On Sat, 24 Dec 2005 18:26:15 GMT, james wrote:

On Fri, 23 Dec 2005 19:30:25 -0500, Scott in Baltimore
wrote:

+ I don't think so, only because I have seen flat ground planes. My Starduster
+ were at a sharp angle. Maybe Scott can knows better. I would think the flat or
+ GP at 90 degrees to the center conductor is fine.
+
+Straight radials would create a 30 ohm antenna.
+45 degree droops create about 50 ohms.
+
+There shouldn't be any current flowing down the outside of the
+shield with a groundplane, so you won't need a balun,
+unlike a dipole that requires equal and opposite phases.
+If you try to feed a dipole with coax, the outer shield
+becomes part of the antenna system, causing high SWR readings,
+(even if the SWR is low), RF interference and degraded performance.
******

At 30 Ohms you will need some matching network to cancel the reactive
portion out and rasie the radiation resistance of the antenna up to
that of 50 Ohms. I would not reccomend direct coax attachment even to
a 1/4 lambda ground plane antenna.

james

Ok, I just ran my 40 meter vertical on a simulator...

R=35.87 jX=.354

SWR=1.39.. now why do I need a matchbax?

But of course a matchbox wont raise the radiation resistance of my
antenna... will it?

"GHB" wrote in message
. net...
The radio shack GP w/ horizontal radial worked but had higher SWR than the
starduster with it's drooping radials. Have you considered using an old
102" SS whip mounted on drooping radials that you would construct? The
drooping radials would allow for an almost perfect 1:1 SWR match but
include
the spring since the vertical element needs to be 108" long. This antenna
would essentialy be a starduster.
wrote in message

Or if you work the upper channels leave the spring off.

yeah, give it to cranus the anus and let him stuff it in his ass

At 30 Ohms you will need some matching network to cancel the reactive
portion out and rasie the radiation resistance of the antenna up to
that of 50 Ohms. I would not reccomend direct coax attachment even to
a 1/4 lambda ground plane antenna.

james


LMAO!


Ok, I just ran my 40 meter vertical on a simulator...

R=35.87 jX=.354

SWR=1.39.. now why do I need a matchbax?

But of course a matchbox wont raise the radiation resistance of my
antenna... will it?

Nor will it fix the basic mismatch.

30 ohms. Oh ****! I better put a 20 ohm resistor is series
with my radio of it's gonna' burn up!

1.5:1 SWR can be 25 or 100 ohms.
25 ohms will draw more current and drop more voltage. (more current X less voltage)
100 ohms will draw less current and drop the voltage less. (less current X more voltage)
50 ohms will draw the most amount of POWER from the source. (equal voltage X equal current = MAX
POWER TRANSFER)

James, you need to learn the power transfer theorum and how
little is actually lost by a 1.5:1 or less SWR. You gain
more with a resonant antenna, then a bit of impedance mismatch.

Vinnie S. wrote:
On Sat, 24 Dec 2005 16:27:10 GMT, "GHB" wrote:


The radio shack GP w/ horizontal radial worked but had higher SWR than the
starduster with it's drooping radials. Have you considered using an old
102" SS whip mounted on drooping radials that you would construct? The
drooping radials would allow for an almost perfect 1:1 SWR match but include
the spring since the vertical element needs to be 108" long. This antenna
would essentialy be a starduster.



Can he make a longer radiating element and put the radials at 90 degrees? That
woulb be easier than drooping the radials.

Vinnie S.

Resonance occurs due to the physical lenght of the radiator plus any
coils minus any capacitance. The electrical match is due to the feedpoint
impedance. An odd quarterwave has a low impedance. Anything else has a
higher impedance. To match 50 ohm unbalanced coax to various types of
antennas, baluns and beta/delta/gamma matches were created.

Some antenna designs have the radials at 90 degrees because that is
where the designer put them to work properly with their design.

On Sat, 24 Dec 2005 20:11:18 GMT, Lancer wrote:

+Ok, I just ran my 40 meter vertical on a simulator...
+
+R=35.87 jX=.354
+
+SWR=1.39.. now why do I need a matchbax?
+
+But of course a matchbox wont raise the radiation resistance of my
+antenna... will it?
****

Okay. Take the matchbox and put it on the shelf. FIrst off I never
said a matchbox but an matching network. Unless you put the matchbox
at the feed point, a matchbox is not a matching network. A matchbox
inserted in the trransmission line acts far different than that of a
matching network at the feed. Then with any basic knowledge of
electronic circuits should reveal that.

A gamma match, beta match, and even simple load elements like a
capcitor or an inductor will facillitate matching. Yes a matching
network can be used to cancel out the reactive portion and transform
the load resistive component to an appropriate level in which maximum
power can be transfered.

Basic electronics. A simple circuits problem that does not need any
fancy smancy computer model to figure out the solutions.

james

On Sun, 25 Dec 2005 06:25:08 -0500, Scott in Baltimore
wrote:

+James, you need to learn the power transfer theorum and how
+little is actually lost by a 1.5:1 or less SWR. You gain
+more with a resonant antenna, then a bit of impedance mismatch.


Scott.

A 1.5:1 SWR means that about 4% of the source power is reflected back
from the load. This is entirely different from antenna efficiency and
how much delivered power is actually radiated. Again your
understanding of antenna efficeincy and radiated power density is
quite lacking.

