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From: Brent Regan <brent@regandesigns.com>
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Subject: Re: Antenna Performance Demo
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  Charles Patton writes:

<<<Burying the radials in the carbon fiber or such that the radials were 
more to the inside would go a long way toward removing the beneficial 
effects of the radials.>>>

Really? That is a very interesting point but you completely lost me on 
your aluminum airplane analogy.

Expanding your logic, in the case of an aluminum airplane, an antenna 
will have poor performance if mounted inside the airplane but we know 
(believe) it will behave much better if mounted outside. Shouldn't the 
aluminum damp the signal as you say the carbon will? We know this is not 
the case so it seems you were right about the "dumb thought". It would 
seem that, as you implied, that the AC impedance of the carbon structure 
is the critical, and unknown, element here. I wonder what is the 
impedance of the carbon skin at COM frequencies. DC, low current 
resistance is on the order of a few milliohms per square inch per inch. 
I doubt that we are so "lucky" as to have the skin impedance at the 
frequencies of interest to be anywhere near the critical damping impedance.

While this is "outside my area of expertise", I had understood that 
damping became less effective as you moved from the high (EMF) potential 
end of the antenna (tip) to the low potential end (ground plane). So, 
how do you bleed off energy that is at ground potential? The current is 
highest at the base but the resistance to the feedline is lowest.

 And just when you thought it couldn't get better, the airplane skin is 
actually two skins separated by the core. What is the effect of the 
capacitive and inductive coupling between the skins?

Even so, I always thought of a ground plane as an electrical "mirror" 
that makes a 1/4 wave antenna "look" like a half wave. It is not part of 
the system that receives the signal other than "holding" one end of the 
antenna so it can resonate. As such, it shouldn't matter if it is 
wrapped in air, carbon or wet noodles. For transmitting, the ground 
plane soaks up the antenna's "reflection" like a sponge. The earth makes 
a good ground plane, so why wouldn't copper/carbon?

One could reason that either the carbon is a good conductor of RF or it 
isn't.  In any case, adding copper radials wont hurt and may help.

Sounds like it is time for more tests!

In the meantime, theories aside, we do have empirical evidence from the 
lab and the field that ground radials on the inside of the carbon skin 
produce satisfactory results. Not being an expert, I tend to rely on 
experience.

Regards
Brent Regan

PS: And what about polarization? Two thirds of the bent whip antenna on 
my airplane is horizontal and therefore 90 degrees out of polarization 
phase with COM ground transmissions. Wouldn't it work better if I took 
the kink out?

Oh, the things we do for vanity and speed.
BR

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       Charles Patton writes:<br>
 <br>
 <font face="arial,helvetica"><font face="arial,helvetica">&lt;&lt;&lt;Burying 
the  radials in the carbon fiber or such that the radials were more to the 
 inside would go a long way toward removing the beneficial effects of the 
 radials.</font></font>&gt;&gt;&gt;<br>
 <br>
 Really? That is a very interesting point but you completely lost me on your 
aluminum airplane analogy. <br>
 <br>
 Expanding your logic, in the case of an aluminum airplane, an antenna will 
have poor performance if mounted inside the airplane but we know (believe) 
it will behave much better if mounted outside. Shouldn't the aluminum damp 
the signal as you say the carbon will? We know this is not the case so it 
seems you were right about the "dumb thought". It would seem that, as you 
implied, that the AC impedance of the carbon structure is the critical, and 
unknown, element here. I wonder what is the impedance of the carbon skin at
COM frequencies. DC, low current resistance is on the order of a few milliohms 
per square inch per inch. I doubt that we are so "lucky" as to have the skin 
impedance at the frequencies of interest to be anywhere near the critical 
damping impedance.<br>
<br>
 While this is "outside my area of expertise", I had understood that damping
 became less effective as you moved from the high (EMF) potential end of
the  antenna (tip) to the low potential end (ground plane). So, how do you
bleed  off energy that is at ground potential? The current is highest at
the base  but the resistance to the feedline is lowest.<br>
<br>
&nbsp;And just when you thought it couldn't get better, the airplane skin is actually 
two skins separated by the core. What is the effect of the capacitive and 
inductive coupling between the skins? <br>
<br>
Even so, I always thought of a ground plane as an electrical "mirror" that
makes a 1/4 wave antenna "look" like a half wave. It is not part of the system
that receives the signal other than "holding" one end of the antenna so it
can resonate. As such, it shouldn't matter if it is wrapped in air, carbon
or wet noodles. For transmitting, the ground plane soaks up the antenna's
"reflection" like a sponge. The earth makes a good ground plane, so why wouldn't
copper/carbon? <br>
 <br>
One could reason that either the carbon is a good conductor of RF or it isn't.
&nbsp;In any case, adding copper radials wont hurt and may help.<br>
 <br>
Sounds like it is time for more tests!<br>
<br>
In the meantime, theories aside, we do have empirical evidence from the lab 
and the field that ground radials on the inside of the carbon skin produce 
satisfactory results. Not being an expert, I tend to rely on experience. <br>
 <br>
 Regards<br>
 Brent Regan<br>
<br>
PS: And what about polarization? Two thirds of the bent whip antenna on my
airplane is horizontal and therefore 90 degrees out of polarization phase
with COM ground transmissions. Wouldn't it work better if I took the kink
out? <br>
<br>
Oh, the things we do for vanity and speed.<br>
BR<br>
 
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