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Blog - Mind your tone... and offset... and input frequency

This week we’re going back to basics. Specifically, setting up your radio with the three items necessary for getting on the air. There are three things in particular that need to be on the money: input frequency, tone and offset. Without these, you will be unable to access a repeater, so it’s pretty important stuff.

In addition, if they aren't set correctly, it will be an extra frustration to deal with in addition to finding the courage to push the key down.

So those three things again are: input frequency, tone and offset.

When I say frequency, I mean the number you key into your radio -- it reflects the repeater's receive frequency. You can find lists of these repeater frequencies in close proximity by using a phone ap. I particularly like the Repeaterbook ap since you can set a distance, choose a specific band, and choose how the information is viewed on your phone.

The functionality is a little more robust on repeaterbook.com. There you can download a .csv format of repeaters by county, by state, by band, or other attributes you’re interested in – like ARES, RACES, linked systems, highway route coverage, who operates the repeater, if it’s open or closed, etc. Good stuff to know.

The next thing you will need is a tone.

Most repeaters, especially those here in the DFW area, will not pass a signal on for retransmission unless it contains a sub-audible tone. Meaning you can’t hear it, but the repeater can.

Just like when you’re talking to someone, their tone of voice has a lot to do with how well you listen. Repeaters are no different. They’re a picky lot. They won’t take just any old tone. It has to be the *right* tone.

Tones actually correspond to a particular number. When the number is set correctly, your radio will transmit the tone along with your audio signal to the repeater. The tone’s presence indicates to the repeater that your signal is intentional and should be retransmitted. If a repeater requires a tone -- setting one is not optional – you must have it set correctly in order to access the repeater.

There are at least two reasons for tones. Usually mine has to do with my dogs. But I digress.

The first reason for a tone is that most repeaters are close to other repeaters, especially here in the metroplex. The repeaters closest together in receive frequency sometimes mix signals. Without a tone, there is no way for the repeater to disseminate what is an intentional signal and what is not, so it’s all retransmitted. Can you imagine how much RF noise there is in DFW? For this reason, tones are pretty much standard operating procedure around these parts.

The second reason is actually the reason why tones were invented in the first place. Repeater access tones were actually created by Motorola to allow different commercial users to share a repeater without having to listen to each other’s conversations. This is why they are sometimes called PL Tones or “Private Line” Tones, which are a Motorola trademark. If you’re old enough to remember telephone party lines, you’ll understand the concept perfectly.

If a repeater requires a tone -- setting one is not optional – you must have it set correctly in order to access the repeater.

Continuous Tone Coded Squelch Systems tones, or CTCSS tones, are optional and the key word to remembering the difference is the term “squelch”. Focus in on that one word if you are confused. If you squelch something -- you remove it. In addition to setting the PL Tone, you *may* also set a CTCSS Tone. PL tones get you into a repeater, CTCSS tones filter out erroneously received signals at your radio's receiever.

Here’s an example for you. The YL Weekly Net is a linked repeater system, meaning there are two repeaters linked together – repeater A (442.325, the KM5R repeater) and repeater B (442.225, the K5HIT repeater).

When repeaters are linked, whatever is transmitted on one, transmits on the other. Here’s the rub. Repeater A and Repeater B have different PL tones. Still, the same holds true. What’s transmitted on one, transmits on the other. But if you have the CTCSS tone set on your radio to only receive PL tones from Repeater A, you will not hear anyone coming in from the linked repeater B, because you have effectively squelched out the other signal.

Does your head hurt yet? Mine does! It took me forever to wrap my head around the whole tone thing. The way I finally remembered it was zeroing in on the word “squelch”.

Alright, let’s put the tones away before someone gets hurt.

The last thing you need to set correctly is offset. Offset is the difference between the repeater’s receive frequency (what you say) and its the transmit frequency (what the other guy hears). Two meter offsets can be either positive or negative but there is a 600 kilohertz difference between the input and output frequency. The 440 or 70 cm band offsets are always positive and have a 5.0 megahertz offset. Most radios have an automatic offset function, but occasional some repeaters will use an atypical offset.

If those little + and – on your radio are as hard to see for you as they are for me, here’s a quick cheat to tell you what you have set. Engage the PTT button and by all means, throw your callsign out there before the kerchunking police arrest you. Look down at your radio and watch the frequency change. If the frequency goes up, it’s a positive offset. If the frequency goes down, it’s a negative offset.

So to recap. The three things you need to get on the air are: input frequency, tone, and offset. You will notice, I didn't tell you how to set them. That's a manual issue. Find yours, dust it off, look up the information and put you a sticky note on all three pages. You won't regret it.