AA8IA Amateur Radio

FSK RTTY Operation


I don’t operate RTTY much. When I do, I use AFSK with my Signalink USB. Seems to work alright. However, there are two problems with AFSK.

  1. When you change frequency/tuning and/or power levels, you end up having to adjust audio levels to ensure that your audio device is not overdriving the radio with audio. This is a real pain in the ass.
  2. When using AFSK, you have to use an SSB mode on your radio. On radios that have a RTTY mode, the filtering is usually better if you use the RTTY mode. In order to use the RTTY mode you must run FSK. I use a Yaesu FT-950. I’ve read where people claim you can get the same filtering in PKT mode and running AFSK on the FT-950, but this hasn’t been my experience. The filtering seems better, but it definitely isn’t the same filtering that you get if you put the radio into RTTY mode.

So, now I am on a quest to get FSK operational on my FT-950. I’ve got one serial port tied up with the CAT control on the radio. I’ve got four USB ports. One of the USB ports has a wireless-N dongle in it. Another USB port has has a Serial-to-USB adapter in it for my CW keying interface. Another USB port has a mouse plugged into it. And the last USB port has my Signalink plugged into it.

In order to use FSK, I would need to create an FSK circuit that uses Pin 3 (TXD) on a DB-9 of a serial port. Output would be fed to Pin 4 on the RTTY/PKT jack on the back of the FT-950. The problem with this is that the RTTY/PKT jack is already in use — my Signalink USB is plugged into it. (the Signalink USB is not using Pin 4 though).

I need to get TXD off of a serial port to feed the FSK circuit, and then I need to take the output and feed it into Pin 4 of the RTTY/PKT jack on my FT-950. I don’t want to use another serial port just for this. So I’m going to attempt to get TXD off of Pin 3 of the serial port that is handling my CW keying, since the CW keying interface is not using Pin 3.

Signalink USB jumper wiring for Yaesu FT-950 6-pin mini DIN

Signalink USB JP-1

My plan is to tap Pin 3 (TXD) and Pin 5 (GND) inside the DB9 enclosure of the CW keying interface, run that wire pair out of the DB-9 enclosure and attach the FSK circuit (very small, will use shrink tubing to button it up). The single wire out of the FSK circuit will be routed into a hole (with grommet) inside the Signalink USB to Pin 4 on the jumper block inside the Signalink USB which currently is not in use and supposedly is routed down the RTTY/PKT cable to pin 4 on the RTTY/PKT jack. In the graphic to your left (taken from the Tigertronics website) you can see that Pin 4 on the right side of the jumper block is not jumpered to anything. This goes to the 9600-baud data / FSK-In pin on the RTTY/PKT jack of the Yaesu FT-950. This is where the output of an FSK circuit should be piped in.

In case you all are wondering why the Signalink doesn’t handle FSK by default, it is because the Signalink USB is a USB-only device. It has no connections to a serial port. And you need to have access to a serial port signal (in this case TXD) for FSK keying. If Tigertronics wanted to support FSK with the Signalink USB, it would require that the Signalink USB also attach to your PC via a serial port as well as the USB port. I can certainly understand why Tigertronics didn’t want to do this. For one, most new PCs do not come with a serial port, but all come with multiple USB ports.

Written by Mike

September 9th, 2010 at 11:53 am

9 Responses to 'FSK RTTY Operation'

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  1. Great post. Why would the Signalink require an actual serial port to support FSK? It sounds like this could be handled over the existing USB connection.

    - Roger

    Roger Wilco

    11 Sep 10 at 9:51 AM

  2. If it could, you’d have to tell me how. I’m not an electronics engineer. From what i’m reading, FSK requires an RS-232 signal for keying. Supposedly, with a third party DLL a few different programs will allow you to use something other than the recommended Pin 3 (TXD) off of the serial port, like DTR or RTS. But, no matter how you slice it, everything I read says it still needs to be a serial port signal. Must be a timing thing. I don’t know JC.


    11 Sep 10 at 11:20 AM

  3. JC – My original post said that my Signalink was plugged into a USB-to-Serial adapter, which was an incorrect statement and was likely what lead you to believe I could pull Pin 3 TXD off of the Signalink. In reality, the Signalink is a USB-only device.


    11 Sep 10 at 11:23 AM

  4. Any idea what type of sound card the Signalink shows up as in device manager?

    Roger Wilco

    11 Sep 10 at 11:32 AM

  5. By now you already know its a TI chip. Thanks for your contribution “Roger”


    11 Sep 10 at 1:16 PM

  6. IF Tigertronics wanted to, they could easily put an FTDI (or similar) USB to RS232 chip inside the SignaLink to be able to do FSK.. then the jumper to pin 4 could easily be done.

    As it is, the SignaLink uses a relay hooked into the audio system to key the radio’s PTT, so I doubt that they’d want to change anything within the SignaLink to accomidate true FSK.


    9 Apr 12 at 4:20 PM

  7. I agree – it’s simple, and cheap, for them to do it if they wanted to. Obviously they aren’t interested. That’s too bad. I think it’s a great interface, so I won’t bash it. But it definitely would be more useful for the hardcore if they did as you suggested.

    I gave mine to a friend to use indefinitely since I prefer to use FSK [and enjoy the better radio filtering] when at all possible.


    9 Apr 12 at 4:28 PM

  8. Want to use FSK to take advbantage of RTTY filters…

    Here is a very basic but still nice little “tip”.

    You can (with most modern radios) take advantage of your FSK-RTTY filters when using AFSK RTTY….
    Simply operate the radio “split”, with the Tx and Rx frequencies the same but in different modes.
    Tx is set to SSB or DIG mode (whatever and however deals with AFSK transmissions)…
    Then set your Rx to the same frequency but in “FSK-RTTY” mode, and you can now select your RTTY filters.
    Probably not all radios will allow this nice little trick but most will.

    Neil - G4ZLP

    23 Sep 12 at 5:02 AM

  9. Excellent suggestion, Neil. Thanks for mentioning it. To be honest, I never gave it a thought to do that. That’s achievable on any modern radio without much ado at all. Although, I’m not sure how many radios support VFO-B tracking VFO-A in frequency. My FT-950 doesn’t. So unless I’m CQing in a contest on one freq for a lengthy period of time, it can become very tedious very quick to have to switch to VFO-B and tune it to where VFO-A is.

    BTW, My Pro interface is still working great. It’s in use any time I’m at the radio.



    24 Sep 12 at 9:01 PM

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