I am really looking for mainly local talking...

vinnie I don't think you included the web address for the 1/4 GP
antenna...

On 23 Dec 2005 13:30:15 -0800, wrote:

I am really looking for mainly local talking...

vinnie I don't think you included the web address for the 1/4 GP
antenna...


Crap. Sorry about that. Usethe 1/4 ground plain.

http://home.att.net/~wizardoz/cbmw/a...i.html#groundp


Remember to cut the center radial long, and trim shorter to adjust SWR. Mount it
on a plastic mast like PVC or ABS. It does not have to be metal since it's
indoors, and there is no wind ot weather. Get the tip as high as possible.

Also, use a 1:1 balun so the coax doesn't radiate. Basically, that is a fancy
term for coiled coax, which should be place just before the feedpoint.

Here is a site to help:

http://www.hamuniverse.com/balun.html

When I built mine, I used two PVC 4 inch couplers glued together. And I wrapped
the coax around it, tying it down with ty-raps. If you need pictures, I can send
them. The purpose of this coil is to choke RF so the coax does not act as a
ground radial or part of the antenna. That is also why it's place as close to
the feed as possible.



Vinnie S.

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 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?

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