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