RTTY FSK TNC - EasyFSK + TinyFSK

The entire project was born out of the need to transmit high-quality FSK RTTY and eliminate serial port problems. It was developed after the CQ WPX RTTY 2025 on CN3A. The hardware is Arduino-based with an Atmel 328 and audio isolators for RX and potential TX (FT8 and other analogue-digital modes). A PA PTT circuit for RTTY was added, and the program was supplemented with a simple PTT sequencer. This is important if you have a complex setup involving multibeaming and want to avoid compromising the RF relay during RX/TX transitions. The PTT sequencer ensures the timing of PTT signals between the TRX and PA. When switching to transmission, the PA PTT is switched first, followed by the TRX PTT and then transmission. When switching to RX, the opposite occurs. First, TRX transmission and TRX PTT are deactivated, and after a set time, PA PTT is also deactivated.

The entire project was made possible thanks to the excellent work of Andy K0SM and his TinyFSK. With his permission, I used this program as the basis for the HW design and supplemented it with a PTT sequencer. More information about the program can be found in the Manual.

This TX TNC provides 45.45, 50 or 75 baud RTTY keying with jitter-free timing moving the bit-banging process to a RTOS.

An external sound card is required for reception – either built into the PC or a higher-quality external one. For transmission, a signal from the sound card is only required for other analog-oriented digital modes, such as FT8, SSTV, AFSK, PSK, etc. The package includes two connecting cables with stereo jacks.

Applications

HAM radio FSK TNC and Audio-modulation interface with PTT option from serial port and PTT sequencer for FSK.

PTT sequencer

The FSK TX TNC allows the use of a PTT sequencer. The CPU uses two outputs for two different PTTs. Thanks to this solution, you can switch the TRX and PA separately (multibeaming, etc.).

This is a necessary solution for larger setups that include switching for multiple directions, multiple PAs, different RX and TX switching combinations, multibeaming, etc.

My Arduino code contains several lines added to the original TinyFSK by Andy K0SM. Thanks to this sequencer, the TRX and PA are switched on sequentially, resulting in the RF relay being switched without RF power. This limits the possibility of destroying or "burning" the RF relay contacts.

Attention! If you switch the internal jumper to COM port keying (RTS), the PTT sequencer will be deactivated. Then PTT TRX and PTT PA will be at the same time.

For more information about PTT sequencer timing, see the Arduino code information.

Arduino software

The device contains TinyFSK code modified by OK2ZAW – PTT sequencer added. You do not need to change anything.

You can also upload the original code from Andy K0SM or your own code to Arduino. The Atmega328 CPU contains the Arduino bootloader, so you can upload the code via USB directly using the Arduino IDE.

Software is under MIT "Expat" license. We are not responsible for any damage

Arduino pinout for your own code:

D8 = LED ON (TNC booted OK)

D10 = PA PTT with sequencer

D11 = FSK keying

D13 = TRX PTT

More at: HamParts.shop