Build a 6 Meter 3.5 dBd gain
Hentenna directional antenna
By Charlie Taylor, K5USS
What do you call a directional antenna that is a full wave loop on 6 meters, is
horizontally polarized but is mounted vertical, has a 50 ohm impedance, and
works great for 6 meter SSB?
You call it the Hentenna.
The Hentenna antenna was designed in Japan back in the 1970s, and many JA
stations are still utilizing them today! The Hentenna gains its name from
the fact that it is strange, or HEN in Japanese. By looking at the
antenna one would think that it would be vertically polarized, but it is in fact
horizontally polarized which is what you want for 6-meter DX openings.
This antenna will give you 3dB gain over a dipole (dBd), is directional, has a
low angle of take off, very little wind resistance, and is easy to build!
This antenna can assist you in getting onto the magic band for just a little out
of pocket expense. I constructed, raised, and tuned this antenna in about
3 hours out of material that I had in the junk box, with the exception of the
steel rods.
I live in an area where antennas that can be seen are not permitted. That
does not mean that one cannot get on the air, you just have to be stealthy about
it. This is an antenna that your neighbors will not see quickly if you
play it right. I raised the antenna out back and then got into my truck to
drive around to the back of the house (zero lot line) to look things over.
Unless you are looking for it you will probably not see it. After cruising
the alley, acting like the neighborhood CC&R spies, I began adjusting the
Standing Wave Ratio (SWR) on the antenna. Getting a 1.3:1 SWR on 50.125MHz
took only 5 minutes, and that includes the time it took to walk from the antenna
to the shack and back a couple of times to get it where I wanted it. I
have good SWR from 50.000MHz all the way up to 51.000MHz (<1.7:1).
The materials I used to build this antenna are:
10 36 copper clad steel rods with a 3/32 diameter (Northern Tools
$4.99 for 14 rods)
8 crimp on connectors without insulation (for 16-14 gauge wire)
4 crimp on connectors without insulation bent 90 degrees
2 alligator clips approximately 1.5 long
1 SO-239 chassis mount connector
2 reinforcing rods or tubes >39 each that are non-conductive
A handful of tie wraps (UV resistant if to be used outside)
Non-conductive string to help support
I chose to make this out of the solid rod to prevent twisting in windy
environments. The rod can be substituted with any electrically conductive
material.
Sides 118 1/8 (3-36 rods and 1-10 rod the connectors will make up
the extra 1/8)
Bottom and top 39 3/8 (either use 2 of equal length or one full length
and the other cut to size)
Below: Hentenna schematic diagram
Ok, lets build it!
Start by taking the rods and soldering them together with the crimp on
connectors in between each section. This provides more strength at your
solder joint and allows you to be able to replace one of the rods if it becomes
damaged at a later date. I found that a small handheld torch was more
efficient for soldering these than a 250-watt gun. Be careful of the open
flame! Solder one complete side at a time. All of the pieces at this time
should be straight. Next take 4 of the crimp on connectors and place them,
one at a time, into a vise and bend them at a 90-degree angle in order to have
the corner pieces. Now it is time to solder the whole outside loop
together. This will be more easily accomplished on a flat surface.
If you try to do this in a vise make certain that all of your corner pieces are
going to match up and everything will be straight. Dont ask how I know
this.
At this time you should have a rectangle that is 118 1/8 tall by 39 3/8
wide. If you are off by a Ό or so it will not hurt anything too
terribly at this frequency, and you will be able to adjust for it in a few
minutes with the SWR adjustment. Next, take a 36 rod and solder an
alligator clip to each end. Make sure the clips are both oriented the same
direction. The end result will be around 39 long and needs to be cut
exactly in half. At each end where you made the cut place a 90 degree bend
in the rod that is Ό long. Bend the rod do not use crimp on connectors
for this. These bends will be used to solder to the SO-239.
Take the SO-239 and place it into a vise, being careful not to damage the
threads. Tin the end of both of the rods, tin the center pin of the SO-239,
and tin one hole at a corner of the SO-239. Solder the rods to the
connector. The rods should be straight out from each other and have an
overall length of around 39 1/8.
Decide what is the top and what is the bottom of your antenna and install your
reinforcing rods. Do this with the tie wraps. From the bottom of the
antenna measure up 24 on each side. This is close to 1/10th of a wave
up from the bottom and will assist you in obtaining 50-ohm impedance.
Place an alligator clip on each of the marks. Now take the weather
resistant string and gently tie it off at the top of your antenna and at the SO-239.
The knot at the top can be tight, but it is recommended that you leave it loose,
or use a slip knot, at the connector since you will need to adjust the height of
the connector.
Now, find a suitable mast and support for your new antenna. I used a 20
foot painters pole and a radio shack roof mount tripod for mine. The
painters pole is made from fiberglass and aluminum and fits nicely into the
tripod. The top mount needs to be insulated from the mast if you will be
using electrically conductive material for it. The bottom of my antenna is 8
feet above ground level, which makes the top almost 18 feet up.
Attach your coax, raise the mast and antenna, make certain it is not going to
fall, and go check your SWR.
Be sure to perform the SWR checks on low power, or use an antenna
analyzer.
If your SWR is high on 50.125 you will need to raise the connector and connector
ends up from the bottom. I moved it 3 at a time and it only took 3
tries to get it pretty much flat. You want to make sure that the connector
setup is parallel with the bottom of the antenna. Re-tie it and check the
SWR again.
Once the SWR is good and you have the antenna in a permanent location you will
want to solder the clips to the sides of the antenna to ensure that nothing
changes. Big birds landing on the connector wire can really mess things up,
again, dont ask how I know this.
Now it is time to hook up to your rig and get on the air! For a test of my
new antenna I tuned into 50.070 MHz to see if I could hear the beacon that the
North Texas Microwave Society has running in EM13. This beacon is 34 miles
from my house putting out ½ a watt.
I was able to copy the beacon perfectly with the Hentenna and could not hear
it at all with the loop in the attic. Not entirely convinced that the
antenna made that big a difference I called Miles, W5RMH, for an on air
performance test of the antenna. He called out to me on 50.135 MHz off of
his vertical antenna and I showed about an S9 on the meter. He then
switched to his 4-element beam and his signal went up to 20/9! Then it was
my turn; I still had my power level at 10 watts and gave a 10 count over the
air. Miles stated that I was about an S9 so I bumped up the power and went
to 20/9. Just to be certain I then switched to the loop in the attic, at
full power, 100 watts, I was less than an S7. This thing does provide
some gain and directivity!
Now all I need is a good E opening!
Good luck with the MAGIC BAND and I hope to hear you calling CQ during the next
opening with your own Hentenna!