Presentation on theme: "RTTY A Primer on the Second Digital Mode Plus a bit of PSK K2YG Jan 9, 2012."— Presentation transcript:
RTTY A Primer on the Second Digital Mode Plus a bit of PSK K2YG Jan 9, 2012
History The first digital radio mode was make/break spark gap transmission, followed by CW, or more properly, Morse or any other on/off switching code over a CW (continuous wave or carrier wave) radio signal. Teletype over wires started in 1849 Emile Baudot (baw-DOUGH) invented modern 5 bit TTY code in 1874; still used today
RTTY (Radio Teletype) History First radio use in the 1920s First commercial use in the 1930s Military use started in the 1930s and replaced on-off signal with two tone frequency shift. TTY and RTTY in various forms were the backbone format for information transmission until superseded by computer systems.
History in Amateur Radio 1946: First contact; used make-break keying. Frequency Shift (FSK) found to be superior in late 40s, but not allowed by FCC regulations. FCC allowed FSK in 1953 Bulky noisy teleprinters supplanted by personal computers in the 80s, beginning the explosion in Amateur RTTY and other formats. Click here to hear what RTTY sounds like:
What is RTTY Radio Teletype is the transmission and reception of Baudot coded text over radio links using Frequency Shift Keying. The Baudot code characters consist of start and stop bits, with five information bits in- between.
Baudot Code Logic 1 or Mark 0 or Space Character: Y Can also be 6 Character: R Can also be 4 Logic 1 or Mark 0 or Space Bit 1 Bit 2 Bit 3 Bit 4 Bit 5 Character: B Can also be ? Bit 1 Bit 2 Bit 3 Bit 4 Bit 5 Logic 1 or Mark 0 or Space Start Bit Bit 1 Bit 2 Bit 3 Bit 4 Bit 5 Stop Bit Character B showing start and stop bits Logic 1 or Mark 0 or Space Bit 1 Bit 2 Bit 3 Bit 4 Bit 5
RTTY Speed Amateur RTTY usually operates at a speed of baud, or approximately 60 words per minute. Other speeds are occasionally used, such as 50 and 75 baud. Commercial RTTY services (very few left) may use other rates and frequency shifts. Baud rate is the number of symbols per second. Each mark or space is a symbol.
Baudot Register Shifting 26 Letters, 10 numbers and a few punctuations and control codes require more than the 32 combinations possible with 5 binary bits. 59 letters, numbers, punctuation, symbols and functions are possible by using two shift registers.
Bit Pattern Down-Shift or Letters Up-Shift or Figures 00000<> 00001T LF 00011O Space 00101H% 00110N, 00111M CR 01001L) 01010R G& 01100I P C:
01111V; 10000E Z" 10010D$ 10011B? 10100S# 10101Y F! 10111X/ 11000A W J' 11011Shift Down (LTRS) 11100U Q K( 11111Shift Up (FIGS)
Shift Characters in Place To transmit characters from both shifts, shift codes are inserted automatically in the string: K FIGS 2 LTRS Y G In this case, six 5 bit characters are required to transmit the 4 characters typed. Special characters include space, line feed, carriage return and up and down shift. Once shifted, shift usually stays in FIGS until LTRS character is sent, and vise versa.
Garbled Shift Characters Signal report sent with good vs. garbled up-shift (FIGS) character. Good Garbled RST 599 RST TOO K2YG KWYG This is a very common occurrence. QWERTY keyboard relationship on next slide.
Figures-shift numbers on the top line of the keyboard correspond to the second line letters located below & a bit to the right of each number Thus a missed FIGS shift would cause the 599 to print as TOO
RTTY Keying Methods Two Methods: Frequency Shift Keying (FSK) and Audio Frequency Shift Keying (AFSK) FSK shifts an un-modulated carrier between two radio frequencies usually spaced 170 hz. AFSK modulates an SSB signal using two 170hz spaced tones which simulate the FSK signal. FSK has very few RF artifacts. AFSK can have suppressed sideband and carrier leakage, as well as modulation products, so proper transmit audio level is important.
RTTY Keying Methods AFSK: Characters typed are converted by software and a sound card into two audio tones to be fed to microphone or data connections on the transmitter. FSK: Characters typed are converted by software into a make-break control voltage which keys a shift in the transmitter carrier radio frequency.
