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From OP: Vertical Or Yagi ? New Antenna Worth Trying ?
On Fri, 15 Jun 2007 08:01:34 -0400, "Robert11"
wrote: Hi, Thanks for link to the Shakespeare Vertical Antenna. Know very little about antennas, but was wondering. Is this vertical whip , or any vertical, a better bet to try as compared to perhaps a "simple Yagi for the Marine bands ? Why ? This Shakespeare vertical whip is described as: It's a 6dB collinear phased 5/8-wave antenna of 8-foot nominal length. Again, I'm about 25 miles due west of Boston Harbor, but would sure like to at least try to pick up some Marine VHF comms from the harbor. Hard for me now at my age to try a whole bunch of antennas, so would like to limit it to what you experts feel would offer the best "chance". Thanks again, Bob -------------------------------------- A 5/8-wave collinear has 3dBd gain. Danny |
From OP: Vertical Or Yagi ? New Antenna Worth Trying ?
On Jun 15, 7:54 am, wrote:
On Fri, 15 Jun 2007 05:59:55 -0700, Danny Richardson wrote: On Fri, 15 Jun 2007 08:01:34 -0400, "Robert11" wrote: Hi, Thanks for link to the Shakespeare Vertical Antenna. Know very little about antennas, but was wondering. Is this vertical whip , or any vertical, a better bet to try as compared to perhaps a "simple Yagi for the Marine bands ? Why ? This Shakespeare vertical whip is described as: It's a 6dB collinear phased 5/8-wave antenna of 8-foot nominal length. Again, I'm about 25 miles due west of Boston Harbor, but would sure like to at least try to pick up some Marine VHF comms from the harbor. Hard for me now at my age to try a whole bunch of antennas, so would like to limit it to what you experts feel would offer the best "chance". Thanks again, Bob -------------------------------------- A 5/8-wave collinear has 3dBd gain. Danny However, a 5/8 is only 48inches, that antenna is a stacked 5/8s colinear and at 8ft 6db would be correct. Allison A stacked dual 5/8 collinear will give appx 3dbd.. A single 5/8 GP will do appx 3.3 dbi give or take.. I recommend a small yagi myself.. It will eat the verticals for lunch if both are in the attic. Course, you have to point it though.. MK |
From OP: Vertical Or Yagi ? New Antenna Worth Trying ?
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From OP: Vertical Or Yagi ? New Antenna Worth Trying ?
I was under the impression that a 1/4 wave was approx 0 dBd, a
5/8ths was approx 3dBd, and a collinear dual 5/8ths was approaching 6dBd Nick |
From OP: Vertical Or Yagi ? New Antenna Worth Trying ?
On Jun 15, 2:10 pm, "Nick" wrote:
I was under the impression that a 1/4 wave was approx 0 dBd, a 5/8ths was approx 3dBd, and a collinear dual 5/8ths was approaching 6dBd Nick Most the textbooks rate the 1/4 wave GP at .3 dbi. The 1/2 wave at 2.1 dbi or 0 dbd. The 5/8 GP appx 3.3 dbi, or 1.2 dbd. The dual 5/8 collinear appx 5.1 dbi or 3 dbd. But.... If you model the antennas, the sloping radial 1/4 GP actually does a bit better.. Appx 1.8 dbi, which is within .3 db of the 2.1 dbi you would see from a 1/2 wave. BTW, these are "free space" numbers. I don't like to confuse people by adding ground effects... Besides, if you do model over ground, you will see the same comparison spread.. It doesn't really change anything.. The gain from a 5/8 GP can be all over the map depending on the radial length used.. Most 5/8's use 1/4 wave radials. No bueno. At an old page I put up, you can see the effect of radial length on the performance of the 5/8 GP. http://web.wt.net/~nm5k/acompari.htm Many people rag on the 5/8 antenna, but the largest problem is due to an old lousy obsolete design which uses the short 1/4 wave radials. If you use longer radials, such as 5/8 or 3/4 you will see the rated gain you would expect from a 5/8 GP. If you use 1/4 wave radials, you can often see less gain at the desired angles than either the 1/2 wave, or 1/4 GP. Of course, all these examples assume no common mode currents on the feedline.. On VHF/UHF, decoupling of the feedline can be as important as the antenna design itself. So if I were to build say a dual 5/8 collinear, or a 5/8 GP with steep 5/8 radials, I would add a decoupling section below the lower element. IE: like an isopole, or whatever.. It used a lower 1/4 wave cone as the decoupling device. You could also add a section of 1/4 wave radials for decoupling.. 6dbd from a dual element vertical? Good luck..A 3 el NBS yagi is only good for about 7.3 dbd, and it will thrash a dual 5/8 collinear. If the height is limited, I would use the highest gain antenna I could scrape up. Even if you have obstructions, it's going to do a heck of a lot better than most any vertical at the same height. MK |
From OP: Vertical Or Yagi ? New Antenna Worth Trying ?
