Roy Lewallen wrote:
Some people can put up a huge
smokescreen and waving of hands about reflected waves of one kind or
another, but at the end of the day the SWR meter can't tell the
difference between a resistor and a transmission line terminated with a
load, if the impedances the meter sees are the same. It's sensitive only
to impedance;

A 20K ohms/volt Simpson may yield an irrelevant screen voltage
reading for a pentode because it loads the circuit down. Hand
waving aside, any instrument can be misused.

An SWR meter designed and calibrated for a Z0=50 standing-wave
environment may yield an irrelevant reading when operated outside
of a Z0=50 ohm standing-wave environment.
--
73, Cecil http://www.qsl.net/w5dxp


----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups
---= East/West-Coast Server Farms - Total Privacy via Encryption =---

Reg Edwards wrote:
Roy, to cut things short, why don't you just say SWR meters don't
measure SWR on anything. All they do is indicate whether or not the
transmitter is terminated with its correct load resistance. So they
are quite useful.

Reg, how about my 450 ohm SWR meter? It just sits there
reading somewhere between 6:1 and 12:1.
--
73, Cecil http://www.qsl.net/w5dxp


----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups
---= East/West-Coast Server Farms - Total Privacy via Encryption =---

Ian White GM3SEK wrote:

Reg Edwards wrote:
Stop fooling and confusing yourselves. The solution to everybody's
problems is simple - just change the name of the thing to TLI.
(Transmitter Loading Indicator).

Or - recalling that what the meter actually measures is the reflection
coefficient - why not go back to the old name of "Reflectometer"?

Trouble is, during steady-state, they only measure the virtual
reflection coefficient which is itself confusing since it is not
the same as the physical reflection coefficient measured by a TDR.
--
73, Cecil http://www.qsl.net/w5dxp


----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups
---= East/West-Coast Server Farms - Total Privacy via Encryption =---

"Cecil Moore" wrote:
An SWR meter designed and calibrated for a Z0=50 standing-wave
environment may yield an irrelevant reading when operated outside
of a Z0=50 ohm standing-wave environment.
___________________

Elaborating, an SWR meter will produce ~ accurate readings for an unknown
termination connected to it via a lossless transmission line of any length,
as long as that line has the same Zo as the sample section in the SWR meter.

It is only when the transmission line Zo varies from the Zo of the SWR meter
line section that accurate measurement of load SWR is problematic.

Selecting line lengths and line impedances to make an SWR meter and/or tx
"happy" when connected to an antenna doesn't necessarily mean that the all
components in the r-f output system have low SWR. The tx may be able to
deliver more power to the net load under those conditions, but SWR may still
exist on the transmission line capable of causing its failure.

RF

"Ian White wrote -
Stop fooling and confusing yourselves. The solution to everybody's
problems is simple - just change the name of the thing to TLI.
(Transmitter Loading Indicator).

Or - recalling that what the meter actually measures is the
reflection
coefficient - why not go back to the old name of "Reflectometer"?

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

It does NOT read the reflection coefficient. It reads only half of
it. At least half of the information lies in the angle of the RC -
which is disregarded, ignored, by the so-called meter.

The magnitude of the RC without its angle is just another worthless
number. It can't be used for anything except to calculate a fictional
SWR.
----
Reg, G4FGQ

Reg Edwards wrote:
The magnitude of the RC without its angle is just another worthless
number. It can't be used for anything except to calculate a fictional
SWR.

Actually, it is pretty useful for a Z0-matched system
since there is one and only one unique solution at the
Z0-match point.

In a Z0-matched system, all forward and reflected voltages
and currents are at the reference zero degrees or at 180
degrees so all the phase angles are known without measuring
them. The physical reflection coefficient is a function of
Z01 and Z02 at a Z0-match point. The sign of the reflection
coefficient corresponds to either zero degrees or 180 degrees
and depends on whether (Z01 Z02) or (Z01 Z02).

Since the great majority of amateur radio systems are close
to a Z0-match, this becomes a useful analysis tool for the
most common cases.
--
73, Cecil http://www.qsl.net/w5dxp


----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups
---= East/West-Coast Server Farms - Total Privacy via Encryption =---

What is the reason a 2:1 SWR can cause such havoc?

How can I avoid this catastrophic condition?

I feed my dipoles with 450 Ohm ladder line, but the last 20 feet or so is 50
Ohm coax, I guess that makes it work ok. I haven't blown up my finals yet.

Lions and tigers and bears Oh my...

"Steveo" wrote in message
news:nceoaqqpc0a3yzz.280620052102@kirk...
if you have over a 2:1 standing wave you can do damage to your finals
or linear

On Tue, 28 Jun 2005 22:15:18 GMT, Lancer wrote:

So thats all my tuner does, lengthen or shorten the coax?

Are you sure about that?
****

Essentially yes. Without having to go into detailed mathematics, it is
the simplest form to explain what is happening.

james

On Tue, 28 Jun 2005 15:53:03 -0700, Roy Lewallen
wrote:

It's a little more complicated than that. The line doesn't simply
multiply or divide the impedance by a constant, like a transformer --
except in the special case of a quarter electrical wavelength line or
odd multiples thereof.
***

Roy

I believe this thread started on rec.radio.cb


and yes your correct here. I just did not want to get into great
details on quarter wave sections and uses of transmission lines as
lumped elements. I though that was beyond the scope of the original
post. I am kind of sorry that I even mentions what I did.

james

Balderdash!

"james" wrote in message
...
On Tue, 28 Jun 2005 22:15:18 GMT, Lancer wrote:

So thats all my tuner does, lengthen or shorten the coax?

Are you sure about that?
****

Essentially yes. Without having to go into detailed mathematics, it is
the simplest form to explain what is happening.

james