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Old October 1st 15, 05:56 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Jul 2006
Posts: 112
Default Parallel coax

In message , John S
writes
On 10/1/2015 3:29 AM, Brian Howie wrote:
In message , Wayne
writes


"Ian Jackson" wrote in message
...

In message , rickman
writes
On 9/30/2015 12:57 PM, John S wrote:
On 9/30/2015 10:12 AM, Ian Jackson wrote:
In message , Jeff
writes
On 29/09/2015 14:31, Jerry Stuckle wrote:
On 9/29/2015 4:40 AM, Jeff wrote:


So let's get back to the original question. Was it ever really
answered? I think it was made slightly more complicated by the fact
that the antenna feedpoint impedance was not purely resistive, but
was actually around 20-j130 (at 14 MHz),

Was there any advantage in having the coax paralleled (both for 20
ohms resistive, and for 20-j130)?


A quick model.

A vertical antenna about 4.2m long with a wire radius of 0.5mm
approximates to what you have . The devil is in the j130 If you use a
1.5uH series L the SWR for the parallel 50ohm line is 1.19: 1 and not a
bad match over the band

Expanding on the original question.... Antenna feedpoint
approximately 20-j130
The ATU drives the antenna through about 15 feet of coax.
Assuming that the ATU provides a +j130 conjugate match, does that
leave the coax with a SWR of 50/20= 2.5:1?
If so, then I will not bother with considering 2 parallel coax.


No the line SWR is still about 36:1. If you run a bit of poke, you might
melt the coax.

If you want a single 50 ohm feed, extend the antenna to 5.7m ( ~50+
j87) and use a series C ~130pf to take out the the +j87. You have to
do this at the antenna end.

It goes without saying you need a good ground.

Brian

What do you think of this while leaving his antenna unchanged?

2.3uH
___
'-----o-----UUU---------------
.-. | ^
| | | |
20 | | C| '
'-' C| 4uH
| C| 50 ohms
| |
--- | .
-130--- | |
| | v
'-----o------------------------
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)


Yes that works too. Lots of ways to do it.

Brian
--
Brian Howie
  #2   Report Post  
Old October 1st 15, 06:09 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: May 2011
Posts: 550
Default Parallel coax

On 10/1/2015 11:56 AM, Brian Howie wrote:
In message , John S
writes
On 10/1/2015 3:29 AM, Brian Howie wrote:
In message , Wayne
writes


"Ian Jackson" wrote in message
...

In message , rickman
writes
On 9/30/2015 12:57 PM, John S wrote:
On 9/30/2015 10:12 AM, Ian Jackson wrote:
In message , Jeff
writes
On 29/09/2015 14:31, Jerry Stuckle wrote:
On 9/29/2015 4:40 AM, Jeff wrote:


So let's get back to the original question. Was it ever really
answered? I think it was made slightly more complicated by the fact
that the antenna feedpoint impedance was not purely resistive, but
was actually around 20-j130 (at 14 MHz),

Was there any advantage in having the coax paralleled (both for 20
ohms resistive, and for 20-j130)?

A quick model.

A vertical antenna about 4.2m long with a wire radius of 0.5mm
approximates to what you have . The devil is in the j130 If you use a
1.5uH series L the SWR for the parallel 50ohm line is 1.19: 1 and not a
bad match over the band

Expanding on the original question.... Antenna feedpoint
approximately 20-j130
The ATU drives the antenna through about 15 feet of coax.
Assuming that the ATU provides a +j130 conjugate match, does that
leave the coax with a SWR of 50/20= 2.5:1?
If so, then I will not bother with considering 2 parallel coax.

No the line SWR is still about 36:1. If you run a bit of poke, you might
melt the coax.

If you want a single 50 ohm feed, extend the antenna to 5.7m ( ~50+
j87) and use a series C ~130pf to take out the the +j87. You have to
do this at the antenna end.

It goes without saying you need a good ground.

Brian

What do you think of this while leaving his antenna unchanged?

2.3uH
___
'-----o-----UUU---------------
.-. | ^
| | | |
20 | | C| '
'-' C| 4uH
| C| 50 ohms
| |
--- | .
-130--- | |
| | v
'-----o------------------------
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)


Yes that works too. Lots of ways to do it.

Brian


Oh, yes of course. I try to avoid capacitors as much as I can because
one end can float with static voltage while an inductor does not. I've
had issues with nearby static lightning discharges.

