- My antennas - up the towers or in the trees, the antennas I use most of the time
- Constructing wire antennas - homebrewing tips
- Antenna experiments - aerials I’ve tried or am planning to try
- 4 squares - on a hot tin roof
- 2x2 quad for 12+17m - a 2 element 2 band nested quad design
- Kites - using kites to lift wire antennas
- Optimising radials - pragmatic advice from a true amateur
This page concerns antennas, the third characteristic of successful DXers, the first being skills and the second, location. Despite the advertisers’ claims, radios trail the field in fourth place.
I have acres of space with two small towers and many big old
trees supporting wire antennas.
The trees make good sky-hooks but the lower side branches
tend to snag the ropes and wires. I trimmed a few of the
easier ones very gingerly from the bucket of a cherry picker
before chickening-out. I could do with a tree surgeon to finish
the job safely and properly.
My first tower was fixed, 12m high, made from welded angle
iron. I think it might once have supported a windmill for a
water pump. It was heavy at about 150kg and probably strong enough to free stand but for safety and peace of mind,
particularly when I’m climbing the thing, I guyed it top and
A second tower, also only about 12m
high, is a wind-up tilt-over design, ideal
for testing and tweaking antennas.
The beams are only about 12-14m off
the ground, quite low in wavelength
terms but it helps enormously to be
perched on top of a 260m hilltop from
which the ground slopes steeply away all
My third tower replaced the first: it tilts
over but doesn’t telescope, so the
stresses on the base and the luffing pulleys are enormous. I was happy to have the base
refurbished and rewelded by Red Steel, an excellent local steel firm in Napier. If you’ve seen the
pathetic mess I make of welding, you’ll understand my relief to get the job done properly!
My current antenna line-up ...
- a full wave wire loop suspended between two trees with the top roughly 20m up. The
antenna is oriented in a North-South plane and fed in a bottom corner (slant polarized) with a
quarterwave of 75 ohm coax to match it to the 50 ohm feedline, through a homebrew choke
balun. It is an excellent DX antenna.
- the 40m loop with an ATU sort of works, OKish.
- another full wave wire loop between two trees, the top about 15m high. Nice!
- a quarter wave wire vertical supported on a roach pole above the tin roof of my workshop.
Works very nicely for such a simple setup. It is just at the right edge of this photo, almost invisible,
a stealth antenna!
- I’m very slowly building a 2-element instant-reverse 5-band quad. Meanwhile I
make do with a neat little 2 element triband Yagi built by my pal Lee ZL2AL (SK). It has an
interesting trapless parasitic feed arrangement with interlaced elements.
- a nice 3 element monoband Yagi below the tribander is on long-term loan from my pal
ZL2AAA. Morrie built it for the ZL7T DXpedition. Evidently it still has plenty of DX left in it.
- I’m using a 5 element monoband Yagi on the higher tower, a solid performer:
- perched above the tribander and 17m beams was a full wave wire delta loop supported on
a homebrew welded bracket holding two weedy fibreglass spreaders and a central PVC pipe. It
worked surprisingly well for such an ugly beast, a temporary antenna that lasted several years until
the fibreglass disintegrated. Since that fell apart, I’m using the 2 ele tribander with an ATU.
All my antennas use homebrew QRO ferrite
The antennas are selected using homebrew
remote antenna switches like this one.
They use “B1B” SPST vacuum relays from
Russia. The relays aren’t exactly cheap but
it sure beats paying $$$ to coax-feed all
the antennas separately.
Note the small dummy load on the
rightmost antenna port, useful to check
from the shack end that the feeder and
switch are working properly.
The long feeders run partly underground. It was a tedious job hand-digging the trenches but the
thought of reducing the local QRM from our computers etc. kept me going.
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Constructing simple wire antennas
Simple wire antennas like dipoles and verticals are dead easy and very cheap to make: here’s how.
