questions about building CB antenna...
 

On Sun, 25 Dec 2005 21:55:26 GMT, james wrote:

On Sun, 25 Dec 2005 15:55:38 -0500, Scott in Baltimore
wrote:

+At least we can discuss things rationally, without resorting
+to name calling and finger poking! Happy Holidaze!
*****

Not my style to insult, it does not get any where.

james
is damned internet newbie an insult?

questions about building CB antenna...
 

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.

questions about building CB antenna...
 

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.

questions about building CB antenna...
 

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
ups.com...
also if I could get a 1/2 wave dipole up would it work as well as the
1/4GP

questions about building CB antenna...
 

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?
******

Lowering the ground radials from 90 degrees to the main radiator to 45
degrees helps to rasie feed impendance.

Feed impendance and antenna tuning are interactive with each other. If
you have to keep them at 90 degrees,then you will have to adjust the
length of the radiator.

james

questions about building CB antenna...
 

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

questions about building CB antenna...
 

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

questions about building CB antenna...
 

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.

questions about building CB antenna...
 

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?

questions about building CB antenna...
 

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?