Audio Tones and RF Relationship RF Readouts for Audio Frequency Shift Keying (AFSK) vs. Frequency Shift Keying (FSK) 20 Mtrs, Lower Sideband. Space Mark Suppressed (2295 hz) (2125 hz) Audio Tones Carrier (0 hz) RF Carriers khz khz khz FSK shows mark or space RF frequency on radio readout. AFSK shows suppressed carrier frequency on readout. AFSKFSKAFSKFSK
Receiving RTTY is really AFSK because the computer sound card and software convert the audio tones you hear into characters Space Mark Suppressed (2295 hz) (2125 hz) Audio Tones Carrier (0 hz) RF Carriers khz khz khz AFSKFSKAFSKFSK
RTTY Waveform Time Mark Amplitude Zero Amplitude at frequency shift Space Amplitude
RTTY Customary Operating Frequencies Band General Contests Unusual , NA NA NA
RTTY Band Non-Contest Popularity Band General Usage Infrequent A few nets , Moderate Growing Most Popular Good when open Heavy use if open Surprisingly good Excellent if open On all bands from 40 to 10, there will be more PSK than RTTY activity except during contests and presence of rare DX.
Frequencies to Avoid Avoid PSK segments at , , , and Avoid Internation Beacon Project beacons (18) at 14100, 18110, 21150, 24930, & FCC Regulations actually allow HF data operation on any amateur frequencies on which Phone is NOT allowed.
License Level Restrictions? Notice that, contrary to CW and SSB operation, General Class license holders can operate on all customarily used RTTY frequencies. Novices & Techs can operate digital (as well as CW & SSB) on 10 Meters.
Simplex vs. Split Operation Split operation by DX stations is more frequent on RTTY because of qrm by calling stations. Even moderately rare DX stations may operate split to improve QSO rate. Operating split sometimes involves only two frequencies: the DX qrg and a calling qrg up one or two khz. Rare DX split may occupy 10 khz or more. Study the DX listening pattern before calling. Calling frequencies are usually up. Split operation is extremely rare in contests.
REMEMBER THIS If you take home only one thing from this presentation, make it the link to AA5AUs RTTY Home Page Contains complete information on setting up and operating RTTY, and MMTTY software Also, join RTTY Contesting as a source for help.
RTTY Software MMTTY – Most Popular? – Free Write Log (not free) Ham Scope Mix W RCK RTTY (not free) RITTY – Not supported, not free but not sold anymore, DOS only, but is the best receiving program in existence (my opinion). There are many programs available. I am familiar only with MMTY and RITTY. Talk to other digitally active club members: K2EZR, KB2FCV, N2FYE, K2GLS, K2MUN, KC2WUF
Hardware you need to run RTTY Radio Computer with Sound Card Interface
RADIO Considerations Any TX/RX capable of SSB will work. Some can run RTTY, a key down mode, at full power; some can not. Check specs. Filter adaptability is important. Will the SSB filters allow a band pass centered on RTTY tones. ( /2 = 2210 khz center qrg). Alternate tones can solve this problem, but may cause others. FSK capable TX/RX usually do not have filter band pass problems
Computer Most currently supported RTTY software will run on Windows XP, Vista and 7. There are programs for other operating systems. Programs are not too demanding of processor and memory, but combined with logging programs like N1MM or Writelog memory and speed requirements increase. Computers w/o serial port will require either a USB serial adapter for PTT or use of vox. Resistance to RFI is important.
Interfacing Computer to Radio Buy a commercially available interface, such as Signalink, Rig-expert, Rigblaster, etc. -or- Build your own. Might be a good club project!
Home Brew AFSK Interfacing TX Audio Computer audio out to radio mic. May need some isolation or attenuation RX Audio Radio audio out to Computer audio in. PTT Line May require a USB to Serial Adapter CQ CQ DE K2YG K2YG K K2YG DE ST0R K2YG
Home Brew Interface Transmit Interface connects between computer audio out and mic connector To TX Mic Connector RF Bypass Capacitor 10k ohms Isolation Transformer 100 ohms From Computer Audio Out Transformer and capacitors needed only to resolve rf interference, audio hum, and other artifacts. Potentiometer can replace resistors.
Simpler TX Interface 3.5 mm plug to microphone jack on Tx/Rx
Receive Interface Receive audio can be connected directly from radio head phone, speaker, or dedicated constant level audio output if available. Isolation transformer and by pass capacitors may be helpful.
