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FT-102 Circuit Modifications for High Fidelity AM




 
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Steve - K4HX
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« on: December 22, 2012, 12:23:39 PM »

FT-102 Circuit Modifications for High Fidelity AM

by Bill, W3DUQ


AF Board
Part Number    Original Value   New Value  
C02  0.1 uF     33 uF  
C03  0.001 uF     remove  
C04  10 uF     33 uF  
C06  0.0022 uF     remove  
C07  1 uF     33 uF  
C08  1 uF     33 uF  
C09  10 uF     33 uF  
C10  4.7 uF     33 uF  
C17  4.7 uF     33 uF  
C19  33 uF     100 uF  
C20  4.7 uF     33 uF  
C21  4.7 uF     33 uF  
C76  0.0027 uF     remove  
C116  10 uF     33 uF  
C124  33 uF     100 uF  

Note: If you desire to use the phone patch input for external audio feed, put 220k in series with the center conductor going to the patch input jack and a 1k to ground from the input audio side of the phone patch jack.

Also remove C04 (10 uF) from the AF unit to reduce the overall audio gain. I also changed R11 from 2.2k to 15k to set the gain properly for vox operation.


AM/FM Board
Part Number    Original Value   New Value  
C12  10 uF     33 uF  
C70  0.01 uF     470 pF  
R03  4.7k     Note 1    
Note 1: Parallel with 180k to set carrier level for extended positive peak modulation.

Set both tone controls on the AF board to 50%. Frequency response is essentially flat from 40-6khz and down 3db at 16 khz. If you want it flat to 16 khz, just turn up the treble tone control a bit.

There is a problem with the ALC kicking in too early on AM. To fix this, connect a 10k resistor between pins 2 and 3 of P22/J15 on the I-F board. This will raise the point at which the ALC kicks in.
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