2006-08-22
The purpose of this web page is investigate how ICOM has designed the pre TX buffer circuit in other newer HF and VHF transceivers, i.e. not IC-746ers and IC-756ers.
If you have the schematics please send to me and I will investigate and publish here.
In the ICOM IC-703 the pre TX buffer is IC101, µPC2709T. This MMIC comes from the same family as the µPC1678G does. It can be seen that in the IC-703 the supply voltage to the TX pre driver is TX-switched so that IC101 is only on when transmitting.
ICOM IC-703 TX pre buffer circuitry. Source: ICOM IC-703 Service Manual.
In the ICOM IC-706MKIIG the pre TX buffer is IC231, µPC2709T. This MMIC comes from the same family as the µPC1678G does. It can be seen that in the IC-706MKIIG the supply voltage to the TX pre driver is permanently connected to 5 V. The device is similar to the one in the IC-703 which does not have the same tendency to malfunction. Perhaps different grounding area and heat transfer in the radio.
ICOM IC-706MKIIG TX pre buffer circuitry. Source: Curtsey Erik, OZ1ES.
Bo, OZ2M, www.rudius.net/oz2m