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## Re: [TowerTalk] Cage dipole alternatives

 To: Bill Aycock Re: [TowerTalk] Cage dipole alternatives "Roger (K8RI)" Mon, 13 Apr 2009 01:42:57 -0400 mailto:towertalk@contesting.com>
 ``` Bill Aycock wrote: > Rick > Interesting alternative. I have a question about the concept. As I > understand it, the "cage" concept needs for the wires to be close enough to > The "cage" is pretty much a regular dipole with a large length to diameter (l/d) ratio as given in the hand book. It's also a very old design and can be found in early literature. It "to me" is an enlargement to the "fan dipole" concept. IOW it matters not (electrically) whether the ends are tied together or not. Physically it makes a big difference as once up the fan dipole is fairly rugged (depending on construction and only needs one support for each end. It also represents a *relatively* small profile compared to an actual conductor of that size. OTOH as I mentioned in an earlier post, it does not handle ice well. The cage will work with only two wires, but it is simulating a large diameter conductor so a few more would be prudent. "I doubt" much would be gained to go beyond 6 or 8, but I've never seen anything definitive as to where rapidly diminishing returns becomes a factor. 4 is likely to provide a reasonable bandwidth. There, yah went and done it...I had to dig out the books <:-)) To Quote the ARRL Antenna Handbook (Pg 9-4, 20th edition) :"The gain and radiation patterns are essentially the same as a thin wire dipole"..."The bow-tie and fan dipole make use of the same Q-lowering principle as the cage for increased match bandwidth." They use a 6" diameter cage for an example. The matched bandwidth should be 1.79 times the matched bandwidth of a single wire dipole for their example antenna. > act as one *large* conductor. How close fits this concept? In the case of a > Fan with diverging wires, where does the "single large conductor" > equivalence fail? > No where specific and yet it'd dependent some what on the separation (think bow tie) and the lengths also play a part. IOW cut one for the higher end of the band and the second for the lower. Add a third for in between. I've never been able to make the multi-band dipole using wires for each band to work as they show it. I've always had to use much more end separation. Adding more wire changes the end effect and capacitance which results in antennas being some what shorter than single wire antennas be they multi-band, cage, or fan. With the cage the length should come out pretty close using the standard formula with the l/d ratio taken into account. As to the antenna that originally raised this question with claims of measured gain of 5 dbd, as I've mentioned before, there could be many reasons for that figure to have actually been measured when comparing two dipoles. In "that test" the antenna likely did show that gain *compared* to the reference dipole, but in the real world the cage is not an antenna with any essential gain over a thin wire dipole as far as any antenna book (including college texts) will show. They are a good antenna, essentially rugged in most aspects and almost twice the bandwidth of a thin wire dipole (depending on size). They are easy to build IF you have the room to lay out the wires. Typically they are not an antenna you want to assemble in a small room.<:-)) 73 Roger (K8RI) > Bill-W4BSG > > ----- Original Message ----- > From: "Rick Stealey" > To: > Sent: Sunday, April 12, 2009 8:28 AM > Subject: [TowerTalk] Cage dipole alternatives > > > >> If anyone would like to discuss other forms of broadband antennas and >> ways to build or model them please join in. >> I believe, although I'm not 100% sure, that discussions of all forms of >> antennas >> are permissible on towertalk. >> >> I started modeling with a simple dipole, got 200 KHz bandwidth, then added >> another element fan-style and got 300 KHz bandwidth. >> >> Then to see what a cage might do I added a third element and made all >> three >> parallel separated by 1 meter. I think that is probably a pretty fair >> approximation, and as time allows I will add more wires and prove that >> connecting them at the far end isn't necessary. >> >> Rick K2XT >> >> _________________________________________________________________ >> Windows Live™: Keep your life in sync. >> http://windowslive.com/explore?ocid=TXT_TAGLM_WL_allup_1a_explore_042009 >> _______________________________________________ >> >> >> >> _______________________________________________ >> TowerTalk mailing list >> TowerTalk@contesting.com >> http://lists.contesting.com/mailman/listinfo/towertalk >> >> >> > > > _______________________________________________ > > > > _______________________________________________ > TowerTalk mailing list > TowerTalk@contesting.com > http://lists.contesting.com/mailman/listinfo/towertalk > > _______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk ```
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