dna@dsd.UUCP (David Altekruse) (08/04/84)
Forwarded from Compuserve. This also applies to VFH packet, N'est ce pas?
Keywords: DEVIATION VHF-FM RTTY MODULATION INDEX MARK SPACE
A commentary on control of modulation index in
VHF-FM RTTY.
FROM W2JUP, FARMINGVILLE, NY
DECEMBER 7, 1983
2230 EST
PART 1-
TONIGHT'S LESSON IS FROM THE FIRST BOOK OF DEVIATION. WE WILL READ
THE PARABLE OF THE MARKS AND THE SPACES.
ONE NIGHT AS I MAINTAINED MY SHEPHERD'S PASTORAL WATCH OVER A LOCAL
REPEATER CHANNEL FLOCK, MY EAR WAS CAUGHT BY THE TWEEDLE-TWEEDLE SOUND
OF THE MARKS AND THE SPACES. I LOOKED TO SEE WHAT BYTES WERE THERE,
AND LO! THERE WERE NO BYTES! ONLY SCARS AND UGLY DISTORTIONS UPON
THE SCREEN AND UPON THE SCROLLS OF PARCHMENT THAT FROM MY PRINTER
FLEW.
I CONSULTED THE ORACLE, LIT TWO LEDS FOR CANDLES, AND THE ORACLE SPAKE
UNTO ME SAYING, "CLOD, THERE ARE NO TRUE MARKS AND SPACES UPON THY
CHANNEL! THESE ARE UNCLEAN AND MUST B SCOURGED FROM THY PAGE! SEEK
THEM OUT AND DESTROY THEM, FOR THEY ARE FROM ANOTHER WORLD AND MUST
BE CLEANSED!"
SO, AS THE ORACLE BAD ME, I WENT FORTH WITH SWORD AND SCREEN AND SOUGHT
THE UNCLEAN BITS AND MARKS AND SPACES. AND, LO!! I DID FIND THEM
DOWN A MERE 15 KHZ, ISSUING FORTH FROM ANOTHER REPEATER, FULL OF SOUND
AND FURY, AND OF GREAT AND FULSOME VOLUME. SO I DID CAUSE THESE UNCLEAN
MARKS AND SPACES TO APPEAR AS IF BY MAGIC UPON THE SCREEN AND SCROLL
OF MY TABERNACLE, WHEREIN I DID EXAMINE THEM. AND TRUE AS SPAKE THE
ORACLE, THEY WERE INDEED UNCLEAN AND FULL OF SORES AND THE BLEMISHES
THAT ARE CALLED SQUARED WAVES.
AND AFTER INVOKING THE ORACLE ONCE AGAIN, I DID SEE THAT THESE UNCLEAN
MARKS AND SPACES WERE FROM THE WESTERN SHORES, FROM THE HOUSE OF A
FALSE PROPHET, A FRIEND, NEWLY COME UNTO THESE DIGITAL MODES. AND
I WENT UNTO THIS FRIEND AND SAID, "FRIEND, WHYFOR ARE THY MARKS AND
SPACES UNCLEAN, AND OF A FULSOME NOISE, AN A PLAGUE UPON OUR CHANNEL?"
AND MY FRIEND SPAKE UNTO ME SAYING, "FORGIVE ME OH MASTER, I KNOW
NOT WHAT I HAVE DONE. I AM NEWLY COME UNTO THIS RTTY ODE AND AM AS
A STRANGER IN THE LAND. ANOINT ME WITH THY WISDOM SO THAT I MAY BE
CLEANSED AND FIND LOVE ONCE MORE IN THE HEARTS OF MY FELLOW MEN."
SO I SAID UNTO THE NEWCOMER, "NEWCOMER, KNEEL AND LEARN. I WILL TELL
THEE OF THE RULE OF CARSON, A GREAT SAGE FROM THE LABORATORIES OF
BELL. HEAR! OH NOVICE, HOW IT IS MEET UPON YOU TO LOOK TO THY "MOD
INDEX". FOR THY SIDEBANDS DOTH APPEAR UPON A CHANNEL IN THE EAST,
AND THE PEASANTS ARE WROTH WITH THEE!. THOU ART TRULY A DEVIANT SOUL,
GUILTY OF MAKING GREAT NOISES UPON THE AIR, AND THY MARKS AND THY
SPACES DO GROW AND INFECT THE ADJACENT CHANNEL, WHICH IS NOT COOL!"
AND THE NEWCOMER KNELT IN SHAME, AND BEGGED FORGIVENESS. HE
SAID, "TELL ME OF THIS RULE OF CARSON FROM THE LABORATORIES
OF BELL, SO THAT I MAY CLEANSE MY ACT AND GET WITH THE PROGRAM
'ERE THEY CAST ME OUT AS AN UNBELIEVER AND AN INFIDEL!!"
AND I SPAKE UNTO THE NEWCOMER SAYING, "OH YE OF LITTLE
SMARTS! GET THEE TO A TEXTBOOK HAVING WITHIN IT THE RULES
OF THE INDICES OF MODULATION. FOR THEREIN LIES THE SECRET
WHICH IS IN THE RULE OF CARSON, WHICH SAYS: "A GENERAL RULE
FIRST STATED BY J.R. CARSON IN AN UNPUBLISHED MEMORANDUM
AT BELL LABS DATED AUGUST 28, 1939 IS THAT THE MINIMUM
BANDWIDTH REQUIRED FOR AN ANGLE-MODULATION SIGNAL IS EQUAL
TO TWO TIMES (THE SUM OF THE PEAK DEVIATION AND TWICE THE
HIGHEST MODULATING FREQUENCY) TO BE TRANSMITTED. IN THE NOTATION
DEFINED AS-
BW EQUALS 2(DELTA F PLUS (2F SUB-M))
WHERE BW EQUALS BANDWIDTH, DELTA F EQUALS PEAK DEVIATION
AND F SUB-M IS THE MODULATING FREQUENCY.
