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DSEFO144-12 Rev 8/19
10)
Using supplied cable ties, secure the balun to the boom exactly as shown in Figure 6
and route so they do not touch any of the elements; this will ensure minimum SWR.
Install
supplied 1 1/8” plastic caps on ends of boom.
Before moving on to the following step, apply a small amount of the supplied Anti-Seize
Compound to the threads of the U-Bolts to prevent galling:
11)
Attach the boom to mast plate to the boom midway between elements D-5 and D-6.
Use the ¼” U-bolts with flat washers, lock washers and nuts. The antenna will be front heavy
at this point but the weight of the feedline, when attached, will cause it to be balanced. If using
multiple antennas in an array, be certain all mounting plates are at the same location. When
attaching the ante
nna to your mast, use the 5/16” U-Bolts, flat washers, lock washers and
nuts.
Once you have the U-bolts installed and the antenna mounted on your support mast and
tightened, you can route your feedline along the mast and over to the driven element and
connector. Dress the coax against the antenna boom and tighten the connector. Seal the
connector body with several layers of good grade vinyl tape. Then apply a layer of butyl rubber
antenna sealer or RTV over the tape. This will provide a good vapor barrier and ensure years
of trouble free performance. The insulated design will make for a very long-lived antenna that
will stand up well in harsh environments.
If you wish to check your work, now is the time to apply power to the antenna. Any work
around RF energy should be done carefully. We do not recommend standing next to an
antenna with many watts of 144 Mhz energy radiating around it. Using an antenna analyzer,
VNA or low power transmitter and SWR bridge, adjust the shorting bars for minimum SWR.
Always keep the shorting bars th same distance from the ends of the driven element.
Generally, good wattmeters can reliably indicate SWR down to about 1.2:1. A high directivity
bridge or coupler can increase accuracy, but 1.2:1 is more than adequate for any installation.
The aperture of this antenna is large enough so that you must elevate the antenna a
minimum of about 10 feet or 3.0 m above the ground. Point the antenna so that there are no
"reflectors" or obstructions for 100 feet directly in front of the beam. A better method would be
to point the antenna straight up toward the sky. Support the antenna on a wooden or metal
pole or tube and tie, or guy, the antenna boom with very light string or line. Now the driven
element will be at T-arm level and ground effects are removed. Most locations are pretty clear
straight overhead as well!
Install a short length of coax (1/2 wave is ideal... The antenna impedance will repeat
each half wave from the antenna regardless of coax imperfections) between the coax
connector and your bridge or wattmeter. If you utilize your 144 MHz transmitter as an RF
source, apply power - observe the reflected power. Turn off the power and adjust the T-Match
bars equally in small increments - 1/8" or 3 mm. is a good starting point. Apply power again
and observe results. If it got better, keep going. If it degraded, change the direction of yout T-
Match movement program and recheck your SWR. At some point, you will observe a null in
reflected power. When you have found it, mark the point on the driven element and tighten the
screws on the shorting bars.
Over the years, performance can degrade due to oxidation. It is a good idea to spray
your handiwork with a good grade of clear paint sealant. As a general rule, the slower drying
sprays tend to be more enduring. Rustoleum "Clear Seal" or Krylon clear spray are
recommended. A few light coats work better than one big one.
