Instructions: AMB-BKT-1
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c)
The NMO radial base has the same features as the other NMO base (see 3-b) plus it has four removable stainless
steel groundplane radials that are installed with the provided Allen wrench. Note that the hole to mount the NMO
radial base is drilled offset from the center, so you can access the Allen screws without having to remove the base
–simply loosen the base to rotate the base to install or remove each radial.
d)
The “VersaBase”attaches to the BKT with the 3/8 inch stainless steel hardware and wing nut, for quick
installation and removal. It will fit the Buddipole
TM
Versabase for their dipole HF antennas (
Versatee not
included)
. It is designed for fixed base but
NOT for mobile use while driving.
4)
Connecting a Ground Counterpoise.
a)
For HF, you can use a simple wire counterpoise connected to the provided heavy-duty solder lug on the ¼ inch
bolt with wing nut (use 14 gauge or smaller, even small gauge flat cable works). Use at least four or more wires
that can be cut to the band or simply use at least four 10 foot long radials which can work on 20m and above. Use
longer radials for the lower bands. Our optional AMB-BKT-1/8 counterpoise rings can fit up to four or eight
3/8x24 stud telescoping whips to form a horizontal counterpoise; whips are available (and will work) up to 12 feet
long. The counterpoise, whichever you use, will work best if elevated ABOVE GROUND and not laid on the
ground unless you can install MANY radials. A counterpoise even 5 or more feet above the ground works fine, but
the higher the better. The counterpoise should be somewhat horizontal but can slope away from the antenna. A
counterpoise that is mostly vertical may not work well.
b)
For V/UHF (6m and above), the counterpoise (groundplane radials) are connected to the ground point bolt near the
antenna base and works best if slightly shorter than a 1/4 wavelength. For single band antennas, the length should
be "cut" for the band; for multi band antennas cut the radials for the lowest band. These can be made from stiff
wire or whip antennas or other radials sticking out from the base of the antenna. Four are recommended, and can
be approximately horizontal or sloping away from the antenna up to a 45 degree angle. Our "NMO radial base”
does NOT require any additional radials for 2m-70cm and can be used as-is or cut for your specific band, from
135-512 MHz.
5)
Antenna and coax suggestions.
Coax connection. Generally, RG-58 size coax works fine for portable or fixed-base installations where the length
of the coax is typically less than 25 feet, especially if you run under 500 watts. You can use any coax you desire.
SWR adjusting device (if needed) for HF antennas, especially those mounted near the ground, to reduce the SWR
to an acceptable level at the antenna resonance point on 160m and 80m, and maybe also on 40m. You may need a
shunt load inductor, UNUN, or additional capacitance to reduce the SWR. Some of these devices need to be
installed at the antenna and if so should be weather resistant (like our
SHUNT-100
).
Ferrite bead filters to reduce HF antenna tuning problems and to help prevent RFI in devices connected to your
radio. For the HF bands, use Mix 31 or other types that are designed to filter the entire HF band. Do NOT use
unknown ferrites as they may not work at HF frequencies! You may want to install at least 3 ferrites, closely
spaced, over your coax / antenna motor cable as close to your antenna as possible. One of these should have the
coax wound 2-3 times around one of the ferrites (improves filtering at the lower frequencies). Also install ferrites
in a similar fashion on your motor/turns counter cable, and install one ferrite on the coax near your transceiver.
Some installations may require 10 or more ferrites on EACH cable, at the antenna end of the cables. A white paper
on this topic can be downloaded for free from our web page:
http://www.repdesign.us/Download.html
Tuning an HF screwdriver / motorized antenna. You can tune your antenna using a DPDT, center off, manual
switch or one of the automatic tuning devices that powers your antenna motor and stops at the resonance point. Do
not confuse these with "antenna tuners", which add capacitance / inductance to match the antenna to the radio -
generally speaking these should NOT be used with "resonant" antennas except to fine tune an SWR that is slightly
too high and can not be reduced by improved grounding, improving the ground counterpoise, installing ferrite
beads or using a load inductor or other device.
Using untuned "whip" antennas. You can use a "CB" whip or longer whip/mast (NOT grounded) which would
only be resonant on one band. To operate other bands you will need some type of antenna tuner.