A sufficient length of suitable antenna/earth wire. Read up on wire antennas or use my
spreadsheet (below) to figure out how much you will need for, say a halfwave dipole or
quarter wave vertical. Aim for heavier wire for longer dipoles (40m to topband) that you
don’t anticipate repairing every few months. Here’s the chart I use to cut wire antennas to
length (prior to trimming anyway):
[Here is the Excel file, now including a sheet with imperial measurements
as well as the original metric version, and some notes on matching stubs]
A feedpoint insulator/connector, with a balun if you are feeding a balanced antenna with coax
(e.g. a conventional dipole). There are several home-brew options here ranging from suitable
pieces of wood, Perspex sheet, plastic or ceramic Tees or open-wire insulators, up to
commercial centre pieces with built-in coax connectors. Personally, I like to make up my own
IP56-sealed plastic balun boxes using a toroid plus stainless steel bolts with stainless wing
nuts for the antenna wires and either SO239 connectors or long coax pigtails terminated with
in-line SO239s (again, to avoid unnecessary connectors and save the odd tenth of a dB -
they all add up!). You should probably use ring terminal connectors of approximately 6mm to
terminate and connect each leg of a dipole at the centre point, but soldered/tinned loops in
the end of the wires will do. For wire verticals, it is possible to solder the antenna wire and
earth wires directly to the feeder, then wrap the feed point with self-amalgam tape.
“Chocolate block” screw-down electrical connectors can be useful when experimenting with
new antenna designs but don’t rely on them for permanent fixtures as they corrode quickly.
Coax or open wire feeder, more than enough to reach from the antenna feedpoint once
erected to the shack or remote antenna switch. Don’t go overboard but a few extra metres
will allow for antenna movement in the wind and positioning the feeder to avoid garotting
passing animals. Open wire feeder has negligible losses but the balun and ATU put the losses
back in and add complexity, so open wire is only really worthwhile for a multiband doublet
antenna, vee-beam or rhombic (dream on).
Antenna end insulators. Ceramic ones will last approximately forever (barring accidentally
dropping them on the ground or over-stressing them) but are heavier and are quite scarce.
Plastic ones will last up to a decade. Electric fence wire insulators are good if you have a farm
supplies shop nearby, as they are designed to insulate tens of kilovolts for longterm outdoor
use. Bits of Perspex or other strong plastic sheet can be cut to size. At a push, you may be
lucky just using the plastic cord (see below) but it tends to start conducting when wet so the
resonant point and match will change in the rain.
Self-amalgamating tape or coax sealant (NOT ordinary insulating tape - it won’t last more
than a few days or weeks, although it does help protect the self-amalg from the sun’s UV).
A wooden winder board on which to wind the antenna. Make these from offcuts of plywood
or thin MDF board approximately 30 x 15cm, with U-shaped notches in both short ends to
hold the wire in place as you wind. Trust me, it’s quicker in the long run to make a bunch of
these up and use them routinely than to untangle the wires and ropes/cords every time you
go to erect a stored antenna.
Plastic cord to hoist the antenna. Fairly cheap, thin nylon or polypropylene cord is fine to hold
out the ends of a small to medium-sized dipole or vertical, and lasts for ages if not over
-stressed. You will need thicker cord or rope (up to about 4-6mm) for large antennas and to
hoist the balun and feeder of a dipole.
Measure out the exact wire lengths you will need and cut the wire. I usually do this by
clamping the end of the wire plus the end of a long tape measure (another toolbox
investment) in the workshop vice (there’s another!) and walking them out into the yard. If
you have, say, a convenient fence or wall at least 10m long and some patience, you could
measure and mark it permanently with paint or similar markers to use it as a giant ruler. Err
on the long side as you will trim the antenna down to resonance later but adding wire would
involve soldering bits on, preferably using a decent butane-powered soldering iron (yet
another worthwhile investment).
Make up the feed point.
Seal the coax feed point with self-amalgam tape or coax sealant. Take care over this as
water in the coax ruins it forever.
Label the feedpoint with the band/type of antenna. I sometimes add short lengths of shrink
-wrap on the centre ends of the antenna wires in order to label them. Marker pens work for
up to a year before fading in the sun.
Erect the antenna and test it for resonance. It’s best and safest to erect it all the way to its
finished position as resonance and match will vary nearer the ground.
Bring the antenna down, trim a few cm off the ends, put it back up, re-test for resonance and
repeat until done. If you get smart, calculating exactly how much you need to trim off, you
will inevitably cut off too much at some point. As I said, err on the long side.
