mmckenna
I ♥ Ø
On paper, the 5/8th's wave antenna should slightly outperform the 1/2 wave antenna.
However, it would be in tenths of a Decibel. That's kind of hard to hear on a radio. Level changes like that are usually only apparent on test equipment or if you are really out on the fringes of coverage. And by fringes of coverage, it might be the 1/2 wave gives you a really crappy signal and the 5/8th's wave gives you a really crappy signal that maybe you can recover a few more words out of.
The beauty of the 1/2 wave antenna is that it will work without a ground plane, although it drops from about 2.4dB of gain to zero. In applications where you don't have a conductive ground plane to mount the antenna on, or the ground plane is less than ideal, they are a good option.
Another thing to consider:
Generally when the gain of an antenna goes up, the bandwidth drops. When the gain goes down, the bandwidth increases.
Bandwidth is the amount of spectrum the antenna will cover while remaining under a certain SWR level.
With the 5/8th's wave antenna, you'd get a few MHz on either side of the center frequency where the SWR would stay below 2:1. But you get 3dB of gain close to that center frequency. That's a good tradeoff where you are only using a narrow slice of spectrum.
If you look at a 1/4 wave antenna, the gain is zero, but they give a lot of useful bandwidth. I've tested the 1/4 wave antennas on my trucks and the SWR will stay below 2:1 from 144MHz up to 174MHz. That's a good option if you want to use more of the spectrum.
Lower gain antennas, with their more spherical radiation pattern also have the benefit of sending more RF above and below the horizon. "Benefit" might not be there for someone out on the plains where all the radio systems are sitting on the horizon.
But, if you are in the mountains where radio infrastructure may be well above or below you, the 1/4 wave antennas can outperform the higher gain antennas. Out where I live, with mountains around me, the 1/4 wave antennas rule. Get out in the flatlands, and you start to see more higher gain antennas.
Same thing happens with sailboats. Usually on a sailboat, the VHF antenna is on the very top of the mast. A traditional VHF marine antenna might have 6dB or so of gain, and it gets that by focusing the radiation at the horizon. That's great if you are on a large vessel or one stable enough where the radiation pattern isn't constantly bobbing around. On a sail boat where the vessel might heel over when under sail, a high gain antenna shooting RF out at the horizon, might now be shooting it out into space, or down into the water. Sailboats usually have a lower gain antenna installed to make up for this. Since there isn't a good ground plane at the top of sail boat mast, they very often use 1/2 wave antennas.
