What's with the repeater offset again?

Foundations of Amateur Radio

As a new amateur one of the initial perplexing issues you're confronted with is setting up your first radio to talk to the local repeater. The question is so common that it's almost an invisible rite of passage to a new licensee. While I'm a fan of learning, there is plenty of that to go round and setting up your radio to talk to a repeater shouldn't be a hurdle to getting on air and making noise.

Ignoring the whole repeater thing for a moment, let's consider your radio. It doesn't matter if it's a handheld, a base station, a boat anchor or something else. To participate in the whole repeater experience, you need to tune your radio to hear it.

Technically, if I told you that you could tune to a local repeater on 146.750 MHz, that would be enough information to get you going, but this depends entirely on a set of standard assumptions that are likely not obvious to you. Let's explore what's going on.

Given that frequency, you can set your radio to 146.750 MHz and in most cases, you'll be able to hear the repeater. To actually participate, you would need to do some more work to get your transmitter to be heard.

As I said, standards are what makes that possible, but like every human endeavour, caution must be applied. As Andrew Tanenbaum said: "The nice thing about standards is that you have so many to choose from." With that in mind, let's proceed. Before you start yelling, I'll add caveats at the end.

Armed with a repeater frequency, you have enough information to get on air, but it assumes that you know a couple of things. So let's delve into those assumptions.

For starters, there is an assumption that you're aware that to operate a repeater you must transmit on a different frequency than what you're listening on. Why that is the case is a whole other discussion which I'll leave for today.

There is the assumption that you know that the two frequencies, one for listening, one for transmitting, are separated from each other by a known distance, a so-called offset.

You're also assumed to know that this offset is fixed but different for each band.

There's more, but let's start here.

For your radio to transmit on a different frequency than you listen, you must tell it to. In many cases tuning your radio to a so-called repeater frequency will already do this for you, but not always.

You might need to specifically program your radio for repeater operation, or turn on the offset mode, or use two memories, or some other thing specific to your radio. Read The Friendly Manual, I know you know how.

The next step is to look at the band you're on. In this case the 2m band. This means that the standard says that the difference between the receive and transmit frequency is 600 kHz. I'm studiously ignoring other bands at this moment because, standards.

At this point you know that your radio should be tuned to 146.750 MHz, it should be in repeater mode and the offset should be 600 kHz. That's when the next question arises, should that be plus 600 or minus 600?

Guess what, another standard. If the receive frequency is less than 147 MHz, the answer is minus 600 kHz. If it's more than 147 MHz, it's plus 600 kHz.

Notice that I didn't specify what happens if it's exactly 147 MHz? That's because nobody knows. Seriously though, the local repeater owner will know, but you can try either and get your answer.

Now for the caveats.

Let's start with the 147 MHz cross-over exception. This isn't global, for example repeaters in California use several different ranges for such a cross-over point.

I also didn't tell you about repeaters on other bands because the offset depends on where you are. In many cases the 70cm repeater offset is 5 MHz, but in Europe it's mostly 7.6 MHz, unless it's 9 MHz. The 10m repeater offsets are often 100 kHz, but sometimes they're 1 MHz, similarly the 6m repeater offset is 1 MHz, except when it's not.

The point being that starting with a receive frequency, there's a great number of assumptions, many of which you'll need to discover for your own location. A great resource which I've mentioned before is the brainchild of Garrett KD6KPC, the repeaterbook.com website and app, maintained by a global group of volunteers, which lists many repeaters and their specific settings, frequencies and locations.

So, armed with this knowledge, I expect that you can now find a local repeater and make use of it. When in doubt, contact the owner and ask for help, they're a friendly bunch. Remember to say thank you!

So, what excuse do you have not to get on air and make noise?

Oh, before I forget, if you don't hear anything, or if transmit isn't doing what you expect, check that you've configured CTCSS, another assumption.

I'm Onno VK6FLAB