Application Note #4
Subject: Can I use a Balanced Antenna?
"I am about finished building the Norcal 38 Special transceiver kit and I want to use your Rainbow Tuner kit in conjunction with it. I will some RG-174 coaxial cable from the PCB to a coaxial connector and then I will connect the coaxial connector to the Rainbow Tuner. From the Rainbow Tuner I will run to a Hi-Q Antenna Center Insulator. From the Center Insulator I will run a balanced antenna on either side of the Center Insulator.
"I was told to use about 48 feet total of #12 stranded copper speaker wire. I will use about 2-3" of RG174 coax from the PCB to the 38 Special. I know that the SWR is critical when using QRP rigs so I am trying to configure it as accurately as possible. So each side of the balanced dipole should be about 24 feet each side. I can watch the SWR meter on the Rainbow Tuner to trim accordingly for best reading. Do you have to calibrate the tuner by some means for accuracy or is it all right as built? Will the tuner will work as outlined here with a balanced dipole antenna?"
Joe N2CX responds ...
Sorry to have to tell you this, but the Rainbow Tuner is intended to work with an end-fed half-wave single wire type antenna, not with a balanced antenna. Tuners for balanced type antennas, unfortunately, are more complicated than the simple one in the Rainbow. However the Rainbow does include an SWR bridge that will work very well with any HF antenna fed with coaxial cable.
Coming soon will be another App Note describing how to make a 30 meter dipole antenna and feed it with coaxial cable and how to hook up the bridge in the Rainbow Tuner to measure the SWR!
Joe E., N2CX
from Southern New Jersey, y'all