tuner - feedline - antenna question ?
 

All,

I am trying to install a trapped 40m dipole in the attic, the antenna is
in place however it is short and resonates at about 7.7 MHz. I decided
to try it by using a tuner close to the transmitter in the shack. The
feedline is 50 ohm coax. On low power the tuner creates a very low SWR.
The transmitter is a solid state 100 watt Heathkit.

However when I transmit according to the SWR Watt meter the system
appears to transmit well over 200 watts. It pined the meter on a 200
watt range. I repeated the test twice and then stopped. When it is
transmitting the SWR reads about 1.1 to 1. The meter works very well and
does not exhibit strange readings on other setups.

My questions a What is happening? What is causing it?

Thanks - Dan

tuner - feedline - antenna question ?
 

dansawyeror wrote:
I am trying to install a trapped 40m dipole in the attic, the antenna is
in place however it is short and resonates at about 7.7 MHz. I decided
to try it by using a tuner close to the transmitter in the shack. The
feedline is 50 ohm coax. On low power the tuner creates a very low SWR.
The transmitter is a solid state 100 watt Heathkit.

However when I transmit according to the SWR Watt meter the system
appears to transmit well over 200 watts. It pined the meter on a 200
watt range. I repeated the test twice and then stopped. When it is
transmitting the SWR reads about 1.1 to 1. The meter works very well and
does not exhibit strange readings on other setups.

My questions a What is happening? What is causing it?

When the transmitter is putting out 100 watts and the
forward power reading is 200 watts, it means that the
SWR is 5.83:1, i.e. the voltage reflection coefficient
is 0.707 and the power reflection coefficient is 0.5.

To get the power delivered to the load, you must subtract
reflected power from forward power. In your case that seems
to be:
Pfwd - Pref = Pload = ~Psource
200w - 100w = 100w = ~100w
--
73, Cecil http://www.w5dxp.com

tuner - feedline - antenna question ?
 

On Sun, 25 Feb 2007 07:14:54 -0800, dansawyeror
wrote:
resonates at about 7.7 MHz.
On low power the tuner creates a very low SWR.
according to the SWR Watt meter the system
appears to transmit well over 200 watts.
When it is transmitting the SWR reads about 1.1 to 1.

Hi Dan,

The Meter is either not as good as you claim it to be (it doesn't
accurately perform at low power); OR
you have common mode problems (classic).

Do you choke the dipole?

73's
Richard Clark, KB7QHC

tuner - feedline - antenna question ?
 

dansawyeror wrote in
:

All,

I am trying to install a trapped 40m dipole in the attic, the antenna
is
in place however it is short and resonates at about 7.7 MHz. I decided
to try it by using a tuner close to the transmitter in the shack. The
feedline is 50 ohm coax. On low power the tuner creates a very low SWR.
The transmitter is a solid state 100 watt Heathkit.

However when I transmit according to the SWR Watt meter the system
appears to transmit well over 200 watts. It pined the meter on a 200
watt range. I repeated the test twice and then stopped. When it is
transmitting the SWR reads about 1.1 to 1. The meter works very well
and
does not exhibit strange readings on other setups.

My questions a What is happening? What is causing it?

Thanks - Dan

Dan,

I assume in all these scenarios, the VSWR meter is between the
transmitter and ATU, and the ATU is adjusted for low VSWR.

You seem to say raise two issues:
-you have adjusted the tuner for a "very low SWR" on "low power"
(whatever each of those means), and when you transmit at "well over 200
watts" the SWR is 1.1:1; and
- your transmitter rated at 100W indicates "well over 200 watts" into a
1.1:1 load.

Re the first issue: If this is to mean the VSWR is higher on higher
power, the most common reason (but not the only one) that VSWR meters
read better VSWR on very low power is to do with the voltage drop across
the diode(s) in the meter. The scale may be calibrated at higher power
where the diode drop is less significant, perhaps even insignificant, and
when you adjust the meter for maximum sensitivity the diode drop
introduces significant error.

Re the second issue, if the instrument is a typical directional
wattmeter, the power output is calculated by deducting the "reflected
power" from the "forward power", but at VSWR=1.1 the "reflected power is
0.2% of "forward power" and insignificant. Otherwise, it might just have
an RF voltmeter sampling the line and calibrated in watts, and which is
only valid at very low VSWR. Transmitters don't often exceed their rated
power by over 100%, so your reading casts doubt on your meter. It sounds
like you need to make another measurement with another instrument to
locate the problem.

