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Sep. 13 - 7 pm PT - ARRL Pacific Division Town Hall Zoom Meeting
DIY Radio Spring 2021 - Tuna Tin "S" CW Transmitter
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
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
Upload Procedure for Arduino Sketches and Required Libraries
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 the default QRP frequencies, band switching for 80, 40, 60, 30, 20, 15 and 10 meters, and tuning steps of 10 Hz, 100 Hz, 1 kHz, 10 kHz and band change.
Sketch -- added band indicator to display
Note: The sketch only changes the frequency of the Si5351 synthesizer. You must change filter component values to use the amplifier stage on the added frequency bands.TunaTinS_Rev12APR21 -- corrected Calibrate_Offset factor for all bands and added 160, 17 and 12 meters. Earlier Arduino sketches had compensated for reference frequency crystal error by adding a fixed offset to the frequency. The 12APR21 and later revisions employ an improved method that applies a proportional correction for the ppm error of the 25 MHz reference crystal and is accurate for all bands. See the link below. Sketch
Instructions to manually calculate the Calibrate_Offset factor (for Rev12APR21 to v2.0.1). We now recommend using the Tuna Tin S later sketches listed below.
TunaTinS_Rev15APR21 -- now also applies the correct Calibrate_Offset factor to the 60 meter band.
Sketch - Video demonstrationTunaTinS_Rev06MAY21 -- Bob Fontana released this revision of his 27MAR21 sketch in his project modifications published in Sept 2022 QST. This version covers 160 through 10 meters, offers a corrected calibration for frequency reference error, tuning steps of 10 Hz, 100 Hz and 1 kHz, and uses a long press on the encoder switch to change bands. Sketch
TunaTinS_v2.0.0 (01 Jan 2022) -- This fork of the Tuna Tin S Rev15APR21 Arduino sketch now adds coverage of all 12 amateur bands from 472 kHz through 50 MHz; the code has been compacted with band constants in arrays; and new synthesizer constants improve the frequency tracking on the 5 MHz, 10 MHz and 24 MHz bands.
SketchTunaTinS_v2.0.1 (24 Dec 2023)
• The encoder push button now toggles the control between "digit adjust" and "digit select" modes.
• A small dot to the left of either the frequency or the step size display lines indicates which is the active mode.
• The tuning steps are now: Band change, 1 MHz, 100 kHz, 10 kHz, 1 kHz, 100 Hz and 10 Hz, in either direction, improving its utility as a general purpose signal source. SketchTunaTinS_Calibration (24 Dec 2023)
Companion to TunaTinS_v2.0.1 SketchTunaTinS_v2.1.0 (31 Dec 2023)
• This sketch requires installation of NT7S's Etherkit Si5351 Library and now adds continuous RF spectrum coverage from 4 kHz to 225 MHz with preset QRP frequencies for all amateur radio 137 kHz through 222 MHz bands.
• Added 1 Hz tuning steps and frequency correction to within 1 Hz at 10 MHz. SketchTunaTinS_v2.1.0_Calibration (31 Dec 2023)
Companion to TunaTinS_v2.1.0 calculates and displays parts per billion (ppb) correction factor for the Si5351 reference frequency crystal in the TunaTinS_v2.1.0 Arduino sketch. Sketch
Project Updates
Project Updates
LTSpice model file for the 7 MHz RF section
While building the Tuna Tin "S" transmitter, we observed that the 3 volt peak output of the Si5351 synthesizer module can only drive the IRF510 MOSFET amplifier to 500 mW output power. The amplifier stage circuits below raise the drive power to the IRF510 sufficiently to achieve more efficient Class E operation and 4-5 watts of power output.
This MOSFET gate driver stage is inserted between the output of the Si5351 module and the 0.1 uF capacitor to the gate of the IRF510 MOSFET. It is frequency-independent, offers the stability and noise immunity of digital switching, requires no additional inductors or transformers, and drives the IRF510 to 7 watts output up to 7 MHz, 4 watts at 10.1 MHz and 2.2 watts at 14 MHz. Potentiometer R5 on the Q2's input adjusts the drive level from the Si5351 module to the MOSFET gate driver. Keying the Si5351 module output yields acceptable Morse element spacing up to about 18 wpm due to interrupt timing limitations. Keying the driver stage as shown in the diagram below yields good higher speed sending. R5 appears as the two fixed resistors R5a and R5b in this LTspice model file as LTspice does not model potentiometers. LTspice Model File Click here for more details.
This driver design by Phil Sittner, KD6RM, uses a single transistor and a toroid impedance transformer. LTspice Model File
Modifications for the Tuna Tin "S" in September 2022 QST
Modifications for the Tuna Tin "S" in September 2022 QST
Bob Fontana, AK3Y, published a Tuna Tin "S" project update on pages 32-33 of the September 2022 issue of QST. His project improvements include: frequency extension; more tuning increments; precision calibration; EEPROM Recovery; and, an improved drive circuit. Current ARRL members may download the complete project summary from the QST in Depth web page at http://www.arrl.org/qst-in-depth
A simple modification moves the output filter to plug-in boards that allow operation on multiple bands.
See full details at https://photos.app.goo.gl/9AkAFW5uVJDciaUf9
We pulled the 7 MHz low-pass filter off the main board, transferred its components onto a plug-in board and soldered the 3-pin header sockets into the existing PCB holes for C4, C7, C9 and L4. C4, a 0.1 uF capacitor, was moved and soldered onto the socket pins under the main PCB. L1 was replaced with 10 turns of 22 AWG wire on an FT37-43 core (not shown in this photo) and was mounted on the main PCB and shared for filter boards for all bands.
Here are Tuna Tin S filters for 3.5 MHz through 14 MHz. With the MOSFET gate driver, we measured maximum power output using a 12 V power supply of: 7 W on 3.5 & 5.3 MHz, 7.5 W on 7 MHz, 4 W on 10.1 MHz and 2.2 W on 14 MHz.
Detail of the 51mm x 33mm Tuna Tin S plug-in Class E amplifier Filter Boards per WAØITP's spreadsheet.
Here are the Class E filter component values for 5W and 12VDC on 1.8 MHz through 14 MHz per WAØITP's spreadsheet. The coil turn numbers are for T37-6 toroid cores.
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