Roy Lewallen wrote:
From my previous posting, the power into the line is 50 watts and the
power out is 25 watts.

To find the loss in dB, take the ratio of input to output power, that
is, 50 divided by 25, to get 2. Now take the base ten logarithm of that.
(The Log key on a calculator is what I use for this complex operation. I
get about 0.301. Finally, multiply that by 10, to get 3.01 dB. 3 is
close enough for most of us.

The RF technician I worked with at Intel was directed by his manager to
report all powers in dB referenced to the signal generator output which,
in the above example, was 100 watts. His figure for dB loss in the transmission
line would be different from yours and you would be the one getting a bad
review for not following directions.

Like I said earlier, your refusal to define the powers being ratio'ed
may spread confusion instead of information.
--
73, Cecil http://www.qsl.net/w5dxp

Jim Kelley wrote:
I think the source of part of the confusion here is that some people
apparently interpret the 'forward power' reading on their meter to mean
the power into their transmission line.

The confusion comes about when the signal generator output power
is used as the reference, as is customary in a number of companies,
including the Intel cable group when I was there. Forward power is
*NOT* measured. Signal Generator Output Power is measured and all
dB measurements are referenced to that power.

The confusion I think stems from the contention that any 'reflected
power' (unfortunate nomenclature IMO) is first sourced and then after
reflection returned back into the source, or to a circulator load as the
case may be. The latter case is certainly correct. The former is
phenomenologically problematic.

Another example of a physicist rejecting engineering principles.
I suggest you review HP's Ap Note 95-1 on S-Paramater analysis to
refresh your knowledge of the engineering definition of power.

|a1|^2 is forward power on the source side.
|b1|^2 is reflected power on the source side.
|a2|^2 is reflected power on the load side.
|b2|^2 is forward power on the load side.
--
73, Cecil http://www.qsl.net/w5dxp

Richard Clark wrote:
By that same logic it follows that the power "into" the transmission
line was in fact never "into" the line at all but into the circulator
input, ...

Very flawed logic as can be proven by observing the modulation
associated with the circulator. That modulation has obviously
made a round trip to the load and back. Sorry about that.
--
73, Cecil http://www.qsl.net/w5dxp

"Cecil Moore" wrote
Reg Edwards wrote:

Cecil, when there are several different power levels at different places
in
a circuit, it is entirely up to you how you reference one to another in
dB.


Now Reg, that just cannot be true.

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

That's funny - _I_ don't have any difficulty in believing it! ;o)
---
Reg

Roy Lewallen wrote:
The concepts of "forward" and "reflected" power are sometimes (but not
often) useful, but have to be carefully confined to a very specific set
of conditions and applications. When you start thinking of them as real
packets of power bouncing around inside and outside a cable, you can
easily be led into a number of traps which you can get out of only by
distorting reality and ultimately reaching conclusions which are more
and more wrong.

Consider an earlier example made up of lossless lines:

100W XMTR---50 ohm---+---one second long 291.5 ohm---50 ohm load

The voltage reflection coefficient at the load is 0.707. The power
reflection at the load is 0.5, i.e. half the power is reflected.

After steady-state has been reached, the XMTR has output 300 more
joules than the load has accepted. A smaller real-world experiment
will easily verify that it is a fact that all energy sourced that
has not reached the load must necessarily be confined to circulating
energy or losses in the transmission line.

Question: In the above example, where are those 300 joules of energy
located and what is happening to them?

We know that 300 joules is wave energy and RF waves always move
at the speed of light, i.e. they cannot stand still. So please
determine how much energy is moving and in which of only two
possible directions.

The knife cuts both ways. Ignoring the energy gives one a very
warped view of reality where TV ghosting cannot exist, RADAR
can't possibly work, there's no such thing as non-glare glass,
and RF energy just sorta slowly mushes side-to-side inside a
transmission line. Can you spell M-A-G-I-C?

I strongly suggest forgetting completely about "forward" and "reverse"
power.

Good way to condemn yourself forever to a non-understanding of
energy movement in a transmission line. If that's your choice,
be my guest but please don't try to pass yourself off as an
energy expert by ignoring energy movement.

Many authors of transmission line textbooks disagree with your
stance.
--
73, Cecil http://www.qsl.net/w5dxp

On Thu, 02 Dec 2004 08:20:03 -0600, Cecil Moore
wrote:
My technician at Intel would have reported
the 11001 watts of feedline loss above referenced to the signal
generator output power of 1100100 watts as was customary.
Sure he would and this would have rendered 110dB
Common stuff that :-)

On Thu, 02 Dec 2004 08:47:23 -0600, Cecil Moore
wrote:
Very flawed logic as can be proven by observing the modulation
associated with the circulator.
And the initial condition violations just keep stacking up
When do we get to the unstated EMP analysis?

On Thu, 02 Dec 2004 09:47:54 -0600, Cecil Moore
wrote:
100W XMTR---50 ohm---+---one second long 291.5 ohm---50 ohm load
And yet more violations of Initial Condition. What was wrong with the
original stub, didn't reach into a hyper dimension of virtual reality?
Do you suppose that the ARRL used such a long line for their table?
But if you are trying to prove they were in another dimension - it
follows. ;-)

Cecil Moore wrote:

The RF technician I worked with at Intel was directed by his manager to
report all powers in dB referenced to the signal generator output
which,
in the above example, was 100 watts. His figure for dB loss in the transmission
line would be different from yours and you would be the one getting a bad
review for not following directions.


Since his manager was Cecil, there may be a good case for worker's comp.
;-)


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Richard Clark wrote:

Cecil Moore wrote:
Very flawed logic as can be proven by observing the modulation
associated with the circulator.

And the initial condition violations just keep stacking up

I know you consider it unfair to your position to bring up
the subject of TV ghosting but perhaps considering such would
enlighten you about EM RF wave reflection energy.

Or maybe you can just explain where the modulation energy was
hiding while it only apparently made a round trip to the load?
--
73, Cecil http://www.qsl.net/w5dxp