Owen

tuner - feedline - antenna question ?
 

In article ,
Cecil Moore wrote:

dansawyeror wrote:
I am trying to install a trapped 40m dipole in the attic, the antenna is
in place however it is short and resonates at about 7.7 MHz. I decided
to try it by using a tuner close to the transmitter in the shack. The
feedline is 50 ohm coax. On low power the tuner creates a very low SWR.
The transmitter is a solid state 100 watt Heathkit.

However when I transmit according to the SWR Watt meter the system
appears to transmit well over 200 watts. It pined the meter on a 200
watt range. I repeated the test twice and then stopped. When it is
transmitting the SWR reads about 1.1 to 1. The meter works very well and
does not exhibit strange readings on other setups.

My questions a What is happening? What is causing it?



two things pop into mind could be your antenna is radiating towards
and into or near your radio and causing some feedback that might effect
the radio and or the meter

there is also the possibility that you have some bad (common mode? etc)
current flowing back down the coax which could also wreck havock


just my guess and double check the above and grounds

put a dummy load into your tuner see if you get proper readings

tuner - feedline - antenna question ?
 

To get the power delivered to the load, you must subtract
reflected power from forward power. In your case that seems
to be:
Pfwd - Pref = Pload = ~Psource
200w - 100w = 100w = ~100w

How can that be? If the meter is basically a directional coupler then the
forward power is just that. Subtracting any reflected power will just give a
stupid answer. The only errors will be due to the directivity of the
coupler, which will give a band of uncertainty which varies with VSWR, and
the error due to the accuracy of the detectors.

My Bird does not subtract any reflected power to give a forward power
reading!! It can't I need to rotate the slug to read reverse power.

73
Jeff

tuner - feedline - antenna question ?
 

"Jeff" wrote in
.com:

How can that be? If the meter is basically a directional coupler then
the forward power is just that. Subtracting any reflected power will
just give a stupid answer. The only errors will be due to the
directivity of the coupler, which will give a band of uncertainty
which varies with VSWR, and the error due to the accuracy of the
detectors.

My Bird does not subtract any reflected power to give a forward power
reading!! It can't I need to rotate the slug to read reverse power.

Jeff, without commenting on whether Cecil's assertions are right or
wrong, you seem to have some misconceptions about what is measured with
your Bird (presumably 43).

The so called "forward power" and "reflected power" are notional values,
but not actual power "components". The only power is the average rate at
which energy passes a point, and it is in one direction or the other.

In fact the power can be calculated taking "forward power" minus
"reflected power", but only in the case where the sampler is calibrated
for Zo being real (as it is in a Bird 43).

My article at http://www.vk1od.net/VSWR/VSWRMeter.htm describes the
operation of a Bruene type of VSWR meter and discusses the power
measurement issue. Though the sampler in the Bird is different to the
Bruene sampler, the Bird samples V and I in a very small region (
regarded a point ) and sums them in the same way as the Bruene circuit.

Owen

tuner - feedline - antenna question ?
 

The so called "forward power" and "reflected power" are notional values,
but not actual power "components". The only power is the average rate at
which energy passes a point, and it is in one direction or the other.

I am sorry, but I disagree, forward power is real and can be measured, or if
you wish separated out with a circulator or isolator. What you are
describing could be called 'transmitted' power or power delivered into a
mismatched load, but that it different from forward power, or the power
delivered by the source.

73
Jeff

tuner - feedline - antenna question ?
 

"Jeff" wrote in
.com:

To get the power delivered to the load, you must subtract
reflected power from forward power. In your case that seems
to be:
Pfwd - Pref = Pload = ~Psource
200w - 100w = 100w = ~100w

How can that be? If the meter is basically a directional coupler then
the forward power is just that. Subtracting any reflected power will
just give a stupid answer. The only errors will be due to the
directivity of the coupler, which will give a band of uncertainty
which varies with VSWR, and the error due to the accuracy of the
detectors.

Depends if the meter is before or after the tuner. If the meter is after
the tuner, then the tuner is taking reflected power and adding it to the
transmitter's contribution.

My Bird does not subtract any reflected power to give a forward power
reading!! It can't I need to rotate the slug to read reverse power.

If you put your bird AFTER a tuner on a line that's near 6-to-1, it will
also show twice as much power as the transmitter is putting into the
tuner. Or a bit less if the tuner is not efficient.


--
Dave Oldridge+
ICQ 1800667

tuner - feedline - antenna question ?
 

