15m Vertical Matching help
 

I've constructed a 1/4-wave 15m vertical from 11' of 3/4" copper tubing
(water type). It's being fed with coax.

Much to my frustration, I am unable to get this thing to resonate w/o
the use of a transmatch. Any tips, ideas or good plans?

73's

-=Jon

"J. Laub" wrote in message
...
I've constructed a 1/4-wave 15m vertical from 11' of 3/4" copper tubing
(water type). It's being fed with coax.

Much to my frustration, I am unable to get this thing to resonate w/o the
use of a transmatch. Any tips, ideas or good plans?

73's

-=Jon
How long are your radials, and where are the? If you used four 11 foot
radials, and drooped them down about 45 degrees, the antenna should look
like 50 Ohms somewhere around 21.2 MHz. Is the SWR better at the high or low
end of the band, i.e. 21.0 or 21.4 ? Coax is 50 Ohms, right. You might want
to look in some charts to see how much effect the fat 3/4 conductor is going
to make, as opposed to wire.

Tam/WB2TT

I took a quick look at the ARRL antenna book. Assuming your 3/4 pipe is
actually 1" OD, resonance will be off by quite a bit. About 6 - 7 inches too
long.

Tam

"J. Laub" wrote in message
...
I've constructed a 1/4-wave 15m vertical from 11' of 3/4" copper tubing
(water type). It's being fed with coax.

Much to my frustration, I am unable to get this thing to resonate w/o
the use of a transmatch. Any tips, ideas or good plans?

Is it ground mounted? And what kind of radial are in use (if any).

Does resonate in your terms mean that you have a low swr?

Mogens

Hi John,

You didn't say, but I assume that you are feeding it against several quarter
wave radials at or near ground level. You will get a feed impedance of less
than 50 ohms, so you will need some matching to get a 1:1 swr. You need to
concentrate on getting resonance irrespective of swr and then match the
anteena feed for minimum swr. This can be done quite simply by putting a
capacitor, usually silver mica, across the coax at the feed point, or by
inserting a transformer between the coax and the antenna to match something
like 10 to 20 ohms to the 50 ohm feed. The capacitor is the easiest to try
first, and you will probably need something between 50 and 100 pf.

I hope you find this useful, and I wish you success. 73, Jack. G3PVG.

"J. Laub" wrote in message
...
I've constructed a 1/4-wave 15m vertical from 11' of 3/4" copper tubing
(water type). It's being fed with coax.

Much to my frustration, I am unable to get this thing to resonate w/o
the use of a transmatch. Any tips, ideas or good plans?

73's

-=Jon

Tam/WB2TT wrote:
I took a quick look at the ARRL antenna book. Assuming your 3/4 pipe is
actually 1" OD, resonance will be off by quite a bit. About 6 - 7 inches too
long.

Tam


What page did u find that table on? This may explain why it tunes (with
transmatch) so much easier on 20 than 15.

Mogens wrote:

"J. Laub" wrote in message
...

I've constructed a 1/4-wave 15m vertical from 11' of 3/4" copper tubing
(water type). It's being fed with coax.

Much to my frustration, I am unable to get this thing to resonate w/o
the use of a transmatch. Any tips, ideas or good plans?


Is it ground mounted? And what kind of radial are in use (if any).

Does resonate in your terms mean that you have a low swr?

Mogens


Yes, ground mounted and using 4 5-1/2ft radials. Bad word choice in
orig post-poor SWR is the problem. The other poster mentioned my pipe
diameter may be an issue. Am looking into that now.

J. Laub wrote:
Yes, ground mounted and using 4 5-1/2ft radials.

Try making one of them 11 feet long and see what happens.
--
73, Cecil http://www.qsl.net/w5dxp


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"J. Laub" wrote in message
...
Tam/WB2TT wrote:
I took a quick look at the ARRL antenna book. Assuming your 3/4 pipe is
actually 1" OD, resonance will be off by quite a bit. About 6 - 7 inches
too long.

Tam
What page did u find that table on? This may explain why it tunes (with
transmatch) so much easier on 20 than 15.

I have the 19th edition. There is a graph on page 2 - 5. Kind of rough, but
I got k=.95 for 1" conductor at 21.3 MHz, which makes the real resonance
21.3x.95=20.235. I did not read the text, but they may give an equation
also.
If the SWR is lower at 21.0 than 21.4, the radiator is too long.

Tam

"J. Laub" wrote in message
...
Mogens wrote:

"J. Laub" wrote in message
...

I've constructed a 1/4-wave 15m vertical from 11' of 3/4" copper tubing
(water type). It's being fed with coax.

Much to my frustration, I am unable to get this thing to resonate w/o
the use of a transmatch. Any tips, ideas or good plans?


Is it ground mounted? And what kind of radial are in use (if any).

Does resonate in your terms mean that you have a low swr?

Mogens


Yes, ground mounted and using 4 5-1/2ft radials. Bad word choice in orig
post-poor SWR is the problem. The other poster mentioned my pipe diameter
may be an issue. Am looking into that now.

First change the radials to 11 feet, and then see what happens. Your SWR at
resonance should be 1.5:1.

Tam/WB2TT