Vertical Antennae matching
 

It seems to me that if I have a vertical antenna with the ATU at the
base of it with coax back to the shack, that all I need is a series
inductor to tune it for frequencies for which it is shorter than 1/4
wave and a series capacitor for frequencies for which it is longer
than 1/4 wave.

What do I do, however, for those frequencies for which it is close
to a half wave? PI network? Or L network?

What do I do, however, for those frequencies for which it is close
to a half wave? PI network? Or L network?

===================================

You very slightly de-tune (decrease) the antenna length, not enough to have
any effect on its radiating properties, such that a simple parallel tuned
matching circuit will cope.

You can connect a coax feedline line either in series with the coil, an
L-network. or tap the coax a few turns up the coil. A very modest ground
connection adjacent to the bottom end of the coil witll suffice.

The same circuit will cater efficiently for quite a wide range of antenna
heights.

I hope you are satisfied with the above description.
---
Reg, G4FGQ

It's not that simple. Getting the antenna resonent is one issue, getting it
matched for 50 ohm coax is the other issue. So a simple inductor or capacitor
won't always work by itself. Helps with resonence, but not impedance.

But a simple inductor AND capacitor always works.

All tuners need at least one capacitor and one inductor.

"Airy R. Bean" wrote in message
...
What do I do, however, for those frequencies for which it is close
to a half wave? PI network? Or L network?

An L network with reactances of several hundred ohms for
both inductor and capacitor.

Rick N6RK

A common solution is to use a parallel tuned circuit, approximately
resonant, with inductor and capacitor reactances of a couple hundred
ohms or so, and the capacitor being adjustable. Connect one end of the
network to ground and the other to the antenna. Connect the feedline
between ground and a tap near the bottom of the coil. Alternately adjust
the tap position and the variable capacitor for the best impedance match.

Roy Lewallen, W7EL

Rick Karlquist N6RK wrote:
"Airy R. Bean" wrote in message
...

What do I do, however, for those frequencies for which it is close
to a half wave? PI network? Or L network?


An L network with reactances of several hundred ohms for
both inductor and capacitor.

Rick N6RK

I'm never satisfied, always driven by the spirit
of curiosity and discovery!

Changing the vertical length is not an option as its
an ally pole supporting a tv antenna; it just happens to be insulated
from the ground.

I was planning to put about 20 radials in green-and-yellow, splaying
out from a single copper stake.

"Reg Edwards" wrote in message
...
What do I do, however, for those frequencies for which it is close
to a half wave? PI network? Or L network?

===================================

You very slightly de-tune (decrease) the antenna length, not enough to
have
any effect on its radiating properties, such that a simple parallel tuned
matching circuit will cope.

You can connect a coax feedline line either in series with the coil, an
L-network. or tap the coax a few turns up the coil. A very modest ground
connection adjacent to the bottom end of the coil witll suffice.

The same circuit will cater efficiently for quite a wide range of antenna
heights.

I hope you are satisfied with the above description.
---
Reg, G4FGQ

Hence the question about Pi and L networks.

"K9SQG" wrote in message
...
It's not that simple. Getting the antenna resonent is one issue, getting
it
matched for 50 ohm coax is the other issue. So a simple inductor or
capacitor
won't always work by itself. Helps with resonence, but not impedance.

I've obtained roller coaster and 350 pF TX capacitor.

"Rick Karlquist N6RK" wrote in message
news:Nb2Xc.42797$9d6.33881@attbi_s54...
"Airy R. Bean" wrote in message
...
What do I do, however, for those frequencies for which it is close
to a half wave? PI network? Or L network?

An L network with reactances of several hundred ohms for
both inductor and capacitor.

Rick N6RK

Presumably the roller coaster could be used for
a vari-tap, but then that means that the whole coil
will always be in circuit.

Time for a quikc .XLS for all bands.....

