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Amateur Radio Association of Nebraska
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Author Topic: GETTING STARTED WITH THE DIGITAL MODES.  (Read 4945 times)
K0YNE
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« on: April 21, 2009, 10:11:22 AM »

I WAS ASKED TO CONTRIBUTE MY EXPERIENCE IN SLOW SCAN TELEVION.
SLOW SCAN WAS ONE OF THE FIRST DIGITAL MODES USING A COMPUTER THAT I TRIED. IN 2005 AT THE KEARNEY HAM FEST, A FELLOW HAM WAS TALKING ABOUT USING A COMPUTER TO RUN FREE SOFTWARE AND SENDING OUT SLOW SCAN PICTURES. SINCE MY CAREER INVOLVED A LOT OF VIDEO,
I WAS IMMEDIATELY ENTRANCED WITH THE IDEA OF RECEIVING SLOW SCAN. GETTING THE NECESSARY
PROGRAM AND A SIMPLE INTERFACE WOULD ALLOW ME TO GET STARTED ON THIS NEW MODE.
BY THE NEXT DAY, I HAD LOCATED THE MMSSTV WEB SITE AND DOWNLOADED THE FREE PROGRAM.
THEN I USED A 1/4 INCH HEADPHONE PLUG ONTO A SHIELDED CABLE AND PLACED A 3.5MM PLUG ON THE COMPUTER END.  I PLACED THE SMALL 3.5MM INTO THE LINE INPUT OF THE COMPUTER AND THE 1/4 INCH PLUG INTO THE HEADPHONE JACK ON THE RADIO. I REDUCED THE VOLUME LEVEL AND TUNED TO
14.230 MHZ . IN JUST A SHORT TIME, ACTIVITY ON THE BAND AND THE RACKET OF THE SLOW SCAN SIGNAL STARTED TO SCAN A PICTURE FROM THE TOP DOWN. IT AMAZED ME TO NO END , TO SEE A
FACSIMILE TYPE OF PICTURE BEING DISPLAYED ONE LINE AT A TIME. THIS WAS JUST THE BEGINNING OF
MY EXPERIENCE OF SETTING UP THE PROGRAM AND THE CORRECTIONS NEEDED IN RECEIVING AND SENDING OF STRAIGHT AND CLEAN PICTURES FROM MY STATION. I ENCOUNTERED SOME RF GETTING INTO THE PICTURE AND HAD TO CLEAN THAT UP SOME. I HAD TO CALIBRATE FIRST OF ALL MY RECEIVE
SOUND CARD SETTING. NOT ALL SOUND CARDS IF ANY ARE EXACTLY ON A PRECISE SAMPLING RATE OF
11,025.00 HZ. THIS IS HOW OFTEN THE PROGRAM SAMPLES INFORMATION ABOUT WHAT IS BEING SENT.
THE VALUE OF 11,025.OO HZ MEANS THAT THIS SAMPLING RATE IS OFTEN ENOUGH TO SCAN THE SUBJECT PICTURE OR TEXT OF PSK FOR EXAMPLE AND THE SENT QUALITY OF THE PICTURE WILL HAVE VERY GOOD DETAILS. SOME SOUND SYSTEMS THAT SAMPLE MUSIC FOR EXAMPLE MAY SAMPLE A PASSAGE OF ONE SECOND OF MUSIC AT 44,100.00 HZ PER SECOND SO NOT TO MISS ALL THE SOUNDS BEING HEARD
WITHIN A ONE SECOND PERIOD. SO NOW YOU KNOW WHAT A SAMPLING RATE IS. ONE SCAN LINE OF THE SSTV PICTURE FOR EXAMPLE IF IT LASTED FOR ONE SECOND WOULD BE LOOKED AT 11,025.00 TIMES. AT THIS RATE, GREAT DETAIL CAN BE SEEN. THE SECOND PART IS SETTING UP THE TRANSMIT PART OF THE INTERFACE. COMMERCIAL INTERFACES ARE MORE SIMPLIFIED AND MANY ARE NEARLY PLUG AND PLAY.  SOME COME WITH SOFTWARE AND USE THE COMPUTERS USB PORT AND THE OTHER END OF THE INTERFACE PLUGS INTO THE ACCESSORY JACK ON THE BACK OF THE RADIO. OTHER INTERFACES CAN BE HOME BREWED, USING AN  ACCESSORY PLUG  AND A SERIAL PLUG THAT WILL GIVE THE OPERATOR A PTT (PUSH TO TALK) WAY OF KEYING THE TRANSMITTER ON. I AM STILL USING A HOMEBREW INTERFACE AND SEEMS TO WORK WELL ENOUGH FOR ME.

