Packet Radio

Ever since I particiated in Winter Field Day and seeing the limitations of pretty much every SSB frequency being taken-up by people with more power than me, and having some success with JS8Call, while others used WinLink, I am started to get more interested in packet radio.

So here’s a 30,000 ft overview of what packet radio is.

Lets say you have some piece of information that you want to send to someone. Maybe “KF0BBY this is AE0RS. Meet met at Whitetail Park for some ham radio fun next Tuesday at 10 AM.”

• How do you relay this to someone one another room? You talk to them.
• How about in across the street? You’d yell it to your neighboor loud enough for them to hear you.
• How about in the next town? You might use your phone to call them, and then say it to them when they pick up their phone.
• How about to someone in another time zone 5000 miles away? You might write it on a piece of paper, put it in an envelope, write their address on it, put a stamp on the envelope and mail it and assume they got the message (esp if they showed up to the park when you said to).
• What if you were to send it via email over the internet? That’s using radio waves and wires, just like a phone.
• What if you were to use your HF radio? Ahhh then you’re taking your voice, turning it into electromagnetic waves, sending it around the earth, bouncing them off the D-layer, maybe, until finally it reaches their HF radio which turns the electromagnetic wave (well, electric part) into sound waves that the operator understands as spoken word.

In each case, you’re relaying the exact same message but in several different mediums. A voice,  a loud voice, then over radio frequency and/or wires (depending on if you were using a cellphone or wired landline), on a piece of paper, radio/wires, radio/wires again.

In a few of the cases, you took teh message, turning it into something that looked absolutely nothing like the message to do the work of transporting your message to somewhere else.

We could think of each of those other non-yelling methods as communicating via Packets. Think of a packet as an the envelope. It contains the message and some information on how and where to deliver it to. This way anyone between you and the recipient can look at the envelope and pass it along until it gets closer and closer to its destination.

Why would you want to use a packet? Because you want to take advantage of the medium the packet can travel in. You can only yell so loud. But if you had a powerful flashlight, you can do morse code at a greater distance than you can yell. We all know that you can use a few watts on SSB and talk to someone a thousand miles away. You just used EM waves to your advantage to send packets of your voice. In all cases, the same message is being sent, just in a different, more advantageous medium.

HF radios operate on the basis of sound and sound only. When you say a word in English, someone that speaks English can understand what you said on SSB or FM.

What if you were a bird and could chirp the same word? And a bird was on the other end that understtood the chirps? Humans in between that were tuned into the frequency couldn’t understand it (unless they got a bird to translate for them).  This is similar to CW. If you know CW then you can speak this easy-to-encode-and-decode method of radio to sort-of talk to someone else that knows CW and can decode it fast enough to have a back and forth conversation in real-time.

Now lets make it more complicated than CW. Lets send REALLY CW really fast. Faster than any human can decode it while they’re listening to it. While we’re at it, so that we can send more informatoin really fast, instead of just having a single tone, lets introduce a bunch of different pitches of tones. Like a whole piano’s worth of tones! Whew! before, it was easy dits and dahs in a nice slow tempo but now its a classical piano symphony that sounds like its in crescendo all the time! We’re gonna need a microprocessor or a computer or software to decode this stuff in real time otherwise its gonna take us weeks to decode the message and we’re gonna miss the fun at the park.

What about RTTY? You can hear the familiar tones while you’re tuning around but you can’t decode it while you’re hearing it. Some HF radios can because they have little microprocessors.

Lets kick it up a notch and code and decode even more information than CW or RTTY. And we all know that bands go up and down and a host of other environmental things happen in real-time that can prevent you from hearing a dit or a dah and you’re left wondering did he mean A or U because A doesn’t make sense in this word so I might have missed the first dit. Well, most packet radio has a feature that can help itself correct small errors. Cool!

Both CW and RTTY are considered digital modes.

That’s packet radio. Information (text, usually) turned into a format that enables us to send alot of it and pretty high speed. The downside is that its no longer human-readable in real time – like spoken words or CW.

