presented by the USA School of Computing Radio Free USA Building a low-power RM transmitter using a Raspberry Pi presented by the USA School of Computing

The Electromagnetic Spectrum Band name Abbreviation ITU band Frequency and wavelength Example uses Tremendously low frequency TLF < 3 Hz > 100,000 km Natural and artificial electromagnetic noise Extremely low frequency ELF 3–30 Hz 100,000 km – 10,000 km Communication with submarines Super low frequency SLF 30–300 Hz 10,000 km – 1000 km Ultra low frequency ULF 300–3000 Hz 1000 km – 100 km Submarine communication, communication within mines Very low frequency VLF 4 3–30 kHz 100 km – 10 km Navigation, time signals, submarine communication, wireless heart rate monitors, geophysics Low frequency LF 5 30–300 kHz 10 km – 1 km Navigation, clock time signals, AM longwave broadcasting (Europe and parts of Asia), RFID, amateur radio Medium frequency MF 6 300–3000 kHz 1 km – 100 m AM (medium-wave) broadcasts, amateur radio, avalanche beacons High frequency HF 7 3–30 MHz 100 m – 10 m Shortwave broadcasts, citizens' band radio, amateur radio and over-the-horizon aviation communications, RFID, over-the-horizon radar, automatic link establishment (ALE) / near-vertical incidence skywave (NVIS) radio communications, marine and mobile radio telephony Very high frequency VHF 8 30–300 MHz 10 m – 1 m FM, television broadcasts and line-of-sight ground-to-aircraft and aircraft-to-aircraft communications, land mobile and maritime mobile communications, amateur radio, weather radio Ultra high frequency UHF 9 300–3000 MHz 1 m – 100 mm Television broadcasts, microwave oven, microwave devices/communications, radio astronomy, mobile phones, wireless LAN, Bluetooth, ZigBee, GPS and two-way radios such as land mobile, FRS and GMRS radios, amateur radio Super high frequency SHF 10 3–30 GHz 100 mm – 10 mm Radio astronomy, microwave devices/communications, wireless LAN, most modern radars, communications satellites, satellite television broadcasting, DBS, amateur radio Extremely high frequency EHF 11 30–300 GHz 10 mm – 1 mm Radio astronomy, high-frequency microwave radio relay, microwave remote sensing, amateur radio, directed-energy weapon, millimeter wave scanner Terahertz or Tremendously high frequency THz or THF 12 300–3,000 GHz 1 mm – 100 μm Terahertz imaging – a potential replacement for X-rays in some medical applications, ultrafast molecular dynamics, condensed-matter physics, terahertz time-domain spectroscopy, terahertz computing/communications, sub-mm remote sensing, amateur radio Source: wikipedia.com

The Electromagnetic Spectrum Source: wikipedia.com

The FCC and Licensing Over 30,000 requests for licenses are received each year. Most are denied. In many areas of the country, no frequencies may be available on which a new station could begin operating without causing interference to existing stations, a violation of FCC rules. The only unlicensed operation that is permitted on the AM and FM broadcast bands is covered under Part 15 of the FCC's rules, and is limited to a coverage radius of approximately 200 feet. FM noncommercial commercial (NCE) stations may be authorized on 88.1 MHz to 91.9 MHz.  No commercial operation is permitted on these frequencies. Both noncommercial and commercial stations may be authorized on 92.1 MHz to 107.9 MHz Source: https://www.fcc.gov/guides/how-apply-radio-or-television-broadcast-station

What is a Raspberry Pi A raspberry pi is a small computer It has HDMI out, video out, USB ports, and an Ethernet connection It uses a SD card as its hard drive You can download prebuilt images for different operating systems from http://www.raspberrypi.org/downloads

Getting Started From the adapter, remove the SD card Insert into the Pi The SD card is spring loaded Connect the Ethernet cable to the Pi Connect the other end of the Ethernet cable to the PC Connect the power supply to the Pi and plug it in to a USB port on the laptop

Using the Pi with no monitor? If you don't have an HDMI monitor available, then you use a program called VNC to use your laptop or desktop to view the Raspberry Pi desktop VNC stands for Virtual Network Computing When you connect with VNC, you will see the desktop of the Pi on your PC, and you will be able to use your keyboard and mouse

How to connect to the Pi At your desks, you will find an SD card that has an image already installed on it This image presets the IP address of the Raspberry Pi to 192.168.31.30 An IP address is a unique number assigned to a machine It is how machines communicate with each other In order for your PC to talk to the Pi, we must change its IP address

VNC Setup Instructions Go to Start -> Control Panel and choose Network and Sharing Center

