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Electronics => RF, Microwave, Ham Radio => Topic started by: cdev on May 18, 2020, 05:04:06 pm

Title: Mini Whip and extracting RF from tall trees
Post by: cdev on May 18, 2020, 05:04:06 pm
It seems that a high impedance Mini Whip can extract signals out of a tall tree prettty well. (without actually connecting any wires to the tree, just hanging it from a reachable branch next to the trunk).  It works much better next to the tree than it does out in the open by itself.
Title: Re: Mini Whip and extracting RF from tall trees
Post by: veedub565 on May 18, 2020, 07:54:41 pm
I've found my Mini Whip to be a very odd thing so this doesn't surprise me.

Mine worked better in the loft, than it does 30m from the house in the middle of nowhere. 
Title: Re: Mini Whip and extracting RF from tall trees
Post by: Syntax Error on May 18, 2020, 08:41:34 pm
Your comment about trees and antennas reminded of a story my old technical instructor used to tell. He served in the Royal Signals Regiment and told us about turning palm trees into effective radio aerials. It was something to do with the unique dielectric properties of palm trees which made them 'inductive' at short wave frequencies. It's a phenomina that's been known about since the dawn of radio. So with this in mind, Google found me this interesting declassified study on the subject.

US Army Electronics command - Performance of trees as radio antennas in tropical jungle forests - 1972


PDF (66 pages)

https://apps.dtic.mil/dtic/tr/fulltext/u2/742230.pdf
Title: Re: Mini Whip and extracting RF from tall trees
Post by: cdev on May 21, 2020, 11:32:41 pm
This is an interesting idea but I wish we had the original, don't you or one with better scanning, because its next to impossible to make out the pictures.

I dont really understand how the antenna coupler is constructed. It sounds quite interesting - especialy if its possible to use trees with consistent results for transmitting. I have two fairly tall trees in my backyard. Both are (just guessing) around 60 feet high. One already has a conventional antenna in it, The other one is a blank canvas waiting to be filled.. :)

Your comment about trees and antennas reminded of a story my old technical instructor used to tell. He served in the Royal Signals Regiment and told us about turning palm trees into effective radio aerials. It was something to do with the unique dielectric properties of palm trees which made them 'inductive' at short wave frequencies. It's a phenomina that's been known about since the dawn of radio. So with this in mind, Google found me this interesting declassified study on the subject.



US Army Electronics command - Performance of trees as radio antennas in tropical jungle forests - 1972


PDF (66 pages)

https://apps.dtic.mil/dtic/tr/fulltext/u2/742230.pdf
Title: Re: Mini Whip and extracting RF from tall trees
Post by: tggzzz on May 22, 2020, 07:36:25 am
Your comment about trees and antennas reminded of a story my old technical instructor used to tell. He served in the Royal Signals Regiment and told us about turning palm trees into effective radio aerials. It was something to do with the unique dielectric properties of palm trees which made them 'inductive' at short wave frequencies. It's a phenomina that's been known about since the dawn of radio. So with this in mind, Google found me this interesting declassified study on the subject.

US Army Electronics command - Performance of trees as radio antennas in tropical jungle forests - 1972


PDF (66 pages)

https://apps.dtic.mil/dtic/tr/fulltext/u2/742230.pdf

I remember seeing a short article where someone used a coconut tree as a TV antenna. ISTR the connection was madeby simply ramming the end of the coax cable (with a spike on it) into the trunk near the ground.
Title: Re: Mini Whip and extracting RF from tall trees
Post by: profdc9 on May 23, 2020, 10:43:38 pm
You might be getting constructive interference between reflections of the wave from parts of the structure at the location of the whip.  Or the wavelength is decreased in the tree because of a high dielectric constant, and there is some resonance of the tree at the wavelength. 
Title: Re: Mini Whip and extracting RF from tall trees
Post by: cdev on May 24, 2020, 02:37:12 am
Come to think of it this particular tree was hit by lightning some years ago and has some visible scars, I would not be at all surprised if there was actually a sort of conductive trace of carbon running down inside of it. A bit higher up on the tree you can actually see something like that.

I had that happen another time and basically, it seriously hurt one of my other trees and it had to be cut down eventually, but this one survived it.