"w4jle" W4JLE(remove this to wrote in message
...
Well said Sir!

Even the "appliance operators" of old had to know how the appliance
worked.

Were I the FCC, your first transmitter and receiver would be built from
scratch and a minimum of 25 CW contacts confirmed before the use of a
purchased rig would be allowed.

Careful, one of the local Ham "Channelmasters" will dub you a
CBPlusser for using the term "contact". It's a pet peeve of his.

Harold Burton
KD5SAK

"Mike" wrote in message ...
Hi Kevin,

If you have to cut bits off the coax to get the SWR down, your aerial isn't
resonant on the frequency being used. The coax is acting like part of the
aerial.
Get the aerial resonant and it doesn't matter what length of coax you use as
the SWR will not change.


This would be true assuming the transmission line is truly 50
ohms. It almost never really is.

I've asked this question before, and i got similar answers. The
point about losses in long lines improving the SWR are true of course.

But my point is that even if the antenna is a true 50 + 0j, if the
coax is not a true 50 ohms, and is more like 55 or 45 ohms, then the
length of the
coax WILL matter, in terms of the measured SWR.


Slick

"Dr. Slick" wrote in message
om...
"Mike" wrote in message
...
Hi Kevin,
If you have to cut bits off the coax to get the SWR down, your aerial
isn't
resonant on the frequency being used. The coax is acting like part of
the
aerial.
Get the aerial resonant and it doesn't matter what length of coax you
use as
the SWR will not change.


This would be true assuming the transmission line is truly 50
ohms. It almost never really is.
I've asked this question before, and i got similar answers. The
point about losses in long lines improving the SWR are true of course.
But my point is that even if the antenna is a true 50 + 0j, if the
coax is not a true 50 ohms, and is more like 55 or 45 ohms, then the
length of the
coax WILL matter, in terms of the measured SWR.
Slick

So if I get the set up:
We have a 50 ohm load (antenna) and a non-50 ohm line with a 50 ohm SWR
measuring device.

With this, the "LINE SWR" is still unchanged with line length, but the
impedance seen by the SWR meter will change with coax length. It will vary
around the Zo of the line per the Smith chart. So.... It will show a
varying SWR on this meter. The non-50 ohm like could be considered a
matching transformer, but it won't be matching what we want.

However, with a 55 or 45 ohm line this is all moot - in the noise as far
as being significant to worry about and won't mean anything in practice.


Steve K;9;d;c;i

Where is the transmission line on which the SWR is measured by the meter?

Reg wrote,

Where is the transmission line on which the SWR is measured by the meter?


Allow me to sell you some.

"Tdonaly" wrote

Reg wrote,

Where is the transmission line on which the SWR is measured by the meter?


Allow me to sell you some.

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

Thanks for the offer. But no thanks. How did you manage to obtain stuff as
rare as Saddan's WMD?

By the way, know any other suckers interested in second-hand, 10-feet coils
of radiation resistance? Guaranteed to work the DX! ;o)

I was assuming between the load and meter

50 ohm LOAD====== (~~55 ohm line)======(50 ohm SWR measuring
device)==generator.

--
Steve N, K,9'd, c. i

"Reg Edwards" wrote in message
...
Where is the transmission line on which the SWR is measured by the meter?

Don't any of you SWR experts have anything to say?

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

"Steve Nosko" wrote -
I was assuming between the load and meter

"Reg Edwards" wrote -
Where is the transmission line on which the SWR is measured by the
meter?

Kevin, the resonance of the antenna is determined by the length of the
antenna! It is not related to the VSWR!!!

If you are using VSWR as an indicator of resonance it is meaningless!

Since your VSWR is changing with length of Coax, I suspect you have RF
on the braid of the coax. Install a series of Chokes or ferrites.

W1MCE

Keven Matthews wrote:
SNIP
The SWR was pretty good across the band. Regardless I started my
evening doing a tidy job with some of that nice 5DFB japanese coax all ready
for the following day. Guess what ? I put on the nice new cable and plugs
and the antenna is no longer anywhere near resonant on 80M. So why am I
getting a better result with a long length of still coiled cable sitting on
my patio rather that a much shorter brand new piece.

SNIP

Note that well-engineered broadcast stations do not accept ANY significant
affect of the length of their transmission line(s) on the SWR/impedance
match of their antenna system, as seen by the transmitter.

Greatest antenna system efficiency and least stress on the transmission
hardware are achieved when transmission line impedance is matched to antenna
input impedance. When that condition exists then the length of the
transmission line is unimportant except for the power lost due to
transmission line attenuation, and the cost to use the length and type of
transmission line selected.

The match of the antenna input to its input transmission line is a function
of their design, AND the installation environment. The physical environment
near the antenna can change its input impedance from the assumed value, and
create an impedance mismatch with a transmission line selected to match the
input impedance assumed for the antenna.

This is usually corrected by an impedance-matching network installed at the
junction of the antenna and its input transmission line. Virtually every
AM, FM and TV broadcast antenna in the US has some means of adjusting the
match between the antenna and its input line to optimise system SWR.

Impedance adjustments can be done at the input end of the transmission line
to the antenna, but will be more narrow-band. Trimming the length of the
main transmission line is another approach, but again, is more
frequency-sensitive than adjusting the match directly at the antenna input
connector.

RF

Visit http://rfry.org for FM broadcast RF system papers.

________________

"Dave Shrader" wrote in message
news:5bzJb.113315$VB2.290693@attbi_s51...
Kevin, the resonance of the antenna is determined by the length of the
antenna! It is not related to the VSWR!!!

If you are using VSWR as an indicator of resonance it is meaningless!

Since your VSWR is changing with length of Coax, I suspect you have RF
on the braid of the coax. Install a series of Chokes or ferrites.

W1MCE

Keven Matthews wrote:
SNIP
The SWR was pretty good across the band. Regardless I started my
evening doing a tidy job with some of that nice 5DFB japanese coax all
ready
for the following day. Guess what ? I put on the nice new cable and
plugs
and the antenna is no longer anywhere near resonant on 80M. So why am I
getting a better result with a long length of still coiled cable sitting
on
my patio rather that a much shorter brand new piece.

SNIP