Foundations of Amateur Radio

Foundations of Amateur Radio

For an activity that's seeped in the art of communication, amateur radio is a diverse collection of people, joined by a common interest and kept together using imperfect language describing an intrinsically complex science in the hope that we can learn from each other to get on air and make noise.

In this cooperative endeavour, language is important.

Let me start with a limerick by Arthur Frackenpohl:

There was a young fellow of Perth Who was born on the day of his birth He married, they say On his wife's wedding day And died when he quitted the earth

Stay with me.

In this day and age, first and foremost, let me give you a short summary, cobbled together from bits and pieces of a new invention, conceived whilst watching the evening sunset in close proximity to the beach.

What this cornucopia of tautologies has to do with our hobby might not be obvious, but let me illustrate.

Consider the phrase: "a compromise antenna", as-in, "Oh, I'd never use that antenna, it's a compromise antenna."

If you've been in this community for any time at all, you'll have heard that phrase and unless someone pointed it out, you might not have realised that it's essentially unhelpful.

Why?

Because as I've said many times before, all antennas are a compromise, by definition. This is true at several levels.

At a fundamental level, an isotropic antenna is a theoretical antenna that radiates equally in all directions - horizontally and vertically with the same intensity. It's infinitely small and operates on all frequencies with infinite bandwidth. It should be obvious, but this antenna cannot physically exist, so every built antenna represents a collection of trade-offs or compromises and no antenna can radiate more total power than an isotropic antenna.

Beyond that, within the physical constraints of antenna building there are many more compromises. Now this might not be immediately obvious, so let me elaborate.

Consider a 28 MHz, seven element Yagi antenna. With a 12m boom, a 5.3m reflector element, a turning circle of 7.5m and weighing in at 53 kilo. At 20m above the ground it has a gain of 17.5 dBi and handles 1.5 kW. It's physically capable of withstanding 180 km/h winds. It's a lovely piece of kit and if you have the space, it's absolutely something you might want to receive for your birthday and bolt to a mast somewhere near your radio.

If all antennas are a compromise, you might ask yourself, how is this beautiful 10m Yagi a compromise?

For starters, its total radiated power is less than an isotropic antenna. It works between 28 and 29 MHz, but nowhere else. It radiates signals really well in one direction, but not in any other. It requires lots of open space and as a fixed installation, it must be on a heavy duty rotator clamped to a tall mast. To actually acquire and install requires more funds than I've spent on all my radios to date.

Some of what I've mentioned might be acceptable to you, some not. For example, if you're always portable, this antenna makes no sense. You make choices to select an antenna that's best suited to the job and in doing so, you are introducing compromises.

Additionally, there are amateurs who would have you believe that a compromise antenna is one with high loss.

High loss in comparison to what?

If you live in an apartment block, there's no way that you can fit that 10m Yagi inside your bedroom, so you compromise and use a magnetic loop antenna instead. If you're on the top of a mountain, there's no opportunity to erect a structure, so you use a self-supporting vertical. If you're in a car, you cannot erect a horizontal dipole and drive down the highway, so you bolt a whip to your jalopy.

All of the choices you make to fit a purpose, an environment, a budget and available material will combine into an antenna that hopefully gets you on air making noise.

When someone tells you that an antenna is a compromise antenna, what they're really saying is that you made compromises that they're unwilling to make. That's easy to say if you have infinite space, money, experience and opportunity. In other words, they're just blowing hot air.

The whole point of antenna building is to find a particular set of compromises that suits your situation at the time that you're doing it. The intent of this hobby is to learn what the impact of a particular choice is and how it affects the operation of an antenna in a specific situation.

Next time you hear the redundant phrase "that's a compromise antenna", ask what compromises they are describing that they don't accept and decide for yourself if they are compatible with what you're attempting to achieve within the resources available to you.

I'm Onno VK6FLAB