FT-102 Circuit Modifications for High Fidelity AM

[Steve - K4HX]

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.