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#1
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I think it would be possible to alter the "beam width" of the omni-antenna
(mobile) and so make it "better." If you take the time to learn EZNEC or MMANA you can view this for yourself in the plot of the radiation pattern.... Regards, John "Ken Bessler" wrote in message news:A8c7e.14295$up2.5543@okepread01... Is it possible to make a mobile 10m antenna that is physically shorter than a 1/4 wave whip yet will preform better than a 1/4 wave whip? -- 73's es gd dx de Ken KGØWX Grid EM17ip, Flying Pigs #1055, Digital On Six #350, List Owner, Yahoo! E-groups: VX-2R & FT-857 |
#2
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"John Smith" wrote in message
... I think it would be possible to alter the "beam width" of the omni-antenna (mobile) and so make it "better." If you take the time to learn EZNEC or MMANA you can view this for yourself in the plot of the radiation pattern.... Regards, John Thanks John but that's not what I meant. For the record, I'm trying to understand some manufacturer's claims that the antenna they sell, while smaller than a 1/4 wave whip on 10m, puts out a better signal. Here are the rules: 1) The antenna is at least 25% shorter than a 1/4 w whip 2) The antenna is made with ordinary materials - no friggin gold. 3) The antenna is omni-directional & vertically polarised 4) The feedline is Flexi 4XL, aka CQ-102 5) The antenna is mounted dead center on the roof of a van. 6) The antenna's mount is non magnetic - I.E. There is a good DC/RF ground at both the base of the antenna & the radio. The way I see it is there is no way to make an antenna that meets all those rules and STILL has more than 2.14dbi gain due to resistave losses. Am I right? -- 73's es gd dx de Ken KGØWX Grid EM17ip, Flying Pigs #1055, Digital On Six #350, List Owner, Yahoo! E-groups: VX-2R & FT-857 |
#3
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Thanks John but that's not what I meant. For the record,
I'm trying to understand some manufacturer's claims that the antenna they sell, while smaller than a 1/4 wave whip on 10m, puts out a better signal. ================================ There ARE such things as Human Rights. Antenna salesmen have to make a living. They have wives, children and mortgages just like anybody else. |
#4
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"Ken Bessler" wrote
For the record, I'm trying to understand some manufacturer's claims that the antenna they sell, while smaller than a 1/4 wave whip on 10m, puts out a better signal. Here are the rules: 1) The antenna is at least 25% shorter than a 1/4 w whip 2) The antenna is made with ordinary materials - no friggin gold. 3) The antenna is omni-directional & vertically polarised 4) The feedline is Flexi 4XL, aka CQ-102 5) The antenna is mounted dead center on the roof of a van. 6) The antenna's mount is non magnetic - I.E. There is a good DC/RF ground at both the base of the antenna & the radio. __________ A perfectly "omni" azimuth pattern is unlikely from a v-pol whip of any length when mounted on the roof of a van, however ~ 2.15dBi lobes could exist in some directions. The electrical environment around the van will shape the pattern further. This could be modeled in NEC to give some insight into the situation. RF |
#5
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The way I see it is there is no way to make an antenna that meets all those rules and STILL has more than 2.14dbi gain due to resistave losses. Am I right? I was a friend of Jim Taylor and Jim Taylor Jr. of Taylor Radio back in the good-ole CB days. Sitting at lunch one day we were discussing the old Big-Stick and Grand Slammer antennas (I think those are the names of the 5/8 wave base verticals most popular in that day). They told me that the market ting departments of the two companies made more antenna gain progress than their engineering departments did. I was slow to understand the statement at that time, so they explained that every time one came out with an ad, the competitor had to match or beat it. While the comparisons started with a 1/4 wave vertical, Jim said that if it continued, antenna manufacturers would have to start comparing gain to their antennas against loaded coat-hangers. In the truck stops, there are several antennas that are shortened 5/8 antennas. I think that is the case with Fire-stick. I can't tell you if it has a gain or loss over a 1/4 wave whip. Just a side-note tho... I have a 706 MKII in the car. I had a 6 meter whip on a mag-mount connected to the HF side where I was listening to a local beacon. I removed the 6 meter whip and replaced it with a White GMS/Volvo CB whip about an inch shorter (the cb antenna is just under 4 feet long.) The signal of the 6 meter beacon came up from 1/2 to full scale. I swapped back and forth and tested the SWR to make sure. The CB antenna was maximum SWR but sounded considerably better. I have several of these antennas so I am planning to try to trim one for 6 meters and use it instead of the whip I am using now. I don't have enough data to determine what causes the improvement, but I believe I have ruled out propagation. Buck N4PGW -- 73 for now Buck N4PGW |
