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Antenna Insulation Dissipation Factor for Non-traditional Configurations

May 24th, 17:52

N2FT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
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I'm looking at making some composite vertical antenna elements to use some materials I have on hand since aluminum tubing has become so expensive. Also thinking about non-traditional elements. I'm wondering how to model the effect of the dielectric constant and dissipation factor for aluminum or copper foils over plastic substrates such as fiberglass, carbon fiber, PVC, or PEX.

For example:

1) I have some 1" diameter fiberglass spreaders that are 11 feet long. I could use them to hold up wires to make a vertical, but what about wrapping them with aluminum or copper flashing foil? I know there will be some reduction in length and dissipation loss, but can anyone steer me to a eay to model this?

2) I have a couple boxes of surplus unidirectional carbon fiber I bought years ago. No doubt I could make some masts, even though carbon fiber has a reputation for interacting with antennas since it's somewhat conductive. What if I wrapped the CF with some aluminum foil flashing tape? Wouldn't most of the current stay in the foil?

3) PEX has a low dissipation factor, but supposed degrades with exposure to UV. Wrapping it in foil would solve that problem, but how can I calculate the loss?

Any suggestions or references would be appreciated.

May 25th, 09:44

W1VT

Super Moderator

Joined: Apr 4th 1998, 00:00
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https://en.wikipedia.org/wiki/Comparison_of_EM_simulation_software

https://en.wikipedia.org/wiki/Elmer_FEM_solver

It may be practical to measure the temperature rise with a thermal camera. There are lower cost versions that work with a cell phone that does the image processing and display.

Zak W1VT
ARRL Senior Lab Engineer
May 29th, 06:26

W1VT

Super Moderator

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Right now, this type of antenna modeling isn't practical for the average ham. Professional Engineers who have mastered this expensive software get paid a lot of money for their services.

Another option may be use Internet services like the Reverse Beacon Network which have a network of stations reporting signal reports. The RBN uses receivers listening for CW signals--it isn't necessary to have a rig interfaced to a computer to use it.
Antennas can be compared by averaging a lot of signal reports.

Zak W1VT
ARRL Senior Lab Engineer
May 29th, 06:30

W1VT

Super Moderator

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
There is also the concept that there is no free lunch. A broadband antenna typically has more loss.

You can reduce the effect of ground by measuring a vertical as two dipole halve back to back. More work, but more accurate measurements can be had doing this. You could also reduce the effect of lossy ground by installing a low loss radial system.

Measure the impedance of antenna elements over frequency. Plot the reactance/resistance ratio over frequency. Usually, an antenna that changes rapidly with frequency has less loss than one with little change.

A NanoVNA can be quite useful for making measurements if you learn how to do the calibration routines to reduce errors. Again, more work better results.

Zak W1VT
ARRL Senior Lab Engineer

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