Carbon Fiber Masts - Good or Bad?

[Marvin VE3VCG]

Light weight gear is important for man portable operations. Recently carbon fiber masts have become available. These are very light and stiff but are reported to generate losses. The amount of loss, if any seems to be somewhat controversial. I've seen several different videos on this subject and would be interested to get any feedback from someone with real field experience using a carbon fiber mast. I'm sharing a video from SOTA Beams demonstrating one of their carbon fiber masts both in the field and in the lab.

[VA3KOT John]

I have never used a carbon fibre mast but logic suggests the effects would be negligible. I have erected an antenna in trees hundreds of times and trees are electrically conductive. Why worry about perfection in an antenna? Every antenna is a compromise in way or another. The object of raising an antenna is to make contacts. If the antenna is slightly lossy it doesn't matter. It takes a loss of 6dB just to lose one S-unit. Is it really important if you get a signal report of 58 instead of 59? (That is assuming the common ham mistake of reporting the S-meter reading as the "S" in an RST signal report - it isn't! See: http://www.radioing.com/hamstart/rst.html)

[VE3WI Dave]

I'm sure I've seen discussions on QRZ.com and eHam.net about the effects of carbon fiber masts.  Some forum searches may yield useful information. 

My opinion: I don't have one of those masts.  I have read that some of the cheaper ones aren't carbon fiber at all, just fiberglass tinted black.  A real carbon fiber mast is made from long fibers wound on the bias, thus will be somewhat conductive.  I wouldn't expect any significant coupling into a vertical mast from a horizontal or near horizontal antenna due to the near 90° angle between the mast and the antenna.  After all, people use steel & aluminum masts to hold up dipoles.  On the other hand, if you tape a wire onto the mast to make a vertical antenna, RF will be coupled into the mast, which will degrade the antenna's performance (degree?).  If you run the wire up inside the hollow mast, I would expect significant shielding.

Suggestion: buy one & do some measurements.  It would make a good TCA article, RAC's always looking for material.

Re effect of trees on antenna emission: two detailed studies were published in QST in the last few years (by Dr. Steve Stearns K6OIK & Dr. Kai Siwiak KE4PT).  If anyone is really interested let me know & I'll lend you the magazines.

73
Dave, VE3WI

[Adam_VE3FP]

The fact that no antenna is perfect, I never worried about some loss. Now days lot of hams are using some form of weak signal digital communications so not so perfect antennas still perform quite well. My 160 meter offset dipole is strung out through several tree branches and I have no problem making contacts. Like John said earlier post, 59 vs 57 report is really not something to worry about but in poor conditions if signal drops 3 or 4 S-units then better antenna would help to pull in the weaker stations.

If I come across one of those carbon fiber masts for a decent price I will get one to use when camping and setup as vertical. I imagine carbon fiber poles are fairly expensive and other alternatives might be better. Until then tree branches will suffice for my installations.

[Marvin VE3VCG]

Thanks for the feedback. Your idea about testing as the basis for an article for TCA is a good one. I have a SOTA beams fiberglass mast but can't do a comparison without first buying a carbon fiber mast, however I'm looking ahead to get one and then testing shall commence.

I'm sure I've seen discussions on QRZ.com and eHam.net about the effects of carbon fiber masts.  Some forum searches may yield useful information. 

My opinion: I don't have one of those masts.  I have read that some of the cheaper ones aren't carbon fiber at all, just fiberglass tinted black.  A real carbon fiber mast is made from long fibers wound on the bias, thus will be somewhat conductive.  I wouldn't expect any significant coupling into a vertical mast from a horizontal or near horizontal antenna due to the near 90° angle between the mast and the antenna.  After all, people use steel & aluminum masts to hold up dipoles.  On the other hand, if you tape a wire onto the mast to make a vertical antenna, RF will be coupled into the mast, which will degrade the antenna's performance (degree?).  If you run the wire up inside the hollow mast, I would expect significant shielding.

Suggestion: buy one & do some measurements.  It would make a good TCA article, RAC's always looking for material.

Re effect of trees on antenna emission: two detailed studies were published in QST in the last few years (by Dr. Steve Stearns K6OIK & Dr. Kai Siwiak KE4PT).  If anyone is really interested let me know & I'll lend you the magazines.

73
Dave, VE3WI

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Thanks for the feedback. Your points are well taken. The general conciseness seems to be that when holding a horizontal wire the loss would be nil. However one might run into a problem with something like an inverted L. The solution then seems obvious enough, don't put up any vertical antenna with an antenna with any vertical components.

I have never used a carbon fibre mast but logic suggests the effects would be negligible. I have erected an antenna in trees hundreds of times and trees are electrically conductive. Why worry about perfection in an antenna? Every antenna is a compromise in way or another. The object of raising an antenna is to make contacts. If the antenna is slightly lossy it doesn't matter. It takes a loss of 6dB just to lose one S-unit. Is it really important if you get a signal report of 58 instead of 59? (That is assuming the common ham mistake of reporting the S-meter reading as the "S" in an RST signal report - it isn't! See: http://www.radioing.com/hamstart/rst.html)

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Thanks for your comments. I currently have have a SOTA beams fiberglass mast, which I've used very successfully in a couple of portable setups. I got it so I could set up a station in various locations where it might not be possible or convenient to use trees.  All the comments seem to agree with the results found in the video.  A carbon fiber mast should have no noticeable effect on an antenna that is strung horizontally. One thing is entirely certain, trees are cheaper than carbon fiber.

The fact that no antenna is perfect, I never worried about some loss. Now days lot of hams are using some form of weak signal digital communications so not so perfect antennas still perform quite well. My 160 meter offset dipole is strung out through several tree branches and I have no problem making contacts. Like John said earlier post, 59 vs 57 report is really not something to worry about but in poor conditions if signal drops 3 or 4 S-units then better antenna would help to pull in the weaker stations.

If I come across one of those carbon fiber masts for a decent price I will get one to use when camping and setup as vertical. I imagine carbon fiber poles are fairly expensive and other alternatives might be better. Until then tree branches will suffice for my installations.

[VA3KOT John]

Carbon fibre and fibre glass masts are not rigid. In fact most of them bend very easily indeed, so an inverted-L's vertical section will be separated from the mast by at least a couple of feet due to the flexing of the mast. Dave's point about running the wire up inside the mast is a good one. The Sotabeam video showed a loss of 0.07dB for wire adjacent to and outside the mast. That would equate to a loss of just over 1/100th of a S-unit.

Just like Adam, I have run wires through trees many times - usually when I am setting up in a Provincial Park for a POTA activation. I am sure the tree must couple with my wire to some extent but I still make lots of contacts.

I own what was originally an MFJ telescoping fibre glass pole. I broke the thin top section by putting too much tension on it, then one day I set it up on a huge tripod. Big mistake, the wind toppled it and it crashed to the ground breaking several sections near the top. I replaced them with sections from a fishing pole from one of the US outdoor stores. If I had the budget I would replace the whole thing with carbon fibre just for the strength.