#6
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Just a side-note tho... I have a 706 MKII in the car. I had a 6
meter whip on a mag-mount connected to the HF side where I was listening to a local beacon. I removed the 6 meter whip and replaced it with a White GMS/Volvo CB whip about an inch shorter (the cb antenna is just under 4 feet long.) The signal of the 6 meter beacon came up from 1/2 to full scale. I swapped back and forth and tested the SWR to make sure. The CB antenna was maximum SWR but sounded considerably better. I have several of these antennas so I am planning to try to trim one for 6 meters and use it instead of the whip I am using now. I don't have enough data to determine what causes the improvement, but I believe I have ruled out propagation. You should have checked several becons in diffearant directions. A few years back a friend and I had several 2 meter antennas that would fit the same mount. While checking out several repeaters in differant directions we found one antenna would be beter in one direction and another in a differant direction . It may have been due to the differance in the lobes of the antennas and the height of the repeaters. |
#7
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On Mon, 18 Apr 2005 15:33:06 GMT, "Ralph Mowery"
wrote: Just a side-note tho... I have a 706 MKII in the car. I had a 6 meter whip on a mag-mount connected to the HF side where I was listening to a local beacon. I removed the 6 meter whip and replaced it with a White GMS/Volvo CB whip about an inch shorter (the cb antenna is just under 4 feet long.) The signal of the 6 meter beacon came up from 1/2 to full scale. I swapped back and forth and tested the SWR to make sure. The CB antenna was maximum SWR but sounded considerably better. I have several of these antennas so I am planning to try to trim one for 6 meters and use it instead of the whip I am using now. I don't have enough data to determine what causes the improvement, but I believe I have ruled out propagation. You should have checked several becons in diffearant directions. A few years back a friend and I had several 2 meter antennas that would fit the same mount. While checking out several repeaters in differant directions we found one antenna would be beter in one direction and another in a differant direction . It may have been due to the differance in the lobes of the antennas and the height of the repeaters. Thanks, That was the only 6 meter beacon I could hear. I knew/know that the one beacon wouldn't be a good sample but I was/am still surprised that the difference was 1/2 scale on the radio. It went from scratchy to full quieting and full scale. I didn't spend much time on it as my objective was to trim the antenna for ten meters. It is interesting though. Buck -- 73 for now Buck N4PGW |
#8
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Ken, KG0WX wrote:
'Is it possible to make a mobile 10m antenna that is physically shorter than a 1/4 wave whip yet will perform better than a 1/4 wave whip?" In general, the full-sized 1/4-wave whip is a very good compromise mobile antenna because it can be self-resonant, and it is almost omnidirectional in azimuth. Physically, slightly shorter than a CB antenna, it is readily available by trimming a CB antenna to resonance, literally, or by using a low-loss variable capacitor in series. It is possible to use an antenna less than 1/4wavelengrh against ground as an efficient radiator but it requires care to minimize loss. Shortening the radiator reduces its vertical directivity. If gain is the performance measure, vertical directivity lost by shortening must be replaced, perhaps by horizontal directivity. Gain from horizontal directivity needs to cover not only lost vertical directivity, but losses caused by loading too-short elements in the array. These elements may produce horizontal directivity where none exists with a sole avertical element. In the September 1973 "QST" is "A Bite Size Beam". This article refers the reader to an earlier March 1973 QST article by Sevick, "The W2FMI Ground-Mounted Short Vertical". Summary: Can you do it? Yes. Is it practical? Maybe. Best regards, Richard Harrison, KB5WZI |
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