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General Description
The Hy-gain Model HT-18HTJR, High Tower Jr. is an omni-directional multiband vertical antenna. It was
designed using stub decoupling for 10 thru 80meter operation with maximum efficiency. The stubs isolate
various sections of the antenna so that an electrical ¼ wavelength exists on all bands. The High Tower Jr.
will withstand 2 KW of RF power. The maximum overall height is approximately 39 feet.
Theory of Operation
Automatic band switching of 10 thru 80 meters is accomplished in the 18HTJR by the use of stub
decoupling. In principle, a ¼ wave shorted stub is effectively an insulator, which decouples various
sections of the antenna thereby maintaining a ¼ wavelength on all bands. The 18 HTJR is fed at a current
point thus maintaining a 52ohm input impedance over an extremely wide bandwidth.
Construction
The main radiator of the 18HTJR is made up of high strength heavy walled aluminum tubing. Pre-cut
wires form a “cage” about supporting crossarms to complete the antenna.
SWR and Feedline
The 18 HTJR is designed to be fed with 52ohm coaxial cable.
RG-8A/U is recommended because of its low loss and high power handling capability. The SWR at
resonance is less than 1.2:1.
Grounding
The 18 HTJR is designed to use a simple grounding system consisting of one 8 foot ground rod as shown in
Figure 1. Radials should be used for best performance.
Installation
The 18 HTJR mounts on a piece of 1-1/4” plumber’s pipe. (Not supplied). The 1-1/4” plumbers pipe
should be at least 8’ long. Drive the pipe into the ground leaving about 20” above ground level as shown in
Figure 1.
Note: The mechanical warranty is void if the guy wires are not used. The antenna will
withstand approximately 40 MPH of wind without guys.
Before you Begin
Before you unpack the antenna, find a good location to assemble it. You will need something to
support the antenna while it is being assembled. A sawhorse or small ladder should be used to prevent the
antenna from resting on the crossarms or wires. The antenna will be 39 feet long when assembled so
moving it after it is put together might not be easy. Pick a place that you can find nuts and bolts easily
when you drop them because you WILL drop them. A few extra of the smaller hardware are included in
the parts pack so you should have some left over when you are finished.
Step-by-Step Assembly
( ) Unpack the 18HTJR and check all parts against the parts list and the illustrations. This will help you to
become familiar with the antenna and aid in assembling. The wires have been separated into packs to make
construction less confusing. Pictures of the assembly process have been used wherever possible. If you
become confused about the location or assembly of a part, some of the other diagrams later in the assembly
may be of help. Take your time assembling the antenna. You should be able to assemble the antenna by
yourself but a friend will make it much easier. When the antenna is finished you will need a friend anyway
to stand it up and mount it. Although the antenna is fairly lightweight, it is big and difficult for one person
to handle.
WARNING
Do Not install this antenna near power lines or other high voltage sources. You will be killed if
this antenna comes into contact with overhead power lines. The antenna should not be mounted
where if it fell, it would contact a power line.
