Presentation on theme: "Digital VHF Weak Signal Modes"— Presentation transcript:
1 Digital VHF Weak Signal Modes Gary Sutcliffe, W9XTKen Boston, W9GAThis was part of a talk on VHF/UHF operating with W9GA and W9FZ on VHF and microwave operation at the 2012 Amateur Electronic Supply Superfest. My part of the talk concentrated on the WSJT digital modes.
2 Esoteric “Space” VHF Propagation Modes Want to make distant contacts beyond “normal range”Aurora - bounce off northern lights6 & 2M, mostly CW, “Donald Duck” on SSBMeteor scatter – bounce off ionized meteor trailsMostly 6 & 2M, SSB, WJSTPopular during meteor showersMoon bounce (EME) – use moon as a reflector6M & up, CW, SSB, WJST2M most popular bandW9XT – DXer at heart, like to work unusual propagation modes – Find these mode interesting – Maybe because of interest in Astronomy.Aurora – point your beam north when there is an aurora. Very raspy sounding on CW. SSB may be uninteligble.Meteor scatter – bounce off shooting starsUsed to be SSB with 15 second transmit periods, needed several long bursts. Heard lots of pings (very short bursts). Low success rate except during best meteor showersSome HSMS – record and play back slowed down, now mostly WJSTMoon bounce Required huge antennas and high power. WSJT lowers the bar.Talk will concentrate on MS and EME
3 WSJT – Weak Signal Joe Taylor Written by K1JT – Joe Taylor3 ModesJT6M – Scatter on 6MFSK441 – Meteor scatterJT65 – Moon BounceEach mode optimized for that type of operationJT6M – weak signals from scatterFSK441 – short bursts, Doppler shiftJT-65 – Very weak signals, slow fading, slow Doppler shiftThe WSJT modes revolutionized VHF weak signal work.Use the PC with DSP. DSP allows digging deep into noise for signals on RX. On TX PC generates the modulating signal.Some of the techniques are used by NASA for communicating with deep space probes.
4 What do you need? Stuff you have Stuff you need to get VHF Transceiver – must have SSB modeAntennaPCStuff you need to getPC/Rig interface (inexpensive – build or buy)WSJT program – Free download!A ham with a basic station can start using them within a couple of hours for $25
5 Sound Card InterfaceYou want to isolate the rig from the PC. RX signals are very weak, TX low level audio, easy to get ground loops and hum.You can build your own.Unified Microsystems SCI-6 Kit. $25Unified Microsystems SCI-6 Sound Card Interface Schematic
6 WSJT Software Free down load Standardized QSO formats – not a rag chew modeStep by step defined sequences30 or 60 second transmit/receive periodsRequires synchronized PC clocks
7 WJST User Interface Similar in all modes Upper – Received signal display – varies with modeCenter – Decoded signalsLower left – Set up – station & GridDate/time – WSJT records RX signal as wave files. These are play backs – date & time is when slide made, not wav file dateLower center RX configuration settingsLower right: Transmit sequence exchanges
8 WSJT QSO Sequence Stations alternate 30 or 60 sec. transmissions: Station 1 Transmission Station 2 TransmissionCQ W9XT EN53W9XT W1XYZ GRIDW1XZY W9XT RPTR RPTRRR73FSK441 and JT6M use 30 second transmissions. JT65 uses 60 second transmissionsFor a QSO to be valid:Both calls copied by both stationsSignal reports exchanged and acknowledged.You keep sending the same thing until you copy the next step in sequence, then go to the one after that.Report differs with mode. WSJT reports are based on report types used before WSJT – S2 was used for SSB MS, TMO for CW EME
9 Meteor Scatter Meteor burst Several milliseconds to maybe 30 seconds, short ones much more commonLonger on 6M, short on 2M, very short 222 MHzMaybe 1 burst per minute visible during a good showerMaximum range out to about miles.Station Requirements50-100W good, more is betterMedium sized antenna bestHigh gain antennas too narrow – don’t know exactly were meteor will appearIn the old days of SSB work – 15 second transmit periods. Took a number of long (5+ second) bursts for complete QSO. Heard lots of pings – short bursts with single word heardWSJT is high speed. Calls and report can get through in ¼ (250 msec) ping.Moderate station is fine. Don’t need elevation on antenna.
