Reg Edwards wrote:
From where do you get your "thousands of volts" - the old wive's monthly
magazines?

Try this, Reg. A dipole is a standing-wave antenna. Most people know
that the voltage 1/4WL away from a current maximum is pretty high.
Since the current is zero at the end of the dipole, all the energy
is contained in the E-field. So what is the voltage when all the
energy is in the E-field?

A 1/2WL dipole is a lot like a lossy piece of 600 ohm transmission
line. 600 ohms is in the ballpark of the natural Z0 of a dipole if
there were no reflections on it, i.e. if it were terminated such
that reflections were eliminated thus turning it into a traveling-
wave antenna.

If one assumes that at the dipole feedpoint, (VF+VR)/(IF+IR) = 50 ohms,
and if the traveling-wave impedance of a dipole is 600 ohms, one can
calculate the ratio of VR to VF. Turns out to be about 0.9. So VF is
about ten times the feedpoint voltage. At the open-circuit at the end
of a dipole, VF adds in phase with VR so the voltage at the open-circuit
end of the dipole is about 20 times the feedpoint voltage.

The feedpoint voltage at 100W is about 70.7V. Therefore, the voltage
at the ends of the dipole is about 1414V RMS. Multiply by 2.8 to get
peak to peak at about 4kv.

When I worked for Schlumberger in the oil fields, we could easily
draw a 4 inch arc if someone got their aluminum hard hat too close
to the mobile radio whip during transmit. How much voltage does it
take to draw a 4 inch arc?
--
73, Cecil, W5DXP



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On Sun, 19 Sep 2004 19:08:28 -0500, Cecil Moore
wrote:

Bob Miller wrote:
Jack, please explain why we need battlefield weapons in a civilian
society.

That's simple. Because the criminals are armed with battlefield
weapons. Don't know about you, but I think it's stupid to take
my 66 year-old fists to a gunfight.

How many times do you need to shoot that beautiful deer before you
drag it to the sausage maker?

Deer don't shoot back. Criminals, including terrorists do, and
sometimes with fully automatic weapons. The criminals obviously
want the ordinary citizens to be disarmed. But why should you
want exactly the same thing as the criminals?

Did you know that the crime rate is falling in the concealed-carry
states? Did you know that a majority of states are concealed-carry
states?

I wonder if those same states might also have the highest number of
crimes of passion committed with firearms? Don't know, just asking.

If you were a criminal, would you really want to take on
someone who might be packin' a concealed Colt .45?

Personally, I wouldn't attack someone packing a cap pistol. But if
your argument is carried to its conclusion, that law abiding citizens
should have guns as big as what the worst criminals carry, then we'd
all be walking around with machine guns. That's fine, until somebody
loses his/her temper.

One of the staples of San Antonio TV news is showing some family on
the South Side mourning the death of yet another kid killed in a
drive-by or whatever -- happens about two or three times a month.

Bob
k5qwg

On Sun, 19 Sep 2004 19:17:09 -0500, Cecil Moore
wrote:
Worse than that. I'm lamenting about every Libertarian
presidential candidate losing every single year.
You lament too much.

On Sun, 19 Sep 2004 18:47:42 -0500, Cecil Moore
wrote:
To keep the thread on topic: IMO, you can't see the forest for the trees.
And how many trees do you have? Got any strange fruit?

Bob Miller wrote:

Personally, I wouldn't attack someone packing a cap pistol. But if
your argument is carried to its conclusion, that law abiding citizens
should have guns as big as what the worst criminals carry, then we'd
all be walking around with machine guns. That's fine, until somebody
loses his/her temper.

One of the staples of San Antonio TV news is showing some family on
the South Side mourning the death of yet another kid killed in a
drive-by or whatever -- happens about two or three times a month.

Bob
k5qwg



Seems to me there is a big difference between people losing their
tempers, and drive by shootings by gang members, such as the fact that
normal citizens don't lose their tempers and shoot strangers. If you
think they do, show me some evidence.

tom
K0TAR

Bob Miller wrote:
One of the staples of San Antonio TV news is showing some family on
the South Side mourning the death of yet another kid killed in a
drive-by or whatever -- happens about two or three times a month.

If laws can stop crime, why haven't the laws against drive-by
shootings stopped the drive-by shootings?
--
73, Cecil, W5DXP


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Mark wrote:
"Is this practical?"

Trees near an antenna cause some loss. It`s hard to quantify in advance,
but in ww-2, the signal corps estimated that hf loss is usually
negligible if horizontal polarization is used (page 241 of 'electrical
communications engineering').

I`ve found that horizontal HF dipoles, directly fed by coax in various
Bolivian Chaco Jungle sites, below the the tree canopy, but not too
close to the trees, communicated well with Cochabamba and La Paz,
Bolivia. So, the dipoles didn`t suffer too much from the trees. The
Signal Corps was right.

Best regards, Richard Harrison, KB5WZI

Dear Cec,

Like Brer Rabbit - I'm saying nuffin.
---
Reg

"Richard Harrison" wrote
Mark wrote:
"Is this practical?"

Trees near an antenna cause some loss. It`s hard to quantify in advance,
but in ww-2, the signal corps estimated that hf loss is usually
negligible if horizontal polarization is used (page 241 of 'electrical
communications engineering').

I`ve found that horizontal HF dipoles, directly fed by coax in various
Bolivian Chaco Jungle sites, below the the tree canopy, but not too
close to the trees, communicated well with Cochabamba and La Paz,
Bolivia. So, the dipoles didn`t suffer too much from the trees. The
Signal Corps was right.

Best regards, Richard Harrison, KB5WZI


Hi Richard, it's not easy to compare your rainforest canopy to loblolly
pines, but at approximately 50' my dipole is well below the pine canopy, and
well surrounded by them. If there is an impact from the pine trees it would
be hard to quantify since the dipole exceeds everyone's expectations for
short and long range performance. We have heard comments that pine-fron
clusters when wet, affect a near field, but that has not been our
experience. Neither does snow, ice or winds. Overall, there appears to be no
effect on the antenna being in fairly close proximity to many tall trees,
and suspended from them.

Best regards,

Jack

Jack Painter wrote:
"Overall, there appears to be no effect on the antenna being in fairly
close proximity to many tall trees, and suspended from them."

That was the Signal Corps conclusion for horizontal polarization at HF.
For vertical polarization, surrounding trees are better energy
absorbers. At VHF and UHF, absorption gets worse and worse as frequency
goes up. Too much foliage is impenetrable at VHF and UHF, regardless of
polarization, humidity, ice, snow and wind.

The Signal Corps advises trying horizontal HF antennas among the trees
to avoid detection by the enemy.

Best regards, Richard Harrison, KB5WZI