MTS DOES NOT ENDORSE THE ABOVE LINKS, ANGELFIRE ADDED THIS
ICOM 745
- Frequency Drift (other than above) 2nd LO unit, Bottom, Right side of radio.
- The 745 2nd LO crystal, is exposed to the world, under the bottom cover. It has two basic problems, it is in the open air below (a internal PS35 compounds the problem) and it uses a large value (30pf) plastic trimmer cap. We have found replacing the trimmer cap with a 8pf ceramic trimmer, and replacing the 6pf ceramic NPO (bottom side of the board) with a 27pf NPO, greatly improves the stability. In the case a PS 35 is used, using a piece of styroform around the crystal, slows the rate of change due to the small heat rise from the internal power supply. We also started adding a ground wire to the 2nd LO crystal, which helps a little more. (use caution NOT TO OVERHEAT the crystal is you choose to do this.)
