Modifications for the ICOM - RogerK

The easiest way to break the connection is to connect the base of Q7 to ground. The base is the lead facing into the centre of thePCB.Date: 04-01-2002 User comment From: Hiroki Ohashi,JI2EVLSubject: other methode for confortable ssb SQLR18 (33k)on Main Unit change 68k. And You set SQL position between 9 and 10 o'clock. You can operate sql open on SSBmode, and sql able on FM mode.It align that FM SQL position to 9 O'clock from 10 o'clock.This modification is read 522 times.top of page27-10-1998(IC-1275) Very fast AGCProblem:For some modes of weak signal communication, it can be desireable to have a very fast AGC (e.g. meteor bursts with a sharprise and a long weak "tail"). The standard fast AGC has a time constant of about 2 secs (!), which also means that a noise pulsecan mute you for quite some time.Note: Never use the noise blanker when receiving high speed CW (Meteor Scatter). The noise blanker mistakes the high speedkeying for noise pulses, and will seriously corrupt the signal.Solution:The solution is to move the "AGC fast" capacitor (C19) to replace the "AGC slow" capacitor (C20). You will loose the "AGC slow"option, but I find "AGC fast" adequate for most signals.Another solution is to switch out the "AGC fast" capacitor (C19) seperately, but then you will get the problem of finding anappropiate front plate switch. I already tried to use the DATA button, but it cannot be activated in CW.Note: a strong signal will be seriously distorted in AGC OFF mode.Implementation:●●remove C20move C19 to the replace C20This modification is read 521 times.top of page27-10-1998(IC-1275) SSB RF GainProblem:The RF GAIN function is different in FM and in SSB/CW modes. In FM mode the RF GAIN controls a PIN-diode at the input of thepreamp. In SSB/CW the RF GAIN simply activates the IF AGC.The use of the preamp input attenuator (the PIN-diode) can be useful also for SSB/CW e.g. if you have connected a mast headpreamp with excessive gain. In this case the attenuator will help you to adjust the signal levels at the mixer, and thus reduceintermodulation and blocking.Solution:The solution is to remove the SSB/CW RF GAIN for SSB/CW (this function is of little use anyway), and enable the FM RF GAINeven in SSB/CW.Implementation:●Cut the lead (FM8V) conneted to (pin5, J6, potmeter PCB, green) about 4 cm from the plug