home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
World of Ham Radio 1997
/
WOHR97_AmSoft_(1997-02-01).iso
/
mods
/
icom
/
ic402.doc
< prev
next >
Wrap
Text File
|
1997-02-01
|
1KB
|
30 lines
IC402
IC-402: S-METER (AGC)
---------------------
A MODIFICATION BY G8LRH IS SHOWN IN DUBUS VHF UHF SHF TECHNIQUE
HANDBOOK 1984. MOST OF THIS MODIFICATION IS IMPORTANT AND SHOULD
BE DONE. ONE PROBLEM SEEMS TO BE LEFT, S-METER READING. ONE
CRUCIAL IMPORTANT POINT, SHOWN ON G8LRH CIRCUIT, BUT NOT
DISCUSSED IN TEXT, IS TO CONNECT A 1K (2K2) RESISTOR BETWEEN
EMITTERS OF Q5 AND Q7. THE 1K RESISTOR TO GROUND FROM EMITTER
(Q7) I DID NOT FIND IMPORTANT, NOR DID I CONNECT THE 47 OHM
RESISTOR AT THE OUTPUT FROM IC3. C22 WAS NOT CHANGED SINCE 100PF
IS QUITE LOW IMPEDANCE WHERE IT IS USED. C35 WAS LEFT AS
ORIGINAL.
TO AVOID TOO HIGH IMPEDANCE IN S-METER CIRCUIT, TWO MODIFICATIONS
ARE MADE:
1) D111SS53 IS LOSENED, AND TWO SILICON DIODES, 1SS53 OR
1N4148 IS INSERTED IN SERIES, DO NOT SOLDER WHEN DIODE IN ON
PCB.
2) CUT THE TRACE GOING TO R31. CONNECT R31 TO EMITTER/Q7.
INSTALL A 10K RESISTORFROM BASE/Q7 TO GROUND (OTHERWISE AGC
WILL NOT FUNCTION PROPERLY)
NOW THE S-METER WILL WORK ON FULL SCALE AND READING SEEMS TO BE
NORMAL FOR A SIMPLE S-METER. ONLY SIMPLE TESTS WERE CARRIED OUT
USING FT-902/MMT432/28 WITH VARIABLE DRIVE (CARRIER LEVEL/DE-
TUNING OF PRE-SELECTOR). SOME FURTHER IMPROVEMENTS MAY BE MADE
LATER WHEN THE RIG IS CONTROLLED.
73 DE JAN-MARTIN ... LA8AK@LA5IV