On 8/30/2010 3:44 AM, Richard Fry wrote:
On Aug 29, 10:38 pm, Roy wrote:

Difficulty in getting power to an antenna is due to the mismatch between
the transmitter and the impedance it sees, rather than between the
transmission line and antenna.

As a simple example, consider a 75 ohm dipole connected to a transmitter
through a half wavelength of 600 ohm transmission line. /etc

Rather than using an example of a balanced antenna having reasonably
high radiation resistance and zero or low reactance at its input
terminals, let us consider a base-fed 10 foot whip at 3.8 MHz -- which
is more along the lines of this thread.

Without using a loading coil, the input Z of that whip is about 0.6 -j
1250 ohms. The SWR that this antenna input Z presents to unmatched 50
to 600 ohm transmission line ranges from 52,167:1 to 5,340:1.

Not much power will be transferred through such a match, which is the
reason for the statements in my quote which you referred to.

RF

Power will indeed be transferred through such a match. Using your
antenna as an example, suppose that a transmitter with output Z of 50
ohms is connected to a tuner that transforms its output impedance to 0.6
+ j1250 ohms. Connect the output of the tuner to a half wavelength 600
ohm transmission line to the antenna. The transmitter will see 50 + j0
ohms, the antenna will see an impedance of 0.6 + j1250 ohms, and full
power will be transferred. Power transfer has nothing to do with the SWR
on the line or the match between the line and antenna.

In practice, the line loss will increase some due to the very high SWR,
but the loss increase won't be much if the matched line loss is low.

I chose a half wavelength for simplicity, but it's not necessary. Other
lengths of line will transform the antenna impedance to different
values. All that's necessary is to readjust the tuner accordingly to
match the different impedance.

Amateurs have successfully been using this method to feed nonresonant
and multi-band antennas for decades.

Roy Lewallen, W7EL

On Aug 30, 3:19*pm, Roy Lewallen wrote:
Using your antenna as an example, suppose that a transmitter
with output Z of 50 ohms is connected to a tuner that transforms
its output impedance to 0.6 + j1250 ohms. /etc

Note that my post stated "UNMATCHED."

RF

On 8/30/2010 3:19 PM, Richard Fry wrote:
On Aug 30, 3:19 pm, Roy wrote:
Using your antenna as an example, suppose that a transmitter
with output Z of 50 ohms is connected to a tuner that transforms
its output impedance to 0.6 + j1250 ohms. /etc

Note that my post stated "UNMATCHED."

RF

I did. You stated:

Without using a loading coil, the input Z of that whip is about 0.6 -j
1250 ohms. The SWR that this antenna input Z presents to unmatched 50
to 600 ohm transmission line ranges from 52,167:1 to 5,340:1.

In my example, the antenna is not matched to the transmission line. Nor,
for that matter, is the transmitter matched to the transmission line. My
point is that power transfer doesn't depend on either of these points
being matched.

Roy Lewallen, W7EL

On Aug 30, 5:52*pm, Roy Lewallen wrote:

In my example, the antenna is not matched to the transmission line. Nor,
for that matter, is the transmitter matched to the transmission line. My
point is that power transfer doesn't depend on either of these points
being matched.

Roy:

My post showing very high input SWR at the base of an unloaded, base-
driven, 10 foot vertical on 3.8 MHz described an UNMATCHED system
resulting from its connection to transmission lines of typical
impedance values. It did not include matching networks, whether
located at the base of the vertical radiator, the output connector of
the transmitter, or wherever.

Then you posted, "Using your antenna as an example, suppose that a
transmitter with output Z of 50 ohms is connected to a tuner that
transforms its output impedance to 0.6 + j1250 ohms. ... The
transmitter will see 50 + j0 ohms, the antenna will see an impedance
of 0.6 + j1250 ohms, and full power will be transferred."

That configuration you posted is a MATCHED system, and its performance
does not disprove the accuracy of my post.

RF

On 8/31/2010 3:09 PM, Richard Fry wrote:
On Aug 30, 5:52 pm, Roy wrote:

In my example, the antenna is not matched to the transmission line. Nor,
for that matter, is the transmitter matched to the transmission line. My
point is that power transfer doesn't depend on either of these points
being matched.