Nick wrote:
I was under the impression that a 1/4 wave was approx 0 dBd, a 5/8ths was approx 3dBd, and a collinear dual 5/8ths was approaching 6dBd Nick 5/8ths isn't what it's advertised it to be. I'd explain it, but I have to finish watching SG1 and then F1 practice session 2. It has to do with "ground planes" and the fact that they are mostly fictional in this case. And that the second 5/8ths doesn't have the needed "ground plane". I'm sure someone else will explain fully. tom K0TAR |
From OP: Vertical Or Yagi ? New Antenna Worth Trying ?
On Jun 15, 6:46 pm, Tom Ring wrote:
5/8ths isn't what it's advertised it to be. I'd explain it, but I have to finish watching SG1 and then F1 practice session 2. It has to do with "ground planes" and the fact that they are mostly fictional in this case. And that the second 5/8ths doesn't have the needed "ground plane". I'm sure someone else will explain fully. tom K0TAR In my opinion, a 5/8 vertical should be set up to be a complete antenna, which means it needs 5/8 on the "other" side.. Running a 5/8 over 1/4 wave radials is fairly perverted.. It's no wonder it doesn't live up to expectations. But a dual 5/8 collinear is a pretty stout vertical, as far as verticals go. I think 5/8 ground planes should use either 3/4 or 5/8 wave radials if one uses actual radials, to more closely simulate a collinear. A dual 5/8 collinear is a complete antenna, and requires no radials at all. I compared all the usual types "lengths" on 10m a few years ago, and my 5/8 GP with four 3/4 wave radials handily beat a base fed half wave, with and without decoupling. I used 3/4 wl radials because I wanted a low Z.. But if I made one with real steeply sloped radials, I think I would make them 5/8 wave. But, I never got around to trying one with 5/8 radials, so not sure how it would compare to my last version. BTW, all my tests were done using "ground/space" wave locally, and were pretty accurate as far as telling which was best. I'm using a low angle path for that type of thing too.. Many of the people I talked to were 20-30-40 miles away. MK |
From OP: Vertical Or Yagi ? New Antenna Worth Trying ?
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From OP: Vertical Or Yagi ? New Antenna Worth Trying ?
On Jun 15, 8:01 pm, John Smith I wrote:
wrote: ... In my opinion, a 5/8 vertical should be set up to be a complete antenna, which means it needs 5/8 on the "other" side.. ... Obviously, OCF antennas must set you off also. JS Fer sure... MK |
From OP: Vertical Or Yagi ? New Antenna Worth Trying ?
John Smith I wrote:
wrote: ... In my opinion, a 5/8 vertical should be set up to be a complete antenna, which means it needs 5/8 on the "other" side.. ... Obviously, OCF antennas must set you off also. JS Yes, they are certainly counter-intuitive ... there is form and beauty in symmetry alright. JS |
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