End Feed Half Wave Antenna Problems
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| Aug 3rd 2015, 14:39 | |
AB2WSTotal Topics: 0 Total Posts: 0 |
I am trying to construct a 40m End Feed Half Wave Antenna (EFHWA) for QRPp that doesn't need a tuner, but am seeing very high SWR in the 40m band. I have read what information I could find in these forums and on the net (http://www.aa5tb.com/efha.html). The antenna was constructed for the 40m CW band as follows: (1) 67' of 24 AWG insulated stranded wire for the radiating element [468/7.0 Mhz= 66.8' which is 1/2 wavelength] (2) ~7' [0.05% of a wavelength] or 34' [1/4 wavelength] of same wire for counterpoise- I tried 2 lengths (3) 9:1 UNUN toroid wound matching unit using a junk box toroid. I used 3 conductor ribbon cable for the winding (http://vk6ysf.com/unun_9-1.htm). (4) 6' BNC-BNC RG58 coax jumper from rig to UNUN I tested the UNUN by putting 470 ohm resistor across the terminals, patch cable to IC-7000; It showed low SWR accross 40m. I tossed the 67' radiator out my 2nd story window in a slight inverted V configuration and tested with no counterpoise, 7' counterpoise, and 34' counterpoise. In all cases the SWR was off scale for 40m; however, it showed low SWR on 80m. Since 67' is 1/4 wavelength on 80m I reconfigured antenna as 34' radiator, 7' counterpoise with UNUN and this tunes up on 40m. It seems I am making 1/4 end feed antennas?!? What is the radiation pattern of a 1/4 wave end feed antenna and can anyone explain why the 1/2 wavelength antenna isn't working? Thanks, James |
| Aug 3rd 2015, 17:43 | |
W1VTSuper Moderator Total Topics: 0 Total Posts: 0 |
The fact that its working where it shouldn't suggests some sort of wiring error. Zack Lau W1VT ARRL Senior Lab Engineer |
| Aug 13th 2015, 12:57 | |
K3DRJTotal Topics: 0 Total Posts: 0 |
How about trying to shorten the 67 foot element 33.5 feet and making the "counterpoise" 33.5 feet and making it look like a center fed halfwave dipole in an "L" configuration? - Jim - |
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