Modifications for the ICOM - RogerK

also changes USB/CW-R.Re-adjusting all of the BFO frequencies is a good idea in any case to compensate for crystal aging. If the passbands sounddifferent in LSB and USB it is a sure sign of mis-alignment due to crystal drift - they should be more or less the same.This modification is read 535 times.top of page27-10-1998(IC-575) Disabling of SBB squelchProblem:Squelching is nice to have in FM mode, but it doesn't really work for SSB, where you will be looking for weak signals. Thereforeyou have to adjust the squelch level every time you change mode. Furthermore I enjoy using FM as a monitoring mode on theSSB calling frequency, so changing the mode happens quite often.Solution:The solution is quite simple. Just cut the connection to the SSB input of the squelch circuit in some way.Implementation: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.This modification is read 534 times.top of page27-10-1998(IC-575) 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 533 times.top of page