Work lots of DX.
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There are several parameters to adjust when it comes to antennas but essentially the choices
come down to gain (in both horizontal/azimuth and vertical/elevation planes, don’t forget) and
pattern. I’ve had good DX results with vertical quarter-waves and inverted-vee dipoles, with
reasonably low take-off angles and more-or-less omnidirectional in azimuth. I’ve never had tall
enough towers at home to make horizontal antennas perform as per the textbooks (except in
local contests where the high-angle radiation is useful) but even ground-mounted verticals seem to
I suspend miscellaneous wire antennas in the trees from time to time. Loops seem to work better
than verticals and dipoles, presumably due to their higher radiation resistance - around 125 ohms
according to the books - and hence higher efficiency. Some experts claim they have lower angle
radiation than dipoles but I’m not sure about that, and both factors presumably depend on their
height above ground. They do seem to be low noise antennas, although that’s purely subjective.
Whatever, loops work well for me.
I was tempted to try 5/8th wave verticals until I read a paper by W4RNL modelling them against
quarter waves and vertical dipoles. The improvements in gain and low take-off angle just don’t
seem worth it. I’m sure multi-element vertical beams would be better.
One day I’ll have to measure my ground conductivity and dielectric constant: meanwhile I use an
estimate based on the ARRL Antenna Book’s values for my type of soil (around 6-9 inches of
topsoil on a clay base on a forested hilltop), namely 5 to 6 milli-Siemens per metre conductivity
and dielectric constant of 13.
My first antenna experiment in ZL was simply to add additional wires in parallel to the existing 40m
quarter wave vertical, using the same coax feed and ground plane. I added 30m and 80m quarter
waves - the 80m one makes an inverted-L. They seemed to work, after a fashion, but were noisy
on receive. That’s a FAIL.
I’m considering an array of quarter wave LF verticals sharing a common feeder, earth mat and tree
The design is based on a receiving antenna shown in The Radiotron Designers Handbook of 1953.
The 160m vertical will be an inverted L as even our tallest trees are not quite 40m - more like 30m
at a guess. The earth mat will be a combination of deer fencing and wire radials. The antennas will
be separated by a convenient distance along the cord - a few metres each(I’ll have to lay the lines
out on the ground to set it up). I could use two cords from the top, alternating the verticals to
spread them laterally as well as along the cord, but the single cord design looks easier. I’m hoping
the magic of resonance will effectively feed one vertical per band, although on 40m the topband
vertical will accept some RF so the match may need adjustment on 40m and the pattern may be
high angle - in which case I’ll just have to try something different (an L-match or low-pass filter
feeding the 160m vertical maybe, a high pass filter for the 40m vertical, a remote relay at the base
or a completely separate 40m antenna).
Yet another possibility is quarter-wave vertical/L for 160m, end-fed on 80m with a relay-switched
matching unit such as those described by AA5TB. So many antennas in mind, so little time!
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I’ve been planning 4-square antennas for ages. It took me so long to get
around to it that I thought about just buying one from the local Four
Square supermarket -->
The design is easy enough: four identical quarter wave vertical antennas
set at the corners of a square with quarter wave sides. Using the
simplest feed arrangement, the antenna fires across the diagonals giving
one of four directions: it needs a negative phase shift on the forward
antenna relative to the sides, while the rear antenna needs a positive
phase shift. The pattern is cardioid.
Patrick TK5EP published a simple circuit for a 4-square hybrid coupler
using three DPDT relays and a 3-core control line to switch directions. I
created an Excel spreadsheet using textbook formulae and the
manufacturer’s AL values for various Micrometals powdered-iron toroids
to confirm TK5EP’s component values for 40m. By my calculations,
T300-2 cores give exactly the right inductance and can handle more
power than the T200-2’s favoured by TK5EP ... but for practical reasons
to do with the length of the fibreglass poles I had on hand, I started with
a 30m version to prove the concept.
The tin roof of my
workshop makes an
roughly 10m square as it
happens (it was
rectangular so I added a
tin roof woodshed to
make it squarer).
