On 10/1/2015 9:16 PM, John S wrote:
On 10/1/2015 2:41 PM, rickman wrote:
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?


No, there is only one cap. The 20 ohm resistor in series with the -130
ohm cap represents the antenna impedance of 20 - j130 ohms.

Way back in the thread...

"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."

Otherwise there is no cap to worry about blowing up.

--

Rick