamer or cone-shaped step drill bit (also worthwhile investments for your toolbox, along with a pillar drill if you can).  If you must, file them to size using a suitable round metal file.  Try to keep the holes round. Fit the switch and the sockets to the box.  Sign and date inside the box, perhaps with a reference to this website, as you will forget what you have done in a few years.  Put the lid on the box and admire your handiwork. Wire up the sockets to the switch using good RF techniques i.e. short, direct runs of wire, preferably multi-stranded insulated wire of about 3-4mm diameter.  Solder them.  [I won’t bother explaining the wiring diagram as if you need that level of help, this is not the hobby for you.] Test the box, using your rig or antenna analyser and either your antennas (if you know they are resonant and well matched i.e. have a low SWR at the shack end of the coax) or better yet a 50 ohm dummy load.  A QRP load will do for the test as you should only need a watt or two to get an SWR reading and confirm that every switch position works without creating a mismatch i.e. the SWR readings should be practically identical whether the switch is in or out of circuit. Label the box.  I use cheap sticky labels and a marker pen to identify which antennas are connected to which positions because I’m always changing them, experimenting with new ones. Back to quick links QRP rigs As well as the Elecraft K2 and K3 radios, I've got various homebrew QRP ‘rigs’ (most are bare patchboards!) in various states of dis/repair about the place.  There’s an OXO somewhere, naturally, and a TEME from Practically Witless magazine many moons ago.  I’ve built these over the years just for the hell of it.  Most of the fun is in building them and after the thrill of making the first few QSOs, I soon lose interest, except for the K2 and K3 that is.  SPRAT, the G-QRP-Club magazine and Pat Hawker’s Technical Topics column in RadCom were the inspiration for most of those projects. Back to quick links A ham’s workbench Parts required: Table, desk, worktop etc. at least a metre square. Soldering iron or soldering station or at least some sort of safe holder for a hot iron. Solder - thin multicore electronics solder, not the crude chunky stuff that plumbers use. Small electrical tools - a selection of screwdrivers, wire cutters, pliers, knives etc. used by small electricians A small vice - nothing major like drugs Bits to build or repair, plus spare parts from the junk box. <Ahem> A junk box.  A box of stuff that will ‘come in handy one day’.  Hide it if you must. Spare time to build or repair bits.  This is my most rare and valuable resource ... Test equipment - a decent multimeter at least and ideally a scope, power meter and dummy load. Tea.  Hot.  Lashings of it. Assembly instructions Remove other stuff from the workbench.  All workbenches have a mysterious physical attraction for stuff.  A box to dump store it in may help (see part #7). Drink the tea. Get bits ready to build or repair. Drink more tea. Find useful bits in the junk box. Remove extraneous stuff that has already started to accumulate. Build or repair things. Celebrate with more tea, even if cold. Put useful spare bits away in the junk box. Leave remaining stuff all over the place ready for step 1 on the next project. By the way, I’m told you really need only two tools in life: WD-40 and duct tape.  If it doesn't move and it should, use WD-40 (or CRC in these parts).  If it moves and shouldn't, use duct tape.   Duct tape is like The Force: it has a light and a dark side and holds the universe together.  It’s well known that WD-40 was invented to stop the multi-billion-dollar US space shuttle from squeaking, and strongly suspected that the ultimate demise of the space shuttle mission was caused by squeaks that exceeded the engineering capabilities of WD-40. Back to quick links Keep notes! Being a scientist by training, I like to keep a little lab notebook or journal with details of the ‘experiments’ that I conduct in connection with amateur radio.  The notebook has proven invaluable over the years, especially so as my memory weakens, and so I commend this simple idea to all hams.  Here are some extracts from my notebooks to show you how they work for me. The circuit diagram here shows how I connected the PC to the keying transistor inside my homebrew keyer rather than fit another transistor inside the D -connector.  It seemed like a good idea at the time (1989).  I really need to change it now since I don’t always have the keyer in use, and it needs to be earthed to the strobe line to prevent random key-down nonsense at boot time. The pages below refer to contests I entered in 1990.  The photo of a 2m masthead preamp  takes me right back to that VHF Field Day when we lost a good hour right at the start of the contest thanks to a wayward blob of solder being pointed at by Chris or Ian.  Grrr.  We stopped using masthead preamps after that incident. Starting at the rear of the notebook and working forward until the book is full (like I said, I’m a scientist!), I record the contests I’ve entered year-by-year.  Here’s the page for 1988 when I started keeping the notebooks.  I was a studen in Leicester at the time and belonged to the Leicester Radio Society. My second radio notebook is nearly full now, giving an average of ten years’ experimentation per notebook.  I guess the records set by Marconi, Hertz and other genuine radio experimenters are safe! "Be a collector of good ideas, but don't trust your memory. The best collecting place for all of the ideas and information that comes your way is your journal." Jim Rohn Back to quick links “The excitement of learning separates youth from old age.  As long as you are learning, you’re not old.” Rosalyn Sussman Yalow

Hawke’s Bay
North Island
New Zealand

39^o 39’ South x 176^o 37½’ East

Locator RF80HL

260m ASL

IOTA OC-036

CQ zone 32

A1 Ops
ARRL
CDXC
FOC
G0FBB
G-QRP-C
M6T
NZART
Voodudes
ZL6QH
ZM4T