SWR read to TX or rather to the antenna ?
 

Hi,
It seems well-known that the SWR value that you read on an external meter or
an antenna tuner is NOT the value measured between itself and the antenna.
The SWR value "picked-up" and that you can change is the one measured
between this meter or tuner and the transceiver (or the linear amplifier but
we consider it as a black box if you use it properly).

But recently I experimented the burning of my PL due to a high SWR, thus
high current, and moisture and the end of the line (really, see image of
PL's here http://www.astrosurf.com/lombry/qsl-...sion-line2.htm, end of
page ).

The distance between my RTX and SWR reader is short, about 1 m. But there
are about 15m between the SWR and the feed point of my antenna where I had
the problem.

So I would like to know if an SWR meter does only read the value upstream or
if the properties of the feedline to the antenna does not influence is
reading.
At first sight it does as during this problem I had a SWR 4:1 on the
external SWR-meter. This value didn't come from the RTX side which built-in
SWR displayed a VSWR 1:1. It really came from the other side, to the
antenna, thus contrary to what I think and what is usually stated about the
functioning of this device...

Can someone explain me this ?

Thanks in advance

Thierry
ON4SKY

It seems well-known that the SWR value that you read on an external meter
or
an antenna tuner is NOT the value measured between itself and the antenna.
The SWR value "picked-up" and that you can change is the one measured
between this meter or tuner and the transceiver (or the linear amplifier
but
we consider it as a black box if you use it properly).

But recently I experimented the burning of my PL due to a high SWR, thus
high current, and moisture and the end of the line (really, see image of
PL's here http://www.astrosurf.com/lombry/qsl-...sion-line2.htm, end
of
page ).

The distance between my RTX and SWR reader is short, about 1 m. But there
are about 15m between the SWR and the feed point of my antenna where I had
the problem.

So I would like to know if an SWR meter does only read the value upstream
or
if the properties of the feedline to the antenna does not influence is
reading.

The SWR meter indicates the value from the meter to whatever is after it.
If you insert a device that has a high SWR (because it becomes defective or
for some other reason ) between the transmitter and SWR meter ( say a switch
or filter), the meter can show a low value if the antenna is ok, but the
transmitter will see a high SWR and may burn out the finals.

The SWR meter indicates the value from the meter to whatever is after it.
If you insert a device that has a high SWR (because it becomes defective or
for some other reason ) between the transmitter and SWR meter ( say a switch
or filter), the meter can show a low value if the antenna is ok, but the
transmitter will see a high SWR and may burn out the finals.

He did not say he inserted anything, just that moisture at the end of his
transmission line caused a fault. If this was the case, an SWR bridge at the
output of his Power Amps should have alerted him to a problem that would
potentially destroyed them.
If you want to use an SWR bridge as a protective device, or indicator, it
must be placed in the proper position in the antenna system. Modern
transceivers have circuits that detect mismatches and reduce power to minimize
failed output devices.


73 Gary N4AST

Someone sed:

"...the meter can show a low value if the antenna is ok, but the transmitter
will see a high SWR and may burn out the finals."

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

It's funny that this old wive's tale about the high SWR "burning out the
finals" still exists. I guess it depends on what the meaning of "high" is.

73, Jack, K9CUN

JDer8745 wrote:
It's funny that this old wive's tale about the high SWR "burning out the
finals" still exists. I guess it depends on what the meaning of "high" is.

If high SWR and the attendant mismatch cannot burn out a final,
I wonder why most commercial finals are protected from a high SWR
by foldback circuitry to avoid damage to the finals?
--
73, Cecil http://www.qsl.net/w5dxp



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I wonder why most commercial finals are protected from a high SWR
by foldback circuitry to avoid damage to the finals?
--
73, Cecil

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

They don't. There isn't an SWR meter on the station.

They are really protecting the finals against excessive deflection of the
TLI. ( Transmitter Loading Indicator.)

But it sure makes a good point of conversation amongst the old wives.
----
Reg, G4FGQ

"JGBOYLES" wrote in message
...
The SWR meter indicates the value from the meter to whatever is after it.
If you insert a device that has a high SWR (because it becomes defective
or
for some other reason ) between the transmitter and SWR meter ( say a
switch
or filter), the meter can show a low value if the antenna is ok, but the
transmitter will see a high SWR and may burn out the finals.

