Bandplans and Edges

Foundations of Amateur Radio

Today I'm going to talk about operating procedures. Before groan and tune out, stay with me for a moment, this is important for all amateurs, even you.

We as amateurs have a range of bands allocated to us. These bands cover a whole chunk of spectrum that we in many cases share with other users. They might either share the same band with us, or the other way around, we with them. Our bands might be right next to theirs or overlap in some part.

To make things more interesting, these bands are unfortunately not uniform across the world. For example, in Australia part of IARU Region 3, the 40m band runs from 7.0 to 7.3 MHz. In Region 2, it's the same, but in Region 1, it only covers 7.0 to 7.2 MHz.

If you look at the 80m band it's worse: Region 1 uses 3.5 to 3.8 MHz, Region 2 uses 3.5 to 4 MHz, Region 3 uses 3.5 to 3.9 MHz, but in Australia we can only use 3.5 to 3.7 and 3.776 to 3.8 MHz and that last little bit, the DX window, only if you hold an Advanced License.

This can have profound implications for your operation on air. If you hear a station, clearly an amateur, callsign, working a pile-up and doing everything right, you may not actually be allowed to work them, even if you're privileged on the band you're listening on.

Things get tricky near the edges of the bands. If you're operating near an edge, you are not allowed to have your signal stray across the band edge, so if you're using an SSB signal, the frequency shown on your radio is not where the edge of your transmission is, the radio is showing where the carrier is, the side-band signal depending on the type, can be another 2.5 to 6 KHz up or down.

So, that's simple right. If you're using a band that uses Lower Side Band, say 80m, you can slide on up to the upper band-edge and start operating right?

Uhm. No. Couple of things. The other side of the side-band doesn't vanish, it's reduced. Depending on the quality of the radio, the reduction is better or worse. Using an amplifier makes this problem bigger. Some radios have good filters on both transmit and receive which changes the picture again. I've not even talked about spurious emissions, harmonics and other artefacts which muddle this picture even further.

The take-away for this is to make sure you know where the band edges are for your station and to make sure that you know what the performance of your actual radio is and where it transmits.

I'm Onno VK6FLAB