SignaLink True CW Keying

What’s a SignaLink?

A SignaLink is a small unit manufactured by Tigertronics which functions as an interface between a computer and transceiver to enable the use of digimodes. The latest version of the SignaLink connects to the computer using a standard USB cable. The connection to the transceiver is made by a RJ45 (ethernet) socket on the rear of the unit. The other end of the RJ45 cable is terminated to suit the radio. Wire jumpers inside the unit allow the SignaLink to be used with any radio. Tigertronics also supply pre terminated RJ45 cables and pre-configured jumper blocks.

In use, the SignaLink is essentially an external USB soundcard and transmit/receive controller. When the radio is in receive mode the unit converts the received audio to data and sends it to the computer via the USB cable. Suitable software then decodes the digitised signal. For transmission the software sends the data to the SignaLink unit where it is converted into an audio signal and then passed to the transceiver. The logic within the unit also places the transceiver into transmit mode while it’s receiving the data stream.

Connection to Kenwood TS-850

The Kenwood TS-850 transceiver has a 13 pin accessory (ACC) socket on the rear panel. This is of interest as although it was originally designed with using a TNC it can be used quite successfully with the SignaLink. Of particular interest are pins 3, 4, 9 and 11 of the ACC socket.

  • Pin 3: Receiver audio output
  • Pin 4: Ground
  • Pin 9: Standby
  • Pin 11: Audio In

What is interesting is the fact that by connecting pin 9 to ground, the radio is placed into transmit, with the microphone input muted. However any audio passed to pin 11 is transmitted making this socket ideal for digimode operation. If the RJ45 cable is terminated to the correct pins and the jumpers installed correctly inside the SignaLink everything should work fine.

Using this “standard” method of connecting the unit CW with the unit is only possible by configuring the PC software to send the CW as an audio tone and transmitting using SSB. This method works quite well, but it must be remembered that the SSB frequency may need tweaking to align with the CW frequency.

Modification to allow true CW

Any modifications will invalidate any warranty and are carried out at your own risk.
This modification also requires the use of a serial port adapter, you can build one for pennies read this article, and two 1N4148 diodes.

The design of the SignaLink allows easy access to the internal components. Simply remove the four hex-head set screw from the front panel and withdraw the entire panel and PCB assembly forwards. I wanted to keep things easy to disconnect from each other, and as I don’t use the “monitor” function of the SignaLink, I decided to make use of the socket provided.

signalink pcb modsLooking at the rear edge of the PCB we can see the RJ45 connector and the USB connector. Between them is the Monitor socket, this simply allows the transmission audio from the PC to be routed to speakers. To be able to use this socket it must be completely isolated from the rest of the circuit. Fortunately, this is quite easy to achieve. Simply cut the PCB tracks as indicated by the red circles. The ground track (nearest the rear edge) is quite short and leads to the plated through hole. The second track that requires cutting leads from the rear of the socket to the small SMD capacitor. It is important to cut both these tracks to ensure isolation of the socket.

jumper connectionsTake a short piece of solid core wire and solder one end to the isolated ground connection of the monitor socket. Route the other end to one of the holes in the jumper block marked “GND” – you should have one spare, this now becomes the ground connection. If there is no spare location in your unit, you will have to solder it to another wire that’s already in a hole marked “GND”.

The next stage will vary depending on how your particular SignaLink is configured. For most configurations you will have at least one of the numbered holes free. In my case, I have numbers 3, 6 and 7 unused. Number 8 is already used for the PTT, thus I decided to use number 7 for CW keying.

SignaLink Jumpersjumper connectionsCut the anode, opposite end to the band marking, to a length of 5mm or so. This end of the diodes will be inserted into holes 7 & 8. You now need to carefully bend, and cut the length to suit, the cathode of one of the diodes so it can be inserted into the hole marked PTT. Bend and cut the cathode of the second diode so it can be soldered to the cathode of the first diode. You now need to take another short piece of solid core wire, I found one of the original jumpers to be just the right length, and solder it to both diode cathodes. The other end of this wire is soldered to the isolated pad near the rear of the monitor socket. Hopefully, the pictures can explain it better 🙂

Terminating the RJ45 cable

At the radio end of the RJ45 cable, it will either be ready terminated with a suitable plug, or be ready for a suitable connector to be installed. Here you have a choice of methods to connect the CW key to the radio. First, however, you must trace the wire in the cable to the one that corresponds to the number you used at the jumper block. If you wish, you may join a length of wire to the correct core of the RJ45 cable and terminate it with a plug suitable for the cw key socket on the radio. Normally you won’t need to extend a ground connection to the cw key plug as the cw socket normally uses the radio ground.

An alternative method which I have used is to make use of an unused pin in the ACC socket of the TS850. To do this I did a simple modification inside the radio to connect the cw key socket to pin 1 of the ACC socket.

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