THEREFORE, IT IS WRIT-
IF THY DEVIATION IS 5 KHZ, AND THY MODULATING FREQUENCY IS
2125 HERTZ FOR THY MARKS AND 2295 HERTZ FOR THY SPACES,
THE RULE OF CARSON SAYS THAT THY MINIMUM BANDWIDTH SHALL BE:
TWO TIMES THE SUM OF (9.250) WHICH COMES OUT TO 18.5 KHZ--
WHICH IS DAMNED WELL GONNA TAKE YOU INTO THE NEXT CHANNEL AND
PISS OFF THE TROOPS!!!
"THEREFORE, OH YE OF HALF A WIT, I SAY UNTO THEE, FORESOOTH!
DROP THY DEVIATION DOWN TO NO MORE THAN 2 KHZ ON SPACE TONE
AND THE BANDWIDTH OCCUPIED BY THY MARKS AND SPACES SHALL BE
ABOUT 13.2 KHZ, WHICH WILL STAY WITHIN THE REALM OF THINE OWN
CHANNEL AND NOT CAUSE BUBONIC SIDEBANDS TO SPREAD OVER THE LAND!!!"
AND I SPAKE UNTO THE NEWCOMER SAYING, "HEAR OH NEWCOMER!"
GAZE UPON THE FACE OF THY WONDROUS SPECTROUS ANALYZER AND
SEE THE TUBE THEREIN, AND JUDGE YE THE MAGNIUDE OF THY
SINS!! SEE WHEREIN AND WHEREFORE THOU CREATETH A FESTERING
AND A CANKERING UPON THE CHANNELS OF THY BAND AND UPON THE
BAND OF THY BROTHERS!!"
AND INVOKING THE ORACLE ONCE AGAIN, I RAISED MY HAND AND THERE
CAME A VISION UPON THE TUBE OF HIS SPECTROUS ANALYZER WHICH
DID APPEAR THUS AS IS SHOWN FOR 40-COLUMN DISPLAYS----
I
I
I
I
I
I
I I I
I I I I I
I I I I I
I I I I I I I
I I I I I I I
I I I I I I I
-3FM -2FM -1FM FC FM 2FM 3FM
WHEREIN FC IS THE CARRIER FREQUENCY
FM IS THE MODULATING FREQUENCY
"LO THE RESULT THEREFROM IS THAT THOU TAKETH UP BUNCHA DUPA
MORE SPACE OF OUR HOLY SPECTRUM THAN THOU THINKETH, OH MENTAL
MIDGET! THOU HAST THE WIT OF A FENCE POST, THE INTELLECT OF A
HOCKEY PUCK!!"
AND THESE THINGS WHICH I COMMAND THEE THIS DAY SHALL BE FOR
A SIGN UNTO THEE, FOR THEY ARE WRITTEN DOWN IN THE FUNCTIONS
OF BESSEL, FROM WHICH THERE IS NO ESCAPE. YEAH, VERILY, WE ARE
ALL SLAVES TO THE RULE OF CARSON AND THE FUNCTIONS OF BESSEL,
AND WOE BE UNTO THSE WHO FLAUNT THEIR MIGHT AND RISK THEIR
WRATH.
AND THEREUPON I SPAKE ONCE MORE UNTO THE NEWCOMER SAYING,
"AND REMEMBER THIS- THERE IS SIGNIFICANT SIDEBAND ENERGY
AS LONG AS THE SIDEBANDS ARE STRONGER THAT 26 DB BELOW THE
UNMODULATED CARRIER, SAYETH THE FCC! HARK! THEY ARE THE HOLY
ONES, KEEPERS OF THE TICKETS AND GIVERS OF THE LAW. DO NOT ANGER
THEM, FOR THEY WILL SMITE THEE AND CAUSE THEE GRIEVOUS WOUNDS.
AND SHOULD THE FEDS IGNORE THEE, THEN THY BRETHREN ON THE CHANNELS
WILL SEEK THEE OUT AND CAST THEE INTO THE WILDERNESS FROM WHENCE
THEE CAME!!!"
"HEAR, OH NEWCOMER!! CLEANSE THY ACT AND GET THEE TO A DEVIATION
METER!! AND BE COOL FOR ALL TIMES."
AND THUS ENDS THE PARABLE OF THE MARKS AND THE SPACES AND THE
ETERNAL TRUTS OF THE RULE OF CARSON. LET THESE WORDS
BE UNTO YOU FOR A LESSON.
GIVEN UNDER MY HAND AND SEAL ON THIS THIRTEENTH DAY IN
THE MONTH OF DECEMBER IN THE YEAR OF OUR LORD 1983
ON THE ISLAND OF LONG---
BY W2JUP, THE PATRIARCH OF FARMINGVILLE.
FROM W2JUP, FARMINGVIILE, NY
4/8/84---0630EST