operated portable from this location once already, using the
31ft. Jacktite fiberglass pole supporting a 27ft. vertical wire
along with the associated ground radials. I made it as far as San
Francisco with 2w on 20 meters. We don't have much in the way of
mountains in IL, so this was as close as I can get ;)
The view from on top is really pretty spectacular for around here.
This area is about 10 miles from my QTH.
I remove the
top whip section from the Jacktite pole and a 1/2" plumbing
elbow with a few inches of stiff plastic tubing over one end fits over
the top of the pole. There is a rubber band attaching the wire to the
tubing to provide a light tension on the wire. I tried
unsuccessfully lengthening the wire to 30ft. It would not tune on any
of the bands with the ZM-2 tuner, but 27ft. works nice and has
repeatable tuner settings that allow for complete extinguishing of the
SWR LED for 40, 30, 20, 17 meters - no matter where I have put the
antenna up. This has saved me on setup time and battery life. I keep
reading that dipoles have more gain, and verticals are the worst choice
for QRP'ers. However, in my
opinion so far this antenna has provided for many more callbacks to my
CQ than my original 44ft Norcal Doublet, and not just from Mt. Hoy.
The 27ft fiberglass supported vertical wire plot is
below. This is the antenna for when there are no trees, or when I want
to operate at areas where wires are not allowed in trees (Like the
entire county forest preserve system here).
Some more pictures of my first visit to Mt. Hoy below.
This ground plane vertical has also made
an appearance at another local 'summit', The landfill hill at Green
Valley Forest Preserve that is second in height in the county only
to Mt. Hoy (Above). This was a great spot to visit as there is a
washroom and picnic tables at the top, and you can drive up there.
I hear it is often crowded though, and its only open in the afternoons,
and only on the weekends, and only the warmer months of the year.
I'm definately going back there though!
I did not pick the best day as far as
the weather for my first visit to Green Valley Hill. The temp was 49F
but the winds were 25-30mph at the top. The Jacktite pole collapsed
into itself once from the counter force of the guy lines. Check out the
bow in the pole and wire that are both normally straight. Like I told
one of the guys on the air, I felt like I was in Antarctica!
I have begun
experimenting with the end fed half wave antennas (EFHWA) for portable
operating now as well. I have found that the colder
it is outside the simpler
the antenna, the better
. The EFHWA antennas substantially reduce my setup time compared
to the other types. I ran into an EFHWA
design by WB3GCK called the "Dollar Store Special"
and started looking at it in the EZNEC demo. I thought his use of
modular counterpoise wires to change lengths was clever. The 50ft
length of that design did not look too good to me at 20meters in the
modeling software though.
So I made 3 half wave wires for 20, 30, and 40
meters that I use with single 1/4 wave counterpoises and so far the on
air results have been
great. I can now understand why I have read about QRPers
liking the end fed half wave antenna so much. They are comparitively
quick and easy to deploy and take down, and small and lightweight.
The Emtech ZM-2 tunes these half wave antennas with their respective
counterpoises just fine (Although it does not claim to).
However after reading up on tuners, I began to worry about the ZM-2
losses matching 50 to 2000 ohms. I had read that losses become very
significant when trying to match above 500 ohms on most tuners, so I
looked around online for some more ideas and maybe a better way.
I think I found it at AA5TB's website
. I liked that he tested his matching network and had only .
of loss and he explained his methods well for this type of
antenna/matcher setup. So I decided to try it out for myself. My goal
was one tuner box for 20, 30, and 40m.
Looking at the EZNEC demo I modeled the EFHWA's for
the three bands using the exact wire gauge of the antennas I had with
quarter wave counter poises and came up with the impedances 1836, 1960,
and 2032 ohms. I selected a turns ratio of 3:19 that would equate
to 2004 ohms.
I did not have any poly varicons, but did have
several air variable caps in the junk box. I selected one of the RX
type of air variable caps I had that had about the same range as the
poly varicons. I found most guys online used a -2 mix toroid for
the matching transformer and I happened to have a T-130-2 in junk
box as well! I love junk box projects - they are just the best.
I wanted to include a SWR indication LED circuit
though to keep this as a 'minimalist' antenna so I did not have to
bring seperate metering.
I was lucky that I could grab some 1W 200 ohm resistors, and a clear
LED at a local Frys store for the Tayloe SWR Bridge, and a plastic box
at RS. I did not have an FT-37-43 core, but substituted a FT-50-43 core
out of the junk box for the detector circuit using the same turns.
Although AA5TB states the magic counterpoise length is .
wavelenths, I could not duplicate this in EZNEC - which with my limited
abilities in the software is not all that surprising. So I stayed with
the standard quarter wave counterpoise lengths. I elected to use bullet
connectors to form one 40m quarter wavelength counterpoise out of the 3
lengths neccessary for all three bands, and remove sections as needed
for 20 and 30m.
Pretty happy guy when it all worked and the light
went out, but it is not perfect all the time. At the third location I
was using this antenna at I had some trouble matching it.
I have found in portable operating that a tuner is almost a must
because every operating location is different and what works
nicely at one spot may not match up good at another. This is just as
true with dipole deployed heights as I also found it to be with this
antenna set. So I have made an extra two foot length of wire
to be attached at the top of the antennas or at the end of the
counterpoise with bullet connectors should it be neccessary for a good
match. Using this extension wire as needed, or selecting different
combinations of the three counterpoise wires has been successful so far
and I have made the contacts with this setup to prove it and now join
the choir of QRP portable Op's who sing their praises of the end fed
half wave antenna.
UPDATE Fall 2008 ON THE EFHWA TUNER
Well I finally ran into a situation that I could not match wire
combinations on ANY band. This was after the ground froze and was also
covered with several inches of snow. So I decided to rewind the
secondary of the transformer with taps at 17, 18, 19, 20, and 21
turns through a rotary switch to provide some additional matching
range. Right now I am thinking that frozen ground and / or snow cover
really affects the impedance of this kind of antenna.
UPDATE Spring 2009 ON THE EFHWA TUNER:
What do you know? I have been out again to 2 of my favorite same spots and all 3 (20, 30, and 40m) half wave wires are tuning fine once again
with the dedicated tuner shown below. There is definately some
interaction between the frozen ground or snow and the impedance of the
half wave antenna that puts it 'out of the ball park' of my dedicated
EFHWA tuner. The ZM-2 still tunes the wires in any weather - though
with some variances of the recorded settings..
Thanks to AA5TB for sharing some great antenna ideas
(He no longer publishes his email address as he was swamped with
emails). Now I can worry about other things besides tuner loss at
Below are some pictures of my EFHWA tuner during
verification testing of the bridge with a SWR meter in line at the
park. I use a piece of heavy duty 3M velcro on the back of the tuner
and attach it to a plastic tent stake in the ground.
This is the plot for the 66.5ft EFHWA below. The 20 and 30m plots are similiar. This is the antenna
for when there is not 2 large trees located together suggesting a
dipole install, when time is more limited, its very cold, or I anticipate being out after dark.
A portable "Shortened Hatted Vertical Dipole" (SHVD) for 15, 17, 20, 30, and 40m is below.
"An antenna for guys who like antennas"