Packet radio is just a medium for transferring messages over radio waves. We all use the internet. The internet does the exact same thing except usually a little bit of RF (wifi), then cables, and then maybe wifi out the other end.

Protocols

A protocol is a fancy word that means you and i have agreed to communicate with each other using a certain language.

International Morse Code can be thought of as a protocol.  If I tell you that I’m going to use morse code over CW then you’ll be able to understand what i’m saying because you’ll on that dit dit dah can only mean 1 thing – the letter “U”.

There are many protocols. Why? Because people have figured out that some ways of communicating work better when there’s alot of noise. Or some ways work better when theres a good, strong signal and you have 12,00 hz of bandwidth to work with. Others have optimized for 3,000 hz.  You know from your ham radio exams that you need more bandwidth to send more data at a faster rate.

You also know that all protocols must be made public because you can’t have secret conversations over US ham radio.

Winlink is an application suite (and a “standard”) that is used to help you send and receive message over packet radio.

ARDOP is an example of protocol that is used to talk over ham radio frequencies. You don’t have to know anything other than the name of the protocol because that tells you what software you need to code/decode those packets.

AX.25 is another example of a suite of protocols.

You’ll hear the word Frame used when talking about Packets. That’s because, say you have a book to send over HF Packet radio. You can’t send all of it at once. You have to split it up into small pieces and send those pieces individually. Each piece is a Frame.

Other words in packet

1. Terminal – a computer of some sort that has a keyboard attached. It could be a phone with a virtual keyboard, too.
2. TNC – Something that takes the text sent in from the Terminal, turns it into packets. Also does the opposite for packets coming in.
3. Radio – your HF (or VHF radio). Takes the musical notes from the TNC and sends it over the air waves.

Note each of the 3 things above does 1 thing and one thing only.

1. Your radio’s only good at pumping watts out. It doesn’t care if you’re talking or your cat is meowing into the Mic or your TNC is giving it tones to play over HF.
2. The terminal is only good at taking in and displaying text.
3. The TNC is only good at translating words to tones (and vice versa). They’re kind of like a sound card.

Your older ham radio can convert RTTY to text in real time. Newer ham radios are literally turning into computers. This means that the 3 “parts” above might be in 1 box with a dial on it soon, rather than being 3 separate small boxes. Some radios can send APRS packets all by themselves. This means they’re doing the job of 1) grabbing a GPS coordinate 2) turning that into text 3) taking the TNC and converting it into tones 4) using their VHF radio and tuning to 144.xxx FM and transmitting coordinates to a repeater. All in 1 tiny handheld Yaesu FT3D or somthing.

There are different types of TNCs. A full-featured one can do more of teh work than a “dumb” one – often called KISS TNC. KISS TNC’s harness a modern computer’s CPU to do alot of the thinking.

Some TNC’s are entirey impleented in software. DIREWOLF, Signal Link boxes, etc need a computer to do their TNC’ing.

The flow of information is something like this:
Computer => ASCII => tnc => AFSK => HF/VHF radio

1. You type some letters into your computer-like device
2. The letters get turned into ASCII – which is a digital way to represent your letters
3. The TNC or Terminal Node Controller turns the ASCII into sounds, maybe using AFSK Audio Frequency Shift Keying – kind of like you whistling a different tone for a different letter.
4. Those tones (sounds) get pushed into your ham radio.
5. A radio that receives this can do the same thing in reverse to get to the letters you typed!

Here’s a PDF from a website – Not Black Magic:AFSK – that explains AFSK including information on how computers can act as TNC’s via software, making it so you don’t need an extra piece of hardware.

I have experimented with APRS and connected my Baofeng HT directly to my Android device. My Android phone converted my coordinates (text) into tones that could be transmitted by my HT to a repeater that understands APRS tones. Then my location was available on the https://aprs.fi website as well as in the app that I was using (which I believe uses data from the same website).

73,

AE0RS