FSK/CW Optically Isolated PC Interface for Keying Ham Transmitters and Transceivers

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Summary: This page describes an FSK/CW PC interface that will allow a PC to key your transmitter producing either a pure FSK or CW signal. The interface is fully optically isolated and RF filtered. Interface board kits or fully assembled and tested boards are available from W3YY. The cost of the kit version, including the PC board, all parts for the board, mounting hardware, and assembly instructions, is $29.00 plus $4.00 shipping and handling in the United States. The cost of the fully assembled and tested board with mounting hardware and installation instructions is $44.00 plus $4.00 shipping and handling in the United States. Interface boards for the FT-1000, FT-1000MP, FT-450, or IC-720 series transceivers are $5.00 more.

I'm a relative newcomer to RTTY, having just started operating RTTY a few years ago, but I really enjoy the mode. What got me going was the availability of free software (MMTTY) that allowed me to operate RTTY with just my sound card equipped PC and normal radio. As much fun as those old teletype printers were, I no longer needed one to start operating RTTY!

Like most newcomers, I initially took the easy way and elected to use AFSK (Audio Frequency Shift Keying) to produce my RTTY signal. This method works by using PC software to generate audio mark and space tones that are sent to the audio input on the transceiver. When you use this method, you're transmitting a SSB signal that contains the mark and space tones. It usually works FB, but like the old Collins 32-S1 that created CW by keying an audio tone into the SSB circuit, you still have a suppressed carrier and, if you don't watch the audio drive level, you'll be splattering.

In 2009, I decided it was time to go to true FSK RTTY operation. What's the difference? With FSK, you are generating a pure CW signal that is being shifted between the mark and space frequencies. You no longer have to worry about your audio drive level. You know you have the purest RTTY signal on the band!

It's easy with most modern transceivers to operate FSK. They provide an input that can be keyed from the PC if you have the right interface. I use MMTTY software for everyday operation and N1MM software with MMTTY in contests. WRITELOG and other ham software will also work. The needed interface is the traditional open-collector solid-state circuit that has been in use since the beginning of ham software development.

My first impulse was to throw together a cheap breadboard-style interface using transistors, but I had always thought that optically isolated couplers, http://en.wikipedia.org/wiki/Opto-isolator, would be the best way to go. The optically isolated couplers are IC-type devices that contain both an infrared LED and photo detector. The output conducts only after seeing the "light" produced by the internal LED. As a result, there is no direct electrical coupling between the input and output. The advantage is that this can prevent unwanted DC and RF coupling between your PC and transceiver.

Next, I rejected the idea of producing yet another breadboard-style interface that looks like a piece of junk. Instead, I thought, why not do this right and build a nice PC board for this project that could be used alone or placed in a nice shielded case.

For the FSK work I needed one interface circuit to do the mark/space RTTY keying and another to key the transmitter via the PTT input. I decided to also add a traditional CW keying interface to the new board so it could replace my old jury rigged non-isolated CW keying interface as well. The result was a very nice interface board that does both my FSK and CW keying with full isolation and RF filtering. Just one cable from the serial port on the PC to the interface handles FSK, PTT, and CW. The board is 1-3/4" by 2-1/2" in size. See picture below.

The FSK/CW Interface Board is a professional two-sided, plated through hole, PC board constructed of FR4 flame-resistant rated material. The fully assembled and tested board is pictured below.

I've been using this board successfully with my FT-2000 and it will work with any modern transceiver that I know of. Another great advantage is that now, when I operate RTTY, I can set the transceiver mode to RTTY and the frequency that my transceiver reports to my logging program is correct. No longer do I have to add or subtract 2.1KHz from spots received or sent like I had to do when operating AFSK using a SSB mode!

If you like RTTY, use FSK. It's pure and will give you the best sounding signal. Click on the links below to see how to wire this interface board to your PC and transceiver.  You can see independent and unsolicited reviews of the FSK/CW Interface Board at http://www.eham.net/reviews/detail/8519.

For more information on RTTY, see AA5AU's excellent web site at http://www.aa5au.com/rtty.html.  For interface specific issues see http://www.aa5au.com/rttyinterface.html. On his site, Don provides a wealth of RTTY information for both newcomers and experienced RTTY operators.

Click on the links below for more information.

General Installation Guide for all Transceivers
Installation Guide for the Elecraft K3 Transceiver
Installation Guide for the Yaesu FT-450 Series Transceivers
Installation Guide for the Yaesu FT-950 Transceiver
Installation Guide for the Yaesu FT-990 Transceiver
Installation Guide for Yaesu FT-1000MP and FT-1000MKV Transceivers
Installation Guide for Yaesu FT-2000 and FTdxDX 5000 Series Transceivers
Installation Guide for the ICOM 703 Transceiver
Installation Guide for the ICOM 706 Transceiver
Installation Guide for the ICOM 718 Transceiver
Installation Guide for the ICOM 746 and 756 Series Transceivers
Installation Guide for the ICOM 761 Transceiver
Installation Guide for the ICOM 765 Transceiver
Installation Guide for the ICOM 781 Transceiver
Installation Guide for the ICOM 7000 Transceiver
Installation Guide for the ICOM 7200 Transceiver
Installation Guide for the ICOM 7600 Transceiver
Installation Guide for the ICOM 7700 amd 7800 Transceivers
Installation Guide for the Ten-Tec OMNI VI+ Transceiver
Installation Guide for the Ten-Tec OMNI VII Transceiver
Installation Guide for the Ten-Tec Orion Transceiver
Installation Guide for the Kenwood TS-480 Series Transceivers
Installation Guide for the Kenwood TS-570 Series Transceivers
Installation Guide for the Kenwood TS-590 Series Transceivers
Installation Guide for the Kenwood TS-2000 Series Transceivers
Service Bulletin 2 - PTT operation with FT-1000MP Series Transceivers

The FSK/CW Interface Board is now available in both kit and assembled form.

The kit includes the printed circuit board, all parts for the board, mounting hardware, ferrite beads, and instructions. All components are of the thru-hole type, which are easy to install and solder. No surface mount components are used.

The assembled board includes the printed circuit board with all parts installed and tested. Mounting hardware, ferrite beads, and instructions are also included.

No cables are provided. For either the kit or assembled board you will have to provide and install the cables that connect the board to the PC and transceiver and, if desired, a case. The interconnection diagram provided with each board provides information regarding what kind of cables are required and how they should be installed.

Complete assemblies with case and cables are not currently available.

Finally, are you one of those with NO COM PORTS - ONLY USB? I've got the perfect answer, a USB-to-Serial Port Converter that allows you to use my interface with a USB port and works with N1MM, MMTTY, and other software as well. This is a high-quality commercial unit with the desirable FTDI chipset, a shielded 10" USB cable, and a 9-Pin DB9 Male COM Port connector. Comes with drivers for XP, Vista, Windows 7 and older OS too. Complete directions for installation and setup with my interface, N1MM, and MMTTY are included. $25.00 plus $3.00 shipping and handling.

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