Telescopic Tube for 18 GHz pole-mast

[Fill]

I'm building a mast to deploy a measurement antenna, a small omnidirectional biconical, with a 1-18GHz range. Carbon fiber seems to be an ideal material which will cause minimal interference or reflections.

I need the mast  (pole) to collapse to < 54 cm (21"), and extend to > 2.5m (100"). It will be supporting a weight centered on pole, and weighing <5 lbs.
Which is the best telescopic solution that Rock West offers? Do I need a custom piece, or can I modify an available design?

Thanks in advance for any assistance, please let me know if I can answer any questions.

[John Kimball]

30 minutes ago, Fill said:

I'm building a mast to deploy a measurement antenna, a small omnidirectional biconical, with a 1-18GHz range. Carbon fiber seems to be an ideal material which will cause minimal interference or reflections.

I need the mast  (pole) to collapse to < 54 cm (21"), and extend to > 2.5m (100"). It will be supporting a weight centered on pole, and weighing <5 lbs.
Which is the best telescopic solution that Rock West offers? Do I need a custom piece, or can I modify an available design?

Thanks in advance for any assistance, please let me know if I can answer any questions.

  Carbon fiber can actually be very reflective to RF signals. Most space and airborne antenna reflectors are made of carbon fiber due to the reflective nature of carbon fiber and of course it's weight and stiffness properties. However, depending on the location of the antenna in relation to your signal, you may be OK. 

The biggest question is how stationary you need the antenna to be at full extension. Telescoping poles are a bit more flexible due to the joints. While 5 lbs is not a lot of weight, extended 100 inches in the air, you can expect to see some swaying. The bigger you can make the tubes (larger diameter tubes), the stiffer it will be. If some swaying is not an issue, then a telescoping system may be the answer. It should also be noted that the fewer joints you have, the stiffer the assembly. In your case, if you can allow for longer compressed length, you will reduce cost and make a stiffer assembly. For example, if you need 21" collapsed X 100" Extended, then you will need 9 sections. However, if you can extend your compressed length to about 36", you can cut it down to just 3 sections.

[Fill]

8 minutes ago, John Kimball said:

  Carbon fiber can actually be very reflective to RF signals. Most space and airborne antenna reflectors are made of carbon fiber due to the reflective nature of carbon fiber and of course it's weight and stiffness properties. However, depending on the location of the antenna in relation to your signal, you may be OK. 

The biggest question is how stationary you need the antenna to be at full extension. Telescoping poles are a bit more flexible due to the joints. While 5 lbs is not a lot of weight, extended 100 inches in the air, you can expect to see some swaying. The bigger you can make the tubes (larger diameter tubes), the stiffer it will be. If some swaying is not an issue, then a telescoping system may be the answer. It should also be noted that the fewer joints you have, the stiffer the assembly. In your case, if you can allow for longer compressed length, you will reduce cost and make a stiffer assembly. For example, if you need 21" collapsed X 100" Extended, then you will need 9 sections. However, if you can extend your compressed length to about 36", you can cut it down to just 3 sections.

Thanks, John.
The mast will be directly under the Tx antenna, the receive antenna is a horn or LPDA 3m away.
I need the antenna to be "completely" (not visibly swaying) when stationary. I'm trying to use as small a diameter tube combination as possible, to minimize the surface area that can reflect. That's true of any material, FWIW. I thought that one of the telescopic solutions had locking couplers at the jointswhich would  achieve the level of stiffness I need. If not, i could fabricate couplers that positively locked sections in place. The 21" requirement is so it can fit in a standard carry-on bag.

do you think I can achieve enough stiffness using carbon fiber, either using the locking mechanisms available or by fabricating my own?

[John Kimball]

15 hours ago, Fill said:

Thanks, John.
The mast will be directly under the Tx antenna, the receive antenna is a horn or LPDA 3m away.
I need the antenna to be "completely" (not visibly swaying) when stationary. I'm trying to use as small a diameter tube combination as possible, to minimize the surface area that can reflect. That's true of any material, FWIW. I thought that one of the telescopic solutions had locking couplers at the jointswhich would  achieve the level of stiffness I need. If not, i could fabricate couplers that positively locked sections in place. The 21" requirement is so it can fit in a standard carry-on bag.

do you think I can achieve enough stiffness using carbon fiber, either using the locking mechanisms available or by fabricating my own?

The locking mechanisms are positive lock, but with any multi-jointed system, you will get some play that you wouldn't get with a bonded or continuous assembly. You also get the fishing pole affect with telescoping assemblies. The smaller the tubes get, the more flex it will produce towards the tip.  For large radio antennas, they need to use guy wires to control sway.