Hi gang,
I'm trying to think of a new antenna for 20 Meters. Had a thought of a
5/8 wave vertical up the side of the house. My calculations tell me this
would be about 41+ feet. Couple of questions:

- is this a good idea?
- can I do it without radials, I'm thinking ground stake, inductor, 41
feet of wire straight up, tapping the inductor at the 50 ohm point with
coax.
- I attempted to model this in NEC2 and for 5/8 at 20M I'm getting an
impeadance at the base at about 7.4613E+01-4.3625E+04j. Does that seem
likely or is my model broken?

Looking forward to what you all think.

Thanks,

-- Rob

Rob Roschewsk wrote:
- can I do it without radials,

Certainly you can do it without radials but you won't
like the results. :-)
--
73, Cecil http://www.qsl.net/w5dxp

"Rob Roschewsk" wrote in message
. ..
Hi gang,
I'm trying to think of a new antenna for 20 Meters. Had a thought of a
5/8 wave vertical up the side of the house. My calculations tell me this
would be about 41+ feet. Couple of questions:

- is this a good idea?
- can I do it without radials, I'm thinking ground stake, inductor, 41
feet of wire straight up, tapping the inductor at the 50 ohm point with
coax.
- I attempted to model this in NEC2 and for 5/8 at 20M I'm getting an
impeadance at the base at about 7.4613E+01-4.3625E+04j. Does that seem
likely or is my model broken?

Looking forward to what you all think.


i've only made one 5/8 wave. i hear a cap works well since the antenna is
overlength and thus inductive.

you need radials too. my 5/8 wave didn't do too good, i suspect too many
trees, and not enough radials.

Gravity

Thanks,

-- Rob

i've only made one 5/8 wave. i hear a cap works well since the antenna is
overlength and thus inductive.

The antenna is short of a 3/4 wave and therefore capacitive, not inductive.
Either a series coil or a grounded tapped coil will work. Radials are a
must.

Dale W4OP

Cecil Moore wrote:
Rob Roschewsk wrote:
If I want something made of wire, and omni directional what would be
my best bet? Inverted-V ?

How about a 1/2WL vertical?
OK. End fed?? How should I feed it? Ladder line like a Zepp??

-- Rob
ka2pbt

Rob Roschewsk wrote:
Cecil Moore wrote:
How about a 1/2WL vertical?

OK. End fed?? How should I feed it? Ladder line like a Zepp??

I would center feed it with horizontal ladder-line
and use it on 20m-10m.

However, a 1/4WL sleeve on the bottom half would
allow you to feed it at the bottom with coax.

Another possibility is a matching network at the base.
Your ground rod might work OK with that.
--
73, Cecil http://www.qsl.net/w5dxp

The sleeve idea sounds interesting.

Could I build it out of say aluminum tubing, run the coax up the center
of the tube to some sort of insulator, shield connected to the braid and
center connected to a wire extending upwards? Could I build the top half
out of tubing as well or does the radiator need to be significantly
smaller than the sleeve?

de ka2pbt

Cecil Moore wrote:
Rob Roschewsk wrote:
Cecil Moore wrote:
How about a 1/2WL vertical?

OK. End fed?? How should I feed it? Ladder line like a Zepp??

I would center feed it with horizontal ladder-line
and use it on 20m-10m.

However, a 1/4WL sleeve on the bottom half would
allow you to feed it at the bottom with coax.

Another possibility is a matching network at the base.
Your ground rod might work OK with that.

Rob Roschewsk wrote:
The sleeve idea sounds interesting.

Could I build it out of say aluminum tubing, run the coax up the center
of the tube to some sort of insulator, shield connected to the braid and
center connected to a wire extending upwards? Could I build the top half
out of tubing as well or does the radiator need to be significantly
smaller than the sleeve?

Cut two 1/4WL sections of tubing. Slip one over the coax and
connect it to the coax braid where the coax enters the
tubing. Leave the outer insulation on the coax. Don't connect
the bottom tube or the coax braid to anything where the coax
comes out. Install an insulator/support to hold the two pieces
of tubing together in a straight line dipole-like configuration.
Tie the coax inner conductor to the upper tubing. With this
configuration, you won't need additional choking on the feedline.

*******************+ ********************+
| ====================+========
1/4WL +--------------------------------- coax
| ====================+========
*******************+ ********************+

*** is the tubing, + is a connection.
--
73, Cecil http://www.qsl.net/w5dxp

Cecil Moore wrote:

Cut two 1/4WL sections of tubing. Slip one over the coax and
connect it to the coax braid where the coax enters the
tubing. Leave the outer insulation on the coax. Don't connect
the bottom tube or the coax braid to anything where the coax
comes out. Install an insulator/support to hold the two pieces
of tubing together in a straight line dipole-like configuration.
Tie the coax inner conductor to the upper tubing. With this
configuration, you won't need additional choking on the feedline.

*******************+ ********************+
| ====================+========
1/4WL +--------------------------------- coax
| ====================+========
*******************+ ********************+

*** is the tubing, + is a connection.

I don't understand how this would work. The tube to coax connection
on the right seems to extend the 1/4 wave tube indefinitely, down the
line. I think I would connect the coax shield to the right tube at
that tube's left end, and add a ferrite current balun around the coax
where it exits at the right end of that tube.

John Popelish wrote:
Cecil Moore wrote:
*******************+ ********************+
| ====================+========
1/4WL +--------------------------------- coax
| ====================+========
*******************+ ********************+


I don't understand how this would work.

Now that you mention it, neither do I. I just copied it from
the 1993 ARRL Handbook, Fig. 3, on page 14-4. I do know how it
works when feeding a balanced antenna. Let me redraw it with
one that I know works.

*******************+ +******************** choke
| +=================================
1/4WL +--------------------------------- coax
| +=================================
*******************+ +******************** choke
--
73, Cecil http://www.qsl.net/w5dxp