Foundations of Amateur Radio

Amateur radio lives and dies with the ionosphere. It's drilled into you when you get your license, it's talked about endlessly, the sun impacts on it, life is bad when the solar cycle is low and great when it's not. There's sun spots, solar K and A indices, flux, different ionosperic bands and tools online that help you predict what's possible and how likely it is depending on the time of day, the frequency, your location and the curent state of the sun. If that's not enough, the geomagnetic field splits a radio wave in the ionosphere into two separate components, ordinary and extraordinary waves.

All that complexity aside, there's at least one thing we can all agree on. A radio wave can travel from your station, bounce off the ionosphere, come back to earth and do it again. This is known as a hop or a skip. If conditions are right, you can hop all the way around the globe.

I wanted to know how big a hop might be. If you know that it's a certain distance, then you can figure out if you can talk to a particular station or not, because the hop might be on the earth, or it might be in the ionosphere. Simple enough right?

My initial research unearthed the idea that a hop was 4000 km. So, if you were attempting to talk to a station at 2000 km or at 6000 km you couldn't do that with a hop of 4000 km.

If you've been on HF, we both know that's not the case.

If you need proof, which you really should be asking for, you should check out what the propagation looks like for any FT8 station, or any WSPR beacon over time and you'll notice that it's not 4000 km.

Just like the crazy network of interacting parameters associated with propagation, the distance of a hop can vary, not a little, but a lot.

In 1962, in the Journal of Geophysical Research D.B. Muldrew and R.G. Maliphant contributed an article titled: "Long-Distance One-Hop Ionospheric Radio-Wave Propagation". They found that in temperate regions such a hop might be 7500 km and in equatorial regions even 10,000 km.

I'm mentioning this because this was based on observations and measurements.

They used frequency sweeps from 2 to 49 MHz though they called them Mega Cycles, using 100 kHz per second, that is, over the duration of a second, the frequency changed by 100 kHz, so each sweep took nearly 8 minutes using only 15 kilowatts, so substantial gear, not to mention expense and availability.

Oh, computers, yes, they used those too. A three tonne behemoth called an IBM 650, mind you, that's only the base unit, consisting of a card reader, power supply and a console holding a magnetic drum unit.

You know I'm going somewhere with this right?

Today, you can do the same measurements with a $5 computer and a $20 receiver. For a transmitter, any HF capable radio will do the trick, though you might not be transmitting long if you stray outside the amateur bands. For power, 5 Watts is plenty to get the job done.

My point is that there is a debate around the future of our hobby and why modes like FT8 are such a controversial topic in some communities.

I'm here to point out that since that publication in 1962 our hobby has made some progress and we can improve on the work done by people who came before us. We could build a glob-spanning real-time propagation visualisation tool, we already have the data and modes like FT8 keep feeding in more.

If you're inclined, you could even make such a plot in real-time for your own station.

So, how long is a hop?

You'll just have to find out.

I'm Onno VK6FLAB