Inverted V Dipole

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Matthew Balmer:
Hi,

I have cut a 20m inverted v dipole and got VSWR 1.2:1 on 20m.

Each end of the dipole is pegged to the ground with a 3m fibreglass pole as a support in the middle.  I understand that this is not a good setup, as the ends of the dipole are too close to the ground.

What is a minimum height off the ground for each of the ends of the inverted v?

Another question, I am considering making a tuner to tune the dipole on 40m aswell.  Should this be possible and enable me to radiate a good signal?  It is not intended to work DX, just for general QSO's when backpacking.


TIA,

Matthew M5EVT

WV2B:
Hi,  To work well on HF bands you should endeavor to get an antenna as high and in the clear as possible, preferably 1/2 wavelength high at least.  The dipole you mention probably won't work too well.  For backpacking a small vertical might work better, especially if near the salt water. A small mobile antenna might work, or you could use two mobile antennas and make a vertical dipole with a tri-pod.  You would also probably do better with a longer random wire strung up into a tree using the tuner, rather than trying to tune the 20 dipole on 40.  73 Duane

Frank Drake:
I used an Inverted Vee for the first few years I was licensed and had very good luck with it. I placed a 55 foot phone pole in the ground next to my garage and a pulley at the top so I could raise and lower the antenna without climbing it. The top was about 50 feet and I spread the wires ( made from telephone "drop wire" ) so they were at 45 degree angles from vertical at the top. The wires were about 66 1/2 feet long and the ends were about 8 feet off the ground. The center was a Hy-Q molded dipole support made of Resin/epoxy. I used good old egg insulators for the ends. The coax was RG-58U cut to about 66 feet as well. Look in the ARRL handbook ( mine is  1997 and is on page 20.10 ) for the antenna info. I never used a balun or a tuner and I worked all the non-WARC bands very well. I think I did well mostly due to just dumb luck, but it was fun! I was running a Heathkit DX-60 and that may have been more of a help than I realized then too. I believe the use of a wood support for the center helped as well. I might have done better had I used a tuner thoough. Today I would have a tuner! If you can't locate a phone pole, you may try to use 2X4 pieces of lumber sandwiched together to get the heighth you need. The older ARRL handbooks had plans for those but I am not sure about the newer handbooks. I had the ends of the Vee pointed North/South and I lived outside Los Angeles so I heard everything in the U.S. I even heard the earthquake as it struck Anchorage since I was listening to a ham in Anchorage at the time.  So if you have the real estate and the wherewithall to put up a Vee, go to it.  You'll work lots of stations.
73,
Frank
KL7IPV

Chris Petersen:
I am afraid that your dipole will not work very well. I modeled it using EZNEC (www.eznec.com) and found the following:

Average gain -6.34 dB
Gain at 20 degrees elevation: -6.6 dBi
Maximum radiation is at 90 degree elevation with a gain of 0.61 dBi
The radiation pattern is omnidirectional.

If you raise the height of the antenna by 3 meters (6 m at the center, 3 m at the ends), the figures change to:

Average gain -1.8 dB
Gain at 20 degrees elevation: 0.34 dBi (Almost 7 dB improvement!)
Maximum radiation at 65 degrees (4.98 dBi)
The radiation pattern is still mostly omnidirectional.

If you can raise the ends to the same height (all 6 meters above the ground), the numbers become:

Average gain: -0.64 dB
Gain at 20 degrees: 2.23 dBi
Maximum radiation at 55 degrees (6.31 dBi)
The front to side ratio is 2.7 dB

The antenna would perform poorly on 40 meters.

If you can, I suggest you download the modeling software and try it on your antenna. The free demonstration version will be good enough for your inverted V dipole.

I hope this helps,
73's Chris, K9EQ

Dale Hunt:
The first step is to attach a 20' (6m) length of string to  each end of
the dipole wires and tie that off to the ground, a bush, or any other
convenient support.  This will get the ends higher in the air.

Raising the center of the dipole will help a lot, though it is difficult
to tall supports when backpacking.  I rely on trees or other natural
supports.  You can tie a rock on the end of a rope and toss it over
a branch (or over the whole tree in some cases) and hoist the
antenna.  There are two approaches:  the common  one is to tie this
rope to the feedpoint and use inverted-vee's.  The other is to tie
one end of your dipole to this rope and tie the other end off to any
other support to make a sloping dipole.  Either works.

My standard backpacking antenna kit has 25' (8m) of feedline and
a set of dipole wires for all bands.  To set it up, I choose the bands
I want to operate and connect those wires to the feedpoint. I throw
a rope over a convenient support (a sock filled with sand will work
when there are no rocks of the right size) and tie it to one of the
wires (often the 40m dipole wire.)  I then hoist the antenna feedpoint
by this wire, and tie the rest of the wires off to bushes/trees/clumps
of grass with strings to make inverted vees.  I can put up a 5-band
antenna fairly quickly with this approach (and have done so in the
dark, while holding a fish in one hand... but that is another story.)

For backpacking, there usually is plenty of room for installing
antennas.  Instead of building a tuner to use your 20m antenna on
40, I would recommend using separate wires on a common coax.
The extra wire (#22 stranded, or thereabouts) will weigh less than
the tuner.  If you just want a single antenna, build it for 40m and
feed it with 300 ohm twinlead, and tune it for 20m.  At low heights,
you probably will have much better results on 40m during this part
of the sunspot cycle, because the high angle radiation will be
reflected back to earth.  (20m is above the 'critical frequency', so
high-angle radiation will just escape off into space.)

There are a lot of other possible antenna configurations, but having
the parts for a set of dipoles will allow you to improvise in the field
when circumstances permit.  (Half of a 40m dipole can be bent into
a circle to make a full-wave loop on 10m, for example.)

I pre-tune my dipoles before I go.  (You can do this in a local park
if you don't have the trees and space at home.)  In my experience,
if I tune the antenna for a center height of 12' (4m) with the ends
at 5' (1.5m)  for a 40m antenna, then just about any "normal" field
installation will provide an adequate match to my rig, so I don't
need to carry a tuner.

Have fun! - Dale WB6BYU

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