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Transmitting tree's ?

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Mercur

New Member
I have been tinkering with various CB radios recently and I was trying to find out if coils of wire (in my case copper) wound around tree trunks and the like would enhance or wreck the transmission from a radio.
I have been trying to test this with two 2 watt Unidens and one digtalker/walker thing with .5watts which i have added about 3 or 4 feet of old 4wd CB anttenna to.
however as I live in an area where there are many other radio signals flying around all the time especially on the cb freq I haven't been too sucessful.
ANy help/ideas would be appreciated.
 

user_88

Member
If you look at the web page here:
Inductance - Wikipedia, the free encyclopedia

You can find a formula for a circular coil in the table for simple circuits in air, which is essentially the case that you are describing ..... The assumption here is that there is not much electrical effect that would be interior to a tree trunk ....maybe some water near the outer bark region.

This formula ... if you look at the top of the table, is divided by µ0 .... generally equal to 4Πx10...-7 ... a relatively small number. Consequently, for your case, you have to take the coil formula result and multiply by µ0.

So, unless you have many turns of wire about the tree, you will not have a significant amount of inductance to affect your transmission line or antenna.

If you were to wrap some wire turns about an iron or steel pipe, you would have a much greater value of L, possibly enough to affect the impedance match and power transfer ...
 
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Mikebits

Well-Known Member
As far as tree bark goes, bark is essentially dead material with no water being fed to it. The water in a tree is mostly in the interior of the tree where tissue is still alive. As the tree goes through secondary growth (Tree gaining girth) The outer tissues are shed off as they are dead tissue.

As far as winding a coil around a tree goes, I think it is a bit more complicated, and I really do not have the know how in this area, but it would seem that if the tree is fat enough you would just be using the same amount of conductor as a long antenna in a shorter area. It would seem that if you could tune it just right, you might find a sweet spot, but I really dunno. I will defer to the radio experts here...:)
 

duffy

Well-Known Member
Seems to me the capacitive effect would be the strongest - the coils of wire around the tree would be one plate on a capacitor, the other other plate would be the vascular cambium rooted to ground. I think a living tree would have more significant amounts of water in that living layer than you guys are giving it credit for.
 

Mikebits

Well-Known Member
Seems to me the capacitive effect would be the strongest - the coils of wire around the tree would be one plate on a capacitor, the other other plate would be the vascular cambium rooted to ground. I think a living tree would have more significant amounts of water in that living layer than you guys are giving it credit for.

I mearly stated that the outer portion of the tree is dead tissue. I never mentioned the inner portion of a tree to any degree. Indeed the living tissue contains water through its xylem and phloem along with electrolytes which is a variable which I have no idea of its affects on inductance and capacitance. Like I stated in my post, I do not have the know how to predict such an antenna... ;)
 
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duffy

Well-Known Member
Me neither - but it's fun to try!

Mercur, could you get out there with a reactance meter and settle this?
 

Mikebits

Well-Known Member
Me neither - but it's fun to try!

Mercur, could you get out there with a reactance meter and settle this?

It would seem that such a rig should work, but I am sure much trial and error would be involved with some method of producing viable conclusions. At best you may be able to come up with a rule of thumb statement after experimentation.

Way to complicated for me to figure out I am afraid to say... :eek:
 

Mikebits

Well-Known Member
My guess is you would just be grounding the signal and making a very poor radiator. Just a guess.

It is not like the tree is a piece of metal. It would not be a direct short, rather a complex impedence of R,C, and L. It would make a Pspice model nightmare I think.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
I would imagine the tree is going to absorb some of the power, the whole idea sounds silly in the extreme, and adding a mis-matched (probably seriously mismatched) aerial system is going to lose lots of power, and probably kill the transmitter.

If you want to use the tree, then stick a probably designed and installed aerial at the top of the tree.
 

Mercur

New Member
Wow thanks guys I really appreciate that, I kinda expected a bit of WT* with this post but Im grateful for the feedback.
I had counted on having at leat a modicum of water near enough to the wire for my purposes but it seems that I would need an awful lot of wire.
Much appreciated
mercur
 

Mikebits

Well-Known Member
I would imagine the tree is going to absorb some of the power, the whole idea sounds silly in the extreme, and adding a mis-matched (probably seriously mismatched) aerial system is going to lose lots of power, and probably kill the transmitter.

If you want to use the tree, then stick a probably designed and installed aerial at the top of the tree.

I see what you are saying Nigel, but it is an intriguing idea. It could be made to work, naturally the tree impedence would be a loss, but perhaps a match can be made using the tree as a LRC element. Silly waste of time, I agree.
 
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stevez

Active Member
Take a look on amateur radio websites and you'll likely find some antenna configurations that work reasonably well given your situation.
 

JimB

Super Moderator
Most Helpful Member
Using a coil of wire around a tree has been tried before, in the 1960s by the US military and was found to be rather ineffective.
The idea of using a coil as a current transformer around a single conductor (the tree) would probably be ok if the tree sap was a bit more conductive and offered less resistance and hence lower loss.
So basically, most of the RF goes to heat up the tree!

JimB
 

duffy

Well-Known Member
Another good guess! JimB wants eddy current losses from circular current flow around the tree.

I don't think the current in the coil will get up high enough to induce much. The far end of that antenna wire isn't connected to anything that could cause significant field current to flow, except for the distributed capacitance between the wire and the tree, and that's like shorting out the windings.
 
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Hero999

Banned
As the tree grows it increase in girth which will either snap the coil or kill the tree if the coil doesn't give.

It sounds like a pretty silly idea to me.
 

Mercur

New Member
Ahh rats i had a look at this with a friends Reactance meter, but being in australia evrything is either very very dry or its wet.
So it being summer i got barely a twitch from the trees I tested; all that happened was I almost set light to the tree bark due to the wire slowly heating up.
 

Hero999

Banned
This isn't a eucalyptus tree is it?

It's not planted next to you or anyone else's house?

They're nice trees but are a fire risk in hot places like Australia.
 

duffy

Well-Known Member
"...in other news, a local man was badly burned today when the eucalyptus tree he was trying to use as an antenna suddenly..."
 
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