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Title: Match on 75M Mobile whip Post by: WU2D on August 05, 2011, 05:44:23 PM Well I finally got a more conventional mobile whip on the air. My minihustler mag mount was not a great situation even though it did work. The good old MO-2 mast is slick and the fold over feature is nice.
This should be a bit more efficient. One thing I did was attempt a shunt match and I can say it worked out better than I imagined. It is simply 13 turns of # 12 enamelled on a 1 1/2 inch PVC form; bottom grounded and coax tapped up 5 turns. The top of the coil feeds the bottom of the mobile whip. This match not only gives a DC ground (very nice for noise and safety), but it takes a modest 1.7:1 match without the device and makes it essentially a perfect match, and without disturbing the resonant frequency too much. I have a small capacity hat that I slip on to reach 3570 for CW. By pulling the whip all the way out I can not quite hit the bottom of the band which is normal for the 75M resonator. With the capacity hat which is simply six 4 inch wires off a brass spoke hub. On the road tomorrow AM. Mike WU2D Title: Re: Match on 75M Mobile whip Post by: AJ1G on August 05, 2011, 05:53:11 PM Looks good Mike - does it bonk on the trunk from the spring? Looks like you're going without any guy lines..makes for a clean look.
Title: Re: Match on 75M Mobile whip Post by: W7TFO on August 05, 2011, 06:38:36 PM Good antenna idea.
Say, what is all that green stuff on the ground? ;) 73DesertDG Title: Re: Match on 75M Mobile whip Post by: WU2D on August 05, 2011, 07:04:18 PM I will definitely put some big monofillament from the rear seatbelt guides from each side out the door to the whip and we will see how it bonks the car - good prophesy on that; I may slip some foam pipe around the thing at the likely contact point. So it may not look so clean by the time I am done with the trip!
Mike WU2D Title: Re: Match on 75M Mobile whip Post by: WU2D on August 08, 2011, 06:29:08 AM The Solar flare did me in on the way up but coming home Sunday, the new antenna did a great job. The Shunt match worked perfectly right across the band. All you have to do is resonate the whip up top. AJ1G says that to get optimal better performance, I need to raise the feed to at least the trunk level or up about 1 ft. I will ponder this.
Mike WU2D Title: Re: Match on 75M Mobile whip Post by: WA1GFZ on August 08, 2011, 09:54:59 AM gee I just did the same type of match on 600M Sunday...but the coil was bigger and the antenna 200 foot inverted U AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
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