Reg,

I was merely agreeing with your comment about reading imaginary SWR on a
nonexistent transmission line. I tried the same thing with the HF
transmitter, which is connected to a Kenwood meter. Same results. In looking
at the Kenwood schematic, it looks like in the absence of any current flow,
it reverts to being a voltmeter, with both diodes getting the same drive.
The thing reminds me of old HP analog voltmeters that always had a dbm
scale. Of course, the dbms were nonsense, unless you were measuring across a
600 Ohm load.

Interesting about you looking at rho max = 1 +SQRT2 10 years before Chipman.
That beats Adler, Fano, and Chu who had it in their 1960 book.

Tam/WB2TT
"Reg Edwards" wrote in message
...
"Tarmo Tammaru" wrote -
"Reg Edwards" wrote -
It is possible to imagine the so-called SWR meter is telling you the
imaginary value of the SWR on a non-existent transmission line. But
it's
hardly of educational value when novices, even experienced engineers,
are
trying to understand what the reading really means. It's as confusing
and
as untruthful as Blair.

Why don't we accept the simple fact that the meter tells us only
whether
the transmitter is loaded with a resistance of a particular value or
not.
Which is no more nor less than what the instrument on the front panel
of your transceiver is provided for.

Then we can forget all about SWR, fwd and reflected power, until
needed
on real ines. Change the name of the meter to TLI.

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

Amen to that. I turned down the power on my transmitter, and measured P
forward and P rev while feeding about 100 feet of unterminated 9913. I
then
REMOVED the coax; i.e. there was nothing connected to the output side of
the
meter. Still measured the same Pf and Pr. (Daiwa meter)

Tam/WB2TT

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

Tam, what did I tell you ?

Your meter twice indicated the correct valuable information : In neither
case was your transmitter loaded with 50 ohms!

To complete the experiment connect a good, + or - 5 percent, 50-ohm
dummy-load to the meter. At 1.9, 3.8 or 7 MHz you can check the quality
of
the dummy load with a DC ohmeter. The actual DC resistance will depend on
how hot is the dummy load. It can probably be adjusted over an appreciable
range just by varying its temperature.

If the meter indicates an SWR less than about 1.15 then again it provides
the correct valuable information : The transmitter load is in the right
ball park. (Over here, Euro-side, we say in the "right street".)

To calibrate the meter, to make it even more "right", there's a little
preset resistor or capacitor inside the meter box. Twiddle it until a
minimum value of SWR is indicated at 7 MHz when the dummy load is
connected.
Or if the user is accustomed to work mostly at higher frequencies then it
can be twiddled at 21 MHz.

A meticulous amateur, proud of his shack and workmanship, may remove the
redundant SWR scale graduations and paint in their place two coloured
bands,
green = good, red = bad, according to artistic preferences.

Incidentally, to accurately determine transmitter power output just use a
diode+capacitor+DC voltmeter across the dummy load and calculate P =
(V-squared) / 100 watts. At HF it will usually be found to be within +/-
10
percent of what a reputable transceiver manufacturer says it is. And it
can
then be forgotten about. A 10 percent difference in power corresponds to
1/15th of an S-unit.

Tam, I'm sure you're already familiar with the foregoing procedures. I
describe them on these walls for the benefit of novices, CB-ers, etc., and
anyone else who studiously reads through these interminable threads in the
vain hope of learning anything from (Z-Zo)/(Z+Zo).

I have a guilty conscience - it was I who began the rho = 1+Sqrt(2) and
rho
= (Z-Zo) / (Z+Zo) threads. My excuse is that I was measuring and
investigating values of rho greater than unity 10 years before Chipman
issued his book in October 1968. But by then I had migrated to an entirely
different field.
----
Reg, G4FGQ