How I ran FT8

General view of the assembly in a hamshack enriched with digimodes
General view of the assembly in a hamshack enriched with digimodes


With this article, I would like to share with you my own experience with DIGI modes. Everyone starts with that, what is available. For me, it's Kenwood TS-870S and older, but capable laptop. Question is, how to connect them, to cooperate in order to operate on FT8. TS-870S bad COM port, can also be used for PTT, I thought so. So there was still a way to connect the audio paths. Many articles on this topic agreed on the need to separate the computer ground and the TCVR to prevent the penetration of the RF signal into the computer.. It is recommended to use transformers with gears as a solution 1:1. In practice, I have not seen a difference with them, with or without them. Is possible, that interference has occurred with cabinet computers with insufficient grounding. The laptop also probably doesn't have a problem.


Next, a way had to be found, how to connect signal paths. Each manufacturer uses a different type of connector. In this case ACC2. A schedule of pins was given in the manual (pins). I didn't want to use the microphone input on the front panel, nor speaker output, to avoid setting the buttons each time the mode is changed. With the ACC2 connector, special care must be taken when soldering, the pins are close to each other. I used shielded cables. On page, where a laptop is connected, are jack connectors 3,5 mm, stereo, while one channel remains unconnected. I connect the cables and after turning on the WSFJ-X program, no stations were displayed in the window. I'm synchronizing the time and the background is starting to fill up with active stations in the band. Eureka! Time is to blame, as sung in one song. It remains to connect the broadcast part. I will set the parameters for the radio as CAT, PTT and audio input and output. However, there is no indication when the broadcast is turned on, no indication, that a signal has been sent. The reason was simple. The TS-870S switches the audio input in ACC2 via another PTT input, like the one via COM. The one in ACC2 called PKS had to be used. Richer for more experience, I set out on a journey further. What does it mean to add a PTT circuit. I chose the S56AL solution because of its simplicity and reliability. The circuit calculates the signal from the computer via the RS-232 interface. I used the RTS pin, but the DTR pin also plays the same role. Because modern computers no longer have RS-232 ports, I used a USB converter. Another option is to use a USB cable with an FTDI adapter, thus eliminating the need for a converter . Isolating transformers (in fact, Tesla chokes with a symmetrical winding) were not ultimately needed, the signal was clear, undistorted even without them, In addition, they muted the signal. Many audio signal connections are designed for cabinet computers, which have an otherwise resolved electronic ground, as such a laptop. In the end, I chose the ZS1AN connection for Kenwood devices. Wiring diagram with the first version of the PTT circuit (PTT circuit) is in the picture 1. D3 is used to signal the active state – on air. D2 glows green when idle. The DB9 connector is used if we have a classic serial port, which is no longer used in ordinary computers, so it can be replaced by the circuit of the picture 2 (see below). DTR can be used instead of RTS (pin 4). Line in and line out are inputs and outputs from the sound card. An external USB audio card was used, to separate audio paths from laptop applications. Nobody probably wants to, to get these unwanted sounds into the broadcast signal. In addition, the audio input and output levels are set only once, at the first start and there is no need to fine-tune anything. I set the AF input value for PKT.IN to 10 mV. Pins in the right part of TX / RX circuit and PTT circuit (TX circuit / RX circuit, PTT circuit) directly correspond to the numbering and designation of the ACC2 connector. The values ​​of the components are given in the diagram.


A picture 1 Wiring diagram with 9 pin D-Sub connector

A picture 2 differs only in PTT circuit. In the USB to FT232RL section, the FT232RL circuit with TLL logic levels was used, allowing connection directly to the USB port. D2 is a classic semiconductor diode of virtually any type. The circuit had a negated RTS signal, therefore, it is connected to the supply voltage.



A picture 2 Wiring diagram, The PTT circuit has terminals for a USB to UART FT232RL converter

So much for the electronic part. It took me a while to set up and master the program for FT8, already mentioned WSJT-X. The program comes with a complete and understandable manual, which is also translated into Czech . The setting itself consists in inserting a call sign, PTT method selection (CAT, COM port or VOX) and audio input and output device selection. These were the most necessary items and who is not afraid to experiment, can try, what varied functions the program is packed with. It was necessary to get acquainted with the controls, to know, when to broadcast and when not. Is known, that many functions are automated, which doesn't stop anyone from learning, what's going on in the background. A detailed description of the control is another chapter, there are plenty of available manuals. In addition to the mentioned manual, there is a summary of operating types from ZL2iFB in English.

In conclusion, I can say with certainty, that the connection works, I am currently using the connection according to fig. 2. I already have some nice routines behind me, and DX connections. The operation from the home station is thus enriched with one new mode.




Open box (85 x 45 x 30). View from the side of the joints. The connections were made by scraping the copper layer. A half-size box would suffice



CAT cable to control TCVR from applications. Because the laptop did not have a DE-9 serial connector, RS232 to USB converter was used (black color)



Digimode devices with cables. The white cable is used to connect to the TCVR to the ACC2 connector. The connections of the audio signals from the TCVR and the laptop and PTT circuit are located in a white box. An external sound card was used to connect the sound to the laptop “3.5mm External USB to 3D Audio USB Sound Card Adapter 7.1 Channel Microphone” . PTT is connected to the laptop via a USB cable with FT232RL circuit

Martin Jánoš, OM1MJ


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