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Carbon Rod Antenna Improvement


It is getting quite popular to use carbon fishing rod as an antenna radiator in Japan recently.

It worked pretty well at high HF bands such as 21MHz band, but the performance was getting poor at low bands. This time I tried to firmly attach the paper clip to the rod surface using clamps in hoping to reduce resistance component in the antenna so that the efficiency should be improved especially at low bands.

The following video shows a recent my activation using a carbon rod.

The antenna performance was improved dramatically even in 14 and 7MHz bands. It apparently indicates the contact resistance at the feeding point is significantly influence antenna performance. I believe connection between sections are capacitive making the effective antenna length shorter but no harm for efficiency.

Carbon rod is very light and rigid (also is getting cheaper!), and it can be a perfect antenna for SOTA activations.

You still don’t believe it? Hey, try it. It works and fun!

Thanks. de JG1GPY Takeshi

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Compare the resistivity of copper to carbon. Now tell me if you think a copper wire or a carbon rod would make a more efficient radiator.

73
Ron
VK3AFW
Diploma in balloon deflation.

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Thank you for the comment. The efficiency of an antenna is defined by some how a ratio between radiation resistance and ohmic resistance: Energy emitted from the antenna and heat dissipated in the antenna.

If the resistance value is relatively small comparing with radiation resistance, the antenna works well. The antenna doesn’t work at low frequencies well as radiation resistance is getting smaller at low bands for limited element length. Pure comparison between copper and carbon material is important but does not give you insight of the antenna. de JG1GPY

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I think that’s flawed logic. The feed point may have a high impedance but if the antenna has a current node somewhere within the carbon section the losses due to resistance could be significant. I suppose a base loaded vertical might work with low losses if the carbon section above the loading coil is significantly shorter than a quarter wavelength. Is that the suggested configuration?

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Feed point registance is not radiation resistance. e.g. radiation resistance of 0.5lambda dipole is 73+j43 and it is nothing to do with your feeding position. Antenna efficiency is related with radiation resistance and ohmic resistance. I still believe an antenna works well if ohmic resistance is relatively small comparing with the radiation resistance. Radiation resistance is getting smaller as element length relative to the wave length becomes shoter; antenna efficiency is getting worse for a given ohmic resistance.

On the other hand, influence of feeding point resistance is more prominent if feed point current is large. I agree with it.

Takeshi JG1GPY

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