He did not say he inserted anything, just that moisture at the end of his
transmission line caused a fault. If this was the case, an SWR bridge at
the
output of his Power Amps should have alerted him to a problem that would
potentially destroyed them.
If you want to use an SWR bridge as a protective device, or indicator,
it
must be placed in the proper position in the antenna system. Modern
transceivers have circuits that detect mismatches and reduce power to
minimize
failed output devices.

Indeed. A good suggestion I could install (in case of)
Thierry



73 Gary N4AST

"Cecil Moore" wrote in message
...
JDer8745 wrote:
It's funny that this old wive's tale about the high SWR "burning out the
finals" still exists. I guess it depends on what the meaning of "high"
is.

If high SWR and the attendant mismatch cannot burn out a final,
I wonder why most commercial finals are protected from a high SWR
by foldback circuitry to avoid damage to the finals?

Indeed.
I always hear and read that a high SWR can destroy the PA final of TX,
cranck coils, etc.

Thierry

--
73, Cecil http://www.qsl.net/w5dxp



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"JGBOYLES" wrote in message
...
The SWR meter indicates the value from the meter to whatever is after it.
If you insert a device that has a high SWR (because it becomes defective
or
for some other reason ) between the transmitter and SWR meter ( say a
switch
or filter), the meter can show a low value if the antenna is ok, but the
transmitter will see a high SWR and may burn out the finals.

He did not say he inserted anything, just that moisture at the end of his
transmission line caused a fault. If this was the case, an SWR bridge at
the

The install was : RTX +50 cm RG58 + AMP + 1m Aircom (like RG213) + SWR +15m
Aircom + G5RV

the built-in SWR of my RTX TS-570D read SWR 1:1. If my external SWR
displayed an SWR 4 that means that it read the info AFTER it, what looks
in contradiction with what ARRL website states in his technical columns...
Who's right ?

Thierry
ON4SKY
http://www.astrosurf.com/lombry/




output of his Power Amps should have alerted him to a problem that would
potentially destroyed them.
If you want to use an SWR bridge as a protective device, or indicator,
it
must be placed in the proper position in the antenna system. Modern
transceivers have circuits that detect mismatches and reduce power to
minimize
failed output devices.


73 Gary N4AST

Reg Edwards wrote:

I wonder why most commercial finals are protected from a high SWR
by foldback circuitry to avoid damage to the finals?

They don't. There isn't an SWR meter on the station.

Reg, I'm talking about commercially manufactured ham radio
finals. Virtually every single one of them has protection
circuitry and virtually every one of them has a built-in
SWR metering system.
--
73, Cecil http://www.qsl.net/w5dxp



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Thierry wrote:
the built-in SWR of my RTX TS-570D read SWR 1:1. If my external SWR
displayed an SWR 4 that means that it read the info AFTER it, what looks
in contradiction with what ARRL website states in his technical columns...
Who's right ?

The SWR between the transmitter and the antenna tuner is usually adjusted for
1:1. The antenna tuner doesn't affect the SWR between the antenna tuner and the
antenna. It can be almost any value. Nothing strange at all about a 4:1 SWR
after the antenna tuner.
--
73, Cecil http://www.qsl.net/w5dxp



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The install was : RTX +50 cm RG58 + AMP + 1m Aircom (like RG213) + SWR +15m
Aircom + G5RV. the built-in SWR of my RTX TS-570D read SWR 1:1. If my external
SWR
displayed an SWR 4 that means that it read the info AFTER it, what looks
in contradiction with what ARRL

Thierry, If your external SWR meter is after the amplifier, in a 50 ohm
system, and it read 4 it could possibly destroy your amplifier output devices.
The fact that the built-in SWR meter in the Kenwood read 1:1 only means the
input match to the Amplifier was good. If the 570 has a built-in tuner, it
will try to get a 1:1 match, no matter what is downstream. It doesn't mean the
output the Amp sees is good.
As for the ARRL, I haven't had the time to look, but I hope they are not
stating that a 50 ohm output Amp operating into 4 mismatch is a good thing.

73 Gary N4AST

The TS 570D is driving the amplifier which shows an excellent load for
the TS 570D!!

