HackerBoxes 0003: Amateur Radio, Arduino Nano, Satellites, Packet, APRS

• Dual Band (2m/70cm) Handheld Radio Transceiver
• Antenna, Earpiece, 1500 mAh Battery, Desk Charger
• Nano AVR Board - Compatible with Arduino IDE and Code
• Nano Prototyping Kit
• Connectors for Transceiver Interfacing
• Hiking Compass (Amateur Satellite Tracker)

Communicating through radio frequency oscillation within an electromagnetic field (commonly called radio communications) is an amazing technology that we often take for granted in the modern world where smart phones, Wi-Fi, satellite television, GPS, RFID cards, and even garage door openers implement radio comm all around us.

A radio communication system minimally includes a transmitter, a channel, and a receiver. The transmitter takes an input signal (such as voice or music) and converts it up to a radio frequency (such as 101MHz for a commercial FM radio station). That radio frequency signal is then driven into a transmit antenna. The transmit antenna agitates the surrounding electromagnetic field exactly as a rock thrown into a lake agitates the water creating ripples. This field is called the channel since it carries the signal from the transmitter (TX) to the receiver (RX).

Some distance away, the ripples in the electromagnetic field move electrons in the receive antenna. Electrons moving is also called electric current. This current is coupled into the receiver and converted from the radio frequency back down to baseband. The resultant signal is (hopefully) just like the original input signal (such as music or voice) that entered the transmitter. Of course any noise, distortion, or interference from the channel will have been added.

When bidirectional communication is desired, each side includes both a transmitter and a receiver. The combination is called a transceiver. In practice, the process of converting the input signal into a radio frequency (RF) signal can mean many different things and is actually an entire field of study. While some radio communication systems, such as 4G mobile phone data, are incredibly complicated, traditional AM/FM commercial radio is comparatively quite simple.

The first thing to say about this transceiver is that it is capable of transmitting on frequencies that require a license to transmit on. If you are not a licensed radio operator or haven't verified the laws in your country, you should not be hitting the PTT (push-to-talk) button on the side of the radio. There is quite a lot to hear and explore in the VHF/UHF bands without having to transmit. We will discuss how to get a license to start transmitting in a later step. Emergency situations are generally an exception to this "no transmitting" rule.

• VHF: 136-174 MHz
• UHF: 400-520 MHz
• Commercial FM: 65-108 MHz (RX only)
• 4W Transmitter

HT is a "handy" acronym for Handheld Transceiver or (in ham radio jargon) Handy Talky.

Have a look at this YouTube video covering some basic features and operation of the Baofeng HT.

To learn more about Ham Radio, you can definitely find a lot of great resources online. You should also drop in on a local Radio Club and see what the members are working on.
You may be interested in getting your Amateur Radio License. It only costs about $15 to take the exam. You need to know some basic electronics, a little bit about how radios work, and then some operating rules. The requirement to pass a Morse Code test as been removed. Pretty much everything you need is covered in this free eBook:

The No-Nonsense, Technician Class License Study Guide

While this information is specific to U.S. licensing, the process is similar worldwide. A quick web search should direct you to clubs in your area and the details on how to get licensed in your jurisdiction.

Amateur Satellites are satellites (or birds) that anyone can receive the signals from using basic radio receivers. Licensed amateur radio operators can also transmit into the satellites using voice (FM, SSB) and data communications (AX.25, packet radio, APRS). OSCAR 1, the first amateur satellite was launched on December 12, 1961. It was only four years after Sputnik I, which was the first satellite of any type.

A few satellites that may be received using just a handheld radio:

• SO-50 on 436.695MHz
• FOX-1A on 145.980MHz
• International Space Station (packet bursts) on 145.825MHz

Birds used for DISH or DirectTV are in high altitude, geosynchronous orbits. They appear to be stationary from the ground. In contrast, amateur radio satellites are in much lower orbits, which means that they move relative to the surface of the Earth. Quite a lot. To discover when a particular satellite is going to be overhead in your area, some computer software is used to display the "ground track" of motion relative to the Earth. There is a long list of such software over at DX Zone and here is a short, quick list:

• Quick and easy web-based tracker
• MacDoppler on OSX
• Nova for Windows
• PocketSat for Android and iOS
• Satellite Explorer Pro for iOS
• Satellite AR for Android

Once you see when and how a satellite is passing overhead, you will need to head outside and find the bearing using a compass. Here are some pointers:

Turn the squelch all the way down (adjust it with the menu or hold the MONitor button down). Don't aim the whip antenna at the bird - hold it perpendicular and try turning it around to test various polarizations. Adjust your receive frequency for Doppler shift: Coming over the horizon, the frequency will be higher than nominal and will fade to lower than nominal as the satellite sets on the other side of the sky. Once you get hooked, you can improve performance with a higher gain whip antenna or better yet, a Yagi directional beam.

A YouTube video of someone working the SO-50 satellite with an HT.

Check out the HackerBoxes Prototyping Video demonstration on YouTube. It covers aspects of the next few steps of this Instructable.

The Nano AVR is a complete ATmega328-based Arduino-compatible in a super tiny package. It has essentially the same functionality of a normal sized Arduino and can be very easily plugged into a breadboard or perf-board.