Jeff wrote:
To get the power delivered to the load, you must subtract
reflected power from forward power. In your case that seems
to be:
Pfwd - Pref = Pload = ~Psource
200w - 100w = 100w = ~100w

How can that be? If the meter is basically a directional coupler then the
forward power is just that. Subtracting any reflected power will just give a
stupid answer.

Subtracting any reflected power will give the power
being delivered to the load. Power reflected from
the load is power that is NOT delivered to the load.

The only errors will be due to the directivity of the
coupler, which will give a band of uncertainty which varies with VSWR, and
the error due to the accuracy of the detectors.

Consider the following example assuming a lossless
tuner and transmission line.

100W source+tuner--x--50 ohm coax-----291.42 ohm load

Assuming the tuner is properly tuned, what forward power
will a Bird read on the 50 ohm coax at point 'x'? What
reflected power? What is the net power being delivered
to the load?

My Bird does not subtract any reflected power to give a forward power
reading!! It can't I need to rotate the slug to read reverse power.

You're right. The operator must measure the forward power
and the reflected power and do the subtraction manually.
In the above example, the Bird will read 200w forward and
100w reflected. The operator must subtract those two values
to determine the net power delivered to the load.

This was my guess as to why the Bird was reading 200w in
the original posting. Note that a Bird between the source
and the tuner does NOT read the SWR on the transmission
line between the tuner and the load.
--
73, Cecil http://www.w5dxp.com

tuner - feedline - antenna question ?
 

Thank you.

I think it may be a common mode problem. There is no choke on the
dipole. I will bring it closer to resonance.

- Dan kb0qil

Richard Clark wrote:
On Sun, 25 Feb 2007 07:14:54 -0800, dansawyeror
wrote:
resonates at about 7.7 MHz.
On low power the tuner creates a very low SWR.
according to the SWR Watt meter the system
appears to transmit well over 200 watts.
When it is transmitting the SWR reads about 1.1 to 1.

Hi Dan,

The Meter is either not as good as you claim it to be (it doesn't
accurately perform at low power); OR
you have common mode problems (classic).

Do you choke the dipole?

73's
Richard Clark, KB7QHC

tuner - feedline - antenna question ?
 

dansawyeror wrote:
I think it may be a common mode problem. There is no choke on the
dipole. I will bring it closer to resonance.

Dan, are you measuring that power on the input or
output of the tuner? If at the output of a transceiver
with autotuner, for instance, the forward power is
the sum of the transmitter power and reflected power.
--
73, Cecil http://www.w5dxp.com

tuner - feedline - antenna question ?
 

Owen Duffy wrote:
The so called "forward power" and "reflected power" are notional values,
but not actual power "components". The only power is the average rate at
which energy passes a point, and it is in one direction or the other.

That statement depends upon the definition of "power"
being used. The IEEE Dictionary has a different
definition of power than does a physics textbook.
The net power is the average rate at which net energy
passes a point. The net power is the difference between
the forward joules/sec and the reflected joules/sec.

Instead of using the word "power", let's switch over to
the dimensions of power, i.e. "joules/second". Those
joules are indeed *actual energy components*.

The so called "forward power" is a forward traveling
EM wave containing energy moving at the speed of light.
There are indeed actual forward joules/sec moving past
a point on the transmission line.

The so called "reflected power" is a rearward traveling
EM wave containing energy moving at the speed of light.
There are indeed actual reflected joules/sec moving past
a point on the transmission line.

Note that an EM wave cannot stand still. According
to the theory of relativity, EM waves always move at
the speed of light (taking VF into account).

Standing waves consist of a forward traveling wave
containing joules/second and a reflected traveling
wave containing joules/second. The joules/second in
those two waves are supplied during the transient
power-on state. During steady-state, that energy has
not yet reached the load. But the total energy contained
in the transmission line during steady-state is exactly
the amount of energy needed to support the forward
traveling wave and the reflected traveling wave. Standing
waves would not be possible without those two real EM
wave energy components traveling in opposite directions.

At power-down, assuming the source is disconnected
from the transmission line, all of the forward wave
energy and reflected wave energy stored in the lossless
transmission line is eventually dissipated in the load.
That happens during a time when the source is supplying
zero energy.
--
73, Cecil http://www.w5dxp.com

tuner - feedline - antenna question ?
 

On Mon, 26 Feb 2007 08:10:49 -0800, dansawyeror
wrote:

I think it may be a common mode problem. There is no choke on the
dipole. I will bring it closer to resonance.

