Elecraft KAT2 - Manual (Page 20)

20
Antenna Considerations
An antenna tuner will not improve your antenna–it can only tune out the antenna's reactance. In general,
use the longest, highest antenna you can put up, and keep the antenna away from power lines and buildings.
The KAT2 will work with a wide variety of antennas, some of which are covered below.
A good ground system will provide efficient radiation, better antenna loading characteristics, less RF on the
chassis, and safer operation. Use a minimum of two radials cut for each band, or at least one or two very
long radials. House plumbing and electrical wiring will provide an adequate ground in some cases, but
tuned radials are always preferred
Do I Need a 1:1 SWR?
No. This is a common misconception. For example, if the SWR is 2:1, the loss in transmitted signal
strength will be around 0.5 dB. Of course the KAT2 always tries to hit 1:1, and with most antennas it will
find an SWR below 1.5:1 on most bands. But even if the SWR ends up at 3:1, the difference in on-air
signals will often be undetectable. If the SWR is higher than 3:1 you may want to try ALT mode (see
Hard-to-match Antennas).
Resonant and Multi-Band Antennas
The KAT2 will tune up nearly any antenna cut for 40 or 80 meters on all bands. With multi-band antennas
such as beams or verticals, the KAT2 will typically improve the match on each band used. It will also allow
operation on additional bands. However, when you tune-up a beam on one of these "no extra charge"
bands, it is likely to become a no-gain or low-gain antenna with an unpredictable radiation pattern.
One useful trick with coax-fed antennas is to short the center conductor and braid together and treat the
coax as if it were a random wire. This will often allow beams and quads to be used down to 160 meters.
Random-Length Antennas
Nearly any piece of wire over about 30 feet long and end-fed can be tuned up on 80-10 meters, and
probably 160 meters as well. Results will vary depending on the actual length of the antenna and whether
you have a useful ground system. Watch for RF problems, which are more likely with end-fed antennas,
especially if they’re exactly a half-wavelength long or any multiple thereof on a given band.
The KAT2 also works well with loops. An untuned loop of wire 30 feet long (or longer), formed into any
shape, can be matched on most of the higher bands. Loops can be very narrow-banded if they're small in
relation to frequency, so you may need to re-tune after relatively small frequency excursions. Use ALT
mode if necessary (see Hard-to-match Antennas, below).
If possible, put up two wire antennas (especially for Field Day, etc.). You can then do quick comparison
tests as often as necessary using
AN T 1 / 2
. With two orthogonal long-wires, differences of one to three S-
units may be observed on some signals.