VSWR doesn't matter?
 

Richard Fry wrote:
"Roy Lewallen" wrote
The problem is that the idea of "reflected energy" turning the
plates hot is so easy to understand, that people aren't willing to
abandon it simply because it isn't true.
_____________

But reflected energy/power does exist.

For an easy example, such reflections are evident in the picture seen
on an analog TV receiver when the match between the transmit antenna
and the transmission connected to it is bad enough.

In analog TV transmit systems with a typical 500+ foot length
transmission line from the tx to the antenna, a 5% reflection from a
far-end mismatch can be quite visible, showing as a "ghost" image
that is offset from the main image as related to the round-trip
propagation time of the transmission line.

Richard,

The round trip time on the transmission line is 1uS+, and the period of
the highest modulating frequency is 0.2uS, so transient performance of
the line is very important.

Run the numbers on typical ham SSB telphony where the rtt is more like
0.2uS+ and the period of the highest modulating frequency is 300uS, is
it any wonder transient performance isn't critical.

So, if a solution in the steady state solution doesn't degrade the
modulation, why complicate matters with pretend partial time domain
solutions. It is half baked thinking in both worlds that drives the
thinking that reflected power *must* be dissipated in the anode.

There is no doubt that under load end mismatch, there is a reflected wave
on the transmission line, and there is no doubt that under some
conditions, the anode dissipates more power, and they may be correlated,
but the simplistic explanation above that is commonly touted is BS.

Owen

VSWR doesn't matter?
 

In rec.radio.amateur.antenna Richard Clark wrote:
On Tue, 13 Mar 2007 16:05:02 GMT, wrote:

The fact that any transmission line and antenna combination can be
replaced with an RLC lumped load at the transmitter output and the
transmitter can't tell the difference is something that a lot of
hams seem to have a problem understanding.

Hi Jim,

Would it be fair to say there are a number of Hams (no need to go into
proportionality, could be equal number) who have difficulties of
understanding with going from lumped, equivalent circuits to antennas
and transmission lines?

The two perspectives are not exclusionary nor mutually incompatible,
only the arguers are.

I'd have to say that as soon as a circuit contains a radiator or a
transmission line the arm waving begins.

--
Jim Pennino

Remove .spam.sux to reply.

VSWR doesn't matter?
 

On Mar 12, 11:50 pm, Roy Lewallen wrote:
The problem is that the idea of "reflected energy" turning the plates
hot is so easy to understand, that people aren't willing to abandon it
simply because it isn't true.

It also isn't true that there is no energy in the reflected wave, that
such beliefs are gobbledegook, and that RF standing wave energy
just sloshes around in a transmission line at less than light speed.
To really understand what is going on, one has to understand
superposition and interference between RF energy waves. You
are on record as not caring to understand reflected energy. Please
don't condemn those of us who are trying to understand.
--
73, Cecil, w5dxp.com

VSWR doesn't matter?
 

On Mar 12, 11:53 pm, Roy Lewallen wrote:
Yes! All that matters to the transmitter is the impedance it sees. It
doesn't know or care that you've mathematically separated the delivered
power into "forward" and "reverse" components. It doesn't know or care
what the SWR is on the transmission line connected to it, or even if a
transmission line is connected at all.

Think about this - if the transmission line is exactly one-wavelength
long
and lossless, the transmitter sees exactly the same impedance as the
load. At the load, we know reflections occur, but they are same-cycle
reflections so during steady-state with no modulation, exactly the
same
conditions exist at the transmitter as exist at the load if the
transmitter
has the same impedance as the transmission line. So even if we
cannot measure the reflections back into the transmitter, they are
no doubt, there - that is, unless one denies the existence of
reflections
in which case, one needs to explain how standing waves are possible
without reflections in a single-source system.
--
73, Cecil, w5dxp.com

VSWR doesn't matter?
 

On 13 Mar 2007 14:19:12 -0700, "Cecil Moore" wrote:

On Mar 12, 11:50 pm, Roy Lewallen wrote:
The problem is that the idea of "reflected energy" turning the plates
hot is so easy to understand, that people aren't willing to abandon it
simply because it isn't true.

It also isn't true that there is no energy in the reflected wave, that
such beliefs are gobbledegook, and that RF standing wave energy
just sloshes around in a transmission line at less than light speed.
To really understand what is going on, one has to understand
superposition and interference between RF energy waves. You
are on record as not caring to understand reflected energy. Please
don't condemn those of us who are trying to understand.

Did you guys on this thread know that it's been proven statistically that five
out of four people have trouble with fractions?

Walt,W2DU

VSWR doesn't matter?
 

On Tue, 13 Mar 2007 16:05:02 GMT, wrote:

The fact that any transmission line and antenna combination can be
replaced with an RLC lumped load at the transmitter output and the
transmitter can't tell the difference is something that a lot of
hams seem to have a problem understanding.

Hi Jim,

Would it be fair to say there are a number of Hams (no need to go into
proportionality, could be equal number) who have difficulties of
understanding with going from lumped, equivalent circuits to antennas
and transmission lines?

The two perspectives are not exclusionary nor mutually incompatible,
only the arguers are.

73's
Richard Clark, KB7QHC

VSWR doesn't matter?
 

On Tue, 13 Mar 2007 21:15:03 GMT, wrote:

The two perspectives are not exclusionary nor mutually incompatible,
only the arguers are.

I'd have to say that as soon as a circuit contains a radiator or a
transmission line the arm waving begins.

Amen

VSWR doesn't matter?
 

Walter Maxwell wrote:
On 13 Mar 2007 14:19:12 -0700, "Cecil Moore" wrote:

On Mar 12, 11:50 pm, Roy Lewallen wrote:
The problem is that the idea of "reflected energy" turning the plates
hot is so easy to understand, that people aren't willing to abandon it
simply because it isn't true.
It also isn't true that there is no energy in the reflected wave, that
such beliefs are gobbledegook, and that RF standing wave energy
just sloshes around in a transmission line at less than light speed.
To really understand what is going on, one has to understand
superposition and interference between RF energy waves. You
are on record as not caring to understand reflected energy. Please
don't condemn those of us who are trying to understand.

Did you guys on this thread know that it's been proven statistically that five
out of four people have trouble with fractions?

Walt,W2DU


Walt,

I didn't know that, but I'm dain bramaged.

73,
Gene
W4SZ

VSWR doesn't matter?
 

Walter Maxwell wrote in
:

On 13 Mar 2007 14:19:12 -0700, "Cecil Moore"
wrote:

Did you guys on this thread know that it's been proven statistically
that five out of four people have trouble with fractions?

That's vulgar!

VSWR doesn't matter?
 

"Owen Duffy" wrote
Richard,
The round trip time on the transmission line is 1uS+, and the period of
the highest modulating frequency is 0.2uS, so transient performance of
the line is very important.
____________

Sorry, sir, but quite a few decades of experience in the analog TV broadcast
industry show otherwise (not to mention an accurate theoretical analysis of
this condition).

For example, a reflection within an analog TV broadcast signal that is
delayed by one microsecond from the main image equates to something like a
10% horizontal displacement of that reflected, or "ghost" image from the
main image (525/60Hz TV standard).

A ghost television image amounting to 5% of the main image, and offset by
10% of the width of even a fairly small display screen is not difficult to
see (or to be objected to) by an "average" observer at an "average" viewing
distance from that display screen.

Reflected r-f power may be less of a concern to amateur radio operators than
it is to commercial operators, but that doesn't mean that reflected power is
non-existent, or even unimportant.

RF http://rfry.org