Group,
Now that the Rainbow kits are out in the world, I've been getting
frequent messages of the form "How can I use my Rainbow Tuner with my
G5RV/Hamstick/Windom, etc." This e-mail is a reply to those who have
asked the question and to those who may wonder about the subject.
Unfortunately, the answer to the question is "You probably can't".
You see the Rainbow Tuner is a special purpose tuner designed to be used
only with a half-wave end fed wire antenna. General purpose tuners that
can be used to match almost any antenna have to be much more complicated
(and expensive) than the simple one in the Rainbow.
The intended application is described in the QRPp and QRP Quarterly
articles presenting the Rainbow and in the descriptive material on the
njqrp web page http://www.njqrp.org
Unfortunately, in their excitement to build a cute little kit, some folks
have misunsderstood that information.
The half wave antenna that the Rainbow is intended for is a very
simple wire approximately one-half wave long that is simple and easy to
use for portable hamming. An article in the upcoming issue of 72, the
NEQRP newsletter, will have more info on EFHWA's (End-Fed Half-Wave
Antennas). At a recent NJQRP meeting, we cut a 46 foot piece of hookup
wire to length, strung it up to a convenient tree as a "sloper" and made
a QRP contact between NJ and Chicago all within 15 minutes using the
Rainbow Tuner.
The Rainbow's tuner circuitry is set up to transform the half-wave's
high impedance down to 50 ohms and has a limited tuning range since the
antenna is nearly resonant. It simply doesn't have the capability to
cope with unpredictable impedances.
The Rainbow manual *does* include a section describing in general
terms how you might go about reconfiguring the tuner for other antennas,
but that is a matter for the experimenter.
On the other hand, the SWR bridge part of the Rainbow *is* useful
with any HF antenna or tuner fed with 50 ohm coaxial cable. It operates
automatically and is self-calibrating to give accurate SWR readings with
HF QRP rigs in the range of about 200 mW to 5 W. And it is small
enough to be built right into the case of even rather small QRP rigs.
If you have any questions about the Rainbow's capability or uses,
contact me at
72/73,
Joe E., N2CX
from Southern New Jersey, y'all
work: jeverhart@cayman.vf.mmc.com
home: n2cx@voicenet.com
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