It has always aggravated me a bit that I had
an IC-706 Mk II G in my radio room that was perfectly capable of operation on 6 meters and I had no antenna for that band.
I resolved for New Years that I would correct that omission. I looked at a number of designs in the various antenna books
from the ARRL that I had on hand and also scanned the Internet for workable designs. Many were found but few coordinated with
the supply of raw materials I had at hand. Then it occurred to me that with a little scaling up, the design for my dual band
(2m/440) antenna that appeared in the pages of QST (Aug. 2006) might do the job.
I set to work to scale the antenna from its original
size up to a length that would work for at least part of the 6 meter band. After much tapping on the calculator I decided
to use 67" for the upper element and 46 1/2" for the lower element with a 1/2" space between them at the feed point. This
would make the antenna 9'6'' tall overall not counting the mounting method at the base of the antenna.
Since I had some lengths of 1" diameter aluminum
tubing on hand as well as a length of 7/8" diameter as well, the antenna was fairly easy to construct. Slipping a piece of
the 7/8" dia. tubing inside a 24" long piece of the 1" tubing, I adjusted the length to 67" and clamped the tubing in that
position. A 46 1/2" piece of the 1" dia. tubing was cut for the lower element.
Two pieces of fiberglass tubing 7/8" OD with
about 1/2" ID were used to complete the antenna. One section was slipped into the bottom of the upper element and the top
of the lower element and secured with short sheet metal screws so that the elements were about 1/2" apart. A hole was drilled
into the fiberglass tube between the two elements to permit the passage of the RG-8x coax down through the inside of the lower
element. The dressed end of the coax was secured to the elements using hose clamps. The center conductor of the coax was clamped
to the upper element and the shield braid was clamped to the lower element.
The second length of fiberglass tube was inserted
around the coax and inside the lower element both for strength and to keep the coax roughly centered inside the lower element.
By countersinking the hole in the bottom of the lower element I was able to secure the fiberglass tube to the aluminum element
with small flat-headed screws that would not interfere with the next step.
In order to mount this antenna on a metal mast,
the antenna must be placed above the mast completely. This requires another length of non-conductive material to bridge the
gap. I chose a 24" long piece of 1" ID PVC pipe because I had it on hand. The lower element was inserted about 6" into the
PVC and secured with sheet metal screws. A hole was drilled in the PVC just below the end of the antenna for the coax to exit.
The PVC pipe was secured to the top of the mast with two stainless steel hose clamps.
Once erected temporarily in my driveway on a
tripod, testing commenced. I found that while using an HT to feed the antenna, the SWR was excellent from 50.1 MHz to almost
52 MHz. This covers the SSB and FM simplex portions of the band fairly well, so I was happy. Unfortunately, the results were
not so good when I tried feeding the antenna with my 706. The SWR was between 1:2.5 and 1:3. Not Good. After checking with
my friend and mentor, Allan, KJ9N who is a Technical Specialist for Antennas and Feed Lines, we decided to try a common mode
choke mounted just below the bottom of the lower element. 11 turns of RG8X coax were wrapped around a short section of 3"dia.
PVC and secured with wire ties and tape. The coil form was screwed to the 1" PVC "stub mast" and testing resumed. Now the
SWR was between 1:1.1 and 1:1.6 from 50.1 MHz to 51.9 MHz. Now I was happy, and so it appeared was the 706.
As you can see from the pictures, the antenna
presents a very slim profile, a virtue not unimportant when the lady of the house has veto power on new antennas. Not only
that, it is mounted right in the middle of the side garden. It must look pretty good.
I have no doubt that the dimensions could easily
be adjusted to cover the 52 to 54 MHz portion of the band. It is even possible that they could be adjusted to cover more than
a 2 MHz portion of the band. I got what I wanted in coverage with the antenna at its current size, however, so I will leave
the experimentation to others.