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HF Digital Communications How to work those strange sounds you hear on the air John Clements Joe Miller Brian Johnston KC 9 ON KJ 8 O W 8 TFI Stephen H. Smith John Mathieson WA 8 LMF AC 8 JW 1 May 2014
Contents Introductions n Why Digital? n Digital Modes of Operation n Hardware : Radio, Computer, and interfaces n
Contents Tips and Tricks n Q&A n
Introductions n John Clements KC 9 ON Licensed in 1979 at age 16 n Retired from electronics manufacturing and IT systems n Active experimenter and home brewer n jwc [email protected] com n
Introductions n Stephen Smith WA 8 LMF Land-Mobile-Radio Systems & Field Engineer n Ham since 1964 n WA 8 [email protected] 8 lmf. net n
Introductions n Joe Miller KJ 8 O SWL since 1967, first licensed in 2006 and collects QSL cards n President of OCARS (W 8 TNO) n Certified Public Accountant n kj 8 o. [email protected] com n
Introductions n Brian Johnston W 8 TFI Licensed in 1976 n Computer operator for a major newspaper n Avid experimenter and home brewer n w 8 [email protected] net n
Introductions n John Mathieson AC 8 JW Licensed since about 2005 n Active in CW and digital modes n [email protected] com n
Why Digital? Send and receive text, images, data, and audio n Some modes work very well in noisy and weak signal environments n n If you can’t hear them you can’t work them is no longer true!
Why Digital? n Some modes can provide error free or reduced error transmissions. n Good for Emergency Communications
Why Digital? Many modes use smaller bandwidths than voice n 97. 1(b) contribute to the advancement of the radio art. n 97. 313(a) use the minimum transmitter power necessary to carry out the desired communications. n
Digital Modes of Operation n There are more digital modes than you can shake a stick at! n RTTY, PSK, QPSK, MFSK, Olivia, MT 63, JT 65, Contestia, Hellschreiber, Throb, Packet, WSPR, SSTV, Free. DV and many more!
Digital Modes of Operation Each have their own good and bad n We will just look at a few popular ones…… n
The Old Timers of Digital CW n CW is the oldest digital mode Started before the birth of radio n Computers are not required n From QRSs in seconds per ‘dit’ n To QRQ speeds greater than 150 WPM n
The Old Timers of Digital RTTY (Radio Teletype) Became popular in the 1950’s using WWII surplus equipment. n 60 WPM / 45 baud (changes per second) n FSK - Shifts between 2 frequencies, typically 170 Hz apart. n Sensitive to QSB and QRN, no error correction. n
PSK 31 One of the first sound card modes n Intended for live keyboard-tokeyboard conversations n 5 conversations fit in the same space as one RTTY signal n 30% slower than RTTY n 40 WPM / 31 baud n Sensitive to QSB and QRN. No error correction but outperforms RTTY n
MFSK 16 Like RTTY but uses 16 different frequency shifts n Old technology mode - required complicated hardware before sound card software was available n Speed of 78 WPM / 62. 5 baud with a 316 Hz bandwidth n ARRL Bulletins are transmitted in MFSK 16 n
MFSK 16 Uses forward error correction (FEC) n Typically this is done by sending redundant data n The cost penalty is extra time to send the data multiple times n Result is greatly reduced errors from QSB, QRN and Multipath propagation n
MT 63 MFSK Variation using 64 frequency shifts n Great for sending large amounts of data n Forward error correction, can lose up to 25% and still have perfect copy n
MT 63 n 3 Modes of operation MT 63 -500 50 WPM 500 Hz BW n MT 63 -1000 100 WPM 1 KHz BW n MT 63 -2000 200 WPM 2 KHz BW n n MT 63 -2000 is widely used by EMCOMM and MARS
Olivia Another MFSK Variant n Has forward error correction like MT 63 n Good with QSB, QRM n Will decode 10 -14 d. B below the noise floor on SSB! n
Olivia n Common bandwidth, shifts, and speeds Mode 500/16 1000/32 BW 500 1000 Shifts 16 32 WPM 20 24
JT 65/JT 9 QRPp & EME Weak signal mode n JT 65 uses 65 shifts in a 355 Hz bandwidth n JT 9 – Fairly new mode n Uses 9 shifts in only 15. 6 Hz bandwidth n Sounds like a constant tone n
JT 65/JT 9 n Very slow mode! 45 seconds long to send 72 bits or ~13 characters n Standard messages typically contains two call signs, a grid locator or signal report, the message type. n
JT 65/JT 9 Now also used on HF n W 6 CQZ wrote “JT 65 -HF” that makes HF operation easy, especially for low power stations. n http: //sourceforge. net/ projects/jt 65 -hf/files n
JT 65/JT 9 n Actual off-the-air RX in central MI with mobile whip on 20 meters.
SSTV n n n Started with dedicated hardware using surplus long-persistence RADAR CRT’s; now all done with sound-card software. Commonly called a “digital” mode, but most SSTV is analog, except for “Easy. Pal” which is actually a general-purpose digital-file-transferover-radio program. 30+ formats exist for SSTV, but most software automatically receives any of them.
SSTV n Weather Fax (We. Fax) is a similar mode. Not used in amateur radio but can be found on the SW bands.
