Application Note #1

Subject: Rainbow Tuner Insertion Loss?

John KO6TS asks ...

"I noticed that the specs for the rainbow tuner say it has a 6 dB insertion loss. Why would I want to use a tuner which reduces my power by 1/4 on transmit and my received signal strength by 1/4? Perhaps I didn't quite understand something correctly. If so, somebody please straighten me out."

Joe N2CX replies:

Believe it or not there is a very good reason to use a bridge with that insertion loss! While you are tuning up with the bridge in line, the loss means that no matter what SWR the bridge sees, it reflects back at worst a 2:1 SWR to the rig. This is important with many simple QRP rigs (the 40-9er is a good example) because they tend to oscillate and generally do strange things with high SWR, making them difficult to use with a tuner. A second reason is that reducing power delivered to the antenna during tuneup is a good QRP practice minimize QRM to others on the tuneup frequency.

When tunerp is complete, the loss is eliminated by switching the lossy bridge out of the feedline to bypass it!

Entiende usted?

OTOH, you *can* leave it in line if you want to reduce your signal for some reason! :-)


Joe E., N2CX
from Southern New Jersey, y'all

Last Modified April 18, 1997 - George Heron, N2APB (
2APB (