An Overview of Digimodes for Ham Radio Theres
- Slides: 38
An Overview of Digimodes for Ham Radio There’s a mode for everyone! Cathy James N 5 WVR
WHAT ARE DIGIMODES? q Any method of coding signals based on digitizing information and sending it over RF q Some consider CW a digital mode, but… Ø For purposes of this presentation, it is not. q As you are about to see, there are many digimodes currently used in amateur radio
1 ST GENERATION: IN THE BEGINNING WAS RTTY q First landline teleprinter built in 1849 ØFive-bit Baudot code created in 1874 q First teleprinter tests over radio waves done in 1922 ØIn commercial service by 1932 ØPrimary means of news service communication in 1940 s q Converted from teleprinter hardware to computer software emulations in 1980 s q Still very popular in amateur radio contests
2 ND GENERATION: BPSK 31 ENTERS THE STAGE q Developed by SP 9 VRC and G 3 PLX in the 1990 s q Quickly became the most popular digimode, overshadowing RTTY
AND DIGIMODES QUICKLY PROLIFERATED q RTTY q PSK q SSTV q Packet q Pactor q Hellschreiber q MFSK q MT 63 q Olivia q JT 65 q JT 9 q Thor q Throb q Domino. EX q LENTUS q COQUELET q POCSAG q AIS q AUTEX q ORBCOMM q ARGOS q HFDL q ……are we done yet? ? ?
AND DIGIMODES QUICKLY PROLIFERATED (2) Some modes form “families” of several closely-related modes q Hellschreiber Ø Feld-Hell Ø FM-Hell Ø MT-Hell Ø PSK-Hell q PSK q. MFSK Ø MFSK 8 Ø MFSK 16 q. MT 63 Ø MT 63 -500 Ø MT 63 -1000 Ø MT 63 -2000 I could go on…and on! Ø BPSK 31 Ø BPSK 63 Ø BPSK 125 Ø BPSK 250 Ø QPSK 31 Ø QPSK 63 Ø QPSK 125 Ø QPSK 250 q. Olivia Ø 1000/32 Ø 1000/16 Ø 500/8 Ø 250/4 Ø 125/4
THE GOOD NEWS q Same hardware Ø Almost all of these modes use the same sound card/cable rig arrangement q Multi-mode software Ø Free software is available that supports more than one mode q Limited usage Ø Only a few of these modes account for most digital usage on HF
How can you create a digimode station?
YOU’LL NEED: q Radio transceiver Ø Pretty much any modern rig that can operate on the frequencies you want to use Ø Older radio may not be sufficiently frequency-stable Ø This is not a good place to use “boat anchors” q A computer with a sound card q A cable to connect sound card to transceiver Ø Some modern rigs connect directly over USB q Computer software to handle coding & display
INTERFACE OPTIONS q You can go fancy… q Or something more basic…
…OR BUILD IT YOURSELF Example from http: //wa 8 lmf. net/ham/tonekeyer. htm
THERE ARE MANY SOFTWARE OPTIONS q Fldigi q Win. Warbler q Multi. PSK q WSJT-X q Ham. Scope q q IZ 8 LY Ham Radio Deluxe Mix. W …and many more What you select will depend on the modes you want to use, which user interfaces you prefer, and support from the developers. You will probably end up with several installed on your shack PC.
