Q1
----------
How is large-scale ground conductivity determined ?

A1
---------
You set up a 1 Kw transmitter using a vertical antenna above 120 ground
radials and measure the ground-wave field strength at a number of
geographical locations at various distances up to 100 miles in daylight.
You then use Sommerfeld's (corrected) formulae to estimate average ground
conductivity for the region.

Q2
---------
What is this knowledge of ground conductivity used for ?

A2
---------
With Sommerfeld's (corrected) formula it is used to estimate the ground-wave
field strength received at various distances up to 100 miles from a 1 KW
transmitter in daylight. Refer to program GRNDWAV3.

Q3
---------
How is a reflection-coefficient determined ?

A3
---------
Its modulus and angle is calculated from complex impedance measurements.

Q4
---------
What is knowledge of the reflection-coefficient used for ?

A4
---------
After discarding half of the information it contains, then tossing a coin to
select one of two possible formulae, it is used to calculate the imaginary
SWR on a non-existent transmission line.

Q5
---------
What is the value of the SWR used for ?

A5
---------
It has no use except as the subject of magazine articles to fill in gaps
between the adverts.

Q6
---------
What is a TLI ?

A6
---------
It is a useful little instrument which indicates whether or not the load on
the transmitter is sufficiently near to a resistive 50 ohms. That is, of
course, if your particular transmitter happens to work best with such an
arbitrary value. (TLI = Transmitter Loading Indicator formally incorrectly
recognised as a swaaarrr meter.)

Q7
----------
What plonk is being imbibed tonight ?

A7
----------
Vintage 2002, Medium White, from a vinyard located in the beautiful Central
Valley at the foot of the Sierra Mountain Range in the State of California,
one of the United States of North America. Good stuff ! I should have
grabbed another bottle at my local supermarket.

----
Yours, Grandad Reg, G4FGQ.

PS: Station is located on the outskirts of the original Great Manufacturing
City of Birmingham, where Boulton and Watt built their immense condensing
steam engines, and where the microwave-oven cavity-magnetron was invented
and constructed, 1940-41, during the air-raids, and generously given to the
World.

Present all-band antenna is a 40-feet sloping 18-gauge wire extending from
the kitchen window, near the extractor fan, to a TV antenna mast, without
the TV antenna, mounted on the house chimney. An automatic tuner is located
under the kitchen sink very conveniently near to the one and only ground
radial - the incoming domestic water supply lead pipe. It does however
extend 5 miles to the area's water reservoir and pumping station.

SWR/Return Loss/Reflection Coefficient

Maybe your post is being taken too seriously, but if knowing and
optimiz(s)ing these parameters is unimportant, please explain why their
disregard can result in the meltdown of transmission line and transmitter
output networks.

RF

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

Regarding the SWR "meter" on the front panel of your transceiver -

Where is the transmission line on which the "measured" SWR is supposed to
lie.

Transmission line is not required in order for RF power to be reflected. If
nothing is connected to the transmitter output connector, then all the power
the tx is trying to produce will be reflected at that point. Return loss
will be zero, and the reflection coefficient will be 100% with respect to
that interface. The equivalent of those parameters in terms of SWR is
"infinite." Barring RF power foldback coming into operation, whatever
circuits that ARE part of that scenario will see additional, and possibly
damaging energy levels.

What do you do with the SWR when you think you know its value? What
further
calculations can it participate in? What else does it tell you which you
don't already know?

Circuit parameters more easily can be adjusted to reduce losses and improve
the safety margins for the RF components in the output system.

I respectfully suggest the whole thing exists only in your imagination and
what you are *really* interested in is whether or not the transmitter is
loaded with its designed-for resistive load, usually but not always 50
ohms.

The mystery can be solved, confusion cleared, instead of lies newcomers
and
learners can be taught the simple facts of life just by changing the name
of
the useful little instrument to TLI in the handbooks.

Regarding prevention of meltdowns - good transmitter designers remember
to
incorporate a fast-acting fuse in HT supply.

If reflected power truly was imaginary, HT supplies wouldn't, as you
suggest, even _need_ a fast-acting fuse to (attempt to) protect them from
meltdown by RF load mismatches.

In any case, a good transmitter designer wouldn't rely on a fuse to protect
the tx from RF load problems. Fuses are OK, and commonly used for AC/DC
fault protection, but are not fast enough to minimize the damage to RF
output networks from high, short risetime mismatches such as arcing, etc.

RF

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

Richard,

I'm sorry I find myself unable to discuss imaginary SWR on non-existent
transmission lines any further.

If you are not interested in an indication of whether or not your
transmitter is correctly loaded with its design value of resistive ohms then
take the precaution of fitting a fast-acting fuse. ;o)
----
Reg, G4FGQ

Reg, G4FGQ wrote:
"I`m sorry I find myself unable to discuss imaginary SWR on non-existent
transmission lines any longer."

SWR is easily measured due to its relation to reflected energy, even
when there is no transmission line. TLI may be a better name for the
reflection indicator.

A perfect match between transmitter and transmission line ensures no
reflection reaches back to the transmitter, so the match also ensures
that all the reflected energy becomes re-reflected energy.

Best regards, Richard Harrison, KB5WZI