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I hope you received my response to you directly (5/31/2003 UTC) after your earlier question about the "C4 tuning jumper recap." My own experience was that the initial settings did place my C-4D's resonant point below 7.0 MHz with my particular installation. I interpret the assembly instructions to mean that antenna resonant frequency for the 40 meter element is determined by adjusting the linear loading wires. I used an Autek Research RF-1 "RF Analyst" to determine the lowest SWR at the shack-end of the coax. I had to move the linear loading jumpers out several inches from the spreader/boom toward the element tips. I adjusted the lowest SWR to my frequency of choice within the 40 meter band. My Force 12 C-4 instructions say, "If [the VSWR] is not less than 1.3:1 in the band, adjust the hairpin by spreading or pushing together the coil for the lowest VSWR in the band." Since the 40 meter dipole's characteristic impedance is not 50 ohms, the hairpin/coil is used as an impedance matching device to help the coax and therefore the transmitter to see a lower VSWR than it would otherwise. Briefly stated, I recommend you adjust the jumpers first and then fine tune with the hairpin/coil. I am very happy with my C-4D. Best wishes with your antenna and gud DX. 73, Jerry K7VIT P.S. Thanks to the reflector for helping me with other questions with your collective knowledge. ----- Original Message ----- From: "WW3S" <ww3s@zoominternet.net> To: <Force12Talk@qth.com> Sent: Wednesday, July 23, 2003 01:44 Subject: [Force 12 Talk] c4 tuning/coil > Finally got the C4 in the air; I've had the C3E for a while and installed > the 40m element a couple months ago and just now got everything in the air > (approx 70'). 2:1 points on 40 are from 6.9 to just about 7.0. I think I > used the midpoint dimensions; I think I have the coil installed correctly > although it is fairly close to the boom. I'm close enough that the autotuner > should match but I'd like to be resonant in the band in case I ever go with > another rig or SO2R. Should I try the jumpers or the coil first? How > sensitive are the jumpers to the tuning? Or should I just leave it be.... > > 73 Jamie WW3S > > -------------------------------------------- Force12Talk mailing list provided as a service by Force 12 Antennas, Inc. Force12 Web Site: http://www.force12inc.com To Submit Message to the List: Force12Talk@qth.com To unsubscribe and view the Message Archive: see http://qth.com/force12/list For problems with the list: contact force12@qth.com |
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