Roy:

My post showing very high input SWR at the base of an unloaded, base-
driven, 10 foot vertical on 3.8 MHz described an UNMATCHED system
resulting from its connection to transmission lines of typical
impedance values. It did not include matching networks, whether
located at the base of the vertical radiator, the output connector of
the transmitter, or wherever.

Then you posted, "Using your antenna as an example, suppose that a
transmitter with output Z of 50 ohms is connected to a tuner that
transforms its output impedance to 0.6 + j1250 ohms. ... The
transmitter will see 50 + j0 ohms, the antenna will see an impedance
of 0.6 + j1250 ohms, and full power will be transferred."

That configuration you posted is a MATCHED system, and its performance
does not disprove the accuracy of my post.

RF

So you're saying that the mismatch between the impedance of an antenna
and the transmission line connected to it doesn't inhibit power flow
when there's a matching network anywhere in the system. But it does
interfere with power flow when there's no matching network?

What if the antenna is 50 ohms and the transmission line is a half
wavelength of 600 ohms, for a 12:1 mismatch? There's no matching
network. The transmitter sees 50 ohms. The antenna sees 50 ohms. What
will interfere with the power flow?

Roy Lewallen, W7EL

On Aug 31, 5:25*pm, Roy Lewallen wrote:

What if the antenna is 50 ohms and the transmission line is a half
wavelength of 600 ohms, for a 12:1 mismatch? There's no matching
network. The transmitter sees 50 ohms. The antenna sees 50 ohms.
What will interfere with the power flow ?

This, and your other what ifs describe a system *different* than the
one in my post.

The performance of the systems you described does not apply to the
system I described, and vise-versa..

RF

In message , Roy Lewallen
writes
On 8/31/2010 3:09 PM, Richard Fry wrote:
On Aug 30, 5:52 pm, Roy wrote:

In my example, the antenna is not matched to the transmission line. Nor,
for that matter, is the transmitter matched to the transmission line. My
point is that power transfer doesn't depend on either of these points
being matched.

Roy:

My post showing very high input SWR at the base of an unloaded, base-
driven, 10 foot vertical on 3.8 MHz described an UNMATCHED system
resulting from its connection to transmission lines of typical
impedance values. It did not include matching networks, whether
located at the base of the vertical radiator, the output connector of
the transmitter, or wherever.

Then you posted, "Using your antenna as an example, suppose that a
transmitter with output Z of 50 ohms is connected to a tuner that
transforms its output impedance to 0.6 + j1250 ohms. ... The
transmitter will see 50 + j0 ohms, the antenna will see an impedance
of 0.6 + j1250 ohms, and full power will be transferred."

That configuration you posted is a MATCHED system, and its performance
does not disprove the accuracy of my post.

RF

So you're saying that the mismatch between the impedance of an antenna
and the transmission line connected to it doesn't inhibit power flow
when there's a matching network anywhere in the system. But it does
interfere with power flow when there's no matching network?

What if the antenna is 50 ohms and the transmission line is a half
wavelength of 600 ohms, for a 12:1 mismatch? There's no matching
network. The transmitter sees 50 ohms. The antenna sees 50 ohms. What
will interfere with the power flow?


In my simplistic world, this is how I understand things:

Provided the TX is followed by a tuner/matcher, which matches whatever
is attached to the tuner output to 50 ohms at the tuner input, the TX
will be happy.

The power loss in the feeder is essentially a function of its inherent
loss (when matched) per unit length, and the SWR on it.

The SWR is a function of the mismatch between the load on the antenna
end of the feeder, and the feeder characteristic impedance. The greater
the SWR and the longer the feeder, the higher will be the loss on the
feeder. 'Lossless' feeder have no loss, regardless of length and SWR.
However, with real-world feeders, the losses rise increasingly rapidly
with increasing SWR.

The impedance looking into the tuner end of the feeder is the impedance
of the load, transformed by length of the feeder, and is also modified
by the loss of the feeder.

The higher the feeder loss, the closer the impedance seen at the tuner
end will approach the characteristic impedance of the feeder. [Long
lengths of lossy feeder - maybe with a nominal termination on the far
end - can make good dummy loads at VHF and UHF.]
--
Ian

Ian Jackson wrote in
:

....
In my simplistic world, this is how I understand things:

Provided the TX is followed by a tuner/matcher, which matches whatever
is attached to the tuner output to 50 ohms at the tuner input, the TX
will be happy.

"Happey" eh!