"Roy Lewallen" wrote in message
...
A common solution is to use a parallel tuned circuit, approximately
resonant, with inductor and capacitor reactances of a couple hundred
ohms or so, and the capacitor being adjustable. Connect one end of the
network to ground and the other to the antenna. Connect the feedline
between ground and a tap near the bottom of the coil. Alternately adjust
the tap position and the variable capacitor for the best impedance match.

Roy Lewallen, W7EL

Rick Karlquist N6RK wrote:
"Airy R. Bean" wrote in message
...

What do I do, however, for those frequencies for which it is close
to a half wave? PI network? Or L network?


An L network with reactances of several hundred ohms for
both inductor and capacitor.

Rick N6RK

There's no reason you can't make the inductor variable instead of the
capacitor -- as long as it has some way of making a variable tap. With
the method I described, you have to be able to adjust both the tank's
resonant frequency and the tap in order to assure getting a match.

Roy Lewallen, W7EL

Airy R. Bean wrote:

Presumably the roller coaster could be used for
a vari-tap, but then that means that the whole coil
will always be in circuit.

Time for a quikc .XLS for all bands.....

"Airy R. Bean" wrote in message
...
Presumably the roller coaster could be used for
a vari-tap, but then that means that the whole coil
will always be in circuit.


You've never seen a roller coaster I take it.

Presumably the roller coaster could be used for
a vari-tap, but then that means that the whole coil
will always be in circuit.


You've never seen a roller coaster I take it.

==================================

He just loves looking for problems where none exist.

On Sun, 29 Aug 2004 00:08:16 +0000 (UTC), "Reg Edwards"
wrote:


Presumably the roller coaster could be used for
a vari-tap, but then that means that the whole coil
will always be in circuit.


You've never seen a roller coaster I take it.

==================================

He just loves looking for problems where none exist.

Rollercoasters are hard to come by these days, aren't they, Reg? I
haven't seen one in 25 years or so now. :-(

--

"What is now proved was once only imagin'd." - William Blake, 1793.

Rollercoasters are hard to come by these days, aren't they, Reg? I
haven't seen one in 25 years or so now. :-(
===============================
Paul, From the above it is clear that you don't visit junk sales and flea
markets all that often ,if ever.

Roller coasters can be found ,be it at gradually increasing prices.
An amateur radio flea market 'pilgrimage' to continental Europe would
,no doubt, provide a good harvest.

In the UK , Birkett -Lincoln has them from time to time.

Frank GM0CSZ / KN6WH

For those of you who lack the necessary technical acumen
to qualify for a Ham Radio licence, the issue is two-fold....
A variable tapping point _TOGETHER WITH_ a variable inductance
require two independently variables, but the roller-coaster
provides you with only one.

"Reg Edwards" wrote in message
...
Presumably the roller coaster could be used for
a vari-tap, but then that means that the whole coil
will always be in circuit.
You've never seen a roller coaster I take it.
He just loves looking for problems where none exist.

At the Wimborne FRS rally, there were two identical
models on adjacent stands in the flea market. One was priced
at £15 and the other at £50 or £60 (I did comment on the
price contemporaneously, but now I've forgotten it because it
wasn't the one that I went for)

I suspect that with the CBisation of Ham Radio, especially here
in Britland with the M3/CB Fools' Licence, that more and more
of these will come on to the second hand market when increasing
numbers of CBers-Masquerading-As-Radio-Hams have no
idea what to do with them, what with their buy-in-a-box complete
stations with auto antennae tuners enclosed.

"Highland Ham" wrote in message
...
Rollercoasters are hard to come by these days, aren't they, Reg? I
haven't seen one in 25 years or so now. :-(
Paul, From the above it is clear that you don't visit junk sales and flea
markets all that often ,if ever.
Roller coasters can be found ,be it at gradually increasing prices.
An amateur radio flea market 'pilgrimage' to continental Europe would
,no doubt, provide a good harvest.
In the UK , Birkett -Lincoln has them from time to time.