20m aerial only 18" long

a member of sadarc the club i go to has made this and says it works very well http://www.sadarc.org.uk/mem6ers/forums/viewtopic.php?f=1&t=24

Sorry Andy, we need the login details for the forum.

Is there any chance you could copy the info?

sorry about that,see if this works

Yes, 20 metre band and a vertical that's 18 inches long!

I've
been monitoring (and latterly joining in) a group on Yahoo that are
interested in the concept of the "EH" antenna. This is a development of
GM3HAT's "Cross-Field antenna" by Ted Hart and others and consists of
two metallic cylinders and a few coils, wound on a piece of plastic
water pipe.

There is a fierce argument between those who say it
does work and those who reckon it's just a dummy-load at the end of a
radiating coax! However, the guys who reckon it works have actually
BUILT them and tried them out. I've had encouraging talks with Conny,
SM5DCO (via Skype) who has built a number of these and loves them for
field days and portable situations where putting up a full dipole is a
problem, and it would seem that this is the answer to a flat-dwelling
ham's prayer! An 80m vertical can be built about 3 feet in length and
160 is still a reasonable size!

Yes, I know, you don't believe it - it's against the "laws of nature"

I
was pretty skeptical too, but I keep my mind open, and the guys who
have built them mostly say they work - well. (Some do say they don't,
but that could be because they are tricky to get working properly)

So,
unwilling to invest large amounts of cash in such a hair-brained idea,
I collected together two aluminium beer cans (sadly the beer isn't
required for the antenna,so I had to drink that
), a piece of 2-inch plastic pipe that has been languishing in the
space between the shack and the back garden wall for goodness knows how
long, and some 1.5 sq.mm. stranded "house" wire from the drum that I
bought (eek!) for making my wire antennas.

"EH" antennas are
a lot trickier to tune than a half-wave dipole or a ground plane, but
Brian G0JCQ mentioned to me that Southport Club has an MFT analyser,
and I'd advise club member trying to build one to use it. I won't go
into full construction details here just now, but the beer cans are cut
open to use the sides as a sheet of metal to wrap around the
pipe-former for the 2 cylinders, a "phasing coil" of a couple of turns
of wire are in-between them, another "tuning" coil below them, and a
smaller "source" coil below that. The antenna is adjusted at each stage
of construction using the MFT (and you probably have to go back to the
last step and retune after each operation!) Finally you get something
that looks like 50 ohms and a 1.1 SWR around 14.160 and 14.240 (it
takes patience!). Here it is:


(Anyone
using this picture for future reference - please note that the bottom
coil is totally wrong and I have changed that completely)

Does it work?

I
"finished" my prototype late yesterday afternoon, and connected the
FT857. A quick look around the band found a station in Oregon (at 5/
working Europeans, and another near Seattle at 5/8 also. The noise
floor was S0 to S1. I have a 20m dipole at about 6-8 feet height (put
there at around the same height as the "EH" so as to do a fair
comparison, and signals were roughly comparable between the antennas (a
bit of QSB made it hard to be sure, but I think the
EH may have been slightly stronger). I keyed-up the 857 and was pleased
to see no smoke coming from it or the antenna, and no "SWR" warning,and
gave the Seattle station a call, but he was in the middle of a pile-up
and I didn't manage to raise him,though I think he was getting part of
my call-sign. More testing required here, but it was so dark by then
that I couldn't read the display on the MFT and was tripping over power
and battery leads in the garden and my fingers were numb, so abandoned
the operation for another day.

Cost?
2 cans of beer, less
the beer inside, a piece of scrap plastic drain pipe (grey is not
ideal, white is better, but it is "close") a couple of yards of wire
(transformer wire is supposed to be better, but I didn't have any in
the junk box), lots of masking tape to hold the coils while you spread
them out and compress them to get the inductance right, "Hot-melt" glue
once you finally get the coils right. Oh yes, a bit of coax and a 259
to feed the thing with.

Is the "EH" just a dummy-load on the end
of a radiating coax braid? That was one reason that I was doing all
this in the middle of my lawn on a cold February day - if anyone can
convince me that the 6 feet of coax from the rig the the "EH" can pick
up Seattle as well as a tuned dipole I'll be very surprised!

More to follow

Stu, G3OCR

oh man EH Antennas, had one here and worked sure but was a dog of an antenna and was sold on sharply. They also make them for 11m now also