THE INTERFACE......RECEIVE
HOME BREWED, SMALL BOARD PERFORATED TO MOUNT RESISTORS AND OTHER SMALL COMPONENTS..
RECEIVE SIDE. COMING FROM THE ACCESSORY PORT OF THE RADIO, A FIXED VOLUME OUTPUT
ENTERS THE BOARD.  A NETWORK OF 2 RESISTOR USED. ONE 2K OHM RESISTOR IN LINE WITH THE AUDIO AND ON THE OUTPUT SIDE OF THE 2K IS A 100 OHM RESISTOR TO GROUND, THIS SHUNT TO GROUND, LIMITS THE FIXED AUDIO OUT. THE AUDIO CONTINUES FROM THE 2K RESISTOR AND BY
SHIELDED CABLE IS PLUGGED INTO THE LINE INPUT BY A 3.5MM PLUG. TO ACCESS THE AUDIO CONTROLS
YOU WILL HAVE TO LOOK FOR AND FIND MIXER INPUT OR RECORD INPUT OF YOUR SOUND CARD
CONTROLS.

TRANSMIT SIDE....INTERFACE
AGAIN, THE ACCESSORY CABLE THAT PLUGS INTO THE BACK OF THE TRANSCEIVER HAS A DEDICATED
WIRE FOR AUDIO OR DATA INTO THE TRANSMIT PORT WIRE. THE AMOUNT OF SIGNAL IN DETERMINES
THE MODULATION LEVEL FOR SSB , FM, OR AM BROADCASTING. SINCE THE COMPUTER IS GENERATING
THE COMPLEX WAVEFORMS WITH VARIOUS MODES SUCH AS SSTV , RTTY AND THE REST, A CABLE OR CONNECTION IS NEEDED AT THE SPEAKER OUTPUT JACK (3.5MM) ON THE COMPUTER. AGAIN A CABLE
IS MADE WITH SHIELD AND A 3.5MM PLUG IS AGAIN USED TO SAMPLE THE OUTPUT. THIS CABLE IS
ROUTED UP TO THE PERFORATED BOARD THAT WILL PROVIDE THE SURFACE TO MOUNT NECESSARY
RESISTORS IN LINE WITH THE SIGNAL FOR TRANSMIT. THE CENTER CONDUCTER FROM THE SPEAKER
OUTPUT HAS A 2K OHM RESISTOR IN LINE IN SERIES AND AGAIN A 100 OHM RESISTOR IS ATTACHED
TO THE 2K OHM AND THE OTHER END OF THE 100 OHM RESISTOR GOES TO GROUND ALSO TO MAKE
A SHUNT TO GROUND, REDUCING THE OUTPUT FROM THE COMPUTER.  THE PLAYBACK OR SOUND OUT
FROM THE SOUND CARD WILL BE CONTROLLED BY THE WAVE AND OUTPUT OF THE PLAYBACK CONTROL.
THIS IS JUST A BRIEF DESCRIPTION OF THE PROGRAM.. ANY OTHER DETAILS MAY BE FOUND ON THE
INTERNET OR AT OUR MEETINGS.
I HOPE THIS WILL GET YOU STARTED AS THE MECHANICS OF THE HOOK UP 
SEE YOU AT THE MEETINGS AND 73'S FOR NOW PAUL K0YNE
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kbasq
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« Reply #1 on: April 21, 2009, 11:41:12 AM »

These are great, keep them coming!

Allen
KB0ASQ
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W6 -- JY1 Here is W6ANON -- How did you get such a fancy call sign?
You must have some political pull
JY1 -- It helps when your King!!
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