Just my paranoia. To each his own.
  #3   Report Post  
Old October 1st 15, 06:18 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Nov 2012
Posts: 989
Default Parallel coax

On 10/1/2015 1:09 PM, John S wrote:
On 10/1/2015 11:56 AM, Brian Howie wrote:
In message , John S
writes
On 10/1/2015 3:29 AM, Brian Howie wrote:
In message , Wayne
writes


"Ian Jackson" wrote in message
...

In message , rickman
writes
On 9/30/2015 12:57 PM, John S wrote:
On 9/30/2015 10:12 AM, Ian Jackson wrote:
In message , Jeff
writes
On 29/09/2015 14:31, Jerry Stuckle wrote:
On 9/29/2015 4:40 AM, Jeff wrote:


So let's get back to the original question. Was it ever really
answered? I think it was made slightly more complicated by the fact
that the antenna feedpoint impedance was not purely resistive, but
was actually around 20-j130 (at 14 MHz),

Was there any advantage in having the coax paralleled (both for 20
ohms resistive, and for 20-j130)?

A quick model.

A vertical antenna about 4.2m long with a wire radius of 0.5mm
approximates to what you have . The devil is in the j130 If you use a
1.5uH series L the SWR for the parallel 50ohm line is 1.19: 1 and
not a
bad match over the band

Expanding on the original question.... Antenna feedpoint
approximately 20-j130
The ATU drives the antenna through about 15 feet of coax.
Assuming that the ATU provides a +j130 conjugate match, does that
leave the coax with a SWR of 50/20= 2.5:1?
If so, then I will not bother with considering 2 parallel coax.

No the line SWR is still about 36:1. If you run a bit of poke, you
might
melt the coax.

If you want a single 50 ohm feed, extend the antenna to 5.7m ( ~50+
j87) and use a series C ~130pf to take out the the +j87. You have to
do this at the antenna end.

It goes without saying you need a good ground.

Brian

What do you think of this while leaving his antenna unchanged?

2.3uH
___
'-----o-----UUU---------------
.-. | ^
| | | |
20 | | C| '
'-' C| 4uH
| C| 50 ohms
| |
--- | .
-130--- | |
| | v
'-----o------------------------
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)


Yes that works too. Lots of ways to do it.

Brian


Oh, yes of course. I try to avoid capacitors as much as I can because
one end can float with static voltage while an inductor does not. I've
had issues with nearby static lightning discharges.

Just my paranoia. To each his own.


But it is connected by a 20 ohm resistor. How bad can that be?

--

Rick
  #4   Report Post  
Old October 1st 15, 06:21 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: May 2011
Posts: 550
Default Parallel coax

On 10/1/2015 12:18 PM, rickman wrote:
On 10/1/2015 1:09 PM, John S wrote:
On 10/1/2015 11:56 AM, Brian Howie wrote:
In message , John S
writes
On 10/1/2015 3:29 AM, Brian Howie wrote:
In message , Wayne
writes


"Ian Jackson" wrote in message
...

In message , rickman
writes
On 9/30/2015 12:57 PM, John S wrote:
On 9/30/2015 10:12 AM, Ian Jackson wrote:
In message , Jeff
writes
On 29/09/2015 14:31, Jerry Stuckle wrote:
On 9/29/2015 4:40 AM, Jeff wrote:


So let's get back to the original question. Was it ever really
answered? I think it was made slightly more complicated by the fact
that the antenna feedpoint impedance was not purely resistive, but
was actually around 20-j130 (at 14 MHz),

Was there any advantage in having the coax paralleled (both for 20
ohms resistive, and for 20-j130)?

A quick model.

A vertical antenna about 4.2m long with a wire radius of 0.5mm
approximates to what you have . The devil is in the j130 If you use a
1.5uH series L the SWR for the parallel 50ohm line is 1.19: 1 and
not a
bad match over the band

Expanding on the original question.... Antenna feedpoint
approximately 20-j130
The ATU drives the antenna through about 15 feet of coax.
Assuming that the ATU provides a +j130 conjugate match, does that
leave the coax with a SWR of 50/20= 2.5:1?
If so, then I will not bother with considering 2 parallel coax.

No the line SWR is still about 36:1. If you run a bit of poke, you
might
melt the coax.

If you want a single 50 ohm feed, extend the antenna to 5.7m ( ~50+
j87) and use a series C ~130pf to take out the the +j87. You have to
do this at the antenna end.

