pics would help I am a visual person... does the ground plane have to
be put at a 45d angle?

On 23 Dec 2005 14:15:11 -0800, wrote:

pics would help I am a visual person... does the ground plane have to
be put at a 45d angle?

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.

BTW, since you are running it indoors, use Belden 9913 coax. It is more flexible
than LMR400 or such.


Vinnie S.

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.

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.

How come I use to see both during the CB era? Radio Shack made a ground plane
with straight radials.



There shouldn't be any current flowing down the outside of the
shield with a groundplane, so you won't need a balun,

There you go. That is one less step !

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.


Thanks, for the info.

Vinnie S.

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

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?

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 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?

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.

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