10 FSK441 – Meteor ScatterThe call signs of both stations were received multiple times from a single 360 msec burst.Once worked a station in FL. He had a home brew coat hanger 4 element yagi on step ladder and 15 watts.Since FSK441 can get the information through on such short bursts, don’t need a meteor shower. Lots of contacts are made using random meteors.
11 Moon Bounce Signal path Station Requirements Round trip to moon and back ~2.4 seconds.250 dB lossStation Requirements100W single long Yagi minimum – work a few really big stations350W, 4 Yagis with elevation – can work equivalent stationsNeed to track moon Az-ElMeteor scatter is only good out to 1400 miles or so. What do you do if you want to work stations further away. Need something else to reflect the signals back to earth. The Moon!250dB is huge. That is what make EME perhaps the most difficult QSO in ham radio.Difference between 1KW and 0.1μW is only 100dB, 2KW and 0.1μW is 103 dB. 10KW and 0.1μW is 110dB.
12 JT65 – Moon bounceBlue line is the time difference – know it is off the moonRed line is the sync line – nice narrow spike is good.Green line is just noise.Upper left moon info. Note at time slide was made the moon was below horizon. The signal and decoded data windows are from a recorded wav file of QSO with DK1CO.This was a good copy and it was 23 dB under the RX noise. A very strong signal!
13 W5UNThis is a very large EME station. Many beginning EME ops have their first QSO with W5UN.In my first QSO with W5UN the amplifier blew up half way during QSO. QSO finished with 50W and single 13 El yagi with no elevation.
14 W9XT “QRP” EME Station Equipment: Yaesu FT-847 All mode transceiver Mirage B2518G 150W 2M ampCushcraft 13B2 13 element Yagis (2)CATV 75Ω hardlineDell PC running XPUnified Microsystems SCI-6 PC I/FPlans for 2012:Increase to 4 YagisKW amp
15 W9GA EME Station Equipment: 144 system: Kenwood TS-711 2M All mode transceiverHenry M 700 W amp2 X 9 el M2 Yagis, hand aimed (not shown)M2 preampLaptop PC50 MHz system:Yaesu FT1000MP mkV w/FTV1000H.B. KW amp with a pair of 3CX800s2 X 6M5X vertically pol, with elevationPC with WSJTAntennas on 144 similar to W9XT, but are set up for temporary use on a mast on back porch. 50 meg system permanent, and used also on E skip.Although 50 meg antennas are vertical, they work well on E skip (and F2) due to ionospheric rotation. Not so good on tropo however.
16 50 MHz EME antenna50 Megahertz; pair of vertical polarized M2 5 elements, with elevation via rotor and crank. Tropo antennas for higher bands in middle
17 QSLs receivedLeft and center column are 144 EME qsls; right column is 50 EME qsls.
18 Scatter Modes Lots of propagation modes F2 – Regular HF propagation mode if high solar levelsEs - Common in spring monthsJT6M lets you make contacts when there is not enough signal to make CW & SSB QSOsI have not used this mode very much. There are other ways to make contacts, but many 6M ops really like it.
19 JT6M – Scatter modes (6M)This is from an attempt to work K7BV. I copied him fine but I had high SWR on my antenna and the rig cut back power. We never made the QSO.The burst was probably from a small meteor. JT6M will also work with meteors as well as other scatter propagation.
20 Ping JockeyA lot of schedules for WSJT modes are made on Ping Jockey.
21 Slide deck will be put up on www.w9xt.com WSJT ResourcesWSJT Download:N0UK Ping Jockey page:Unified Microsystems:Inexpensive PC sound card to radio interface kitON4KST chat page:Slide deck will be put up onWSJT SummaryLot of funTechnology available only to NASA 10 years ago.Enables small stations to make contacts only big guns could do before
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