It goes without saying you need a good ground.

Brian

What do you think of this while leaving his antenna unchanged?

2.3uH
___
'-----o-----UUU---------------
.-. | ^
| | | |
20 | | C| '
'-' C| 4uH
| C| 50 ohms
| |
--- | .
-130--- | |
| | v
'-----o------------------------
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)


Yes that works too. Lots of ways to do it.

Brian


Oh, yes of course. I try to avoid capacitors as much as I can because
one end can float with static voltage while an inductor does not. I've
had issues with nearby static lightning discharges.

Just my paranoia. To each his own.


But it is connected by a 20 ohm resistor. How bad can that be?


I don't understand. Do you mean the antenna's feed point resistance of
20 ohms? My understanding of the installation is that the antenna is not
directly connected to ground. Am I off track here?
  #5   Report Post  
Old October 1st 15, 06:27 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Nov 2012
Posts: 989
Default Parallel coax

On 10/1/2015 1:21 PM, John S wrote:
On 10/1/2015 12:18 PM, rickman wrote:
On 10/1/2015 1:09 PM, John S wrote:
On 10/1/2015 11:56 AM, Brian Howie wrote:
In message , John S
writes
On 10/1/2015 3:29 AM, Brian Howie wrote:
In message , Wayne
writes


"Ian Jackson" wrote in message
...

In message , rickman
writes
On 9/30/2015 12:57 PM, John S wrote:
On 9/30/2015 10:12 AM, Ian Jackson wrote:
In message , Jeff
writes
On 29/09/2015 14:31, Jerry Stuckle wrote:
On 9/29/2015 4:40 AM, Jeff wrote:


So let's get back to the original question. Was it ever really
answered? I think it was made slightly more complicated by the fact
that the antenna feedpoint impedance was not purely resistive, but
was actually around 20-j130 (at 14 MHz),

Was there any advantage in having the coax paralleled (both for 20
ohms resistive, and for 20-j130)?

A quick model.

A vertical antenna about 4.2m long with a wire radius of 0.5mm
approximates to what you have . The devil is in the j130 If you use a
1.5uH series L the SWR for the parallel 50ohm line is 1.19: 1 and
not a
bad match over the band

Expanding on the original question.... Antenna feedpoint
approximately 20-j130
The ATU drives the antenna through about 15 feet of coax.
Assuming that the ATU provides a +j130 conjugate match, does that
leave the coax with a SWR of 50/20= 2.5:1?
If so, then I will not bother with considering 2 parallel coax.

No the line SWR is still about 36:1. If you run a bit of poke, you
might
melt the coax.

If you want a single 50 ohm feed, extend the antenna to 5.7m ( ~50+
j87) and use a series C ~130pf to take out the the +j87. You
have to
do this at the antenna end.

It goes without saying you need a good ground.

Brian

What do you think of this while leaving his antenna unchanged?

2.3uH
___
'-----o-----UUU---------------
.-. | ^
| | | |
20 | | C| '
'-' C| 4uH
| C| 50 ohms
| |
--- | .
-130--- | |
| | v
'-----o------------------------
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)


Yes that works too. Lots of ways to do it.

Brian

Oh, yes of course. I try to avoid capacitors as much as I can because
one end can float with static voltage while an inductor does not. I've
had issues with nearby static lightning discharges.

Just my paranoia. To each his own.


But it is connected by a 20 ohm resistor. How bad can that be?


I don't understand. Do you mean the antenna's feed point resistance of
20 ohms? My understanding of the installation is that the antenna is not
directly connected to ground. Am I off track here?


My bad. I didn't realize that was the antenna. But the capacitor could
be bypassed with a large value resistor if static charge is your
concern. A kohm should do the job without impacting the circuit
significantly. But wait! Isn't the -130 cap also the antenna then?

--

Rick


  #6   Report Post  
Old October 1st 15, 07:37 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: May 2011
Posts: 550
Default Parallel coax

On 10/1/2015 12:27 PM, rickman wrote:
On 10/1/2015 1:21 PM, John S wrote:
On 10/1/2015 12:18 PM, rickman wrote:
On 10/1/2015 1:09 PM, John S wrote:
On 10/1/2015 11:56 AM, Brian Howie wrote:
In message , John S
writes
On 10/1/2015 3:29 AM, Brian Howie wrote:
In message , Wayne
writes


"Ian Jackson" wrote in message
...