The antenna elements are
wires, attached to
fibreglass roach poles
using rings of heatshrink
tubing. The poles are a
push-fit into surprisingly
strong adjustable angled
base fittings made to hold
Sky satellite dishes, a
arrangement. The purple
wire is the earth connection to the coax outer, relying on metal to
metal contact of the fitting to the galvanized steel shed to couple it in
to the main roof area.
The calculated inductance values in the hybrid coupler on 30m require
8 turn coils on T300-2 cores, but for some as-yet unknown reason,
my shiny new LCR meter from Hong Kong measures them at more
than twice the target inductance (the calculations and inductance
values are correct, but the meter is wrong, although it measures
small potted inductors of a similar value correctly). The coupler needs
two 156pF capacitors: I could only find 100pF HV capacitors in my
junk box, so added some coax tail capacitors in parallel in the first
Here’s the coupler with the original 100pF capacitors in place, just before I added the coax tails.
The toroids are cable-tied to a chunk of PVC pipe to keep them in place. The device on the right is a
50 ohm ceramic power resistor bolted to an over-sized heatsink, since I didn’t know how much
power would be lost due to imbalances in the system.
The hybrid coupler phasing/switching box is inside the workshop, screwed to a rafter under
the tin roof. It’s more accessible and waterproof
there than it would be sitting outside.
Morrie ZL2AAA gave me some 150pF mica capacitors
and confirmed the calculated inductance values with his
LCR meter (thanks Morrie!). Perhaps I should dust off
the old scope to check the phasing too ... but anyway,
it works! I get about 2 or 3 S-points difference front-to
-back and signals are about 1-2 S-points lower off the
sides. At last I can tell whether signals from Europe are
coming via the long or short path. Direction switching is
instantaneous of course.
Unfortunately, erecting a tower next to the workshop messed up the 4-sq beam pattern and
matching so eventually I reverted to a single quarter wave vertical ground plane instead, and that
does just fine.
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2x2 nested quad for 12+17m
In the Antennex article “Adjacent band quad behavior”, LB Cebik W4RNL used antenna modelling to
calculate and optimise the characteristics of two-element two-band (hence “2x2”) nested spider
quads for various combinations of the upper HF bands. In a follow-up Antennex article “Sneaking
Up on 2-Element Common-Feed Quads - Part 3: Dual Band Quad Beams With Common
Feedpoints” W4RNL adapted the design for a common feed located at the normal feed point half
way along one side of the smaller quad. This arrangement slightly distorts the driver of the larger
quad and affects all the design figures, but modelling shows minimal effects:
The calculated free-space gain (around 7dBi) and front-to-back ratio (20-30dB) are quite
respectable for such a simple design:
Azimuth plots show reasonably clean patterns predicted on both bands:
Feedpoint impedances are calculated to be around 100 to 125 ohms being mostly resistive with
just a little reactance. I guess a 2:1 toroidal balun at the common feedpoint would present a good
match for 50 ohm coax, reducing the common mode current if a balun were not used.
Here are the element dimensions in inches from W4RNL’s follow-up Antennex article, with the
17m element spacing
12m element spacing
Total wire length
Using the spider quad design (i.e. spreaders radiating from the centre point of the array), the
spreaders would need be about 10 feet (3m) long. I should be able to fabricate a spider centre
using a short boom of square steel box section with angle-iron supports welded on at 62 degrees
to attach the support arms. To attach the antenna to a round steel mast (a 2” diameter steel
scaffold pole in my case), the end of the mast will need to be grooved to fit the corner of the box
section steel, and then welded on: in practice, I’ll probably weld on a short stub of smaller diameter
steel pipe that will sit snugly inside the main mast, with a locking pin through the main mast and
stub to stop the antenna turning relative to the mast.
So, the bill of materials looks like this:
Wire: copper house wire?