The amplifier is driving a different load with a 4:1 VSWR. This is a 36%
reflection of the power. If your Amplifier is vacuum tube with tuning
controls it is not a serious condition. You can vary the loading
controls for reasonable output without damage. If your amplifier is
solid state then you have to do something to correct the VSWR because it
presents a load to the amplifier that is outside the designed load range.

Deacon Dave, W1MCE

Cecil Moore wrote:

Reg Edwards wrote:

I wonder why most commercial finals are protected from a high SWR
by foldback circuitry to avoid damage to the finals?


They don't. There isn't an SWR meter on the station.


Reg, I'm talking about commercially manufactured ham radio
finals. Virtually every single one of them has protection
circuitry and virtually every one of them has a built-in
SWR metering system.

I'll stand to be corrected because my RF design activity, C-Band and
S-Band satellite circuits, ended in the mid 80s. Back then, an antenna
load outside of the design range causes higher emitter currents in the
bi-polar solid state devices. These higher currents are the damage
producers. So, circuits were added to control the maximum emitter
current. Today's semiconductor technology is different but I still
suspect that localized voltage or current stresses are a function of the
load.

We used to design for a plasma enhanced environment with an intrinsic Zo
range between 120 to 377 ohms, or, slightly more than 3:1 VSWR at the
antenna. BTW, the circuits continued to operate at almost 10:1 VSWR!!

"JGBOYLES" wrote in message
...
The install was : RTX +50 cm RG58 + AMP + 1m Aircom (like RG213) + SWR
+15m
Aircom + G5RV. the built-in SWR of my RTX TS-570D read SWR 1:1. If my
external
SWR
displayed an SWR 4 that means that it read the info AFTER it, what
looks
in contradiction with what ARRL

Thierry, If your external SWR meter is after the amplifier, in a 50 ohm
system, and it read 4 it could possibly destroy your amplifier output
devices.
The fact that the built-in SWR meter in the Kenwood read 1:1 only means
the
input match to the Amplifier was good. If the 570 has a built-in tuner,
it
will try to get a 1:1 match, no matter what is downstream. It doesn't mean
the
output the Amp sees is good.
As for the ARRL, I haven't had the time to look, but I hope they are not
stating that a 50 ohm output Amp operating into 4 mismatch is a good
thing.

No no, they only tell that a SWR-meter place this way read the SWR "between
itself and the RTX"...
I am not agree with this sentence... as my SWR 4:1 was well read AFTER it,
thus between itself as they state and the antenna rather !

Thierry


73 Gary N4AST

"Dave Shrader" wrote in message
news:ri_Ob.101568$8H.152471@attbi_s03...
The TS 570D is driving the amplifier which shows an excellent load for
the TS 570D!!

The amplifier is driving a different load with a 4:1 VSWR. This is a 36%
reflection of the power. If your Amplifier is vacuum tube with tuning
controls it is not a serious condition. You can vary the loading
controls for reasonable output without damage.

Hi,

Correct. This is well what I did, rotating the amplifier load knob (a
kenwood TL922) to reduce the SWR as I could not reduce it another way
(antenna side) due to my defect balun.

73
Thierry

If your amplifier is
solid state then you have to do something to correct the VSWR because it
presents a load to the amplifier that is outside the designed load range.

Deacon Dave, W1MCE

"Thierry" To answer me in private use http://www.astrosurf.com/lombry/post.htm wrote in message ...
"Cecil Moore" wrote in message
...
JDer8745 wrote:
It's funny that this old wive's tale about the high SWR "burning out the
finals" still exists. I guess it depends on what the meaning of "high"
is.

If high SWR and the attendant mismatch cannot burn out a final,
I wonder why most commercial finals are protected from a high SWR
by foldback circuitry to avoid damage to the finals?

Indeed.
I always hear and read that a high SWR can destroy the PA final of TX,
cranck coils, etc.