A Closer Look at the Digimodes
WHAT DO THEY SOUND LIKE? q CW (for ref. ) q RTTY q Feld-Hell q PSK 31 q SSTV q MFSK q MT 63 q Olivia 8/500 q Thor 8 q Throb-4 q Domino. EX-8 q JT 65 A q AMTOR q CLOVER q Contestia q FM-Hell q Packet (1200) q Pactor
PSK: THE PLACE TO START 14. 070, 7. 071 q PSK 31 is one of the top-two most used digimodes q You can find a PSK 31 contact *somewhere* on HF almost any time on any date q QRP is often enough power; 20 – 25 watts is usual max q “Warbling” sound q PSK is short for Phase Shifted Keying Ø Similar to FSK, Frequency Shifted Keying q Why “ 31”? q PSK run at 31 baud (signals per second) is the same width as CW q It can send characters at about the same rate that a fast typist can type them q A large number of signals can fit into a narrow band
PSK 31 ON WINWARBLER SOFTWARE
PROBLEMS WITH PSK 31 q Poor dynamic range Ø Cannot copy weak signals next to strong signals Ø Solution: Gentleman’s Agreement keeps power to about 25 watts q Very slow if you are transmitting large files rather than live keyboard chats Ø Solution: use wider, faster PSK modes! Ø BPSK 125 on VHF is ideal for rapid file transfer; used for emcomm Ø BPSK 125 is overkill for live chats, as no one can type that fast! PSK 31 PSK 125 q Does not handle certain paths well, e. g. multipath or polar Ø Solution: use a digimode that doesn’t depend on phase
JT 65 – WEAK SIGNAL DX AT ITS BEST 14. 076, 7. 076, 1. 838, 3. 576, 10. 139 q JT 65 is the “other” most-used digimode (besides PSK) q You can find a JT 65 contact *somewhere* on HF almost any time on any date q QRP is often enough; 20 – 25 watts is usual max Ø Significantly wider bandwidth than PSK 31 q JT is short for Joe Taylor, K 1 JT, Nobel prize winner Ø Invented the JT modes based on new mathematical coding algorithms q Originally developed for meteor paths on VHF Ø Experimentation by hams showed that it worked very well on HF Ø Quickly adopted for DXing by those with limited power and antennas Ø If you have a marginal QTH, e. g. apartment, this is your mode! q Amazing DX is possible
JT 65 ON JT 65 -HF SOFTWARE
PROBLEMS WITH JT 65 q So popular that the sub-band can be wall-to-wall q Requires extremely accurate timing (less than 1 second deviation from reference time) Ø Solution: use software to sync computer clock with online reference clocks q Extremely limited messages Ø Ø Ø CQ N 5 WVR FN 34 N 5 WVR K 1 JT FN 20 K 1 JT N 5 WVR -5 N 5 WVR K 1 JT R-06 K 1 JT N 5 WVR 73 q VERY slow, useless for chat Ø Each line above requires 48 seconds to send Ø Solution: None. For chatting, use a different mode.
RTTY: THE CONTESTER’S MODE 14. 070 -14. 081, 7. 070 -7. 081 q RTTY is short for Radio Tele Type q RTTY is seldom used outside of contests Ø But it’s by far the most popular digimode for contesting Ø The only digimode that has major contests dedicated to it q Good luck finding an RTTY contact outside of a contest q Usable at 50 watts, but benefits from more power q The only digimode routinely used with amplifiers > 100 watts q Significantly faster than PSK 31
RTTY ON MMTTY SOFTWARE
PROBLEMS WITH RTTY q Seldom used outside of contests Ø Solution: set up a sked for testing and experimenting q Software configuration can be a pain Ø Solution: set up a sked for testing and experimenting! q Hard to tune, and tuning is critical q There are only 5 bits in the BAUDOT code Ø Only 32 characters available Ø Must shift between LETTERS and FIGURES mode to handle both letters and numbers Ø Upper-case only, no lower-case letters for special characters Ø 599 vs. 5 NN?
