Elecraft KX3 Owner's Manual - Manual (Page 6)

6
Antennas
You can use any resonant antenna having a 50-ohm
(approximate) load impedance with the KX3.
Examples can be found in the ARRL Antenna
Handbook and other sources. A simple inverted “V”
or dipole can be very effective.
Antenna jacks: The BNC antenna jack, identified
at right, is used on 160-6 m. The SMA jack shown
is supplied with the KX3-2M/4M module (pg. 25).
The basic KX3 has a hole plug at this location.
Field Antennas: Field operation often calls for
non-resonant, ad-hoc wire antennas. For example,
you might use a single wire of 25’ (7 m) or longer,
tossed in a tree using a fishing weight or large hex
nuts. Another popular field antenna is the short,
loaded whip with interchangeable loading coils.
If you use a short whip, vertical, or a single
wire, a counterpoise of some kind is necessary
(described at right) to carry the return current. No
counterpoise is needed for a dipole, since one half
of the diplole carries return current.
SWR: One measure of how close an antenna is to
resonance is its SWR (standing wave ratio). The
KX3 displays SWR in TUNE mode (pg. 14). An
SWR of 1.0:1 (
1.0-1 on the KX3’s display) is
considered a “perfect” match. To ensure safe
operation, the KX3 reduces power if SWR is high.
Using An Antenna Tuner (ATU): An ATU will
allow the KX3 to “see” a good match (i.e., a low
SWR) even with non-resonant antennas. This
allows the transmitter to deliver full power, and can
improve receiver sensitivity. An ATU may also
allow one antenna to be used on multiple bands.
You can use an external ATU (e.g., an Elecraft T1
or KXAT100) or internal (e.g., the KXAT3 option,
pg. 25). The KXAT3 stores matching information at
multiple points within each band.
Feedline: You can connect a wire antenna directly
to the KX3 without any coax or other feedline. (A
male BNC to binding-post adapter can be used,
such as Elecraft #BNC-BP.) However, many
antennas will function better when their feed point
is well above ground. A multi-band, random-length
antenna can be fed with twin-lead, then connected
to a balun (balanced-to-unbalanced converter, such
as the Elecraft BL1 or BL2), which in turn is
connected directly to the transceiver.
Grounding and ESD Protection
Connecting the chassis to a driven ground rod can
provide some protection against lightning and
damage due to electrostatic discharge (ESD). When
used in a building, the rod should also be bonded to
other building grounds. Connect the ground (or a
counterpoise for a whip or single-wire antenna) to
the KX3 at the thumb screw indicated below, on the
right side panel. The back thumb screw on the left
side can also be used.
Portable Station Ground: When you’re operating
from a temporary location, you can use one or more
radials as a counterpoise. This can simply be a set
of wires tied together at one of the KX3’s ground
points, then laid out on the ground in all directions.
When possible, use at least one 1/4- wavelength
radial for each band used. The length in feet can be
calculated from 234 divided by F, where F is the
operating frequency in MHz. If the wires are laying
on the ground, subtract about 20% from their
length. Random-length (untuned) counterpoise
wires can also be used when necessary.
Pedestrian Mobile Ground: The KX3 can be
operated hand-held—even while walking—with a
short whip antenna. Such antennas may provide
acceptable performance in receive mode without a
ground. However, if you plan to transmit, you’ll
need a trailing ground wire to serve as a minimal
counterpoise and greatly improve your transmitted
signal. This is true even if the KX3 indicates a low
SWR in TUNE mode (without a counterpoise, the
SWR reading can be misleading). 13’ is a good
choice for a trailing ground wire. This length is
about optimum on 20 meters, and is usable on 40-6
meters as well, assuming you’re using a multi-band
whip (or an antenna tuner). Small-diameter coax
such as RG-174 works well for a trailing wire
because it resists getting tangled while you walk.
2 m 160-6 m Ground
SMA BNC