Thierry

I may be confused now after reading all the posts, but if you have a
good SWR on the rig that is driving an amp, this is normal, even with
a mismatch to the amp. The amp probably has a tuned input circuit.
It's not going to change much if any, if the SWR to the amp goes high.
Or I don't believe anyway...You should run a meter before the amp, on
the antenna side, to also measure the SWR to the amp. The meter in the
rig is just looking at the tuned input circuit of the amp. You need
another one if you want to keep the amp happy. A solid state amp is
much more critical than the tube amps as far as SWR. But I still
prefer to keep a tube amp under 2 to 1, unless I lower the power
level. But I've run 3:1 or worse many times with my henry 2K classic,
and it never complained. As long as you are within the loading range
of the amp, it's perfectly fine. I think the tubes do run a bit hotter
if the SWR is excessive. Thats why I'll drop the power a bit. When I
do run the amp, I almost always have a good match, IE: coax fed
dipoles, yagis, etc... and I almost never use a tuner. I haven't
actually run my amp in about 4 years. I have it dismantled, and have
been too lazy to order new caps and out it back together. I really
don't need it most of the time. It's handy if I want to brown the food
in a certain area.
MK

"Mark Keith" wrote in message
m...
"Thierry" To answer me in private use
http://www.astrosurf.com/lombry/post.htm wrote in message
...
"Cecil Moore" wrote in message
...

Thierry

I may be confused now after reading all the posts, but if you have a
good SWR on the rig that is driving an amp, this is normal, even with
a mismatch to the amp. The amp probably has a tuned input circuit.
It's not going to change much if any, if the SWR to the amp goes high.
Or I don't believe anyway...You should run a meter before the amp, on
the antenna side, to also measure the SWR to the amp. The meter in the
rig is just looking at the tuned input circuit of the amp. You need
another one if you want to keep the amp happy.

Is this really necessary Mark ?
My config is TX (+built-in ant.tuner and SWR) + AMP + SWR + antenna.
The TX antenna tuner can match the load upo to 2.5:1 to get SWR 1:1 on its
terminal, not further.
The AMP load/plate knob are tuned in the proper band in order to get the
lowest SWR (read on the external one, place just after him)
The SWR, the exernal one placed between the amp and ant, read, in my
opinion, the SWR towards the antenna, not toward the RTX conrrarily to what
state ARRL in its Q&A column.
You speak of inserting another SWR between rtx and amp ? why for ? I do not
understand its utility from the moment I can fine-tune the the amp with the
SWR placed just after it, toward the antenna (in practice in adjusting the
plate on the right band and then the load, in adjusting with accuracy this
latter the SWR increases or descreases). It enough.

NB. at the time of my tests all worked fine, my amp gave all its 850W
although much reduced due to high SWR 4 (I emitted about 300 W) and no one
rig was damaged. Of course I never worked longtime this way but I did some
SSB QSO (thus theoretically enough to burn something) and I had to tune my
RTX to reduce the SWR the best I could. Of course I do never suggest to
proceed this way to nobody but instead to find a solution to get the lowest
SWR (say below 2:1 or even 1:1 if you antenna permits).

Thierry
ON4SKY
http://www.astrosurf.com/lombry

A solid state amp is
much more critical than the tube amps as far as SWR. But I still
prefer to keep a tube amp under 2 to 1, unless I lower the power
level. But I've run 3:1 or worse many times with my henry 2K classic,
and it never complained. As long as you are within the loading range
of the amp, it's perfectly fine. I think the tubes do run a bit hotter
if the SWR is excessive. Thats why I'll drop the power a bit. When I
do run the amp, I almost always have a good match, IE: coax fed
dipoles, yagis, etc... and I almost never use a tuner. I haven't
actually run my amp in about 4 years. I have it dismantled, and have
been too lazy to order new caps and out it back together. I really
don't need it most of the time. It's handy if I want to brown the food
in a certain area.
MK

Cecil, why do you insist on deliberately missing the point?

There is NO SWR meter!

It is a misnomer.

It is a TLI.

This misrepresentation continues to confuse, mislead people trying to
understand what is really a very simple application of an antenna tuner.

In this application the phrase SWR should be banned from the dictionary.
---
Reg, G4FGQ

.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........

Reg Edwards wrote:
Cecil, why do you insist on deliberately missing the point?
There is NO SWR meter!

Reg, my name "Cecil" means "blind" but I'm not blind. Should
I change my name? A rose by any other name smells just as sweet.
The thing is named an "SWR Meter". It's written right on all of
mine. Never mind that all it does is a phasor addition between
a voltage proportional to the voltage and a voltage proportional
to the current.
--
73, Cecil http://www.qsl.net/w5dxp



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Someone sed:

"I always hear and read that a high SWR can destroy the PA final of TX,
cranck coils, etc."

