FT301.MOD

DISPLAY LED'S:

THESE RUN HOT AND OFTEN BURN OUT SEGMENTS. CURE IS TO REDUCE OPERATING

VOLTAGE WHICH TYPICALLY RUNS >5V. FROM VOLTAGE REGULATOR Q2 ON THE MAIN

CHASSIS. A 1N400 DIODE IN SERIES WITH THE OUTPUT OF Q2 DROPS NEARLY A VOLT FROM

THE SUPPLY VOLTAGE. IF THE DISPLAYS STILL WORK OK, THEY WILL RUN COOL.

(PREVIOUSLY, OTHERS HAVE REMOVED RED PLASTIC LENS FOR BETTER VENTILLATION,

OR HAVE EVEN DRILLED HOLES THRU TOP OF RIG.)

SPEECH PROC:

OFTEN FT301'S HEARD ON THE AIR HAVE HAD DISTORTED AUDIO. A SINGLE I.C CONTAINS

ALL THE MIC AMPLIFICATION AND ALSO DRIVES THE RING MODULATOR IN THE SSB

TRANSMIT PATH. THIS AMP IS DRIVEN TO HORRIBLE DISTORTION IF THE STOCK (HANDHELD)

MIC IS USED AT FULL CLOCKWISE MIC GAIN SETTING. THIS IS THE WRONG PLACE TO HAVE

CLIPPING OCCUR. ALSO RESPONSE OF AMP IS FAR TO "GENEROUS." SUGGEST LIMITING LOW

END RESPONSE WITH SERIES 2. UF CAP (MUST BE MYLAR OR NON-POLAR) AT MICROPHONE

CONNECTOR. HAVE IGNORED THE FACT THAT THE HI END RESPONSE OF THAT AMP GOES WELL BEYOND 50 KHZ. R.F. CLIPPING IN MY FT301 WAS ACTUALLY ONLY ABOUT 6Db.

DUE TO THE LACK OF RF GAIN IN THE CLIPPER STAGES. THIS CURE FOR LOW GAIN WAS MOST

EFFECTIVE: AN EXTRA STAGE OF GAIN IS AVAILABLE FOR THE TAKING ON THE "NB UNIT" CARD.

(Q201 IS NORMALLY USED ONLY WITH THE PROCESSER OFF AS AN ALTERNATE RF PATH)

RIG Q201 IN SERIES Q202, AND KEEP BOTH STAGES POWERED UP REGARDLESS OF POSITION

OF "RF PROC" SWITCH. WITH THE EXTRA STAGE, IT IS EASILY POSSIBLE TO KEEP THE RING

MODULATOR IN THE LINEAR REGION AND STILL DEVELOP 15 TO 20 Db. OF RF CLIPPING. TO

IMPLEMENT THIS CHANGE: JUMPER PINS 10 & 11 ON THE N.B. CARD SUPPLIES VOLTAGE).

OPEN 1 K R205 AT WIPER TO VR201, LET IT HANG. OPEN .01 C204 AT TRANSFORMER,

AND JUMPER TO WIPER OF R205 WITH SHORT LEAD (UNSHIELDED SEEMS OK). RUN VR201

AT NO MORE THAN ABOUT 3/4 GAIN. WITH HIGH LEVELS OF RF CLIPPING, IT IS IMPORTANT

THAT THE AUDIO BE RATHER LACKING IN BASS TO AVOID A MUDDY SOUND. PREEMPHASIS

ACCROSS THE FULL AUDIO BANDPASS SOUNDS PRETTY BAD, SO I WOULD UP WITH A .1 CAP IN

SERIES WITH THE WIPER ON THE MIKE GAIN CONTROL AND FINALLY SHUNTED THAT CAP WITH

ABOUT 1000 OHMS (ADJUST THAT VALUE OF RESISTANCE TO GIVE GOOD ARTICULATION AND

STILL BE SEMI-PLEASANT.

I haven't tried or verified this, proceed at your own risk!