Modifications for the ICOM - RogerK

29-10-1998(IC-275) Splitting into RX- and TX pathsProblem: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 691 times.top of page19-07-1998(IC-28) ICOM IC-28A AND IC-28H ext frqTo make the IC-28 transmit 138-174 MHz, cut D21 (no retuning required). D21 is a tiny glass diode standing on-end near thecenter of the upper circuit board, accessible by removing the top cover. The IC-28 is the only convertible ham rig I know thatcovers the 170-MHz federal government (including national park) frequencies.[source: W9MKV]Date: 16-01-2002 User comment From: Giovanni Luce, N8IWKSubject: no cut 28-H modThe 28-H can be modified by removing a wire from a connector that connects to d21. Simply trace the circuit from d21 to theconnector and pull the wire out by pressing the small metal tab on the connector and wrap it in electrical tape.The radio then can easily be "unmodified" by simple plugging the wire back into the connector.Unsure of pin# or connector number as I modified one over 10 years ago, and didn't bother to note pin or connector number.This modification is read 1294 times.top of page