===========

I've always heard that too. And I always heard that if you break a mirror,
you'll have seven years bad luck.

73 de Jack, K9CUN

Thierry wrote:

SNIP
Hi,

Correct. This is well what I did, rotating the amplifier load knob (a
kenwood TL922) to reduce the SWR as I could not reduce it another way
(antenna side) due to my defect balun.

73
Thierry

No! You did not reduce the VSWR!! You increased the loading of the
amplifier!

If you remember, VSWR is a measure of the impedance mismatch of the
antenna and the impedance of the transmission line MEASURED AT THE
ANTENNA. There is NOTHING you can do at the RTX/Amplifier to change it!

The PLATE and LOAD controls on your TL922 allow you vary the values of
'C' in the output stage of the amplifier and therefore vary the range of
tuning from typically 8 to 400 ohms.

DD, W1MCE

JDer8745 wrote:
Someone sed:

"I always hear and read that a high SWR can destroy the PA final of TX,
cranck coils, etc."

I've always heard that too. And I always heard that if you break a mirror,
you'll have seven years bad luck.

A high SWR can indeed destroy unprotected solid-state finals by causing
over-current and/or over-voltage. If finals cannot be damaged by the
impedance mismatch accompanying a high SWR, why do the transceiver
manufacturers waste money on protection circuitry? Of course, a tuning
network between the final and the feedline will usually alleviate the
problem through matching.
--
73, Cecil http://www.qsl.net/w5dxp



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Dave Shrader wrote:
If you remember, VSWR is a measure of the impedance mismatch of the
antenna and the impedance of the transmission line MEASURED AT THE
ANTENNA. There is NOTHING you can do at the RTX/Amplifier to change it!

Of course there is, Dave, just hit the tune button connected to your
remote auto-tuner. :-)
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil Moore wrote:

Dave Shrader wrote:

If you remember, VSWR is a measure of the impedance mismatch of the
antenna and the impedance of the transmission line MEASURED AT THE
ANTENNA. There is NOTHING you can do at the RTX/Amplifier to change it!


Of course there is, Dave, just hit the tune button connected to your
remote auto-tuner. :-)

Gee Cecil, I didn't know you contributed to "Old Men's Tales". Next
you'll be telling us that you got your VSWR down to ZERO :-)

Dave Shrader wrote:
"Next you`ll be telling us that you got your VSWR down to Zero :-)"

Just to demonstrate that there are lurkers:
No, I`d bet Cecil would quit at 1:1.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
Dave Shrader wrote:
"Next you`ll be telling us that you got your VSWR down to Zero :-)"

Just to demonstrate that there are lurkers:
No, I`d bet Cecil would quit at 1:1.

Heck Richard, I often quit at 2:1. :-)
--
73, Cecil http://www.qsl.net/w5dxp



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"Dave Shrader" wrote in message
news:H5cPb.89261$Rc4.431228@attbi_s54...
Thierry wrote:

SNIP
Hi,

Correct. This is well what I did, rotating the amplifier load knob (a
kenwood TL922) to reduce the SWR as I could not reduce it another way
(antenna side) due to my defect balun.

73
Thierry

No! You did not reduce the VSWR!! You increased the loading of the
amplifier!

OK, ok ok, I interpreted my result and left some words in my kbd....
In fact what I wanted to say is that in adjusting the load I see as a side
effect or for consequence to change the value read on the SWR-meter (more of
less input power, hence more or less reflected power due to a high SWR at
the end of the line, but of course most of the time the value of the SWR,
whatever the input power I used stay constant. (this is shorter to say that
my TL modified the SWR...;-))

Thierry


If you remember, VSWR is a measure of the impedance mismatch of the
antenna and the impedance of the transmission line MEASURED AT THE
ANTENNA. There is NOTHING you can do at the RTX/Amplifier to change it!

The PLATE and LOAD controls on your TL922 allow you vary the values of
'C' in the output stage of the amplifier and therefore vary the range of
tuning from typically 8 to 400 ohms.

DD, W1MCE