5/8th Wave Antennas Why does the 5/8th have gain, and how much gain does it have?
Jef - N5JEF
Tonight someone on the Elmer net was asking about ⅝λ antennas with regard to a ground plane. I tried to explain that a ⅝λ antenna is already a complete antenna, so it doesn't require a ground to make it complete the way a ¼λ wave antenna does. Further, a ⅝λ antenna gets its gain (lower-angle radiation) from ground reflections further out from its base.
Here's a page that I think explains ⅝λ antennas very well and clears up some myths and folklore: https://www.w8ji.com/VHF%20mobile%20vertical.htm
As a related matter, it seems that few people realize that a ¼λ whip with a decent ground plane has 3dB gain over a full-length vertical dipole twice its length.
- Jef N5JEF