Digital Voice The future of radio? ? n About ½ the bandwidth n n 1. 25 KHz wide using a 16 QPSK signal FM-quality noiseless voice on HF! n Most activity on 14. 236 MHz n Free software at: http: //freedv. org n
Digital Voice n Requires 2 sound cards One for radio-to-speaker (RX) n One for mic-to-radio (TX) n n USB sound cards are cheap n From $1. 80 to $25
Hardware n Only 3 components needed Radio n Computer n Audio / PTT Interface n
Hardware n How much does it cost? Assuming you have the radio and computer……. n Build your own interface from free to $25 n Buy commercial interfaces from $60 -300 n
Hardware Radio n Almost any USB HF Transceiver n n Older mechanical analog VFO rigs may NOT be stable enough for narrow modes like PSK 31 but work well on modes like RTTY and SSTV. Newer radios with stable frequency synthesizers are best.
Hardware Computer Big and fast not required n Most “XP” computers work fine! n Minimum Requirements n Available USB or RS-232 port n Sound Card n 1 GHz CPU, 256 MB RAM n 300 MB Drive space n Depends on software - YMMV n
Interfaces Receive Start today with a simple attenuator cable n Parts are about $10 at Radio Shack, cheaper elsewhere! n wa 8 lmf. net/miscinfo/Univers al-Sound-Card-Cable. pdf n
Interfaces Transmitting n Transmitting is a little more complex PTT keying n Isolate the audio to prevent ground loop hum & noise issues. n
Interfaces Commercial n Several Manufacturers MFJ n West Mountain (Rig Blaster) n Tiger. Tronics n Some models include cables n Other models require purchasing cables for your rig n
Interfaces Commercial n Better models include a sound card built in n n Your internal PC sound card is available for regular use Prices from $60 - $300
Interfaces Homebrew n As basic as two 600 -600 ohm audio transformers, a few resistors, and a $1. 00 opto-isolator chip for PTT keying.
Interfaces Homebrew Computer Audio In Radio Receive Audio Out
Interfaces Homebrew Computer Audio In Radio Spkr/Aux Audio Out Computer Speaker/Line Audio Out Radio Mic/Aux Audio In
Interfaces Homebrew Computer Audio In Radio Spkr/Aux Audio Out Computer Speaker/Line Audio Out Radio Mic/Aux Audio In Serial Port RTS Pin Radio PTT Line
Interfaces Typical Setup
Tips and Tricks Power n n Reduce your power! n These modes either run at 100% duty cycle (like keydown CW), or use multiple tones sensitive to intermodulation distortion. n Keep peak power out well below keydown CW maximum to minimize distortion. n Keep ALC to zero! Turn off all speech processing or compression !
Tips and Tricks Jacks n Use the Auxiliary, Accessory, “Data”, or “Packet” jacks on the radio. Most radios from the major manufacturers have one or more of these jacks on the rear panel n These jacks have constant-level audio input & output, and PTT lines n
Tips and Tricks Jacks n Typical Jacks 6 -pin Mini-DIN 13 -Pin Full-size DIN
Tips and Tricks Jacks No need to adjust the volume or mic gain all the time n No need to unplug the speaker to hear the radio n No need to swap the mic in and out n
Tips and Tricks Jacks n Some radios have an audioout (RX-audio out) line in the microphone jack. If so, a single cable to the front of the radio can provide all connections.
Tips and Tricks RSID n Use Reed-Solomon Identification Short code at the beginning of a transmission which identifies the mode n Several programs automatically detect this and pop up a box n
Tips and Tricks Sound Device n Check your sound card settings in the control panel! Turn off special effects n Turn off pass-thru or “Listen to this device” modes n Set rate to 16 bit 48000 Hz n
Tips and Tricks Sound Device n Use the mixer to adjust your transmit audio using a dummy load and short 5 -10 second intervals
Tips and Tricks Waterfalls RTTY-45 PSK 31 JT 65 MFSK 16 Digital Voice JT 9
Tips and Tricks Waterfalls MT 63 Olivia SSTV
Tips and Tricks Frequencies n Common PSK 31 frequencies 1. 828 3. 580 7. 035 n 10. 140 14. 070 18. 100 21. 070 24. 920 28. 120 Other modes are usually a few KHz from this area
Tips and Tricks Frequencies SSTV 14. 230 is popular n Digital Voice 14. 236 n n MI Digital Traffic Net (MIDTN) n 3. 583 Mhz Olivia 8/500 n Tu, Th, & Sa 8 PM local n http: //www. midtn. ws/
Tips and Tricks References ARRL www. arrl. org/hfdigital n Ham Radio Deluxe – Free V 5 n n n WA 8 LMF. net/miscinfo FLDigi n www. w 1 hkj. com/Fldigi. html
Tips and Tricks References n JT 65/JT 9 hflink. com/jt 65/ n n Free. DV (Digital Voice) n n www. physics. princeton. edu/p ulsar/K 1 JT/wsjtx. html www. freedv. org Olivia www. oliviamode. com
Tips and Tricks References n Software: n n Ham Radio Deluxe V 6 www. hrdsoftwarellc. com Interfaces n n n Commercial Sites MFJ Rig. Blaster Signal. Link www. mfjenterprises. com www. westmountainradio. com www. tigertronics. com
Getting started on FLDigi Home: http: //www. w 1 hkj. com/ Downloads: http: //www. w 1 hkj. com/download. html Beginners’ guide: http: //www. w 1 hkj. com/beginners. html
… n This presentation and other notes can be found here: n n http: //kc 9 on. com/hamradio/hf-digital-modes/ http: //WA 8 LMF. net/miscinfo