I've removed thousands of feet of LMR-400 feedline from radio sites as a process to source and eliminate IMD, mixing gremlins and unwanted effects. Most all of it was in duplex service, but not every example.
> I believe the issues with LMR were resolved years ago > Chuck. Can you refresh the group on some of the > primary issues? No resolved issues that I've seen news of, Times Microwave LMR-400 is still constructed with dissimilar metals, copper and aluminum subject to galvanic corrosion. There are three conditions that must exist for galvanic corrosion to occur. First there must be two electrochemically dissimilar metals present. Second, there must be an electrically conductive path between the two metals. And third, there must be a conductive path for the metal ions to move from the more anodic metal to the more cathodic metal. If any one of these three conditions does not exist, galvanic corrosion will not occur. Times Microwave LMR-400 feed line meets all three conditions for galvanic corrosion to occur. Often when design requires that dissimilar metals come in contact, the galvanic compatibility is managed by "finishes and plating". The internal finishing and plating selected facilitate the dissimilar materials being in contact and protect the base materials from corrosion. When the feed-line even slightly vibrates (IE wind movement) the internal finishing and plating is modified and eventually it will start to break down. In addition to potential Galvanic Corrosion issues you can actually experience signal generation (noise) when the feed line moves in the wind (or by manual physical movement). The same mechanism is what allows a dry-cell battery to produce electricity. And dissimilar metals contacts can also become potential (point contact) diodes, another page of RF fun. Hope that helps explain it... cheers, skipp