In message , rickman
writes
On 9/30/2015 12:57 PM, John S wrote:
On 9/30/2015 10:12 AM, Ian Jackson wrote:
In message , Jeff

writes
On 29/09/2015 14:31, Jerry Stuckle wrote:
On 9/29/2015 4:40 AM, Jeff wrote:


So let's get back to the original question. Was it ever really
answered? I think it was made slightly more complicated by the
fact
that the antenna feedpoint impedance was not purely resistive, but
was actually around 20-j130 (at 14 MHz),

Was there any advantage in having the coax paralleled (both for 20
ohms resistive, and for 20-j130)?

A quick model.

A vertical antenna about 4.2m long with a wire radius of 0.5mm
approximates to what you have . The devil is in the j130 If you
use a
1.5uH series L the SWR for the parallel 50ohm line is 1.19: 1 and
not a
bad match over the band

Expanding on the original question.... Antenna feedpoint
approximately 20-j130
The ATU drives the antenna through about 15 feet of coax.
Assuming that the ATU provides a +j130 conjugate match, does that
leave the coax with a SWR of 50/20= 2.5:1?
If so, then I will not bother with considering 2 parallel coax.

No the line SWR is still about 36:1. If you run a bit of poke, you
might
melt the coax.

If you want a single 50 ohm feed, extend the antenna to 5.7m ( ~50+
j87) and use a series C ~130pf to take out the the +j87. You
have to
do this at the antenna end.

It goes without saying you need a good ground.

Brian

What do you think of this while leaving his antenna unchanged?

2.3uH
___
'-----o-----UUU---------------
.-. | ^
| | | |
20 | | C| '
'-' C| 4uH
| C| 50 ohms
| |
--- | .
-130--- | |
| | v
'-----o------------------------
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)


Yes that works too. Lots of ways to do it.

Brian

Oh, yes of course. I try to avoid capacitors as much as I can because
one end can float with static voltage while an inductor does not. I've
had issues with nearby static lightning discharges.

Just my paranoia. To each his own.

But it is connected by a 20 ohm resistor. How bad can that be?


I don't understand. Do you mean the antenna's feed point resistance of
20 ohms? My understanding of the installation is that the antenna is not
directly connected to ground. Am I off track here?


My bad. I didn't realize that was the antenna. But the capacitor could
be bypassed with a large value resistor if static charge is your
concern. A kohm should do the job without impacting the circuit
significantly. But wait! Isn't the -130 cap also the antenna then?


Yes. I guess I should have enclosed the combination in a box to
represent the antenna. Sorry.
  #7   Report Post  
Old October 1st 15, 08:41 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Nov 2012
Posts: 989
Default Parallel coax

On 10/1/2015 2:37 PM, John S wrote:
On 10/1/2015 12:27 PM, rickman wrote:
On 10/1/2015 1:21 PM, John S wrote:
On 10/1/2015 12:18 PM, rickman wrote:
On 10/1/2015 1:09 PM, John S wrote:
On 10/1/2015 11:56 AM, Brian Howie wrote:
In message , John S
writes
On 10/1/2015 3:29 AM, Brian Howie wrote:
In message , Wayne
writes


"Ian Jackson" wrote in message
...

In message , rickman

writes
On 9/30/2015 12:57 PM, John S wrote:
On 9/30/2015 10:12 AM, Ian Jackson wrote:
In message , Jeff

writes
On 29/09/2015 14:31, Jerry Stuckle wrote:
On 9/29/2015 4:40 AM, Jeff wrote:


So let's get back to the original question. Was it ever really
answered? I think it was made slightly more complicated by the
fact
that the antenna feedpoint impedance was not purely resistive,
but
was actually around 20-j130 (at 14 MHz),

Was there any advantage in having the coax paralleled (both
for 20
ohms resistive, and for 20-j130)?

A quick model.

A vertical antenna about 4.2m long with a wire radius of 0.5mm
approximates to what you have . The devil is in the j130 If you
use a
1.5uH series L the SWR for the parallel 50ohm line is 1.19: 1 and
not a
bad match over the band

Expanding on the original question.... Antenna feedpoint
approximately 20-j130
The ATU drives the antenna through about 15 feet of coax.
Assuming that the ATU provides a +j130 conjugate match, does that
leave the coax with a SWR of 50/20= 2.5:1?
If so, then I will not bother with considering 2 parallel coax.

