RadioBanter - my SWR reading

RadioBanter (https://www.radiobanter.com/)

- Antenna (https://www.radiobanter.com/antenna/)

- - my SWR reading (https://www.radiobanter.com/antenna/126325-my-swr-reading.html)

Richard Harrison wrote:
Power did not exist at the far end of the line until it was transported
there by the line. The line moved the power from the 1st place to the
2nd place. It moved!

Here's a physical analogy. We light a butane lighter at one
point and observe the flame. We close the lighter and move
to another point 100 yards away. We light the lighter again
and observe the flame. Did me move the flame by 100 yards?
Or did we convert energy into power at one point, then
move the energy source to another point and convert the
energy into power?

If you move watts of power then you should be able to
measure that movement in watts/sec or joules/sec/sec.
Have you ever measured such?
--
73, Cecil http://www.w5dxp.com

Cecil, W5DXP wrote:
"Have you ever measured such?"

My Bird Model 43 Instruction book says:
"---designed to measure power flow and load match in 50 ohm coaxial
transmission lines."
I`ve used it many times.

Best regards, Richard Harrison, KB5WZI

Cecil Moore wrote:
Gene Fuller wrote:
If you ever come to the realization that there is a difference between
transient conditions and steady-state conditions, along with the
realization that standing waves are actually useful, ...

Please explain how those waves can exist without energy,
i.e. without joules/sec passing a point.

No waves of power needed, average or not.

Please stop doing that, Gene. You know that I don't believe
in "power waves". What you are trying to deny is that EM
waves contain energy that can be measured at a point in
joules/sec = watts. That argument just won't fly.

Cecil,

I did not say anything that denied that EM waves contain energy.

Where this entire controversy always gets hung up is the difference
between the traveling wave model where the waves go back and forth over
the entire length of the transmission line, and the standing wave model.
In the traveling wave model it is necessary for the wave energy to
traverse back and forth along the entire line. This leads to the
condition where energy is flowing in both directions at the same time at
any given point in the line. In the standing wave model the energy
simply sloshes back and forth within a single half-wave loop. No energy
collisions; no problems at all.

As I have said many times, these are mathematical representations, not
physical "reality". Neither is more correct than the other. No physical
measurement can tell the difference. But it is often useful to use the
most convenient model that does not carry unwanted artifacts and other
baggage.

Oh, by the way, it is not possible to measure energy at a point. Energy
has an extrinsic, not intrinsic, character. It would be educational to
read any good physics text to understand what energy really means and
how conservation of energy laws are constructed.

73,
Gene
W4SZ

"Roy Lewallen" wrote:
All the power produced by the transmitter arrives at the antenna
less whatever is lost as heat in the transmission line.
_________

Roy,

If a transmitter produces r-f power, and a load connected to that
transmitter via a transmission line dissipates any of that r-f power, then
would you not agree that such an r-f transmission line conducts at least
whatever r-f power is dissipated by that load?

And if such a transmission line can conduct power in one direction
(incident), it can also conduct power equally well in the opposite direction
(reflected), until the net result of incident + reflected causes line
failure.

When the Zo of a transmission line matches the Zo of a load at its far end,
then that far-end Z absorbs nearly 100% of the power delivered there by that
transmission line.

If those impedances are not matched, a reflection is generated that may lead
to the real-world, destructive and periodic effects on the transmission line
that I reported from personal experience, earlier in this thread.

RF

Richard Fry wrote:
"Roy Lewallen" wrote:
All the power produced by the transmitter arrives at the antenna
less whatever is lost as heat in the transmission line.
_________

Roy,

If a transmitter produces r-f power, and a load connected to that
transmitter via a transmission line dissipates any of that r-f power, then
would you not agree that such an r-f transmission line conducts at least
whatever r-f power is dissipated by that load?

Of course.

And if such a transmission line can conduct power in one direction
(incident), it can also conduct power equally well in the opposite direction
(reflected), until the net result of incident + reflected causes line
failure.

No.

When the Zo of a transmission line matches the Zo of a load at its far end,
then that far-end Z absorbs nearly 100% of the power delivered there by that
transmission line.

This occurs whether or not there's an impedance match. If I connect my
transmitter to a 50 ohm dummy load via a half wavelength 300 ohm line,
all the transmitter's power (less the line loss) is conveyed via the
transmission line to the load. This is in spite of a 6:1 mismatch at the
load.

If those impedances are not matched, a reflection is generated that may lead
to the real-world, destructive and periodic effects on the transmission line
that I reported from personal experience, earlier in this thread.

In my example, as at any time the load and line aren't matched, there
will be standing waves of voltage and current on the line, which can
lead to line failure. In the example you gave, it was almost certainly
the high current points which caused it. If you'll pick up any
transmission line text, you'll be able to quickly see exactly what happened.

You still haven't explained how these imagined power waves cause
periodic effects. Please re-read my last posting -- is it some kind of
phase angle associated with the power waves, or is there some mechanism
by which they vary with position along the line? I'm looking forward to
your mathematical description of what you think is happening. You can
find mine in any textbook on transmission lines. If you'd like, I can
recommend a half dozen or more.

Roy Lewallen, W7EL

James Barrett wrote:
Hi, I just got my new (used) HF rig, and I strung up a half wave dipole
for 10 meters using 28.4 mhz in my calculations. Several hours later I
am getting an SWR reading of 2:1 at 28.4mhz. Is that pretty good or
should I try to do better?

I appreciate any opinions.

Jim

Jim,

whatever the in and outs as discussed in this thread, if you cut and
resonate at 28.4, have the dipole at a decent height, feed it with
50 ohm coax you should get better than 2:1. Do you know what the
actual resonant frequency of the dipole + feeder is?

As an example I have a ten metre dipole in my loft, some 25 feet
above ground. It resonates at 28.44 at the end of approx 10 metres
of 50 ohm coax, the SWR is 1.4:1 . The bandwidth at 2:1 is 28.25
-28.63. At 2.5:1 it is 28.160-28.760. This is before the ATU, after
the ATU the TX sees from 1:1 to 1.4:1 over the whole of ten metres.
See http://www.radiowymsey.org/FanDipole/FanDipole.html

Charlie.

--
M0WYM
www.radiowymsey.org

Owen Duffy wrote:

SNIP FROM HERE ON UP TO THE OP

The guy is looking for answers to his problem and you lot just want
to massage egos! FFS, give the guy some input and hold back on the
theorising.

Next time the OP has an aerial question he's unlikely to come here :(

--
M0WYM
www.radiowymsey.org

Richard Harrison wrote:
Cecil, W5DXP wrote:
"Have you ever measured such?"

My Bird Model 43 Instruction book says:
"---designed to measure power flow and load match in 50 ohm coaxial
transmission lines."
I`ve used it many times.

Would you agree it is indirectly measuring joules/sec
not watts/sec? That would be energy flow.
--
73, Cecil http://www.w5dxp.com

Gene Fuller wrote:
In the standing wave model the energy
simply sloshes back and forth within a single half-wave loop. No energy
collisions; no problems at all.

The problem is that it is impossible for EM waves to
do that. An EM wave flows in one direction until it
encounters a physical impedance discontinuity. It
cannot "slosh back and forth" in reality.
--
73, Cecil http://www.w5dxp.com