I am working on the design of a sensor that needs to measure the
forward and reflected power in unison at or very near the feed point
of the antenna drive by a very short 4 inches of less feed line over a
range of 10 to 100 Mhz at power level less the 100 ma. The feed lines
will be potted in a plastic to water proof it so the sensors will be
embedded with them.

The ideal solution from a manufacturing and calibration point of view
would have the antenna come right out of the network of the amplifier
with no feed line to act as a transformer over a wide range of
frequencies.

This is not a class project as most of the regulars know I well beyond
that by nearly 40 years.

I can see a number of ways how to do it with a coaxial feed but open
wire is less expensive and easier to manufacture and make repeatable.
I realize at least the reflected power will have to amplified to be
measures by equipment in my price range.

I seem to remember that a piece of open line placed parallel to the
driven line and properly terminated will read voltage nodes on the
line and possibly the forward and reflected power. It has been a very
long time since I read that and was not paying much attention at the
time. I think it was in a CQ when it was still in the small format
with Wane Green as editor.

Any help or ideas welcome.

Thaks
Gordon Couger W5RED

At 100MHz, 4 inches of line, even embedded in plastic with a relative
dielectric constant of 4, is less than 0.07 wavelengths, and of course
even less at lower frequencies. I suspect it's not transmission line
SWR but source loading that you may be interested in. It may suffice
to simply measure the source output voltage. If you really want that
transmitter loading indicator, put in a simple transformer coupler.
Even if you meant 100mW instead of 100mA, that's still enough to drive
a simple, inexpensive diode detector. Yes, coupled lines will work,
too, though the coupling will change appreciably over the 10:1
frequency range, and a transformer coupler will be nearly "flat."

Cheers,
Tom

(Gordon Couger) wrote in message . com...
I am working on the design of a sensor that needs to measure the
forward and reflected power in unison at or very near the feed point
of the antenna drive by a very short 4 inches of less feed line over a
range of 10 to 100 Mhz at power level less the 100 ma. The feed lines
will be potted in a plastic to water proof it so the sensors will be
embedded with them.

The ideal solution from a manufacturing and calibration point of view
would have the antenna come right out of the network of the amplifier
with no feed line to act as a transformer over a wide range of
frequencies.

This is not a class project as most of the regulars know I well beyond
that by nearly 40 years.

I can see a number of ways how to do it with a coaxial feed but open
wire is less expensive and easier to manufacture and make repeatable.
I realize at least the reflected power will have to amplified to be
measures by equipment in my price range.

I seem to remember that a piece of open line placed parallel to the
driven line and properly terminated will read voltage nodes on the
line and possibly the forward and reflected power. It has been a very
long time since I read that and was not paying much attention at the
time. I think it was in a CQ when it was still in the small format
with Wane Green as editor.

Any help or ideas welcome.

Thaks
Gordon Couger W5RED

On 3-Mar-2004, (Gordon Couger) wrote:

am working on the design of a sensor that needs to measure the
forward and reflected power in unison at or very near the feed point
of the antenna drive by a very short 4 inches of less feed line over a
range of 10 to 100 Mhz at power level less the 100 ma. The feed lines
will be potted in a plastic to water proof it so the sensors will be
embedded with them.

The ideal solution from a manufacturing and calibration point of view
would have the antenna come right out of the network of the amplifier
with no feed line to act as a transformer over a wide range of
frequencies.

This is not a class project as most of the regulars know I well beyond
that by nearly 40 years.

I can see a number of ways how to do it with a coaxial feed but open
wire is less expensive and easier to manufacture and make repeatable.
I realize at least the reflected power will have to amplified to be
measures by equipment in my price range.

Gordon,
Take a look at the Return Loss Analyzer at:

http//www.qsl.net/n2pk/

or

http://users.adelphia.net/~n2pk/VNA/VNAarch.html

Ken Fowler, KO6NO

Ken Fowler wrote:
"---at or very near the feed point of the antenna drive by a very short
4 inches or less---."

The Bird Model 43 has a width of 5.125 inches including the 50-ohm coax
connectors. You can be sure Bird didn`t make the length of that
precision coax fixture any longer than necessary.

Insertion of even 5 inches of additional coax in a mismatched feedline
at VHF changes the tuning and the match between source and load. It`s
desirable to minimize disturbance of the antenna match when the meter is
inserted and withdrawn from the line.

Ken likely has different reasons for making his metering line section
come in under 4 inches in length

Best regards, Richard Harrison, KB5WZI