Foundations of Amateur Radio #188:
January 11, 2019
Add a comment about this article!
Fan Vertical Antenna
One of the single most recurring topics
within our community is that of antennas.
Everywhere you look is a story or a photo or
a website or a contact about an antenna that
came into being because somebody had an idea.
Now if you've been in the ideas field for a
while you'll have learnt that having the idea
is often just the start of the process. After
that there's planning, sourcing, building and
testing. If you're lucky you'll end up with
something and a story to tell. If you manage
to persist you might even end up with a
The other day I managed to have an idea that
I'd not seen anywhere else. As it turns out
and perhaps not unsurprisingly, I'm not the
first to have this idea. Despite that, what
struck me is that I'd not seen or heard of
this combination of antennas before.
As you might recall, one of my earlier forays
into antennas consisted of purchasing a set
of mono-band antennas. I intended to use
these on my car while operating mobile, but
despite countless unsuccessful attempts at
making them work, the project ended up being
abandoned and written up as a learning
That said, each of these antennas works just
fine on a roof, just not on the roof of my
Recently I'd been reading about how much
separation is needed between antennas that
are resonant on different HF bands and my
research unearthed the idea that while they
might affect each other to some degree the
overall effect appears to be not that large.
Combing that with an antenna called a fan
dipole, I wondered if I could do the same
with some vertical antennas. As it turns out,
yes you can. It's sometimes referred to as a
Before I get too carried away. A fan dipole
is an antenna that consists of a set of
dipoles that are all fed from the same feed
point. Imagine three or four dipoles, each
for a different band, with each centre
connected to the same balun. Each of the legs
are spaced apart so they're not touching.
After a bit of tuning you'll end up with a
combination antenna that works on each band.
The beauty of this is that it takes up the
same amount of space as the largest dipole
and you'll only need one feed line, rather
than several. You'll also only need two sky
hooks, so you won't have to plant a forest
before setting up your antenna farm.
For all those reasons I wondered if I could
make a single feed point for all my vertical
antennas and get the same benefits. At one
point I got so excited that I started
modelling this in cocoaNEC, an antenna
modelling tool based on NEC2, but my learning
curve exceeded my skill set, so I had to
postpone that in order to actually do some
income generation instead.
Discussion with fellow amateurs encouraged my
tomfoolery, unearthed prior work and assured
me that it would work and since then I've
started down the procurement phase and have
now got some SO239 connectors, a piece of
metal and ideas to space holes evenly with a
central socket to connect my coax to. I plan
to solder all the connector centres together
with some thick copper wire and use the metal
plate to connect all the shields together.
The only fly in the ointment at this point is
my unhealthy relationship with drills. You
might remember that I managed to drill a hole
in my hand a while back - all healed, I was
incredibly lucky, a delightful scar to remind
me - so if at all possible I'd like to avoid
such a thing. Last time all I wanted was to
make a single hole bigger, this time I've got
four 16mm holes to drill.
You'll be pleased to learn, just as my
partner was, that I'm now able to use a drill
press and I even splurged and added a vice,
so if I'm not too clumsy, I should be able to
avoid stitches this time around.
What I'm hoping to achieve is a little group
of vertical antennas, connected to the same
coax, mounted on the metal roof of the house,
all but invisible to our neighbours without
needing to swap antennas in and out like I
currently do and actually use those lovely
mono-band antennas I purchased so long ago. I
may have to experiment with radials and
tuning and no doubt there's still a gap
between theory and reality, but I'll let you
know how I go.
My question to you is, what antenna project
are you working on?
I'm Onno VK6FLAB
To listen to the podcast, visit the website:
http://podcasts.vk6flab.com/. You can also
use your podcast tool of choice and search
for my callsign, VK6FLAB. Full instructions
on how to listen are here:
All podcast transcripts are collated and
edited in an annual volume which you can find
by searching for my callsign on your local
Amazon store, or visit my author page:
http://amazon.com/author/owh. Volume 7 is out
Feel free to get in touch directly via email:
email@example.com, follow on twitter: @vk6flab
(http://twitter.com/vk6flab/) or check the
website for more: http://vk6flab.com/
If you'd like to join a weekly net for new
and returning amateurs, check out the details
at http://ftroop.vk6flab.com/, the net runs
every week on Saturday, from 00:00 to 01:00
UTC on Echolink, IRLP, AllStar Link and 2m FM
via various repeaters.
There are no comments on this article: