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CDX,
I think my loop diameter is larger then Bob's because I started with a diameter that would get me as close as mechanically practical to the 20 degree angle suggested in the Avanti patent for maximum gain. Then I just adjusted the radial length to peak the gain and make the entire assembly equal to a 1/4 wave electrical length again.

I'm in the USA and Bob is in the UK. Our 11 meter AM/SSB bands in the USA are below the UK FM band. This could also account for the question of radiator length you asked about. Also keep in mind the point at which the gamma match contacts the main radiator will also influence apparent main radiator length to some degree. I find my tap point is lower then stock. I'll also mention on 11 meters this antennas SWR is not easy to set if you're not at least 36 feet above the ground. My resonance shifted slightly lower then desired when the antenna was installed higher.

Your comment about the collinear was a great idea we both thought was good. I built FM broadcast prototypes and even filed a design with the PTO years ago. The FM collinear antenna was called the Phazor. Bob has some pictures. No matter how you adjusted the radiator lengths and phasing section, you could not get the full expected 3 db increase in gain.

Best I could get was around a 1.5 db increase if everything was tuned perfect with the collinear. If not, all types of unexpected things could happen like strong directional lobes at the expense of uniform omni-directional gain. I believe the long 7/8 wave design is a poor choice for the bottom section of a collinear since much energy is radiated off it's surface before it can drive the next section. I later favored the phasing of multiple antennas rather then collinear stacking a single antenna to increase gain on VHF.

<blockquote data-quote="Shockwave" data-source="post: 172332" data-attributes="member: 10882">CDX,I think my loop diameter is larger then Bob&#039;s because I started with a diameter that would get me as close as mechanically practical to the 20 degree angle suggested in the Avanti patent for maximum gain. Then I just adjusted the radial length to peak the gain and make the entire assembly equal to a 1/4 wave electrical length again. I&#039;m in the USA and Bob is in the UK. Our 11 meter AM/SSB bands in the USA are below the UK FM band. This could also account for the question of radiator length you asked about. Also keep in mind the point at which the gamma match contacts the main radiator will also influence apparent main radiator length to some degree. I find my tap point is lower then stock. I&#039;ll also mention on 11 meters this antennas SWR is not easy to set if you&#039;re not at least 36 feet above the ground. My resonance shifted slightly lower then desired when the antenna was installed higher.Your comment about the collinear was a great idea we both thought was good. I built&nbsp; FM broadcast prototypes and even filed a design with the PTO years ago. The FM collinear antenna was called the Phazor. Bob has some pictures. No matter how you adjusted the radiator lengths and phasing section, you could not get the full expected 3 db increase in gain.Best I could get was around a 1.5 db increase if everything was tuned perfect with the collinear. If not, all types of unexpected things could happen like strong directional lobes at the expense of uniform omni-directional gain.&nbsp; I believe the long 7/8 wave design is a poor choice for the bottom section of a collinear since much energy is radiated off it&#039;s surface before it can drive the next section. I later favored the phasing of multiple antennas rather then collinear stacking a single antenna to increase gain on VHF.</blockquote>

[QUOTE="Shockwave, post: 172332, member: 10882"] CDX, I think my loop diameter is larger then Bob's because I started with a diameter that would get me as close as mechanically practical to the 20 degree angle suggested in the Avanti patent for maximum gain. Then I just adjusted the radial length to peak the gain and make the entire assembly equal to a 1/4 wave electrical length again. I'm in the USA and Bob is in the UK. Our 11 meter AM/SSB bands in the USA are below the UK FM band. This could also account for the question of radiator length you asked about. Also keep in mind the point at which the gamma match contacts the main radiator will also influence apparent main radiator length to some degree. I find my tap point is lower then stock. I'll also mention on 11 meters this antennas SWR is not easy to set if you're not at least 36 feet above the ground. My resonance shifted slightly lower then desired when the antenna was installed higher. Your comment about the collinear was a great idea we both thought was good. I built FM broadcast prototypes and even filed a design with the PTO years ago. The FM collinear antenna was called the Phazor. Bob has some pictures. No matter how you adjusted the radiator lengths and phasing section, you could not get the full expected 3 db increase in gain. Best I could get was around a 1.5 db increase if everything was tuned perfect with the collinear. If not, all types of unexpected things could happen like strong directional lobes at the expense of uniform omni-directional gain. I believe the long 7/8 wave design is a poor choice for the bottom section of a collinear since much energy is radiated off it's surface before it can drive the next section. I later favored the phasing of multiple antennas rather then collinear stacking a single antenna to increase gain on VHF. [/QUOTE]

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