MFJ-9402 Instruction Manual 2 Meter SSB Transceiver
6
TWO-METER ANTENNA SYSTEMS
While serious VHF DXers sometimes construct huge antenna systems, it's quite easy to
achieve outstanding results with only a modest installation. Here are some tips for
selecting antennas and getting top performance from your new VHF-SSB station:
•Antenna Selection: Before purchasing your antenna, first survey the site where you
plan to install it. For a densely wooded area or location with nearby obstructions,
consider mounting a smaller light-weight antenna as high as possible to get above RF-
absorbing foliage and ground clutter. For open locations, a larger antenna (with more
gain) mounted at a lower height may yield better results. Also, assess your "hardware"
options. If you have a tower with a strong rotor available, a single long-boom antenna
is probably the best choice. However, if you are restricted to a roof-top installation
using TV hardware, a mid-size yagi--or a stacked array using two or more short-boom
yagis--may make more sense. When starting out, even a single 5 to 10-element yagi on
a good TV mast can yield very good results. Remember, VHF antenna systems are
easy to expand and upgrade over time, so there's no need to do everything at once!
•Feedline Routing: For best performance, 2-meter yagis should be mounted as high
and in the clear as possible. However, at 144 MHz, it's also important to factor in
feedline loss. If you must add 50 additional feet of coax to gain only 10 feet in height,
it may not be worth the trouble! Take time to plan out and measure feedline runs
before making a final decision. Also, calculate your anticipated line loss using the data
from coax-loss charts. Feedline attenuation greater than 1-2 dB will begin to make a
discernible difference in your station's weak signal performance.
•Coax Cable: RG8X foam coax may be sufficient for short direct cable runs (no more
than 50 feet). However, for longer runs, it really pays to install high-quality low-loss
cable such as 9913--or a more-flexible equivalent. Be sure to seal exterior connectors
against moisture with silicon compound or rubber tape--water incursion damages low-
loss cables very rapidly. To reduce loss, avoid installing unessential in-line devices
such as coax switches, barrel splices, and power meters. Also, use premium
connectors, install them carefully, and avoid sharp bends or kinks in the feedline.
•Rotor: A light-duty TV rotor handles most small or mid-sized yagis, but long-boom
arrays require the extra torque and breaking action of a "ham" rotor.
•Safety: Never install antennas where they can accidentally fall and contact power
lines or residential entrance cables. For electrical-hazard protection, permanently
ground the mast outside the building using a ground system with multiple rods. Also,
always disconnect the feedline from the radio at the first sign of threatening weather
(even nearby strikes may damage sensitive receiver circuitry). Finally, never install
antennas alone. Make sure someone knows where you are and what you are doing so
they can render assistance in the event of an unexpected problem or accident.
