Please consider this to be written in red ink, or it may turn out to be my
blood.

The interminable arguing about losses in transmitters, tuners, transmission
lines, antennas, baluns, matching sections, ground systems, etc., never
reach any conclusions because half the time the participants, without being
aware of it, are are not talking about the same things. The internal
impedance/resistance of the source appears in the arguments and then
disappears of its own accord or somebody re-introduces it an attempt to
prove a point and then finds it convenient to forget about it. Confusion
reigns. Hackles rise. Blood pressure soars. Threats of Legal Action are
made.

This is because hardly any of the participants have ever been aware there
are two sorts of loss. Education has been neglected. Both can be described
in terms of decibels or even S-units. The performance of given black box in
a transmission system can be analysed in two different ways, each way
usually having a different loss in terms of decibels but when assessing
overall performance it is vital to understand which sort of losses are
involved.

There are "Transmission Losses" and there are "Insertion Losses."

There will now be raised voices of protest - "This bloody Limey is
insulting our intelligence again". "We have read books about Insertion Loss
as recommended by our professors". Invitations to tea parties can be
expected.

Transmission loss, of course, is that defined by the ratio ( Pout ) / (
Pin ) of a network or a single section of a network. Overall loss being the
product of the ratios of individual sections. The transmitter's performance
is usually unknown, it can be considered to be external to the system and
omitted from an analysis.

Insertion loss applies to individual sections of a number of cascaded
sections. It is the *change* in overall loss which results from inserting
the individual section in a cascade. Numerically it is the difference in
dBs between 'before' and 'after' the insertion.

Consider the tuner, an impedance-transforming network. It is clear the
insertion loss of a correctly operating tuner is in fact a *Gain* and
differs considerably in dBs from overall system loss before it was inserted.

There is an excellent small book which I once read "Transmission Line
Transformers" (baluns wound on ferrite cores), which contains many
transformer measurements of loss versus frequency. The author states
explicitly all measurements are in terms of the loss when a transformer is
*inserted* between specified generator and load impedances. I venture to
guess not a single amateur has ever considered the additional (transmission)
loss due such a transformer which may occur when both the generator and
terminating impedances are unknown or at least are considerably different
from the standard resistances between which the transformer has been
designed.

The moral is - don't mix the two sorts of loss when trying to analyse how a
transmission system works. Don't use insertion loss formulae anywhere in a
system when the transmitter's internal impedance is not known. To use
Scattering Matrix and circulator parameters, intended to simplify
calculations at UHF and microwaves, is asking for trouble and disagreement.
As has been amply demonstrated.

On the other hand, mention of transmitter internal impedance may force an
analysis into considering the insertion loss of the feedline which I'm sure
would not be welcome. If anybody knows what it is for rice-cakes don't tell
anybody.
----
Reg.

Reg, G4FGQ wrote:
"Consider the tuner, an impedance-transforming network. It is clear that
the insertion loss of a correctly operating tuner is in fact a "Gain"
and differs considerably in dBs from overall system loss before it was
installed."

It`s early morning in England so Reg is likely snoozing. He probably
wanted to instigate before turning in. I`ll bite. The decibel (dB)
expresses gain, loss, and relative power levels. Its logarithmic
character allows addition and subtraction to keep track of system gains
and losses.

An amplifier can increase power so it can be a +dB insertion in a
system. The amplifier is an active device. A tramsformer can change
volts and amps by transformation of impedance (V/I), or the transformer
can give isolation between circuits.Because the transformer is a passive
device, it can`t be a +dB insertion in a system. It must be a -dB
insertion in a system despite a "voltage gain" in some cases. A good
transformer usually is very efficient, so its power loss is small, but
it`s still a loss. The same is usually true of an antenna tuner.

Best regards, Richard Harrison, KB5WZI

On Wed, 20 Aug 2003 00:53:43 +0000 (UTC), "Reg Edwards"
wrote:

I venture to
guess not a single amateur has ever considered the additional (transmission)
loss due such a transformer which may occur when both the generator and
terminating impedances are unknown or at least are considerably different
from the standard resistances between which the transformer has been
designed.

It is largely true, but it sure demonstrates your not having followed
recent correspondence to that exact matter. -ehh- You will observe
no more quarter than I found. ;-)

73's
Richard Clark, KB7QHC

George, W5YR wrote:
"This is some times referred to as reflection gain and results from the
presence of more power in the load than absence of the tuner would
permit."

Words work best when their meanings are agreed. It is generally agreed
that the decibel (abreviated db) is a logarithmic unit used in
communication work to express power ratios. (The definition is
Terman`s.) The Bell System used the abreviation db, not dB.

An audio output transformer is used with a low-impedance speaker to
better match a high-impedance source for a louder signal than the
voice-coil in series with a tube would produce. Still, a good
transformer is usually said to have low loss, not give more gain .

