VSWR AND AUTOMATIC TUNING
 

If a transceiver has an in built automatic antenna tuning and matching
unit, is there any point in measuring the VSWR as a way of ascertaining
its performance?

Obviously this would be measured with a thru line meter which would be
placed in the feeder system. However, I have been thinking and it
would appear that the tuning and matching unit would become part of the
antennas impedance (its late and I hope that makes sense).

The reason I ask is because I am trying to find out how well certain
transceivers will perform with antennas which are designed for
different systems.

VSWR AND AUTOMATIC TUNING
 

Big Nose wrote:

If a transceiver has an in built automatic antenna tuning and matching
unit, is there any point in measuring the VSWR as a way of ascertaining
its performance?

NOPE! The VSWR in the line = The VSWR in the line = The VSWR in the
line = The VSWR in the line. The internal tuner does absolutely nothing
[NOTHING] to the VSWR in the line.

The internal tuner will make the radio 'happy' within it's tuning range,
but it does NOTHING about the VSWR in the line!



Obviously this would be measured with a thru line meter which would be
placed in the feeder system. However, I have been thinking and it
would appear that the tuning and matching unit would become part of the
antennas impedance (its late and I hope that makes sense).

The reason I ask is because I am trying to find out how well certain
transceivers will perform with antennas which are designed for
different systems.

VSWR AND AUTOMATIC TUNING
 

Dave wrote:
Big Nose wrote:

If a transceiver has an in built automatic antenna tuning and matching
unit, is there any point in measuring the VSWR as a way of ascertaining
its performance?


NOPE! The VSWR in the line = The VSWR in the line = The VSWR in the
line = The VSWR in the line. The internal tuner does absolutely nothing
[NOTHING] to the VSWR in the line.

The internal tuner will make the radio 'happy' within it's tuning range,
but it does NOTHING about the VSWR in the line!



Obviously this would be measured with a thru line meter which would be
placed in the feeder system. However, I have been thinking and it
would appear that the tuning and matching unit would become part of the
antennas impedance (its late and I hope that makes sense).

The reason I ask is because I am trying to find out how well certain
transceivers will perform with antennas which are designed for
different systems.


To elaborate just a bit on Dave's comment, remember that the VSWR is
determined only by the LOAD (antenna) impedance and the LINE
characteristic impedance. The source (transmitter) impedance does not
enter into the determination of VSWR.

One way tuners are tested is with dummy loads of various resistances
(and/or reactances). QST published some articles on this a few years ago.

Good luck.

Chuck, NT3G

VSWR AND AUTOMATIC TUNING
 

"Dave" wrote in message
. ..
Big Nose wrote:

If a transceiver has an in built automatic antenna tuning and matching
unit, is there any point in measuring the VSWR as a way of ascertaining
its performance?

NOPE! The VSWR in the line = The VSWR in the line = The VSWR in the
line = The VSWR in the line. The internal tuner does absolutely nothing
[NOTHING] to the VSWR in the line.

The internal tuner will make the radio 'happy' within it's tuning range,
but it does NOTHING about the VSWR in the line!



Obviously this would be measured with a thru line meter which would be
placed in the feeder system. However, I have been thinking and it
would appear that the tuning and matching unit would become part of the
antennas impedance (its late and I hope that makes sense).

The reason I ask is because I am trying to find out how well certain
transceivers will perform with antennas which are designed for
different systems.



Agree.

But, whether you're doing your testing or operating afterward, there's
usually some value in knowing the VSWR in the line. It may only serve to
clue you to a problem -- and that's info worth having. I'm depending on the
slightly risky assumption that most tuners you test will be able to match to
a less-than-ideal antenna system with high VSWR in the feedline -- one
that's not putting much power into the air.

I had a USN antenna experience with an improperly-modified shipboard HF XMIT
antenna. The Radiomen said it was hard to
tune to it, the reflected power was always high and they never seemed able
to "get out on it" (meaning poor reception reports from the distant end).

When we put the antenna right, all their problems went away.

VSWR AND AUTOMATIC TUNING
 

On Fri, 7 Apr 2006 22:04:32 -0700, "Sal M. Onella"
wrote:

I had a USN antenna experience with an improperly-modified shipboard HF XMIT
antenna. The Radiomen said it was hard to
tune to it, the reflected power was always high and they never seemed able
to "get out on it" (meaning poor reception reports from the distant end).

When we put the antenna right, all their problems went away.

Hi OM,

What was the problem, and what did you do to fix it?

73's
Richard Clark, KB7QHC

VSWR AND AUTOMATIC TUNING
 

"Richard Clark" wrote in message
...
On Fri, 7 Apr 2006 22:04:32 -0700, "Sal M. Onella"
wrote:

I had a USN antenna experience with an improperly-modified shipboard HF
XMIT
antenna. The Radiomen said it was hard to
tune to it, the reflected power was always high and they never seemed
able
to "get out on it" (meaning poor reception reports from the distant end).

When we put the antenna right, all their problems went away.

Hi OM,

What was the problem, and what did you do to fix it?

73's
Richard Clark, KB7QHC

The antenna was a trussed whip for 10-30 MHz. The truss frame was
stabilized by four turnbuckles connected to the base through ceramic
insulators. One of the RM's had bonded across the insulators. We were
about to do a routine megger check when my partner spotted it. We couldn't
believe our eyes.

EMI bond straps are appropriate for a lot of things topside. That wasn't
one of them. :-)

"Sal"
(John, KD6VKW; USN 1962 - 1982)

PS: Radiomen are no more, per se. They and the Data Processing Technicians
were rolled into a combined rating of Information Systems Technician - IT.
Where it was once hard to find somebody in Radio Central who knew anything
about RF, it is now twice as hard. For me, it's called Job Security, so I'm
not _really_ complaining.