Monday, August 2, 2010

I am using a G5RV on 80-6 meters. How efficient is this antenna on 6 meters?

Q Dave, WD8DK, asks, “I am using a G5RV on 80-6 meters. How efficient is this antenna on 6 meters? I have been told that it is very inefficient on this band. In fact, I have been told that a 1/2 wavelength dipole is more efficient than the G5RV on 6 meters. Any comments?”

A On 20 meters, where the G5RV was designed to operate, it boasts a little gain over a conventional half-wave dipole. Given a reasonably efficient feed line (450-Ω line) and a good antenna tuner, there’s no reason why the G5RV can’t be at least as “efficient” as, say, a coax-fed dipole in the HF bands. 

However, on 6 meters the G5RV acts as a long-wire antenna,
with an azimuthal pattern with multiple, very narrow lobes. The
narrow lobes are what give it gain, but also what make its performance compared with a regular garden-variety dipole inferior in direc-tions other than the ones it favors. The EZNEC plot shown in Figure 1 assumes that the antenna is mounted as a flat top at 50 feet above average ground. The G5RV has significantly more gain than the simple dipole, but it achieves this mainly in four, narrow-beamwidth directions. For the rest of the azimuths, its pattern has nulls that the dipole covers well. 

Any multiband antenna is a compromise, but most of us can’t have five or more dipoles hanging in our backyards. On 6 meters I would recommend a separate antenna designed for that band. There are a couple of inexpensive 6-meter wire antenna designs on the ARRL TIS Web site at Go there and click on “Antenna Projects,” and then “Other VHF Antennas.” 

Figure 1—This is an EZNEC plot of a G5RV antenna on 6 meters compared to a dipole cut for 6 meters. The solid line represents the G5RV pattern while the dashed line represents the dipole. Notice that the G5RV is creating numerous narrow lobes of radiation.

From QST November 2000