Let's compare the same antenna in different locations...

Foundations of Amateur Radio

Let's compare the same antenna in different locations...

Over the years I've spent many hours building and testing antennas. I've talked about this and discussed how there is essentially an infinite variety of antennas that can exist. To give you a sense of this, picture a basic dipole antenna, two bits of wire, same length, connected to a feed-point. We're doing this experiment in space, so we're not concerned with trees or rope, or the ground for that matter, more on those shortly.

We can make this dipole straight, or we can make it into a V-shape, or bend over the edges, or make each side into a half-circle and join them, or make them into a spiral, or kink the wires, or bend them over, or any number of variations. Every time you change something, the antenna radiation pattern changes and the antenna behaves differently. While at its heart the antenna might still be considered a dipole, essentially a change in radiation pattern effectively means a different antenna.

In those changes or wire orientation alone we have already defined an infinite number of antennas, but that only scratches the surface. We can build an infinite variety of physical antennas. Consider the design of vertical antennas, loop antennas, log periodic antennas, yagi antennas, slot antennas, and beverage antennas to name a few.

Once you start investigating antennas you'll discover just how many options there are and once you've acquired the antenna of your dreams, the work is only just beginning.

To explain why this is the case, consider the process of finding an antenna to buy or build. You'll find breathless reports of how amazing an antenna is and how it allowed the operator to hear a mosquito land on the back of a container ship in the middle of a tropical cyclone whilst the sunspot activity was at an all time low. Right next to those reports you'll find another amateur describing how their dummy load performed better and cost less.

If not those specific examples, you'll have no doubt found both positive and negative reviews for the very same antenna, often side-by-side and if you don't, you're not looking hard enough.

Leaving aside the notion that someone is trying to discredit a commercial competitor or that the antennas are inadvertently physically different, because someone put it together incorrectly, there's plenty of opportunity for other reasons for this wide range of opinion.

Let's take the popular G5RV antenna, invented in 1946 by Louis G5RV, who became a silent key on June 28, 2000. The antenna is a multi-band HF antenna and there are plenty of people offering plans and kits for this antenna. Ignoring the differences in plans, let's imagine that two amateurs purchased the exact same G5RV from the same batch from the same supplier. Both erect their antennas at their home shack, or QTH and get on air to make noise. At a local BBQ they get together and compare notes only to discover that the two antennas are behaving completely differently.

How is this possible? What other factors might cause this experience?

You're not going to like my answer, but "it depends". The height at which the antenna is erected, how tight you pull it between two trees, how you feed it, the type of coax you use, how much power your transmitter uses, how close it is to another object like a fence or a house, what type of ground is below the antenna, what the local noise floor is like, which direction it's oriented, which day you use it and finally, what colour clothes you're wearing at the time.

That last one isn't strictly true, but it serves to highlight that some differences exist that are so innocuous as to be laughable, for example, have you considered the type of tree and how much foliage there is, when the lawn below the antenna was last watered, etc. My point is that some differences aren't obvious, but they can, and do, make an antenna behave differently.

In other words, the environment around two identical antennas is hardly ever the same and thus the antenna system as a whole, since the environment and the antenna together combine into a system, are never the same.

This means that when you go about finding an antenna that's suitable for you, the reviews you read are only part of the story. If the antenna needs ground radials that are physically not possible at your site, then that antenna is unlikely to be suitable for your situation, regardless of the glowing reviews.

As I said, in my time I've built and bought plenty of antennas. I've also tried several by way of my local amateur radio club. I've operated a mobile station from my car, set-up a portable station in numerous locations using the exact same antenna, and learnt that while the environment is almost never discussed, it has by far the biggest influence on the performance of your antenna.

My recommendation is to pick an antenna, any antenna, cheap is good, and start. Play with it, change how you erect it, set it up in different locations and I'd highly recommend that you do this with a friend. Between the two of you the shared installation can be used as a baseline to compare your own antenna against and if you're both comparing notes against what you built together, you'll both have a better chance of understanding what particular difference matters in your own setup.

I'm Onno VK6FLAB