As regards the problem of VHF hum when the inverter is on, I suspect that if there is no other obvious problem with the inverter that it is not really the problem. The fact that you have a hum on the VHF indicates that it is receiving its DC with an AC waveform superimposed on top. This could be from several potential causes, but here are my suspicions listed in order: 1. The battery bank that feeds the inverter is becoming high internal resistance. This is indicative of batteries that are near their end. 2. There is a high resistance connection to the battery and the sequence of how the wires that feed the various loads that the battery supplies and/or charge the battery (i.e. from alternator if charged that way) are attached to the battery. For example, if the ground post clamp on the battery feeds not only the inverter but also your electronics, then any resistance at this post (i.e. crud between the post clamp and the post itself) will cause a variable voltage drop that is dependent on the instantaneous current being drawn. This high current could be either the draw of the inverter, or the charge current from the alternator. The same logic will be true for problems at the positive clamp. One thing that I can't remember if you listed was if the hum is always present. For example, is it only there when the engine is running? Does the hum change frequency with engine speed? These would lean towards high resistance batteries and/or the bad battery post clamp contact. If the hum is there even with the engines off, and more importantly if it does not change with engine speed, then it likely is the constant 60 Hz hum from the inverter, and may still be the battery connections, but also could be a high resistance connection in the AC common side from the inverter and not easy to track down. Let us know what you find. Hope this helps narrow down the sources. Ken Bloomfield www.tellicolady.com