A resonant antenna is just that, a resonant antenna. It will often
give the widest possible bandwidth for SWR and radiation efficiency.
That is all. Physically short or exceptionaly long antenna can be made
to operate over a small frequency bandwidth with equal or better
radiation efficiency. For example consider electrically short loop
antenna can be as efficient as 98% in radiation. Due to their low
radiation resistance the antenna is quite high in Q. Thus a relatively
small bandwidth for efficient radiation.

SWR is the measure of power delivered to the load and what is
reflected back from the load to the source. Nothing more, nothing
less. It is a measure of what is happening inside the transmission
line. Not necessarily the performance of the antenna. Just because you
have a 1:1 SWR does not mean that all the power is being radiated. In
fact in some installations as little a 10% is actually being radiated.
The rest is heat.

james

On Sat, 24 Dec 2005 19:21:36 GMT, Lancer wrote:

+On Sat, 24 Dec 2005 18:26:15 GMT, james wrote:
+
+On Fri, 23 Dec 2005 19:30:25 -0500, Scott in Baltimore
wrote:
+
++ I don't think so, only because I have seen flat ground planes. My Starduster
++ were at a sharp angle. Maybe Scott can knows better. I would think the flat or
++ GP at 90 degrees to the center conductor is fine.
++
++Straight radials would create a 30 ohm antenna.
++45 degree droops create about 50 ohms.
++
++There shouldn't be any current flowing down the outside of the
++shield with a groundplane, so you won't need a balun,
++unlike a dipole that requires equal and opposite phases.
++If you try to feed a dipole with coax, the outer shield
++becomes part of the antenna system, causing high SWR readings,
++(even if the SWR is low), RF interference and degraded performance.
+******
+
+At 30 Ohms you will need some matching network to cancel the reactive
+portion out and rasie the radiation resistance of the antenna up to
+that of 50 Ohms. I would not reccomend direct coax attachment even to
+a 1/4 lambda ground plane antenna.
+
+james
+
+So what reactive component does a 1/4 wave monopole have? How much
+loss do I have on my 40 meter 1/4 wave vertical fed directly with RG-8
+coax? Should I put a coil or capacitor at the feedpoint of my
+vertical?
****

Lancer there is only one real solution for an antenna that will match
a 50 Ohm feedline. That is when the antenna is 50 + j0 Ohms. Or 50
Ohms resistive. There are an infinite number of complex solutions
that will yield a magnitude of 50 Ohms impedance. What solution yours
is will be totally unique to your location and installation. No way
for me to predict that. Therefore there is no way that I can predict y
our losses. Either from load reflections as well as radiation
efficiency of your antenna. Then again if the magnitude of the
imedance of your antenna is 30 Ohms then you may choose to live with
the reflections in the transmission line as well as any looses due to
inefficiency do to the actual radiation resistance what ever it is for
your installation.

Loss in an antenna, that is radiation efficiency, is dependant on the
radiation resistance of the antenna. This also sets the Q or quality
factor of the antenna. That is the bandwidth in which there is
reasonably efficiency of the antenna (70.7%).

Actually a coil or capacitor is best inserted in the radiator. Choice
of base load or loads at other locations are for another discussion.
The reactive component value will mainly depend on the physical length
of the radiator and its reference to lambda.

james

On Sat, 24 Dec 2005 19:26:15 GMT, Lancer wrote:

+On Sat, 24 Dec 2005 18:28:50 GMT, james wrote:
+
+On 23 Dec 2005 14:55:34 -0800, wrote:
+
++also if I could get a 1/2 wave dipole up would it work as well as the
++1/4GP
+*****
+
+As for efficiency somewhat similar. The two will have entirely
+different radiation patterns. It will be these two differning patterns
+that will make one better or worse for a particular propogation path.
+
+james
+
+He's talking about mounting his dipole vertical. How different is the
+radation pattern of vertical dipole than a 1/4 GP?
*******

Gee I seem to have lost that in the translation.

Even still the two will have different radiation patterns depending on
how high the vertical mounting of the 1/2 lambda antenna is about
virtual ground.

james

On Sun, 25 Dec 2005 06:32:53 -0500, Scott in Baltimore
wrote:

+Vinnie S. wrote:
+ On Sat, 24 Dec 2005 16:27:10 GMT, "GHB" wrote:
+
+
+The radio shack GP w/ horizontal radial worked but had higher SWR than the
+starduster with it's drooping radials. Have you considered using an old
+102" SS whip mounted on drooping radials that you would construct? The
+drooping radials would allow for an almost perfect 1:1 SWR match but include
+the spring since the vertical element needs to be 108" long. This antenna
+would essentialy be a starduster.
+
+
+
+ Can he make a longer radiating element and put the radials at 90 degrees? That
+ woulb be easier than drooping the radials.
+
+ Vinnie S.
+
+Resonance occurs due to the physical lenght of the radiator plus any
+coils minus any capacitance. The electrical match is due to the feedpoint
+impedance. An odd quarterwave has a low impedance. Anything else has a
+higher impedance. To match 50 ohm unbalanced coax to various types of
+antennas, baluns and beta/delta/gamma matches were created.
+
+Some antenna designs have the radials at 90 degrees because that is
+where the designer put them to work properly with their design.
*******

The only time an antenna is resonant is when the feed impendance is
real. That is when the imaginary portion of the antenna is zero.
Therefore the feed point impendance is R + j0. Resonance does not have
to occur at 50 + j0 Ohms.

There are an infinite solution to where the magnitude of the impedance
is equal to a magnitude of 50 Ohms.


james