We've used 1 km of coax to feed a remote Beverage (3 wavelength, 60 degrees, for VK and far east). 750m of the coax is RG6U, with copper braid. The results were poor, despite a 10dB head amplifier at the end of the Beverage, so we measured the coax attenuation on part of the run by putting 25W into the coax and measuring power into a 50 ohm power meter. I appreciate this isn't 75 ohm like the coax but extra losses from 1.5:1 SWR should be low.
The measured loss in the first 250m segment was ~ 6dB and about ~9dB in the second segment, 15dB total over 500m. This is way higher than published figures (eg at http://www.timesmicrowave.com/cgi-bin/calculate.pl) which suggest about 3dB per 250m. I'm thinking that the copper plating on the RG6/U inner conductor is too thin. N6LF gives the skin depth at 2MHz as 40uM (Conductors for HF Antennas, Rudy Severns, QEX November/December 2000). Does anyone have any typical figures for the plating thickness of RG6/U or have evidence that attenuation figures at 2MHz are much higher than expected? 73 Jeremy G3XDK _______________________________________________ UR RST IS ... ... ..9 QSB QSB - hw? BK