PTT Circuit PTT circuit using single transistor. A USB to serial adapter is needed if computer has no serial port; or use VOX (not recommended for contesting). Computer Serial Radio PTT Line Connector (Probably in Mic Connector)
A Much Simpler PTT Interface
FSK Interfacing Interfacing for FSK operation requires a transistor switching circuit similar to the PTT line shown before, connected between the computer serial or USB port and the FSK capable radios FSK input, instead of the TX audio line to the mic input. This is more problematic than AFSK if a USB to serial adapter must be used because of baud-rate specifications of USB adapters available.
MMTTY - RTTY Software Software written by JE3HHT, Makoto Mori, thus the program name. It is free and downloadable from: Excellent instructions and other RTTY advice is available at Screen looks like:
Demodulator Section displays most set up parameters such as filter, tuning, shift, and squelch control.
Control section: Manual transmit/receive toggle and some RTTY decoding options.
Macros: user pre-entered text sent by clicking buttons or using F keys and Control key plus numbers
Tuning Displays, including FFT, XY Scope and Waterfall
QSO Data, for automatic insertion in Macro qso content, and for log entry
Received Text Window
Text to be Transmitted Window Also known as type ahead
This is the way the Demodulator box should appear after opening MMTTY. Mark and Shift are set to standard RTTY values. In this setting, the Bandpass Filter (BPF) Squelch (SQ) and Automatic Frequency Control (AFC) have been turned on by the user.
It is actually best to leave the AFC off, and to tune the received signal very carefully. This assures you are on the same frequency as the other station without the possibility of moving out of your RX bandpass.
The BW menu controls the BPF bandwidth. 60, the default, is OK. The button sets the default mark, shift, BW and demodulator, as set on the decode page. The button automatically tunes in the RX signal by changing the RX mark and shift to match the received signal tones.
The button causes the TX tones to match the RX tones, assuring both stations are on the same frequency. However, using AFC can move your frequency far from the station you are calling, or cause the mark and shift tones to creep out of the radios band pass. Safest bet is to NOT use AFC or NET, and tune stations in carefully using the tuning displays. AFC is best used if someone calls you slightly off frequency, if youre in a net or if youre running a contest frequency.
Mark Menu sets alternative mark frequencies. If your radio does not have satisfactory filters at hz, you can change the mark to fit your filters. For example, Elecraft K2 filters cannot reach as high as needed, so a 915 hz mark is used. The shift should remain at 170. Stations you work will not be aware of any difference. If the default values are different, turn on NET to match TX tones to the new RX tones.
activates the squelch, which helps to avoid garbage characters caused by noise printing on receive. The squelch threshold is controlled by sliding the line in the middle of the level meter back and forth. Activates the notch function, which provides 1 or 2 notches between the mark and shift signals, indicated by a red arrow head (adjustable) on the FFT signal display. First use, requires right mouse click to initiate location on FFT display.
The button flops mark and space tones to allow working stations not observing the mark as lower rf frequency convention. (Upside-down) The button controls cycles through demodu- lator formats: IIR (default), FIR and PLL (PLL uses less CPU capacity). The Auto Threshold button should probably be off for signals near noise level.
Control Buttons The button forces and shows an up-shift or FIGS code being transmitted or received to shift to the figures register of the baudot code needed to print numbers. The button (unshift on space) causes the FIGS register to automatically return to the LTRS register when a space is received. This can help to avoid garbage print when a received LTRS code is garbled. There is much controversy about the efficacy and ramifications of this practice. The button turns on transmit and sends any copy in the transmit window. F9 does the same thing. The button returns to receive. F8 does the same.
FFT XY SCOPE WATERFALL The FFT Display shows frequency across the horizontal axis and amplitude vertically. Width of display is adjustable from 0.5 to 3 khz in five steps. It is best to turn off AFC and tune your radio so the mark and space signals are on the two lines. My opinion
FFT XY SCOPE WATERFALL If you click a spot in the audio passband, MMTTY will center that spot in the FFT display. This action changes the mark and space frequencies. If AFC is on and the signal has not already been tuned, a left click between the mark and space signals moves the band pass close enough to allow automatic tuning. This also changes the mark and space frequencies and can be quite confusing. Right clicking the FFT displays turns on the notch function centered at a red arrow head.
FFT XY SCOPE WATERFALL The XY display is a computer representation of the oscilloscope crossed-ellipses display that used to be the way RTTY signals were tuned, in the days of TUs (terminal units) and oscilloscopes. For perfect tuning, one ellipse should be vertical, the other should be horizontal. If they are not at exact right angles, the station youre working is not using the same shift as you (which should be 170 hz ). A few stations use 200 hz, sometimes because they are running hardware designed for 200 hz shift.
