Topband: High Impedance RX Antennas

[Dennis W0JX]

 There is an old saying "The enemy of good is perfect."  You will be driven crazy by chasing down every slight variance from the ideal. That being said, it is important to check out the obvious areas where flaws can create big problems. Indeed, the feedline coax, typically RG6 CATV line, is a major contributor to array performance problems.  The cheap, big box cable is covered with PVC and that stuff hardens and tightens up over the years. This allows water to enter the shield and the water easily migrates for long distances, creating a high resistance. Spend the money upfront and buy quality cable that is flooded.
The idea of using cable that has a solid copper conductor has merit. But even with that, a bare copper conductor will oxidize over time. I find myself cleaning these conductors on an annual basis with the eraser end of a pencil (recommended by Lee K7TJR).
I have also had F connector failures on my combiner box and on a common mode choke. Sometimes the imported female connector center contact just fails for no reason. The alternative Amphenol connectors are very expensive at about $8+ each but I am considering replacing the connectors with these higher grade parts.
Also, the so-called "water-proof" compression connectors are often not. The connection must be waterproofed effectively.  Also, condensation from humidity can be a big problem. Here is northeast Ohio, the environment is humid for the majority of the year. I have poured water out of a 75 ohm preamp that was sheltered in a good enclosure!
These complex phasing arrays are by no means plug and play. Each installation will be unique depending on layout and surrounding objects. There are three tools necessary to get them and keep them working:  1.) a good portable signal source to feed the antenna preamps (I use an Elecraft XG-3 with a home brew impedance transformer at the input);  2.) a portable transceiver to measure signal out of the system at various points (My KX3 does a great job); and an accurate antenna analyzer to measure impedances and to measure feedlines and phasing lines for the proper electrical lengths. N6RK is right. There can be considerable difference in RG6 impedance so you need to check it out.  
 
 73 Dennis W0JXMilan, OH