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Vertical Antenna Performance Considered

vertical antenna performance

I have never been a fan of vertical antenna performance. My experience with them has always underwhelmed. Let’s consider why.

Most verticals are quarter-wave monopoles fed against ground. Your vertical pipe is half the antenna and the ground itself other other half. In 1975 I bought a Hustler 5BTV trap vertical for 80-10 meters, shown left above. At first, I mounted it on my apartment roof, then in the backyard when I bought a house. I could always get a good SWR but not much signals, especially on the lower bands.

Now, I will be the first to admit that I never did a good job with ground radials. Lacked the interest, knowledge, space and tools to do it right. My research indicates two problems. First, short verticals have very low radiation resistance. Second, most cheap and cheerful ground systems contain very high loss. Traps add loss resistance, as well.

Since an antenna’s efficiency is a function of radiation resistance divided by total resistance, you might end up with RRAD of 5Ω and total resistance of 30Ω which gives you a 17% efficiency. If you compare this to a trap dipole, you can see a huge difference. Dipoles might have a RRAD of 70Ω and a RLOSS of 5Ω, so you end up with 93% efficiency.

Now you know why most vertical antenna performance is poor, especially short ones with poor grounds. At best, for a full size monopole, your radiation resistance will be around 30Ω. Even a good ground system on a city lot will have RLOSS of around 15-20Ω. So, at best you get 60% efficiency.

My second vertical antenna in the 1990’s was the Cushcraft R7, shown above right. This was an end-fed vertical dipole with lots of resonators covering 40-10 meters. It worked a lot better than the 5BTV, but still a far cry from a high dipole or beam antenna.

Short Vertical Antenna Performance

So as I build my very short flying saucer resonator vertical, I have very modest expectations. I know I can achieve resonance, where reactance jX drops to zero and a feedline match becomes purely resistive. I know that my high ground loss resistance will get me in range of a low SWR against a 50Ω cable.

But will the resonators increase RRAD enough to give me some decent efficiency? Only time will tell.

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