HELLSCHREIBER: THE VISUAL TEXT MODE q Completely different from any other digimode q Very rare, but there is a club dedicated to it Ø Look for nets or skeds Ø Occasionally you’ll get lucky (e. g. , Chile on 40 meters!) q 25 watts is usually enough for good contacts q Named for its inventor, Rudolph Hell Ø Developed in the 1930 s q Works much like a continuous one-line FAX message q Special fonts developed to maximize signal readability • Feld-Hell • FM-Hell
FELD HELL ON IZ 8 BLY SOFTWARE Slanted text indicates timing error; use Tools Menu to adjust correction factor
PROBLEMS WITH HELLSCHREIBER q Many variant sub-modes Ø FM-Hell, PSK-Hell, MT-Hell Ø Solution: many are readable in Feld-Hell mode q Few software programs support it Ø Solution: Use IZ 8 BLY or Multi. PSK q Very rarely heard Ø Solution: Use nets, or set up skeds Ø Join the Feld Hell Club! Over 5000 members today • https: //sites. google. com/site/feldhellclub/Home
PACKET: VHF FOR MAILBOXES q Packet was very popular in 1990’s Ø 2 -meter 1200 baud forwarding network was built across the country Ø Disappeared when Internet became common Ø Rebuilt regionally after 9/11 to handle emcomm q Operates on VHF FM q Can handle live chats, emails, or file transfer q Requires actual hardware Ø e. g. TNC/packet modem such as PK-232 MBX Ø Some may have used sound cards, but not recommended Ø Packet Modems have built-in mailboxes for unattended operation q Text appears in “bursts” of several characters at a time, unlike PSK which is slow and continuous
PROBLEMS WITH PACKET q Slow Ø Limited to 300 baud on HF Ø Too slow to be useful; better modes exist Ø Limited to 1200 baud on 2 meters Ø Fast enough for mail transfer or slow chats Ø Solution: Use on the 440 MHz band! Ø 9600 baud will transfer files rapidly and reliably
PACKET (9600 BAUD) ON AEA PK-96
MT 63: FOR REALLY BAD PATHS q Designed for paths that experience fading and interference q Complex scheme encodes text in matrix of 64 tones over time and frequency Ø “Overkill method” offers error correction at the receiving end while still providing a 100 WPM rate Ø Problem: Wide bandwidth (1 k. Hz standard, 500 Hz & 2 k. Hz optional) Ø Solution: Use on VHF/UHF – can even go through an FM repeater! q Fldigi has good support for MT 63, including file transfers q Strong potential for emcomm usage q Soundcard mode, no TNC needed q I would like to see MT 63 get more use!
MT 63 -2000 ON FLDIGI
MT 63 -2000 ON FLDIGI WITH EMCOMM FORM!
MFSK 16: CHAT MODE FOR POOR PATHS q Multiple Frequency Shifting Key q Seldom used, but very effective Ø Deserves to be used more often Ø I have found it will get through when PSK 31 won’t q 16 tones with Fast Fourier Transform (FFT) decode Ø Uses Constant Phase Frequency Shift Keying q Continuous Forward Error Correction (FEC) sends all data twice with an interleaving technique to reduce errors from impulse noise and static crashes. q Signal width is similar to JT 65 A Ø Text appears in “bursts” of several characters at a time, unlike PSK which is slow and continuous q My best-ever DX chat QSO was MFSK 16 to New Zealand
OLIVIA: FAST CHAT MODE FOR POOR PATHS q MFSK variant that is highly resistant to QSB (fading) and noise (QRM) Ø Includes Forward Error Correction (FEC) Ø Can work signals you cannot hear q Created in 2005 by Pawel Jalocha (SP 9 VRC) q Used in various widths, but all are much wider than PSK 31 Ø The wider the sub-mode, the higher the bandwidth and faster the transmission q Very rare Ø I have never made an Olivia contact Ø Suggest making a sked with another user if you want to try it
JT 9 – NARROW WEAK SIGNAL DX 14. 076 + 2 k. Hz q JT 9 is the “other” JT mode recommended by Joe Taylor for HF q 5 watts is usual max! Ø Bandwidth similar to PSK 31 q Amazing DX is possible – but not very popular Ø May replace JT 65 A on HF someday, but right now QSOs hard to find Ø Problem seems to be more inertia than any issues with the mode
NOT ENOUGH MODES FOR YOU? q AMTOR is an expansion of RTTY that operates at 100 baud and include Forward Error Correction (FEC) q CLOVER is a PSK mode which provides full duplex QSOs and adapts to conditions by constantly monitoring the received signal and shifting modulation scheme q THROB is yet another new DSP sound card mode that uses FFT to decode a 5 tone signal; attempts to push DSP into the area where other methods fail because of sensitivity or propagation difficulties q Enough! Make it stop!
FOR MORE INFORMATION: qhttps: //www. nonstopsystems. com/radio-sounds. html qhttp: //www. w 1 hkj. com/Modes