RadioBanter - View Single Post

September 26th 05, 07:22 PM

wrote:

Reg Edwards wrote:

Errr, no, the meter is telling what it sees at the point of

measurement.

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

But the meter is not seeing an SWR because an SWR does not exist.

Nonsense.

Where is the 50-ohm transmission line on which the SWR is imagined or
supposed to lie?

In my personal case, there is 50 Ohm transmission line between the
transceiver and the SWR meter, then a length of line to a coax switch,
then several lines out to antennas.

You seem fixated on haveing some magical length of transmission line
being necessary for a SWR to exist. This is nonsense.

As you are unable to answer that question, the remainder of your
argument (which, as I say, arises because of the SWR meter misleading
misnomer) falls flat on its face.

You are an intelligent person. I don't doubt you have no problems
with understanding what the so-called SWR meter really indicates. But
you didn't learn this from observations of the SWR meter - as you
already know it tells lies!

Babble.

A SWR meter indicates what is. Knowing what the reading really means
is a matter of education, not veracity.

Just to reiterate, the so-called SWR meter indicates only whether or
not the load on the transmitter is a resistive 50 ohms. If it is not
50 ohms it will not tell you what it actually is. Not that you need to
know what it actually is because you will readjust your tuner, without
thinking about it, to make it equal to 50 ohms. Which corresponds to
no deflection of the meter needle.

With some education and multiple measurements, you can caluclate
the actual impedance if one desires.

What tuner? What makes you believe everyone has a tuner?

Actually no one has a tuner. To tune an antenna you must make physical
adjustments to the length, location, size, etc. to the antenna. What one
has is an impedance matching network. Modern transmitters are set to
expect a characteristic impedance of 50-ohms. If the transmission line
and antenna system is not 50-ohms you must insert various values of
capacitance and inductance so as to make the transmitter think it is
looking at 50-ohms. Older, read tube, transmitters, read finals,
generally have adjustable inductance and capacitance elements between
the output plate/s and the transmission line. Adjusting these does the
same thing as using an external transmatch.

If we are going to be picky lets be accurate. Now, having said this if I
happen to be wrong on any specific element I welcome correction not scorn.
Dave WD9BDZ

The TLI is a very useful and valuable device. It does not lead
novices and old-wives (who ought to know better) into false ideas, or
cause confusion and misunderstandings within the amateur fraternity.
Professionals dismiss SWR for what it is worth anyway.

The only one I see confused is you and professionals use SWR all the
time and in many systems it is extremely important.

Goodby to SWR except on lines where it matters and where it can be
measured. Which, in practice, are very few.

If one knows what they are doing, SWR can always be measured.

---
Reg, G4FGQ.