Hi Dan,

One very simple test is to fire up your rig and note the SWR. Patch
in a short, loose length of transmission line to the existing run
(about an eighth wave) and fire up the rig again.

Did the SWR change?

If so, you are being SWR whipped by Common Mode currents.

You can keep introducing different lengths of line until you find 1:1
(unlikely, but perhaps close) and let it go at that. This will be a
single frequency solution, but take care that it does NOT cure Common
Modality. Instead, it adds a vertical component to your transmission
(maybe).

This is not always good as that same transmission line (plus
extension) may run past RF sensitive devices (like intercoms, VCRs,
light dimmers, etc.) that go whacko. It may also fill in the nulls of
your dipole (sometimes good, sometimes bad).

73's
Richard Clark, KB7QHC

tuner - feedline - antenna question ?
 

On Mon, 26 Feb 2007 10:25:10 -0000, "Jeff" wrote:

I am sorry, but I disagree

Hi Jeff,

Your appologies aside, it is the convention you are disagreeing with.
The injection of such terminology as
'transmitted' power
is not part of conventional usage in this discussion. The trap here
of inventing terms is that your term would not account for Ohmic loss
as either forward or reverse power in the balance sheet (and this loss
could well be the source of mismatch); and yet this loss would have a
definite impact on what is "transmitted."

A simple instance proves this. Add a 14 Ohm resistor in series at the
feed to a perfect quarterwave radiator. The reverse reading would be
nada, the forward reading would NOT be "transmitted" power. Further,
the conventional usage of terms seen in this thread would still be
accurate.

73's
Richard Clark, KB7QHC

tuner - feedline - antenna question ?
 

" Your appologies aside, it is the convention you are disagreeing with.

I think that most engineers would disagree, what you are describing is the
power delivered into the load, both forward and reverse power exist both by
convention and as a real entity.

The injection of such terminology as
'transmitted' power
is not part of conventional usage in this discussion.

Perhaps that is sloopy wording on my part, I sould have said 'power
transmitted to the load'; I was not implying radiated power.

73
Jeff

tuner - feedline - antenna question ?
 

On Mon, 26 Feb 2007 18:10:42 -0000, "Jeff" wrote:

what you are describing is the
power delivered into the load,

Hi Jeff,

Perhaps you should re-read your original complaint.

Perhaps that is sloopy wording on my part

So it would seem. ;-)

73's
Richard Clark, KB7QHC

tuner - feedline - antenna question ?
 

Jeff wrote:
Perhaps that is sloopy wording on my part, I sould have said 'power
transmitted to the load'; I was not implying radiated power.

Indeed, "transmitted power" could simply mean power
from the transmitter, i.e. "source power".
--
73, Cecil http://www.w5dxp.com

tuner - feedline - antenna question ?
 

"Jeff" wrote in
.com:

The so called "forward power" and "reflected power" are notional
values, but not actual power "components". The only power is the
average rate at which energy passes a point, and it is in one
direction or the other.

I am sorry, but I disagree, forward power is real and can be measured,
or if you wish separated out with a circulator or isolator. What you
are describing could be called 'transmitted' power or power delivered
into a mismatched load, but that it different from forward power, or
the power delivered by the source.

Jeff,

You dropped a number of terms he
- 'transmitted' power;
- power delivered into a mismatched load;
- forward power;
- power delivered by the source;

The power delivered to a load (of any kind) from a lossless transmission
line section, is the same as the power delivered by the source. In the
case of the lossy line, then the line characteristics and load impedance
also need to be taken into account to calculate the power lost in the
line section, and it is not as simple as using up a dB/100' rating in a
table (unless the line is matched).

You assertion that you have travelling forward and reflected power waves
on the transmission line runs into a problem when you try to analyse the
combination of both at a point (eg the input to the line) as power
doesn't combine vectorially.

When you devise configurations with circulators, isolaters, directional
couplers, hybrids etc to "trap and reroute" reflected power, you have
probably changed the nature of the load on a line section and that
accounts for why the reflected power seems to have been isolated from
forward power.

Owen

tuner - feedline - antenna question ?
 

"
The power delivered to a load (of any kind) from a lossless transmission
line section, is the same as the power delivered by the source.

So it is your contention that power is not reflected at a mismatch. The wave
certainly is so the power contained in the reflected portion must be as
well.

