kam.20


      --  KANTRONICS KAM HF FRONTEND MODIFICATION UPDATE  --

I HAVE USED THE KANTRONICS KAM MODEM FOR OVER FIVE YEARS NOW.

I RECENTLY RECEIVED A KANTRONICS KAM-PLUS MODEM.  AFTER COMPARING THE
SCHEMATICS OF THE KAM AND THE KAM-PLUS, I CAME UP WITH THIS MODIFICATION 
FOR THE KAM TO UPGRADE IT TO THE IMPROVED FRONTEND AGC AND LIMITER USED IN
THE KAM-PLUS HF MODEM.

THE SPECS FROM THE MANUALS FOR THE KAM AND THE KAM-PLUS ARE AS FOLLOWS:
  AUDIO INPUT:  HF
FM SENSATIVITY  20MVPP (KAM)
FM SENSATIVITY   2MVPP (KAM+)
AM SENSATIVITY 100MVPP (KAM)
AM SENSATIVITY  40MVPP (KAM+)
DYNAMIC RANGE   GREATER THAN 60DB (KAM)
DYNAMIC RANGE   GREATER THAN 80DB (KAM+)

IT IS A SIMPLE MODIFICATION REQUIRING ONLY SOME CARE AND A FEW PASSIVE
COMPONENTS.   REPLACING ONLY 4 RESISTORS, ADDING A RESISTOR AND A CAPACITOR
AND REMOVING ONE DIODE AND REVERSING ANOTHER DOES THE TRICK.   THE DYNAMIC
RANGE OF THE INPUT CIRCUIT IS MUCH BETTER WITH THIS MODIFICATION INSTALLED
IN THE KAM.

WITH THE HELP OF THE SCHEMATIC AND THE COMPONENT LAYOUT DIAGRAM FOR THE
KAM THE LOCATION OF COMPONENTS IS SIMPLE AND THE USE OF A SOLDER SUCKER
TO CLEAR THE HOLES FOR THE DOUBLESIDED PCB WILL FACILITATE A CLEAN JOB.
COMPONENTS TO REPLACE:

     OLD   NEW

R17  470   100     (ALL 1/4 WATT CARBON RESISTORS.)
R18  47K   68K
R19  2.2K  10K
R27  15K   2.7K

PROCEDURE:

REMOVE CR11 AND RE-INSTALL WITH POLARITY REVERSED.
REMOVE CR5 AND DISGUARD.
ALTERNATIVELY CR5 COULD BE LEFT IN PLACE AND CR11 COULD BE REMOVED BUT
THE PHYSICAL LOCATION OF CR5 MAKES IT'S REMOVAL CONVENIENT FOR MOUNTING
THE ADDITIONAL 100K RESISTOR'S GROUND TERMINATION.

LIFT THE END OF R13 THAT IS COMMON WITH R1.

INSERT ONE END OF A .1UF 50V CAPACITOR INTO THE PCB HOLE VACATED BY THE
END OF R13 COMMON TO R1; SOLDER IN PLACE.
CONNECT THE OTHER END OF THIS CAP TO THE FREE END OF R13.

INSTALL A 100K 1/4W RESISTOR BETWEEN THE FREE END OF R13, THE .1UF CAP
AND GROUND...USE THE PCB HOLE VACATED BY REMOVING CR5 (GROUND SIDE).
YOU END UP WITH A TRIPOD OF COMPONENTS R13, THE ADDED 100K RESISTOR
AND .1UF CAPACITOR.

CAUTION:  SOME PCB HOLES HAVING DOUBLE SIDED TRACES MAY NEED TO BE 
SOLDERED ON BOTH SIDES OF THE BOARD TO INSURE A THROUGH BOARD SOLDER JOB.

THIS COMPLETES THE UPDATE MODIFICATION FOR THE KAM.
YOU WILL NOTICE A BETTER DYNAMIC RANGE FOR INPUT SIGNALS TO THE KAM
AND AN IMPROVED LIMITER USING THE FM/AM FRONT PANEL SWITCH. I NOTICED AN
IMPROVEMENT IN THROUGHPUT WHEN OPERATING AMTOR/PACTOR.  I ALSO NOTED IMPROVED
CW RECEPTION USING THE 'AM' POSITION OF THE FM/AM SWITCH PROVIDING PERFECT
COPY ON 160M CW SIGNALS. 

I WOULD APPRECIATE ANY FEEDBACK ON THIS MODIFICATION OR OTHER IMPROVEMENTS: 
K5HK AT K7BUC.AZ.USA.NA (APLINK) OR MAIL TO MY HOME ADDRESS.

73,  CARL YOUNG, K5HK /MM2
     ABOARD SS KAINALU

HOME QTH:  983 LESTER AVE.
           RENO, NV 89502