Some years ago, the ARRL decided to stop issuing a DXCC certificate for just RTTY and merged the various digital modes all together for a single ‘digital’ certificate. I obtained the ‘digital’ certificate back in 2012 with just RTTY QSOs and was always a little sad that my certificate said ‘digital’. Last year, I heard […]
The post DX Century Club – RTTY first appeared on QSO365.QSOs made: 2,022DXCC entities worked: 141New DXCC entities worked: 4Total DXCC worked and confirmed: 286 Solar cycle 25 is really starting to ramp up now and this is demonstrated clearly by the fact that for the first time in many years, the country I’ve worked the most is the USA with 436 QSOs. Unsurprisingly, 15m is […]
The post Review of 2022 first appeared on QSO365.I’ll kick off with the statistics for the whole of 2021 and then go into the details. QSOs made: 8,265Unique QSOs made: 5,776Average QSOs per day: 22.6Days missed: 0 <- This is the most important statistic, it means that QSO365 #3 was a success. DXCC entities worked: 168New DXCC entities worked: 1Total DXCC worked and […]
The post QSO365 #3 is complete – Ten QSOs per day in 2021 first appeared on QSO365.
September 1985, I purchased a Kenwood TS-430S and became more active in amateur radio. In the apartment where I was living, I snuck wires out of a second floor window and began to make contacts.
In October, I got the notion to try some Radio Teletype (RTTY). I built a demodulator using a circuit I've forgotten. Perhaps it used a couple of NE567 chips. Having a demodulator, I needed to translate the five-level Baudot characters into ASCII that I could display on the terminal.
(I purchased a Wyse 85 VT-220 emulator terminal in August of 1985, so I was no longer constrained by the 64x16 screen and 1200 bps limitations of the CT-64)
I wrote a program for Flex09 to decode 45 Baud RTTY by bit-banging a PIA pin. I couldn't use the MC6850 ACIA, because it does not support 5 bit characters.
A delay loop established character timing:
Each pass through the loop consumes 8 clock cycles. With the right value loaded in X, fairly precise timings could be accomplished. A value close to 250 would be 1 ms on a 2 MHz machine. By calling this loop repeatedly, timings of 11 and 22 ms are measured.
I connected the demodulator output to PIA Port B, pin 0. The program looks at this pin, waiting for a zero. Finding one, it calls the delay loop for 1 ms and checks again. If the pin is still zero, it waits 10 ms and checks Port B pin 0. A continued zero at this point indicates a start bit. The 11 ms total delay places us right in the middle of the start bit.
The next sequence waits 22 ms and then samples of value of Port B, pin 0. It does this five times. These samples are shifted into a byte value, which used to look up an ASCII character in one of two tables -- one for letters, and one for figures -- according to the shift mode. This character is then sent to the terminal, and we go back to waiting for a start bit.
The resulting program is about 300 bytes long. Despite the simplicity, I had little success decoding RTTY signals.
In hindsight, there are several reasons for this.
At some point, I distinctly copied "RY RY RY RY RY RY RY" from someone, but not much else. Later, I figured out this meant my program, at least, was working.
In November 1986, I decided to use serial chip that could do five-level Baudot. The MC6850 only allows 7 and 8 bit characters, so I needed a different chip. The NS8250 could do 5, 6, 7 and 8 bit characters, and sports a programmable bit rate generator for all the common RTTY rates. Hence, I added an NS8250 UART to the baud-rate generator board.
Funny, though -- I never wrote software to use the NS8250. In February 1989, I removed the NS8250 and its associated circuitry.
I didn't become active in RTTY on the air until 2005, using Cocoamodem.
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