No the line SWR is still about 36:1. If you run a bit of poke, you
might
melt the coax.

If you want a single 50 ohm feed, extend the antenna to 5.7m (
~50+
j87) and use a series C ~130pf to take out the the +j87. You
have to
do this at the antenna end.

It goes without saying you need a good ground.

Brian

What do you think of this while leaving his antenna unchanged?

2.3uH
___
'-----o-----UUU---------------
.-. | ^
| | | |
20 | | C| '
'-' C| 4uH
| C| 50 ohms
| |
--- | .
-130--- | |
| | v
'-----o------------------------
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)


Yes that works too. Lots of ways to do it.

Brian

Oh, yes of course. I try to avoid capacitors as much as I can because
one end can float with static voltage while an inductor does not. I've
had issues with nearby static lightning discharges.

Just my paranoia. To each his own.

But it is connected by a 20 ohm resistor. How bad can that be?


I don't understand. Do you mean the antenna's feed point resistance of
20 ohms? My understanding of the installation is that the antenna is not
directly connected to ground. Am I off track here?


My bad. I didn't realize that was the antenna. But the capacitor could
be bypassed with a large value resistor if static charge is your
concern. A kohm should do the job without impacting the circuit
significantly. But wait! Isn't the -130 cap also the antenna then?


Yes. I guess I should have enclosed the combination in a box to
represent the antenna. Sorry.


So there is no cap, right? No cap, no worry. Oh, wait again. I see
there are two circuits being discussed. So *that* cap can be bypassed
with a 1 kohm resistor and not impact the circuit, right?

--

Rick
  #8   Report Post  
Old October 2nd 15, 06:32 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Nov 2012
Posts: 989
Default Parallel coax

On 10/2/2015 2:34 AM, Jeff wrote:
___
'-----o-----UUU---------------
.-. | ^
| | | |
20 | | C| '
'-' C| 4uH
| C| 50 ohms
| |
--- | .
-130--- | |
| | v
'-----o------------------------
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)


Yes that works too. Lots of ways to do it.

Brian

Oh, yes of course. I try to avoid capacitors as much as I can because
one end can float with static voltage while an inductor does not. I've
had issues with nearby static lightning discharges.

Just my paranoia. To each his own.

But it is connected by a 20 ohm resistor. How bad can that be?


I don't understand. Do you mean the antenna's feed point resistance of
20 ohms? My understanding of the installation is that the antenna is not
directly connected to ground. Am I off track here?


My bad. I didn't realize that was the antenna. But the capacitor could
be bypassed with a large value resistor if static charge is your
concern. A kohm should do the job without impacting the circuit
significantly. But wait! Isn't the -130 cap also the antenna then?


What capacitor???????????

The 20-j130 is the impedance presented by the antenna at the feed point
to gnd, there is no physical capacitor, the 4uH to gnd will provide a dc
path for any static.


Yes, that is what I said. "Isn't the -130 cap also the antenna then?"

I was confused because of poor trimming when someone posted about a
different matching network using a capacitor and a reply saying they
don't like capacitors because they fail. With the context not being
clear I thought they were talking about the capacitor in the diagram
with the inductive matching network, but as you say, this capacitance is
just part of the antenna.

--

Rick
  #9   Report Post  
Old October 1st 15, 07:34 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Jul 2006
Posts: 112
Default Parallel coax

In message , John S
writes
On 10/1/2015 11:56 AM, Brian Howie wrote:
In message , John S
writes
On 10/1/2015 3:29 AM, Brian Howie wrote:
In message , Wayne
writes


"Ian Jackson" wrote in message
...

In message , rickman
writes
On 9/30/2015 12:57 PM, John S wrote:
On 9/30/2015 10:12 AM, Ian Jackson wrote:
In message , Jeff
writes
On 29/09/2015 14:31, Jerry Stuckle wrote:
On 9/29/2015 4:40 AM, Jeff wrote:


So let's get back to the original question. Was it ever really
answered? I think it was made slightly more complicated by the fact
that the antenna feedpoint impedance was not purely resistive, but
was actually around 20-j130 (at 14 MHz),

Was there any advantage in having the coax paralleled (both for 20
ohms resistive, and for 20-j130)?

A quick model.

