Tuesday, 26 May 2009
Vertical half-wave aerials for 4m
I have a Wouxun handheld for four metres which I use for Summits on the Air activations. While talking to Ros G6GVI on 23cms he pointed me to his design for a vertical half-wave aerial for 4m on the Four Metre Website. http://www.70mhz.org/halfwav.htm I have made one and it works at least as good as the half wave Watson I have up at home. Others have had success with J-Poles and Slim Jim antennas made from ribbon cable, but there seems to be a wide variation in the measurements dependent on the cable. I have made J-poles and Slim Jims for two metres successfully in the past but I had no luck with the one for 70mHz.
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Hi - using 300 Ohm ladder line, the correct dimensions for the 70Mhz slim jim can be found at:
ReplyDeletewww.summitsbase.org.uk/tiki-index.php?page=4m+J-pole
I have made this one and it works perfectly.
I previously tried several designs, all of which failed miserably!
Steve, MW0KST
The dimensions of the 70Mhz Slim Jim at www.summitsbase.org.uk/tiki-index.php?page=4m+J-pole
ReplyDeleteonly seems to work for a certain type of 300 ohm ribbon. It certainly does not work for the cable I have here. I suspect it is to do with the carbon content of the black plastic used in the insulator in Mike's design. I have made 10 versions from the grey coated cable I have but could not get any of them to work. It is not really surprising when you model a Slim Jim or J-pole at 4M the gap between the 1/4 stub and vertical section should be about 6 inches and we only have a 1/4 inch gap using 300 ohm ribbon.
New URL for this article on summitsbase is http://www.summits.org.uk/tiki-index.php?page=4m+J-pole
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