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BM, One thing I saw that I wanted to point out to you is that imitation wood you are using for the spreader insulators on the cone may be robbing you of performance. I'm not familiar with that material but I know the Sigma has a very large RF potential between the cone and main radiator as you move upwards from the base.

If the insulator material conducts any RF this will cause loss of gain with the antenna because the insulator will load down the RF feeding the radiator. At high power this would cause the insulator to arc. At low power it may not become apparent it has lowered the performance of the antenna. The easiest way to tell is to throw a sample of the plastic in the microwave. If it melts or burns in under 60 seconds, I'd reject it even at HF.

[QUOTE="Shockwave, post: 414062, member: 10882"] BM, One thing I saw that I wanted to point out to you is that imitation wood you are using for the spreader insulators on the cone may be robbing you of performance. I'm not familiar with that material but I know the Sigma has a very large RF potential between the cone and main radiator as you move upwards from the base. If the insulator material conducts any RF this will cause loss of gain with the antenna because the insulator will load down the RF feeding the radiator. At high power this would cause the insulator to arc. At low power it may not become apparent it has lowered the performance of the antenna. The easiest way to tell is to throw a sample of the plastic in the microwave. If it melts or burns in under 60 seconds, I'd reject it even at HF. [/QUOTE]

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