major.io words of wisdom from a systems engineer

Getting started with ham radio repeaters

Amateur radio is a fun way to mess around with technology, meet new people, and communicate off the grid. Talking directly to another radio on a single frequency (also called simplex) is the easiest way to get started. However, it can be difficult to communicate over longer distances without amplifiers, proper wiring, and antennas. This is where a radio repeater can help.

What’s in scope

This post is focused on fairly local communication on VHF/UHF bands. The most common frequencies for local communication in these bands are:

  • 2 meters (~144-148MHz)*
  • 70 centimeters (~420-450MHz)*

* NOTE: Always consult the band plan for your area to see which part of the frequency band you could and should use.

Of course, you can do some amazing things with weak signal VHF (which can be used to commuinicate over great distances), but we’re not talking about that here. The HAMSter Amateur Radio Group is a great place to get started with that.

We’re also not talking about radio bands longer than 2 meters (which includes high frequency (HF) bands). Some of those bands require advanced FCC licensing that takes additional studying and practice.

Keeping it simple(x)

Simplex radio involves communication where radios are tuned to a single frequency and only one radio can transmit at a time. This is like a simple walkie-talkie. If one person is transmitting, everyone else listens. If someone else tries to transmit at the same time, then the waves will be garbled and nobody will be able to hear either person. This is often called “doubling up”.

This method works well when radios are in range of each other without a bunch of objects in between. However, it’s difficult to talk via simplex over great distances or around big obstables, such as mountains or hills.

Repeaters

Repeaters are a little more complex to use, but they provide some great benefits. A repeater usually consists of one or two radios, one or two antennas, duplexers, and some other basic equipment. They receive a signel on one frequency and broadcast that same signal on another frequency. They often are mounted high on towers and this gives them a much better reach than antennas on your car or home.

I enjoy using a repeater here in San Antonio called KE5HBB. The repeater has this configuration:

  • Downlink: 145.370
  • Uplink: 144.770
  • Offset: -0.6 MHz
  • Uplink Tone: 114.8
  • Downlink Tone: 114.8

Let’s make sense of this data:

  • Downlink: This is the frequency that the repeater uses to transmit. In other words, when people talk on this repeater, this is the frequency you use to hear them.

  • Uplink: The receiver listens on this frequency. If you want to talk to people who are listening to this repeater, you need to transmit on this frequency.

  • Offset: This tells you how to calculate the uplink frequency if it is not shown. This repeater has a negative 0.6 offset, so we can calculate the uplink frequency if it was not provided:

145.370 - 0.600 = 144.770
  • Uplink/Downlink Tones: Your radio must transmit this tone to open the squelch on the repeater (more on this in a moment). The repeater will use the same tone to transmit, so we can configure our radio to listen for that tone and only open our squelch when it is detected.

Opening the squelch

Transmitting radio waves uses a lot of power and it creates a lot of heat. There are parts of a radio that will wear out much more quickly if a radio is transmitting constantly. This is why receivers have a squelch. This means that a radio must transmit something strong enough on the frequency (or use a tone) to let the repeater know that it needs to repeat something.

You may come across repeaters with no tones listed (sometimes shown as PL). This means that you can just transmit on the uplin frequency and the repeater will repeat your signal. These repeaters are easy to use, but they can create problems.

Imagine if you’re traveling through an area and you’re using a frequency to talk to a friend in another car. As you’re driving, you move in range of a repeater that is listening on that frequeny. Suddenly your conversation is now being broadcasted through the repeater and everyone listening to that repeater must listen to you. This isn’t what you expected and it could be annoying to other listeners.

Also, in crowded urban areas, there’s always a chance that signals might end up on the repeater’s listening frequency unintentionally. That would cause the repeater to start transmitting and it would increase wear.

Two repeaters might be relatively close (or just out of range) and the tone helps each repeater identify its own valid radio traffic.

Tuning the tones

Most repeaters have a tone squelch. That means you can blast them with 100 watts of radio waves and they won’t repeat a thing until you transmit an inaudible tone at the beginning of your transmission.

As an example, in the case of KE5HBB, this tone is 114.8. You must configure a CTCSS tone on your radio so that the tone is transmitted as soon as you begin transmitting. That signals the repeater that it’s time to repeat. These signals aren’t audible to humans.

If you know you’re tuned to the right frequency to transmit (the uplink frequency), but the repeater won’t repeat your traffic, then you are most likely missing a tone. There’s also a chance that you programmed the uplink and downlink tones into your radio in reverse, so check that, too.

Repeater transmit tone

Some receivers will transmit a tone when they broadcast back to you, but some won’t. If you can transmit but you can’t hear anyone else when they talk, double check your radio’s settings for a tone squelch on the receiving side. Your radio can also listen for these tones and only open its squelch when it hears them.

I usually disable receiver squelch for tones on my radio since the repeater operator could disable that feature at any time and I wouldn’t be able to hear any transmissions since my radio would be waiting for the tone.

Testing a repeater

First off, please don’t test a repeater unless you have a proper amateur radio license in your jurisdiction. In the United States, that’s the FCC. Don’t skip this step.

Once you get your repeater’s frequencies programmed into your radio properly and you’ve double checked the settings for sending tones, you can try “breaking the squelch.”

Press the transmit button on your radio briefly for about half second and release. You should hear something when you do this. For some repeaters, you may hear a KERRRCHUNK noise. That’s the sound of the repeater squelch closing the transmission now that you’re done with your transmission. On other repeaters, you may hear some audible tones or beeps as soon as you release the transmit button.

Once you have it working properly, stop breakng the squelch and introduce yourself! For example, when I’m in my car, I might say: “W5WUT mobile and monitoring.” That lets people on the repeater know that I’m there and that I’m moving (so I might not be on for a very long time).

Good luck on the radio waves! 73’s from W5WUT.