DIY Radio 2021 #1

DIY Radio Video Playlist

DIY Radio Tuna Tin "S" CW Transmitter Project

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.

Homebrewing: The Fine Art of Smoking Parts

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.

Our DIY Radio Zoom meeting videos are posted here.  

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Click to see our DIY Radio 2019 Project
Tuna Tin S Arduino Sketch Repository
  1. 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 rewrite
  2. TunaTinS_Rev09APR21 -- added default QRP frequencies and band switching for 80, 40, 60, 30, 20, 15 and 10 meters
    Sketch                             -- added band indicator to display
  3. TunaTinS_Rev12APR21 -- corrected Calibrate_Offset factor for all bands and added 160, 17 and 12 meters
    Sketch                             -- Instructions for calibration procedure
  4. TunaTinS_Rev15APR21 -- corrects the applied value of Calibrate_Offset also for the 60 meter band.
LTSpice Model Files

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)
Carol Milazzo,
May 15, 2021, 6:19 PM
Carol Milazzo,
May 15, 2021, 6:19 PM
Carol Milazzo,
May 15, 2021, 6:19 PM