You assertion that you have travelling forward and reflected power waves
on the transmission line runs into a problem when you try to analyse the
combination of both at a point (eg the input to the line) as power
doesn't combine vectorially.

I was not trying to analyse the combination of any wave on the line ("power"
waves, whatever they may be, or anything else), I was merely noting that you
can quantify and measure the power contained the both the forward and
reflected waves and they are real quantities.

Jeff

tuner - feedline - antenna question ?
 

Owen Duffy wrote:
You assertion that you have travelling forward and reflected power waves
on the transmission line runs into a problem when you try to analyse the
combination of both at a point (eg the input to the line) as power
doesn't combine vectorially.

But it does combine according to the following formula
which is the irradiance equation from the field of
optics.

Ptot = P1 + P2 + 2*SQRT(P1*P2)cos(A)

where 'A' is the angle between V1 and V2 and V1 is
the voltage associated with P1 and V2 is the voltage
associated with P2.

The first time I saw this equation was in Dr. Best's
Nov/Dec 2001 QEX article on Transmissions Lines. It
really does work for "adding" the two powers in two
coherent waves.
--
73, Cecil http://www.w5dxp.com

tuner - feedline - antenna question ?
 

Jeff wrote:
I was not trying to analyse the combination of any wave on the line ("power"
waves, whatever they may be, or anything else), I was merely noting that you
can quantify and measure the power contained the both the forward and
reflected waves and they are real quantities.

The joules/sec are real quantities but whether joules/sec
is power depends upon the definition of "power". Some say
the joules/sec in a reflected wave is not power and they
produce a definition of "power" from a physics book to
prove it, i.e. no work done. To satisfy the purists you
may need to change your statement to: "I was merely noting
that you can quantify and measure the joules/sec contained
in both the forward and reflected waves and they are real
quantities."
--
73, Cecil http://www.w5dxp.com

tuner - feedline - antenna question ?
 

Cecil Moore wrote in
:

Owen Duffy wrote:
You assertion that you have travelling forward and reflected power
waves on the transmission line runs into a problem when you try to
analyse the combination of both at a point (eg the input to the line)
as power doesn't combine vectorially.

But it does combine according to the following formula
which is the irradiance equation from the field of
optics.

Ptot = P1 + P2 + 2*SQRT(P1*P2)cos(A)

where 'A' is the angle between V1 and V2 and V1 is
the voltage associated with P1 and V2 is the voltage
associated with P2.

Cecil,

A is not a property of P1 or P2, and cannot be derived from them. I
maintain that you cannot vectorially combine P1 and P2.

Owen

tuner - feedline - antenna question ?
 

"Jeff" wrote in
.com:


"
The power delivered to a load (of any kind) from a lossless
transmission line section, is the same as the power delivered by the
source.

So it is your contention that power is not reflected at a mismatch.
The wave certainly is so the power contained in the reflected portion
must be as well.

The danger in the "power is refelected at a mismatch" explanation, is
that it follows that power reflected at a mismatched antenna flows back
toward the transmitter and is at least partially absorbed in the PA as
heat. Though that is a popular belief, it is not supported by fact.

The power at a point in a transmission line is P=real(V*conjugate(I)).
This expands to four terms, and people arbitrarily allocate the terms
forward power and reflected power to just two of the four terms because
they happen to be VfIf and VrIr.


You assertion that you have travelling forward and reflected power
waves on the transmission line runs into a problem when you try to
analyse the combination of both at a point (eg the input to the line)
as power doesn't combine vectorially.

I was not trying to analyse the combination of any wave on the line
("power" waves, whatever they may be, or anything else), I was merely
noting that you can quantify and measure the power contained the both
the forward and reflected waves and they are real quantities.

The Bird 43 does not measure power directly, it responds to Vf or Vr
components at a point as explained in the article I quoted. The article
deals with the conditions under which readings can be converted to power,
and whether forward power or reverse power are of themselves meaninful.

If you have read it and disagree, then thats ok. If you can identify
flaws in the article, constructive feedback is welcome.

Owen

tuner - feedline - antenna question ?
 

Owen Duffy wrote:
A is not a property of P1 or P2, and cannot be derived from them. I
maintain that you cannot vectorially combine P1 and P2.

P1 is a property of V1^2/Z0, A is a property of V1.
P2 is a property of V2^2/Z0, A is a property of V2.
There is an unbroken chain of cause and effect.
It is true that one cannot directly vectorially
combine P1 and P2 because P1 and P2 are not vectors.

