This page has
on some of
can should build, but just remember Byrne’s Law:
In any electrical circuit, appliances and wiring will burn out to protect the fuses.
- 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.
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
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
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
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
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
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
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
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
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
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
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.
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.
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
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
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
Back to quick links
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
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
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
Tea. Hot. Lashings of it.
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
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
"Be a collector of good ideas,
but don't trust your memory.
The best collecting place for
all of the ideas and
comes your way
is your journal."
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“The excitement of learning separates youth from old age. As long as you are learning, you’re not old.”
Rosalyn Sussman Yalow