A vertical antenna about 4.2m long with a wire radius of 0.5mm
approximates to what you have . The devil is in the j130 If you use a
1.5uH series L the SWR for the parallel 50ohm line is 1.19: 1 and not a
bad match over the band

Expanding on the original question.... Antenna feedpoint
approximately 20-j130
The ATU drives the antenna through about 15 feet of coax.
Assuming that the ATU provides a +j130 conjugate match, does that
leave the coax with a SWR of 50/20= 2.5:1?
If so, then I will not bother with considering 2 parallel coax.

No the line SWR is still about 36:1. If you run a bit of poke, you might
melt the coax.

If you want a single 50 ohm feed, extend the antenna to 5.7m ( ~50+
j87) and use a series C ~130pf to take out the the +j87. You have to
do this at the antenna end.

It goes without saying you need a good ground.

Brian

What do you think of this while leaving his antenna unchanged?

2.3uH
___
'-----o-----UUU---------------
.-. | ^
| | | |
20 | | C| '
'-' C| 4uH
| C| 50 ohms
| |
--- | .
-130--- | |
| | v
'-----o------------------------
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)


Yes that works too. Lots of ways to do it.

Brian


Oh, yes of course. I try to avoid capacitors as much as I can because
one end can float with static voltage while an inductor does not. I've
had issues with nearby static lightning discharges.

Just my paranoia. To each his own.


Good point.

Brian
--
Brian Howie
  #10   Report Post  
Old October 1st 15, 07:56 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Nov 2007
Posts: 568
Default Parallel coax

In message , Brian Howie
writes
In message , John S
writes
On 10/1/2015 3:29 AM, Brian Howie wrote:
In message , Wayne
writes


"Ian Jackson" wrote in message
...

In message , rickman
writes
On 9/30/2015 12:57 PM, John S wrote:
On 9/30/2015 10:12 AM, Ian Jackson wrote:
In message , Jeff
writes
On 29/09/2015 14:31, Jerry Stuckle wrote:
On 9/29/2015 4:40 AM, Jeff wrote:


So let's get back to the original question. Was it ever really
answered? I think it was made slightly more complicated by the fact
that the antenna feedpoint impedance was not purely resistive, but
was actually around 20-j130 (at 14 MHz),

Was there any advantage in having the coax paralleled (both for 20
ohms resistive, and for 20-j130)?

A quick model.

A vertical antenna about 4.2m long with a wire radius of 0.5mm
approximates to what you have . The devil is in the j130 If you use a
1.5uH series L the SWR for the parallel 50ohm line is 1.19: 1 and not a
bad match over the band

Expanding on the original question.... Antenna feedpoint
approximately 20-j130
The ATU drives the antenna through about 15 feet of coax.
Assuming that the ATU provides a +j130 conjugate match, does that
leave the coax with a SWR of 50/20= 2.5:1?
If so, then I will not bother with considering 2 parallel coax.

No the line SWR is still about 36:1. If you run a bit of poke, you might
melt the coax.

If you want a single 50 ohm feed, extend the antenna to 5.7m ( ~50+
j87) and use a series C ~130pf to take out the the +j87. You have to
do this at the antenna end.

It goes without saying you need a good ground.

Brian

What do you think of this while leaving his antenna unchanged?

2.3uH
___
'-----o-----UUU---------------
.-. | ^
| | | |
20 | | C| '
'-' C| 4uH
| C| 50 ohms
| |
--- | .
-130--- | |
| | v
'-----o------------------------
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)


Yes that works too. Lots of ways to do it.

I'm taking the opportunity to refresh my admittedly rudimentary skills
with the Smith Chart - and in particular, single- and double-stub
matching (little used for over 50 years!!).

However, in Wayne's situation, the length of the coax is only 15'. On
14MHz, that's just over a quarterwave (taking the velocity factor into
account). But even with a horrendous SWR, how much loss does this length
of 213 coax have? It might be a lot more convenient to do all the
matching in the warmth and comfort of the shack.

I have done exactly this with a 130' inverted-L Marconi-type antenna,
fed at the far end directly with around 100' of old (early 1960s)
semi-airspaced TV trunk cable (with a good ground there). It worked fine
on 160-80-40m (the bands I was interested in working), but it loaded up
fine up to 10m - and as it seemed lively enough on receive, I'm sure it
would have put out a reasonable signal. Although I eventually treated
myself to a remote automatic ATU, I'm not convinced the system works any
better than it did with the direct coax connection.
--
Ian


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