However, the ability to combine the P1 and P2 of
coherent EM waves dates back to before you were born.
Optical engineers didn't have the luxury of being
able to measure the phase angles. All they could
measure was the total amplitude. Please don't try
to tell us that their total amplitude measurements
were wrong throughout the 20th century and are
still wrong in the 21st century.

The rules for combining P1 and P2 when they are
coherent are known as the irradiance equations in
optics. Dr. Best applied them to RF quantities.
Please reference "Optics", by Hecht, 4th edition,
page 388 and Dr. Best's, "Wave Mechanics of Transmission
Lines, Part 3: ..." in the Nov/Dec 2001 issue of "QEX".
--
73, Cecil http://www.w5dxp.com

tuner - feedline - antenna question ?
 

Owen Duffy wrote:
The danger in the "power is refelected at a mismatch" explanation, is
that it follows that power reflected at a mismatched antenna flows back
toward the transmitter and is at least partially absorbed in the PA as
heat. Though that is a popular belief, it is not supported by fact.

That only applies to mismatched systems. For systems
Z0-matched by an antenna tuner, the situation becomes
trivial to understand. The reflected energy is re-
reflected by the Z0-match provided by the properly
tuned antenna tuner. It's all explained in my energy
analysis article at: http://www.w5dxp.com/energy.htm
--
73, Cecil http://www.w5dxp.com

tuner - feedline - antenna question ?
 

Cecil Moore wrote in news:wnIEh.2899$8x.278
@newssvr14.news.prodigy.net:

Owen Duffy wrote:
A is not a property of P1 or P2, and cannot be derived from them. I
maintain that you cannot vectorially combine P1 and P2.

....
It is true that one cannot directly vectorially
combine P1 and P2 because P1 and P2 are not vectors.

Thanks

....

tuner - feedline - antenna question ?
 

Owen Duffy wrote:
Cecil Moore wrote in news:wnIEh.2899$8x.278
It is true that one cannot directly vectorially
combine P1 and P2 because P1 and P2 are not vectors.

Thanks

That doesn't mean that there are not valid rules for
combining P1 and P2. Optical engineers have been doing
it for decades. RF engineers seem to lag behind.

You seemed to be questioning the validity of the power
combination equation. Have you changed your mind?
--
73, Cecil http://www.w5dxp.com

tuner - feedline - antenna question ?
 

Cecil Moore wrote in
:

Owen Duffy wrote:
The danger in the "power is refelected at a mismatch" explanation, is
that it follows that power reflected at a mismatched antenna flows
back toward the transmitter and is at least partially absorbed in the
PA as heat. Though that is a popular belief, it is not supported by
fact.

That only applies to mismatched systems. For systems
Z0-matched by an antenna tuner, the situation becomes
trivial to understand. The reflected energy is re-
reflected by the Z0-match provided by the properly
tuned antenna tuner. It's all explained in my energy
analysis article at: http://www.w5dxp.com/energy.htm

Cecil, it seems that between the two of you, you are constructing a
picture that (in a lossless line for simplicity) if the Bird 43 reads
100W forward and 50 watts reflected, the power radiated (ignoring
antenna ohmic losses) is 100W, but 50W is reflected toward the
transmitter... but that's allright because the 50W will be reflected by
a Zo matched PA, and energy is conserved on the line.

The reality is that the Bird responds to Vf and Vr (depending on the
orientation of the slug), and in the special case where the sampler is
calibrated to respond to |Vf| and |Vr| for a purely real ratio of V/I
(Zn=Rn+j0 which is 50+j0 in the case of the '43), on the line at the
point of the sampler, then the average power passing that point is a
single number, it is |Vf|^2/Rn-|Vr|^2/Rn. The foward and reflected power
readings are not meaningful in themselves, but you can deconstruct rho,
and (knowing Zn) |Vf| and |Vr| from them.

Owen

tuner - feedline - antenna question ?
 

Owen Duffy wrote:
Cecil, it seems that between the two of you, you are constructing a
picture that (in a lossless line for simplicity) if the Bird 43 reads
100W forward and 50 watts reflected, the power radiated (ignoring
antenna ohmic losses) is 100W, but 50W is reflected toward the
transmitter... but that's allright because the 50W will be reflected by
a Zo matched PA, and energy is conserved on the line.

Please don't insult our intelligence. If the Bird reads
100w forward and 50w reflected, the power radiated by
the antenna is 50w, neglecting losses.

