DIY Radio Spring 2021
DIY Radio Spring 2021 - Tuna Tin "S" CW Transmitter
The December 2020 issue of QST p. 30 featured Bob Fontana's do-it-yourself article entitled 'The Tuna Tin "S",' subtitled "A Bare-Bones Synthesized QRPp Transmitter". QRPp means the transmitted signal is less than 1 watt. Our "Elmers" will guide you in building this CW transmitter comprised of 2 circuits: an Arduino controlled digital readout Si5351 frequency synthesizer that outputs a square wave into an IRF510 RF amplifier with a band pass filter that transmits an FCC-clean CW signal. Choose one of 3 bands: 80, 40 or 20 meters. Plug in a Morse key and a battery. Rotate a single knob to choose the displayed frequency. Depress the key and it transmits. Bare-bones is the operative word so that any club member should be able to build a working rig with assistance of virtual meeting attendees. For less than the cost of a book, a ham can build a working transmitter that can be heard on an existing receiver.
An Arduino Nano microcontroller is the brains of the rig executing 4 pages of software that can be modified to add new features. Our group building project will be conducted with Zoom meetings (the next one is pending schedule). Phil Sittner and Bob Mix have developed a kit that is better than Phil's working prototype. The kit includes all the parts. You just provide a low wattage soldering iron with a fine tip, 60/40 rosin core solder, solder wick, needle nose pliers, diagonal cutters, wire stripper, basic soldering skill and a desire to have fun. You will need a computer to load the software to the Arduino Nano, and a multimeter and 50 ohm dummy load to test the completed unit. There is no assembly manual, but we can probably guarantee your rig will work. The 50 ohm dummy load can be as simple as a 1/2 watt 50 ohm BNC terminator or two 1/2 watt or greater 100 ohm resistors (not wire wound) in parallel.
Links
Bob Mix KF6ABC presented the Tuna Tin S at our 2021 Homebrew Contest Night.
Some Tuna Tin S photos: https://photos.app.goo.gl/k5NymtWacWS3mm9y7
DIY Radio Zoom meeting videos are posted here.
Join groups.io online discussion group https://groups.io/g/DIYRadio to receive news updates.
Facebook group https://www.facebook.com/groups/DIYRadioBuilders
TunaTinS_Rev27MAR21 -- added provision for 5 fixed frequency CW channels on 60 meters
Sketch -- fixed EEProm code so that header changes to Band will trigger rewriteTunaTinS_Rev09APR21 -- added default QRP frequencies and band switching for 80, 40, 60, 30, 20, 15 and 10 meters
Sketch -- added band indicator to display
Note: The sketch only changes the frequency of the Si5351 synthesizer. You must change the filter component values to use the amplifier on additional frequencies.TunaTinS_Rev12APR21 -- corrected Calibrate_Offset factor for all bands and added 160, 17 and 12 meters
Sketch -- Instructions for calibration procedureTunaTinS_Rev15APR21 -- corrects the applied value of Calibrate_Offset also for the 60 meter band.
Sketch - Video demonstration
LTSpice Model Files
LTSpice model file for the 7 MHz RF section
Adding a driver stage between the Si5351 and the IRF510 can increase the output power to 5-6 watts.
LTSpice model file with 5 watt 7 MHz RF section (Complementary Symmetry Push Pull Amplifier)
LTSpice model file with 5 watt 7 MHz RF section (2N3866 amplifier with Toroid transformer)