Getting Three Bands for the Price of One

Rather than carry around a separate coil for each desired band of operation, not to mention the potential costs of a mast plus all of those coils, I happened upon a simple solution to use a single coil for 3 bands. Simply put, I use a 15M 100W coil and interchange longer whips into it to resonate it on 17 and 20 meters. So I only need to carry around a 40M coil, a 15M coil, and a few whips to cover 40M, 20M, 17M and 15M.

In addition to cost savings, there are other benefits. Because the antenna isn't so heavily loaded on the lower frequencies, the Q is less, which means more operating bandwidth. With a 20M coil you might end up having to adjust the whip for the low or high end of the phone band, where with this setup one length is good for the entire phone band. With less loading, the antenna also ends up being more efficient.

The downside of this setup is the additional length of the antenna, which means hitting power lines and low flying airplanes, or at least the lights in the drive-thru. Short of hitting anything, the only consideration I made was to make sure the mast is well supported with a rigid guying scheme to accomodate for the small additional wind loading.

The following is a table of the whip lengths used to resonate the coils for the different bands. Your mileage may vary depending on antenna installation differences, but should get you in the ballpark.

Back to the Mobile Main Page

Back to the K5LXP Home Page

© 2001 Pane Relief Computer Services

---