Pload = Pfor - Pref

The situation at the output of a lossless tuner is:

Pfor = Psource + Pref

Please honor the conservation of energy principle in your
postings.
--
73, Cecil http://www.w5dxp.com

tuner - feedline - antenna question ?
 

Cecil Moore wrote in news:QeJEh.2909$8x.1740
@newssvr14.news.prodigy.net:

Owen Duffy wrote:
Cecil, it seems that between the two of you, you are constructing a
picture that (in a lossless line for simplicity) if the Bird 43 reads
100W forward and 50 watts reflected, the power radiated (ignoring
antenna ohmic losses) is 100W, but 50W is reflected toward the
transmitter... but that's allright because the 50W will be reflected
by
a Zo matched PA, and energy is conserved on the line.

Please don't insult our intelligence. If the Bird reads

Of course it is nonsense, but it is a logical development based on Jeff's
words "What you are describing could be called 'transmitted' power or
power delivered into a mismatched load, but that it different from
forward power, or the power delivered by the source" and your words "For
systems
Z0-matched by an antenna tuner, the situation becomes trivial to
understand. The reflected energy is re-reflected by the Z0-match provided
by the properly tuned antenna tuner".

The steady state solution of the ratio of V/I at the input to a real
transmission line section (ie lossy) that has a load of some arbitrary
impedance is solved using equations that do not include forward and
reflected power terms. The power at any point is the real part of
V*conjugate(I) at that point, no matter whether it is at the source,
load, line input, output or anywhere along the line.

Owen

tuner - feedline - antenna question ?
 

On Mon, 26 Feb 2007 20:38:00 GMT, Owen Duffy wrote:

The danger in the "power is refelected at a mismatch" explanation, is
that it follows that power reflected at a mismatched antenna flows back
toward the transmitter and is at least partially absorbed in the PA as
heat. Though that is a popular belief, it is not supported by fact.

Hi Owen,

This denies experience.

73's
Richard Clark, KB7QHC

tuner - feedline - antenna question ?
 

Owen Duffy wrote:
Of course it is nonsense, but it is a logical development based on Jeff's
words ...

Please don't blame me for someone else's words.

The irradiance (power) equations from optical engineering
for the combining of electromagnetic power from two EM waves
are accepted as a fact of physics. Do you really think that
the amateur radio community should reject that fact
of physics?
--
73, Cecil http://www.w5dxp.com

tuner - feedline - antenna question ?
 

Richard Clark wrote in
:

On Mon, 26 Feb 2007 20:38:00 GMT, Owen Duffy wrote:

The danger in the "power is refelected at a mismatch" explanation, is
that it follows that power reflected at a mismatched antenna flows back
toward the transmitter and is at least partially absorbed in the PA as
heat. Though that is a popular belief, it is not supported by fact.

Hi Owen,

This denies experience.

Do you mean the experience that the PA may (but not necessarily) run
hotter on other than its rated load impedance?

Could that be exlained without introducing transmission lines and the
reflected power issue by examining how the PA works on a load different
to its rated load?

I suggest that if a PA / line / load situation transforms the actual load
to some arbitrary impedance Z at the PA end of the line, the PA will
peform exactly as if the PA were directly loaded by a lumped constant
load of Z. The explanation of any heating effects or changed operating
voltages is in the effect of the load impedance Z (however it is
obtained) on the PA.

Does that make sense?

Owen

tuner - feedline - antenna question ?
 

Owen Duffy wrote:
I suggest that if a PA / line / load situation transforms the actual load
to some arbitrary impedance Z at the PA end of the line, the PA will
peform exactly as if the PA were directly loaded by a lumped constant
load of Z.

Yes, that is true for the performance of the PA.
Certainly not true for the performance of the
transmission line or antenna.

My favorite quotation by an antenna guru on this
newsgroup is that "a 50 ohm antenna can be replaced
by a 50 ohm resistor without changing anything".
If that were true, we don't need antennas. :-)

I'm going to be away from my computer for 48 hours.
--
73, Cecil http://www.w5dxp.com

tuner - feedline - antenna question ?
 

Cecil Moore wrote in
:

Owen Duffy wrote:
Of course it is nonsense, but it is a logical development based on
Jeff's words ...

Please don't blame me for someone else's words.

A selective partial quotation to misrepesent what was actually written
Cecil!

Owen

tuner - feedline - antenna question ?
 

Cecil Moore wrote in
t:

Owen Duffy wrote:
I suggest that if a PA / line / load situation transforms the actual
load to some arbitrary impedance Z at the PA end of the line, the PA
will peform exactly as if the PA were directly loaded by a lumped
constant load of Z.

