RadioBanter - Bird Brained Question

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Bird Brained Question

Woudn't the bird consitute but a tiny capacitance to ground and thus not
experience an RF burn of consequence?

"Cecil Moore" wrote in message
...
AA5QT wrote:
For the first time in many years, I'm about to put up a 20 meter
monobander on
a tower. The XYL is asking questions I cannot answer, specifically
relating to
RF and birds. I wouldn't want to be a bird sitting on an element when a
KW is
supplied to it? Are my concerns valid?

I've tried to chase Starlings away by applying 100W to my 20m rotatable
dipole. Some fly away. Some just sit there and tingle, jumping around
and ruffling their feathers. On my antenna, the only place guaranteed to
chase away a bird is the feedpoint with one foot on each side.
--
73, Cecil http://www.qsl.net/w5dxp

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Chuck wrote in message ...
Woudn't the bird consitute but a tiny capacitance to ground and thus not
experience an RF burn of consequence?

After all, birds sit on high voltage distribution lines with no ill effects.
At some point, I guess, corona leakage becomes a factor. You don't see them
sitting on the 100kv+ stuff.

"WB2JKX" wrote in message
...

Chuck wrote in message ...
Woudn't the bird consitute but a tiny capacitance to ground and thus not
experience an RF burn of consequence?

Let's see here...
First, The bird must have some fundamental capacitance to the rest of the
known universe. lets take a stab and say it is 10pf since he is pretty far
away from almost everything. I'm sure there is a formula for the
capacitance of a 4 inch diameter sphere somewhere...
Second, Lets model this as 10pf to ground.
Now, what's the current through this 10pf at the tip of the antenna
(assuming his foot-element contact resistance is well below the Xc)...We're
at 20M, 15M or 10M, so, without resorting to math, Xc is pretty low, in
general terms. Hmmm could be substantial even at 100W, no?
Sounds like his poor feet could indeed get enough to make life difficult.

After all, birds sit on high voltage distribution lines with no ill
effects.
At some point, I guess, corona leakage becomes a factor. You don't see
them
sitting on the 100kv+ stuff.

Completely different situation due to the 60 HZ. The 10pf would lead to
negligible current... "Just don't get one foot on each wire, Son. Your
Unkle Tweety did that and there was a loud pop and he was gone in a bright
flash. Some feathers and a bad smell was all that remained."

"On the other hand, son, getting to the top of one of those really high man
made trees with wires and your feathers'll all stand on end! Its really
cool! Just don't let your mother catch you doing that."

--
Steve N, K,9;d, c. i My email has no u's.

Birds also sit on high-tension lines carrying many amps at thousands of
volts.
Makes you wonder if it interferes with their built-in compass.

"AA5QT" wrote in message
...
For the first time in many years, I'm about to put up a 20 meter
monobander on
a tower. The XYL is asking questions I cannot answer, specifically
relating to
RF and birds. I wouldn't want to be a bird sitting on an element when a
KW is
supplied to it? Are my concerns valid?

Gary K5QT

---
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Checked by AVG anti-virus system (http://www.grisoft.com).
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"WB2JKX" wrote in message
...

Chuck wrote in message ...
Woudn't the bird consitute but a tiny capacitance to ground and thus not
experience an RF burn of consequence?

After all, birds sit on high voltage distribution lines with no ill
effects.
At some point, I guess, corona leakage becomes a factor. You don't see
them
sitting on the 100kv+ stuff.

A more valid comparision is how much of a wavelength does the bird's two
feet shunt on the antenna wire? I'd suspect the problem would increase with
frequency; becoming very painful in the VHF regions.

Peter

Hal wrote,

Birds also sit on high-tension lines carrying many amps at thousands of
volts.
Makes you wonder if it interferes with their built-in compass.

There seems to be a general belief, around here (Belmont CA), that the changing
magnetic
fields from power lines retards children's development and lowers their
collective IQ. Has anyone noticed whether or not birds are acting
any more retarded than usual?
73,
Tom Donaly, KA6RUH

"Steve Nosko" wrote in message
...

"WB2JKX" wrote in message
...

Chuck wrote in message
...
Woudn't the bird consitute but a tiny capacitance to ground and thus
not
experience an RF burn of consequence?

Let's see here...
First, The bird must have some fundamental capacitance to the rest of the
known universe. lets take a stab and say it is 10pf since he is pretty
far
away from almost everything. I'm sure there is a formula for the
capacitance of a 4 inch diameter sphere somewhere...
Second, Lets model this as 10pf to ground.
Now, what's the current through this 10pf at the tip of the antenna
(assuming his foot-element contact resistance is well below the
Xc)...We're
at 20M, 15M or 10M, so, without resorting to math, Xc is pretty low, in
general terms. Hmmm could be substantial even at 100W, no?
Sounds like his poor feet could indeed get enough to make life difficult.

After all, birds sit on high voltage distribution lines with no ill
effects.
At some point, I guess, corona leakage becomes a factor. You don't see
them
sitting on the 100kv+ stuff.

Completely different situation due to the 60 HZ. The 10pf would lead to
negligible current... "Just don't get one foot on each wire, Son. Your
Unkle Tweety did that and there was a loud pop and he was gone in a bright
flash. Some feathers and a bad smell was all that remained."

"On the other hand, son, getting to the top of one of those really high
man
made trees with wires and your feathers'll all stand on end! Its really
cool! Just don't let your mother catch you doing that."

i havent noticed a problem with injured birds on the broadcast towers. FMs
up to 100,000 W ERP. (about 14,000 W per bay in my case).
5,000 W AM towers both non and directional including top loaded arrays. not
a problem either (in fact i have had birds nest in them)

I have one site that uses open wire transmission lines to feed a 5 tower
array... 10.4 amps of RF at the common point. up to 10 amps of base current.
located in a wildlife refuge. still no birds frying themselves.

now i have been burnt a few times working on this thing... maybe it goes to
show that birds ARE smarter then radio engineers.

Tdonaly wrote:
Has anyone noticed whether or not birds are acting
any more retarded than usual?

I trap Starlings and House Sparrows, enemies of my Purple Martins.
I caught two Cardinals in my ***unbaited*** bird trap. I moved
the trap to my enclosed front porch where the lattice work has
one inch square openings. I caught two House Wrens in my unbaited
trap sitting on my front porch inside the lattice work.
--
73, Cecil http://www.qsl.net/w5dxp

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