FFT XY SCOPE WATERFALL Some hams like the waterfall display that has become popular for PSK31. MMTTY offers a waterfall that is directly lined up with the spectrum display above it. You can use this display to tune your radio, rather than use AFC. Displays can be turned on and off, and adjusted in the view menu.
More Parameter Choices There are many parameters than can be changed in MMTTY. One of the most important is the setup MMTTY item in the Option menu. All the parameters discussed here and many more are controllable on these screens. The next slide shows one of six screens in which most parameters can be set. Information for these will require another session. I do not mess with most of them! The View and Profile menus on the bar shown above include other options.
DONT WORRY In most cases you can run MMTTY without even looking at the Set Up MMTTY screens.
Macros Ctrl + Number initiated text and function memories F-key initiated text and function memories
Ctrl + Number initiated text and function memories F-key initiated text and function memories These macros require the control key plus a number to be pressed simultaneously. Also, a mouse click will send the macro. Macros can turn on and off the transmitter, as well as perform additional functions. These macros require only an F key, or a mouse click
Macro Content Sample Macros can be defined by right clicking on the macro button. This particular macro, sent by turns on transmit, sends K2YG once, and turns off transmit.
Another Macro Content Sample This macro turns on transmit, sends contacts call sign, thank you, contacts name, rst twice, my name, my qth, brief station description, how copy then contacts name & call, my call, and returns to receive.
Macro Command List This list can be found in the MMTTY Help Files
Macros are very important in contesting, and quite handy for chasing DX in a pile-up. However, MMTTY stand alone is NOT good for contesting. A compatible logging program such as N1MM makes contesting a breeze.
You can type into the transmit buffer and click TX (F9) anytime to send what you are typing.
RTTY QSOs There is not as much rag chewing on RTTY as there used to be. PSK has more spontaneous rag chewing. As with other modes, DX QSOs can be almost as short as contest contacts, and semi-rare to rare DX QSOs may be even shorter than contest contacts. Here is an example.
Sample Rare DX RTTY QSO DX: CQ CQ CQ DE STØR STØR UP 2-4 ME: DE K2YG K2YG K2YG DX: K2YG K2YG ME: STØR TU DE K2YG DX: K2YG QSL QRZ DE STØR UP The ME parts of this qso should be in your macros. The DX stations call can be inserted automatically with most software.
PSK31 Developed by Peter Martinez, G3MPX, (released in 1998) on ideas created by a Polish Ham (SP9VRC). PSK31 most popular digital mode with radio amateurs. Easy to use and effective at low power. PSK31 is a Phase Shift Keying mode. 31 indicates the theoretical bandwidth of hz. Speed: 32ms per bit equals about 50 wpm. PSK31 is a narrow bandwidth mode because of the keying mode (phase v. frequency shift), speed and other parameters.
The PSK31 mode most used is BPSK, or Binary PSK, in which the phase shift is 180° During each 32 ms period, a phase shift either occurs (logic 0) or does not occur (logic 1). 32 ms /bit
PSK Code PSK uses Varicode, a Huffman code that uses between 1 and 10 bits for each character, and supports all ASCII characters (Baudot does not.) The more frequently used characters are assigned the shorter codes.
PSK Code 00 always starts a new character (instead of start and stop bits as in baudot). There are no 00s within any character code. A space between characters is 1. Lower case e is 11. Upper case E is All lower case letter codes are shorter than upper case letters. If a PSK contact is marginal, try using all lower case letters.
DigiPan Software for PSK DigiPan SoftwareHandles: BPSK31 BPSK63 (Faster) QPSK31 and QPSK63 (Quadrinary - 4 phase code, some error correcting) FSK31 Pactor (RX only) Multi-channel Reception
Multiple PSK31 Signals Plus MFSK PSK31 Sound
PSK Pros PSK can be effective under very weak signal conditions. May be usable even when audio is almost indiscernible. More activity than RTTY except in contests and DXpeditions. Effective multi-signal reception possible.
PSK Cons Seems not to synch-up as quickly as RTTY Not used as much as RTTY for contesting. DX Pile-ups more difficult to run than RTTY PSK has latency of about ½ second.
Other Digital Mode Sounds Amtor ARQ Amtor FEC JT65A MFSK Packet Pactor
There are many digital formats used in Amateur Radio. We should discuss them in the future. Volunteers are welcome!
RTTY PPT Presentation courtesy of the New Providence Amateur Radio Clubf Photo by K2YG/1 IOTA NA-046