Alex, I am using the MFJ-1225 RTTY / CW Receive Computer Interface" I purchased off eBay "used" for $24 (shipped) about 2 months ago. I couldn't design and build a simple interface package for less than that price. Connecting to my T102 via the two-wire "Kantronics" connection on the back. I found that the unit works well, but according to their schematic, the switches for RTTY / CW and NORM / REV don't do what they say in reference to the connections on the back. The NORM / REV switch is actually choosing between RTTY and CW outputs from the "XR-2211 FSK Demodulator" I.C. feeding the RTTY / CW switch selection which is choosing the Normal or Reverse connections on the "General" output connectors. There was also a missing wire to GND and missing current limit resistors to the L.E.D.s on the schematic. Usual MFJ attention to detail. The MFJ-1225 is a "crippled" version of the MFJ-1224 unit which also has "transmit" control and is much better designed.
I just leave the RTTY / CW and NORM / CW push switches out, and the "Kantronics" connection to the T102 works. I also changed L.E.D.s to modern "High Efficiency" types and re-calculated the current limit resistors. I used red for Power, green for Lock and yellow for Data. The CMOS inverters driving the old style L.E.D.s don't have the current output needed to make the brightness very visible. They should have used NPN transistors. I tested the unit with a "TTY audio feed" from Amateur Radio Teletype (RTTY) <https://www.rtty.com/> as this was a nice clean source. Finding clean sources on the shortwave is more difficult. Amateur radio can sometimes be received, but RTTY is not used much other than "contesting", and the transmissions are very short and sporadic. Hard to get the radio tuned in, and then they are gone. Here in California, I can receive the RTTY marine transmission from KPH on Saturdays. Regards, PeterN On Wed, May 6, 2026 at 3:18 AM Alex <[email protected]> wrote: > What are you using as a TU? > > I was toying with the idea a few years ago of building a minimal RTTY > interface for my T102 with a couple tone decoder ICs, but I ended up > working on MFORTH instead. > > > On May 6, 2026 7:22:24 AM UTC, Peter Noeth <[email protected]> wrote: > >> B9, >> >> I was working on a RTTY decoder, and I was using the BASIC program " >> RTTY.BA (https://ftp.whtech.com/club100/tel/rtty.ba)" and "RTTY.DO ( >> https://ftp.whtech.com/club100/tel/rtty.do)" as a guide. This program >> will receive a serial data string on the RS232 port from the "Terminal >> Unit" (which converts two alternating audio tones to digital "1" and "0" >> levels. It can also send data to the "Terminal Unit" to change the digital >> "1" and "0" levels to the same two audio tones. >> >> I wanted to make a program only for receive. I was using the "RTTY" >> program to understand how the PIO timer, which is used for the UART baud >> clock, was set to make the UART work at the odd speeds that were used "in >> the old days" by the BAUDOT encoded teletypes. >> >> John, >> >> The "Inside the Model 100" book by Carl Oppedahl does not list FF8Dh. >> The last address noted is FF8B which is noted as "address of baud rate". >> >> I have seen the notation in the "Covington ROM Map", and I believe this >> is where Ken got the same notation in his ROM listing (in his personal >> library on the Club100 page). But it doesn't seem that Robert Covington >> ever wrote a book on the Model 100. For such a detailed ROM listing, I >> would have expected that he would have. He must have been involved in >> accessories for the Model 100 in some capacity. >> >> Regards, >> PeterN >> >>
