Modifications for the ICOM - RogerK

Problem:This is a general transceiver problem. If you want to use the transceiver as part of a bigger setup (i.e. with external PA &preamp or with a transverter), it is convenient to have separate access to the RX and the TX of the transceiver. Otherwise youneed two coaxial switches every time you add a new accessory. With split RX/TX paths you only need one switch - at theantenna. Furthermore split RX/TX paths eliminates the need for a change-over sequencer.On the other hand it is also nice to have the transceiver working normally when you are using it barefoot.Solution:The solution is to jump wire the RX path (between RX and the RX/TX switching) trough the rear side of the transceiver with 2BNC connectors. In normal state these connectors are connected via a short cable. In case you need to "split up" the transceiver,you remove the short coax cable, and you obtain direct access to the RX. The TX is still available using the common connector.note: If you are always using your transceiver barefoot, without connecting any PA, preamp or transverter, this modification willoffer no benefit.Remove the back cover. If you place the holes for the BNC connectors next to and aligned with the two existing DIN-connectors,then ICOM have left enough space on the inside for the connections. You can also add other desired outputs like a phono plug forAF OUT.The RX cable runs between J4 on the RF YGR PCB and the PA unit.note: In my IC-275H the PIN-diode for the FM RF gain is shared with the RX/TX switch and placed in the PA unit. This meansthat the control voltage passes through the RX cable.Therefore the breaking of the RX cable will cancel the FM RF gain function (the SSB/CW RF gain is working on the AGC and is notaffected). The solution is to install a new PIN-diode (D5) on the RF-YGR PCB. The PCB has already room for it. To avoid shortcircuitingthe control voltage the jumper placed in stead of C86 on the RF-YGR PCB, should be replaced by a 1nF capacitor.This modification is read 523 times.top of page27-10-1998(IC-475) Modification of cw pass band (BFO)Problem:In these transceivers ICOM has chosen to shift the CW passband up 200 Hz compared to the SSB passband. This makes it moredifficult to copy SSB signals in CW mode.Solution:The extra BFO coil that is added in CW-R is short-circuited, and the BFO is re-adjusted for proper CW RX/TX-tracking and forpreferred USB/CW passband.Implementation:●short-circuit Lcw in the BFO compartment.For readjusting the BFO you need another transceiver (TRX2) with correct tracking.1. Receive on TRX2 and transmit in CW. Adjust the VFO (with the RIT off !) of TRX2 until you have the desired side tone in CWmode. (e.g. 800 Hz - can be found by beating the tone with the side tone oscillator).2. Transmit on TRX2 and adjust Ly (CW-R) until you have the desired side tone in CW mode. (you are setting the ~800Hz