Boom: 2”x2” steel box section
Spreader supports: angle iron
Spreaders - bamboo
8 x 10’
8 x 3 m
Cable ties to secure wire to spreaders
x 16 plus a couple for the feeder
Sleeving to support wire corners
16 x 4” long
16 x 10 cm
Locking pin - offcut of Number 8 wire
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Big parafoil kites are ideal for lifting wire aerials, given quite a bit of wind and lots of space. Parafoils
are spar-less, nylon kites that fold up into a small rucksack. Their aerofoil section (rather like a
skydiver's parachute) gives loads of lift and they are fairly static in the sky (no good for aerobatics
or fighting, ideal for hoisting aerials). My 5 ft-wide parafoil kite will lift a top-band quarter-wave wire
in a decent steady wind (Beaufort force 3 or above), and I've used it to hoist vertical dipoles,
inverted-Vees etc. using slotted plastic twin-feeder rather than coax (it's lighter and lower loss). In
fact, it gives so much lift that it's a real handful in a strong breeze (force 5+) - I struggle to pull it
down. For lots more ideas on kite and balloon-hoisted LF antennas, visit G4VGO’s site.
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Optimising radials for verticals
There’s a lot of information (and some misinformation!) circulating in amateur circles about radials
for verticals. Much of it is based on decades-old research conducted for commercial broadcasters,
who have the space and resources to install and maintain over 100 radials per antenna. A fair
amount of more recent advice draws on purely theoretical studies using antennal modelling
software ... which presumably also draws on the decades-old research just mentioned. Quite a lot
of what we read (... including my own musings ...) is essentially anecdotal (“It works really well: I
work loads of DX!”). Unfortunately rather few hams have done the legwork to demonstrate,
conclusively, what does or doesn’t work in a typical amateur setting, or to answer very common
yet basic questions such as:
How many radials should I put down?
How long should they be?
Should I lay them on the surface, bury them or elevate them?
What if I can’t lay them out symmetrically?
So, it’s a refreshing change to read a scientific study of radials for vertical antennas by a dedicated
amateur, Rudy Severns, N6LF. It’s obvious from Rudy’s excellent articles in QEX that he knows his
stuff. He has carefully researched the professional and amateur literature and then designed and
painstakingly conducted the controlled experiments to check out various theories in practice.
If you have the time and interest, I recommend studying all 7 articles in the series. If not, here are
the takeaways :
- Use sixteen to thirty-two ¼λ radials on the ground
, or at least four elevated ¼λ
If you don’t have the space for ¼λ radials, lay down a larger number of shorter ones.
The shorter your antenna, or the poorer your soil, the more you need a good ground system.
A surface-radial ground system will affect the resonant frequency and you may have to adjust
the vertical height for that.
Aside from the earth system, work hard at making the antenna itself more efficient. In other
words, use high-Q loading coils, use top loading to minimize the size of loading coils, minimize
conductor loss and so on.
Note that sixteen is not a magic number for on-ground radials. The experimental data indicate
marginal improvements with more radials but rapidly diminishing returns probably make the effort
pointless above about 32 radials and, as the last bullet suggests, we are probably better-off
optimising other parts of the system (such as the radiator, the feeder, the rig, the operator and the
QTH - plenty of improvement opportunities!) rather than the radials. Unless you are absolutely
desperate to squeeze the last tenth of a dB out of your earth mat,
there is no practical value in
going beyond 32 radials
. Those guys who lay out 100+ radials will do their utmost to convince
you that it was well worth the effort, and in psychological terms they may be right, but scientifically
-speaking, they are somewhat deluded. Just because 120 radials happens to be the standard in
broadcasting doesn’t mean it is appropriate.
If you use too few on-earth radials (e.g. just 4), their lengths become critical - in other words they
are resonating, which leads to the counterintuitive finding that reducing their lengths to hit
resonance may actually improve their efficiency!
Experiments simulating installations where there is no room for ¼λ radials right around the base of
a vertical indicate that symmetry is fairly important. Efficiency is slightly reduced if one quarter of
the circle is empty, and losses mount to as much as 3 dB (half your power!) if you can only lay
radials in a semicircle. However, substituting the missing radials with more, shorter ones in the
directions that you can lay radials offsets the effect a bit.
Another fascinating insight from Rudy’s experiments is that numerous factors affect the
effectiveness of the radials, including for example the soil conductivity which varies with geology,
moisture levels and band. Unless you can measure and control these factors, theoretical
calculations from antenna modelling may not hold true in real installations, hence the value of
careful experimental studies like Rudy’s.
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