VNC Setup Instructions Click on Change Adapter Settings Right Click on Local Area Connection Then select Properties

VNC Setup Instructions Choose Internet Protocol Version 4 Then select Properties

VNC Setup Instructions Enter 192.168.31.31 for the address and 255.255.255.0 for the Subnet mask

How do we access the Internet ? One solution to this problem is to purchase a wireless dongle for the Pi If you don't want to purchase this, you can use your laptop as a proxy In order to set up your laptop as a proxy, you will need to install a proxy server The URL http:// www.soc.southalabama.edu/~lynn/cfitsresources has instructions about how to download a program called Squid

What is Squid? Squid is a well known proxy server What you will find at the URL are instructions about how to download a windows port of Squid and set it up On the PCs, we already have Squid on it Squid listens at port 3128 by default We must configure the PC to allow the Pi to connect to port 3128

Squid Setup Instructions Go to the Control Panel and choose Windows Firewall Click Advanced Settings

Squid Setup Instructions Choose Inbound Rules Click New Rule

Squid Setup Instructions Click Port

Squid Setup Instructions Type in 3128 for the port number Click next

Squid Setup Instructions Choose Allow this connection

Squid Setup Instructions Choose public and private

Squid Setup Instructions Enter the name Squid for the service

Squid Setup Instructions Go to the Control Panel and open Administrative Tools

Squid Setup Instructions Double-click on Services

Squid Setup Instructions We see the Squid service Click on Start the service

Squid Setup Instructions After you click Start, you see the Squid service has started

SSH and VNC What we will use to connect to the Pi from the PC is SSH SSH stands for Secure Shell It is a standard program for connecting to servers It provides an encrypted connection We can also tunnel ports through the connection Tunneling means instead of connecting as your normally would where traffic is exposed, the connection to the distant server goes through the encrypted connection

How do you use SSH? A popular tool to use SSH is putty On your laptops is a Java program that uses SSH to tunnel a connection to the Pi It carries the VNC connection On your local machine port 52873 will be translated to port 5901 on the Pi Turn on the Pi if you haven’t already Double-click ConnectToPi.jar and click Connect to Pi. You should then see the Pi desktop.

ConnectToPi.jar Step 1: Click the button that says Connect to Pi Step 2: Click the box that says you have read the agreement and click OK Step 3: Click the box for Don't warn me about this again Step 4: Success!

What is available on the Pi? This version of the operating system contains Python 2 and Python 3 Mathematica Web browser Games Scratch

The terminal We can open a terminal so we can type commands At the top, you will see an icon for the LX Terminal This is the equivalent of the command prompt in Windows

Some simple commands In order to view the files in a directory, we use the command ls To see a detailed list, we use the command ls -l The change to a different directory, we use the command cd One thing that is important to know is that, as the user pi, we do not have access to files in all directories We also don't have the ability to run all programs

sudo In order to access these files, we must elevate the privileges of the pi user In order to do this, we must precede a command with the word sudo This elevates the pi to the superuser To see this in action, change to the directory /etc and type nano test If you click CTRL and O to save the file, you will be told you don't have permission Now change the command to sudo nano test and try to save the file

Wget Setup Wget allows us to download files via the command line Edit the configuration file for wget

Wget Setup Verify the http_proxy is set to our proxy

We now edit the configuration file for apt (Advanced Packing Tool)

Type in the following to use the proxy. Make sure you include the ;

Turning the Raspberry Pi into an FM Transmitter Type the following commands at the command prompt wget www.icrobotics.co.uk/wiki/images/c/c3/Pifm.tar.gz gunzip Pifm.tar.gz tar xfv Pifm.tar.gz Attach a cable to pin 7 sudo ./pifm sound.wav 100.8 pifm will play only wav files To convert mp3 files to wav files, type the following commands apt-get install libav-tools avconv -i mp3file -ac 1 -ar 22050 -b 352k filename

How to transfer files to and from the Pi We can transfer files to and from the pi using ssh We can use the program pscp to download from the site where we downloaded putty This program allows us to transfer files on the command line If you want to use a graphical interface, you can use the program WinSCP

How to use pscp Since your pi is connected to your PC, we will transfer files directly from the PC to the Pi c:\tem\pscp file pi@192.168.31.30:/home/pi This says to take the file and transfer it to the pi. In order to transfer using ssh, we must first login. The account is specified before the @. After the IP address, we must have a colon followed by the location where we want the file to be placed on the pi After we hit enter, we will be prompted for the password. It is pi123

Clean Up After you are finished, reset the network settings to DHCP on the laptop