Yes, that is true for the performance of the PA.
Certainly not true for the performance of the
transmission line or antenna.


Please explain?

Owen

tuner - feedline - antenna question ?
 

On Mon, 26 Feb 2007 23:24:13 GMT, Owen Duffy wrote:

Could that be exlained without introducing transmission lines and the
reflected power issue by examining how the PA works on a load different
to its rated load?

Hi Owen,

Let's treat this like the Chinese Box problem.

If you didn't know what the load was, could you explain it any
differently? No. Apriori knowledge is not a proof.

73's
Richard Clark, KB7QHC

tuner - feedline - antenna question ?
 

Richard Clark wrote in
:

On Mon, 26 Feb 2007 23:24:13 GMT, Owen Duffy wrote:

Could that be exlained without introducing transmission lines and the
reflected power issue by examining how the PA works on a load different
to its rated load?

Hi Owen,

Let's treat this like the Chinese Box problem.

If you didn't know what the load was, could you explain it any
differently? No. Apriori knowledge is not a proof.

Richard, I content that:
- the power output of the PA; and
- the efficiency of the PA may be (and usually are) sensitive to the load
impedance.

A steady state analysis is usually adequate for most ham radio
applications, though there may be cases where establishment of steady
state brings its own issues. This discussion is about the steady state.

Though it is often asserted that the PA will get hotter as a result of
"reflected power" being dissipated in the dynamic output impedance of the
PA, and that this may / will damage the PA, the power explanation doesn't
work numerically in the general case.

The constrained ratio of V/I is an aspect of the field setup in a
transmission line, and the launching of a reflected wave to reconcile the
load V/I with the constrained (Vf+Vr)/If-Ir) at the load end of the line
is a solution for what happens on the transmission line. At the source
end of the line, (Vf+Vr)/If-Ir) at that point (a function of (Vf+Vr)/If-
Ir at the load end, and the complex propagation coefficient and Zo of the
line) give us the equivalent (complex) impedance seen by the PA, and we
can predict / explain the behaviour of the PA (maximum power out,
efficiency) on that equivalent load. This method of analysis does work
numerically.

Owen

tuner - feedline - antenna question ?
 

On Tue, 27 Feb 2007 01:07:12 GMT, Owen Duffy wrote:

Richard Clark wrote in
Let's treat this like the Chinese Box problem.

If you didn't know what the load was, could you explain it any
differently? No. Apriori knowledge is not a proof.

Richard, I content that:

Contend or offer in contention.

- the power output of the PA; and
- the efficiency of the PA may be (and usually are) sensitive to the load
impedance.

This is not contending nor contention and is content only for a non
sequitur. The line following a tuner exhibits considerable loss (poor
efficiency) that can only occur on the basis of power and mismatch.
You yourself offered in other correspondence that it exceeds cable
attenuation specifications found only in a matching condition. To
suggest that a PA's sensitivity is somehow exhalted in the face of
identical, ordinary behavior of a passive component is hardly
seperable. Consider the simple substitution to your quote:
- the power output at the terminus of the line; and
- the efficiency at the terminus of the line may be (and usually are) sensitive to the load
impedance.

continuing on...
A steady state analysis is usually adequate for most ham radio
applications, though there may be cases where establishment of steady
state brings its own issues. This discussion is about the steady state.

I expressed nothing of transitory behavior.

Though it is often asserted that the PA will get hotter as a result of
"reflected power" being dissipated in the dynamic output impedance of the
PA, and that this may / will damage the PA, the power explanation doesn't
work numerically in the general case.

Heat is the outward proof of power and is always demonstrable in both
specific and general cases. Occurrences of other, significant
radiation from the source (as long as that source physically occupies
a substantially minor region of wavelength) is exceedingly difficult
to achieve.

You don't offer a numerical proof of a general case, and given that
the general case must allow for the specific cases already allowed in
your discussion above - that may be an untenable assertion for you.
Those specific cases are demonstrably caloric and must follow the same
math you suggest.

I suspect you are trying to argue differences by degree (no pun
intended as to heat); but I seriously doubt you can produce the math
to do that. The arguments that flow from that involve what is called
source resistance, and those arguments are legion in this forum (where
naysayers embrace a refusal to accept or name ANY value - a curious
paradox and an engineering nihilism I enjoy to watch).

73's
Richard Clark, KB7QHC