I also run a GME AE4018K1 Antenaa which is actually a 6db rating, works perfect.
Please note : The packaging of this antenna quotes a gain of 4.5db but this only refers to the whip top (just the black fibreglass section) and doesn't take into account the effective gain (EIRP) overall as a result of the elevated feed section (the chrome section between the whip top and spring) which takes the overall effective gain to 6db. Its this 6db figure that we quote as its been the recognised industry standard gain figure for this design of antenna for over 20 years, in fact all other manufacturers quote 6db or 6.5db for this type of antenna, GME chose to quote just the whip section.
No one in this thread has quoted the reference for the gain figure of their antenna - ie dBd or dBi. Mat quoted his antenna as 6 dB when he should have said 6 dBi. Shonky quoted the same antenna as 4.5 dB when he should have said 4.5 dBd.
dBd means you are comparing your antenna to a dipole, dBi means you are comparing your antenna to an isotropic antenna (I'm still waiting for someone to build one of those.
Isotropic radiator - Wikipedia, the free encyclopedia) The calculated difference between the two antennas is 2.2 dB or in other words a dipole antenna has a 2 dB gain when compared to an isotropic antenna.
When I was actively engaged in the radio industry the term dBi was only used for microwave antennas. The reference for the rest was dBd. Since then the advertising executives have got into the act and introduced the dBi for land mobile antennas. Not many of them use the correct 2.2 dB conversion ratio, some use 2.0 and an increasing number are using 2.5 dB. I have even seen 3 dB used. Antennas never measure to the exact 0.5 dB mark, they are rounded up or down to the nearest one so there is room for fudging there as well.
This brings us back to the original question of whether 3 or 6 dB is the ideal antenna gain. Unless the supplier quotes the reference for the quoted figure you could have one 3 and one 6 dB antenna that are pretty well identical antennas. To me a 4.5 dBd antenna is the ideal way to go. The vertical pattern is not too sharp for hilly country.
The elevated feed piece has me puzzled. Back in the days when the 70 MHz band was the predominant band we did not have much in the way of gain antennas as they were too long. basically we had ground plane, dipole and an antenna called a co-axial dipole or bazooka antenna. The co-axial quarter wave bit at the bottom did nothing more for the quarter wave bit at the top than the ground plane does when the quarter wave element is mounted on top of a car. In other words a co-axial dipole has the same gain as a conventional one.
When we got into using UHF for land mobile we increased the radiator on the top of a car to 5/8 wave and added a 1/2 wave section above that with a phasing coil. this produced a 4.5 dBd antenna. Later on when applications arose that did not produce a good ground plane (fibreglass etc) manufacturers mounted the 4.5 dBd whip on a co-axial 1/4 wave base to replace the ground plane. Suddenly these antennas cease being co-axial antennas and become "elevated feed antennas" and then the bull started working overtime.
Matt, the difference in gain figure difference you are quoting comes from GME still quoting the old industry standards and the fairies in the other organisations inflating their figures by using dBi (and then also a little conversion fudge.) Don't be fooled by those quoting the antenna gains referenced to an isotropic antenna.
PeterD