The power loss in the feeder is essentially a function of its inherent
loss (when matched) per unit length, and the SWR on it.

Wrong.


The SWR is a function of the mismatch between the load on the antenna
end of the feeder, and the feeder characteristic impedance. The

Well, the SWR at the load end is a function of Zl and Zo (both complex
quantities)... but the 'notional' SWR varies along the line as accounted
for by the complex propagation coefficient, in most practical cases at
HF, SWR decreases smoothly from load to source.

greater the SWR and the longer the feeder, the higher will be the loss
on the feeder. 'Lossless' feeder have no loss, regardless of length
and SWR. However, with real-world feeders, the losses rise
increasingly rapidly with increasing SWR.

See your earlier misconception regarding loss being a simple function of
SWR.


The impedance looking into the tuner end of the feeder is the
impedance of the load, transformed by length of the feeder, and is
also modified by the loss of the feeder.

You got that right.


The higher the feeder loss, the closer the impedance seen at the tuner
end will approach the characteristic impedance of the feeder. [Long
lengths of lossy feeder - maybe with a nominal termination on the far
end - can make good dummy loads at VHF and UHF.]

Yes, but is it of practical application in a transmit scenario? If the
input impedance due to a severly mismatched load is at all close to Zo,
then you have lost most of the transmitter power in the line.

The "make a good dummy load" recipe doesn't address the power rating,
especially where most of the power is dissipated in a very short length
of cable.

Owen

On Sep 1, 4:11*am, Ian Jackson
wrote:
The impedance looking into the tuner end of the feeder is the impedance
of the load, transformed by length of the feeder, and is also modified
by the loss of the feeder.

That's the result of the 50 ohm Z0-match achieved at the input of the
tuner which is responsible for the transmitter's "happiness". A Z0-
match causes the incident reflected energy to be redistributed back
toward the antenna through a combination of reflection and destructive
interference.
--
73, Cecil, w5dxp.com

Roy,

The mention of reactance means we are talking in the frequency domain,
and a steady state solution is being discussed.


Roy Lewallen wrote in
:

....
Power will indeed be transferred through such a match. Using your
antenna as an example, suppose that a transmitter with output Z of 50
ohms is connected to a tuner that transforms its output impedance to
0.6 + j1250 ohms. Connect the output of the tuner to a half wavelength

Does the use of "output impedance" here mean that he transmitter can be
validly represented by a Thevenin equivalent circuit, and that "output
impedance" is the Thevenin equivalent source impedance.

Without getting into that arguable postion and reinforcing the notion
that a transmitter rated for a nominal 50 ohm load has a source impedance
of 50+j0, you could say:

.... Using your antenna as an example, suppose that a transmitter designed
to operate into a load Z of 50+j0 ohms is connected to a tuner that
transforms the antenna (0.5-j1250) to its preferred load impedance (50
+j0). Connect ...


600 ohm transmission line to the antenna. The transmitter will see 50
+ j0 ohms, the antenna will see an impedance of 0.6 + j1250 ohms, and
full power will be transferred. Power transfer has nothing to do with
the SWR on the line or the match between the line and antenna.

In practice, the line loss will increase some due to the very high
SWR, but the loss increase won't be much if the matched line loss is
low.

I chose a half wavelength for simplicity, but it's not necessary.
Other lengths of line will transform the antenna impedance to
different values. All that's necessary is to readjust the tuner
accordingly to match the different impedance.

And:

All that's necessary is to readjust the tuner accordingly to deliver the
transmitter its rated load impedance.


Amateurs have successfully been using this method to feed nonresonant
and multi-band antennas for decades.

Roy Lewallen, W7EL


As you will have noted, some band the term 'match' around with abandon,
and it means different things in different contexts, and to different
readers.

Take a transmitter designed for a 50+j0 load, connected by an electrical
half wave of 70 ohm coax to a 50 ohm load. Is it 'matched'? Well, from
the information, it is correctly loaded, it is designed for a 50+j0 load,
and it has a 50+j0 (approximately) load. We don't actually know the
source impedance, and even if we did, it this case, whether the
transmitter is 'matched' to the line, and whether the line is 'matched'
to the load is unimportant.

'Output impedance' is another term that is used differently, some use it
to mean the equivalent source impedance, some to mean the required load,
and some insist the foregoing are naturally the same, or will be if the
transmitter is 'matched' for maximum power output.

Owen