If you haven't worked with Arduinos much before, this Instructable is great beginner's guide.

Please note that a lot of recent Nanos use the CH340/CH341 serial driver chip. A driver (available for OS X, Windows, and Linux) for the CH34x chips generally needs to be installed on your computer for the Arduino IDE to communicate to these boards. Here is a video on the topic.

The Nano Prototyping Kit can be used to prototype various circuits using the Arduino Nano.

• Prototyping Perfboard
• 4/22 cable
• 1K Resistors
• 10K Resistors
• 100K Resistors
• 100nF Capacitors
• LEDs
• Momentary Push Buttons
• Buzzer

The jacket can be removed from the 4/22 cable to reveal four different colors of solid 22 gauge wire for prototyping.

Since the Nano fits right onto a solderless breadboard, that can be a great way to test and tweak interface circuits. However, circuits built up on solderless breadboard are not particularly robust, so it is nice learn how to make a "permanent" prototype using simple perfboard.

Morse Code is a method for encoding information that uses short symbols for frequently used transmissions and longer symbols for lesser used transmissions. For example, E and T are one symbol, while Q and Z are four symbols. Radio operators call Morse Code transmissions CW (continuous wave) because they are generated by on-off-keying (OOK) a continuous wave carrier. Because the carrier is a single frequency, CW is very low bandwidth and thus, very efficient in both power and spectrum usage.

This experiment can be built with the Nano Prototyping Kit either on the perfboard or on a solderless breadboard. Typed text can be received from a computer over the USB port and then CW can be generated from that text. The CW can be seen on an LED and heard on a buzzer.

A project that can be easily modified from this would be generate the CW from a block of hard-coded text instead of from the USB serial channel. For example, you could program the Nano to generate CW from a chapter of a book or text copied from a website. Then you could practice listening to the buzzer output and "copying" (or writing down) the letters you hear. This is a fun way to learn to use Morse code.

Check out this Instructable and this other Instructable for similar examples and more sample code.

Attachments

• Serial2Morse.ino
  Download

What if you want to transmit the CW signal on the radio instead of listening to it on the buzzer? Audio band signals can be coupled into and out of the radio through audio ports originally intended for connecting headphones and microphones. These audio band signals can be encoded for CW or (as we will see later) other digital modes such as Packet Radio.

Handheld radios generally use two audio connectors (one 3.5mm and one 2.5mm) to interface audio in (MIC), audio out (SPK), and push-to-talk (PTT). Some also provide power and/or data pins. The illustration and pinout information shown here is for Kenwood and Baofeng handhelds. Pinouts for other radios are readily found online.

2.5mm Audio Plug

• Tip: Speaker +
• Ring: Data TX (data from the radio)
• Sleeve: Speaker – / PTT / Data GND

3.5mm Audio Plug

• Tip: +5V supply from radio
• Ring: Mic +
• Sleeve: Mic – / PTT / Data Rx (data to radio)

A 3.5mm stereo to 2.5mm stereo audio patch cable (Amazon) can be used for connectorizing the ports on the radio. Simply cut the patch cable in half to expose all six signal lines from the connectors. These lines can then be soldered into whatever circuit you wish to interface with.

For data interfacing, a TTL to USB module, such as those used for programming microcontrollers, may be used as shown in the diagram. Dedicated USB interface cables (Amazon) are also readily available. The data interface can be useful for programming operating frequencies into the radio. Have a look at the CHIRP open source software package.

Packet radio is a digital mode of radio communications. It uses packet switching technology to transmit digital data via radio or wireless communications links. The data is bundled into packets or datagrams similar to those in networks associated with computer LANs or the Internet. When working Packet Radio, a terminal node controller (TNC) is the device that interfaces between the computer and the radio. The TNC is a lot like a telephone modem - if you are old enough to know what that is.

Have a look at the TAPR Introduction to Packet Radio page.

You can create your own TNC using the Nano Prototyping Kit to interface a computer to a handheld radio. One great example is the Mobilinkd TNC. Also check out the M0PZT Arduino KISS TNC.

APRS is a radio-based system for real time communications. All of the data is ingested into the APRS Internet System (APRS-IS) and distributed globally for ubiquitous and immediate access.

APRS is best known for map displays where anyone can place information on their map. The information is distributed to the maps of other users in the area or monitoring the area. The attached information can include GPS localization, weather stations, alerts and various other data objects. APRS was first developed in the 1980s by Bob Bruninga, callsign WB4APR. Bob is currently a senior research engineer at the United States Naval Academy.

APRS can be interfaced using a Packet TNC and also via APRS software (such as APRSdroid) running on a computer or a mobile device such as a smartphone or tablet.

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Were you able to pull in a signal from an Amateur Satellite? Have you done anything super tiny with the Nano AVR? How about the Morse Code Practice project or a Packet Radio TNC? Please share your success (below or on the HackerBox Facebook page) and certainly let us know if you have any questions.

Who will be the first to get a new amateur radio license and make their first handheld contact? If you already have a license, maybe you can be the first to solder up your own itsy, bitsy, nano packet radio node and use it to make a digital mode contact?

Thank you for being part of the HackerBox adventure. Please keep your suggestions and feedback coming. HackerBoxes are YOUR boxes. Let's make something great!