I have no problem with "reflection gain", but I would have looked for a
definition.

Best regards, Richard Harrison, KB5WZI

In itself, it the tuner has I^2R losses to be sure, but if the antenna
radiates 100 watts with the lossy tuner in place and only 20 watts without
it, how wrong it is to claim an insertion gain of 80 watts for the tuner?

Very wrong!
Tuner is not attributing gain to nothing. It has losses due to losses in its
components, doesn't matter how you slice it.
When you match antenna to transmitter output (especially solid state 50 ohm
type) and make transmitter happy to produce full 100W output, you are not
adding "gain" from/by the tuner.
That transmitter when looking to mismatched load cuts power back to 20W, when
you insert tuner, you are not making up 80W in the tuner (gain?) but making
transmitter produce full output. You are now putting 100W in and getting some
90W out, 10W lost in the tuner, but antenna is getting 90W from the combo.
Where is the gain in the tuner?
Looks like things are getting ridiculous here. No tuner (passive) has a gain,
it has always loss.

Yuri

This is another example of the problems that can result from
misunderstanding the term "mismatch loss". People have been talking
about its reciprocal (or negative, in dB) here, and calling it
"reflection gain", a term I hadn't heard before but I don't doubt the
term is legitimate.

I've posted fairly extensively about "mismatch loss" on this newsgroup.
You should be able to find the postings easily with a Google search. The
main point is that "mismatch loss" (and its reciprocal "reflection
gain") don't really represent loss in the dissipative sense, but rather
"power that coulda been but ain't". It's a useful concept, but one just
asking for misinterpretation and misuse by people who don't really
understand what's happening. Hopefully a look at my previous postings
will clarify the matter for you. Once you understand what "mismatch
loss" really is, the concept of "mismatch gain", or "reflection gain" as
it's being called, should be easy to comprehend.

Roy Lewallen, W7EL

Yuri Blanarovich wrote:
In itself, it the tuner has I^2R losses to be sure, but if the antenna
radiates 100 watts with the lossy tuner in place and only 20 watts without
it, how wrong it is to claim an insertion gain of 80 watts for the tuner?


Very wrong!
Tuner is not attributing gain to nothing. It has losses due to losses in its
components, doesn't matter how you slice it.
When you match antenna to transmitter output (especially solid state 50 ohm
type) and make transmitter happy to produce full 100W output, you are not
adding "gain" from/by the tuner.
That transmitter when looking to mismatched load cuts power back to 20W, when
you insert tuner, you are not making up 80W in the tuner (gain?) but making
transmitter produce full output. You are now putting 100W in and getting some
90W out, 10W lost in the tuner, but antenna is getting 90W from the combo.
Where is the gain in the tuner?
Looks like things are getting ridiculous here. No tuner (passive) has a gain,
it has always loss.

Yuri

Roy, if you MUST set yourself up as an object lesson, it is better to do so
as a warning rather than as an example.

Cec, for the benefit of users of this newsgroup would you mind, please,
checking your IEEE dictionary for the meaning of "Insertion Loss/Gain".

To add to the quite unnecessary confusion, people insist on inventing fresh
names for this fairly obvious phrase which has been in use by communications
engineers for the last 70 years at least.
---
Reg.

Reg Edwards wrote:

Roy, if you MUST set yourself up as an object lesson, it is better to do so
as a warning rather than as an example.

Cec, for the benefit of users of this newsgroup would you mind, please,
checking your IEEE dictionary for the meaning of "Insertion Loss/Gain".

Well Reg, do you want the definition for 1. audible noise measurements,
2. data transmission, 3. fiber optics, 4. overhead power lines, 5. broadband
local area networks, 6. channel signal loss, 7. general insertion loss, matched
generator insertion loss, matched load insertion loss. ????
--
73, Cecil http://www.qsl.net/w5dxp



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Well Reg, do you want the definition for 1. audible noise measurements,
2. data transmission, 3. fiber optics, 4. overhead power lines, 5.
broadband
local area networks, 6. channel signal loss, 7. general insertion loss,
matched
generator insertion loss, matched load insertion loss. ????
--
73, Cecil http://www.qsl.net/w5dxp

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

Cec, that is exactly the sort of reply I expected. ;o)

In the present context it can be stated -

INSERTION LOSS due to an electrical network is the additional loss
dissipated in a load when the network is inserted between a generator and
its load. It may actually be a gain. It can be calculated only when both
generator and load impedances are known.
----
Reg.

Reg Edwards wrote:
INSERTION LOSS due to an electrical network is the additional loss
dissipated in a load when the network is inserted between a generator and
its load. It may actually be a gain.

Well Reg, speaking of loads, given all the possible definitions,
does that apply when one (not you) shoves the network up one's
posterior? :-)
--
73, Cecil http://www.qsl.net/w5dxp



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