Hi Uwe,

I'll try to remember to send the scan from home tonight. It is just
under 4 megabytes, so it will take a while to download, but it is ten
pages from the RSGB book, which seems to explain things better than
the ARRL article you have (which is the one I also scanned,
separately). The RSGB pages I scanned includes I think four different
designs, maybe five, as well as some elemental theory.

Yes, I think the Monimatch uses coupled transmission lines, which is
what a microstrip (or stripline) coupler is. The microstrip version
is (generally) a piece of printed circuit board with a ground plane
(uninterrupted copper foil) on one side, and a straight trace on the
other side, which is the "through" line, with another trace parallel
to the first trace and a small distance away, which is the "coupled"
line. You terminate the coupled line at one end (to avoid
reflections), and put a detector at the other end, usually just a
diode detector for SWR monitoring. That tells you the power in one
direction. Then for convenience, you can put an identical coupled
line on the other side of the through-line, and terminate it at the
opposite end compared with the first coupled line, and put a detector
on it at the other end, and that monitors the power in the other
direction. So you get two DC outputs, one for "forward" power and one
for "reverse" power. One important point that is usually
glossed-over, is that diode detectors will respond with an output
voltage proportional to the input RF voltage above some level, but
with an output voltage proportional to the input RF _power_ at lower
levels. You should design the coupling to operate in one or the other
of those regions, if you want to more easily make quantitative sense
of the readings. (An even better way to do it would be to have a
calibrated step attenuator between the "forward" coupled line and the
forward detector, and then adjust the attenuator for equal outputs
from the two diode detectors. Then the attenuator setting tells you
the load's return loss, from which you can find the SWR if you wish.)
It's also possible to use phase-sensitive detectors and get the
complex load impedance...that's essentially what an S-parameter
network analyzer does.

Cheers,
Tom


Uwe Langmesser wrote in message ...
Hi Tom,

No, I don't know the article you mentioned.
I just got the ARRL Antenna Book and there is a plan for a directional
coupler using some plumbing hardware and I could see myself building that,
but again there are some issues about available parts (thru feed caps in
particular).
From my (limited) understanding these couplers would be the aquivalent of
the "plugs" used in meters like the Bird 43 or the URM120.

But I am not sold on this design and would certainly want to look at the
article you mentioned. And yes, I do have a slow phone connection, but if
you are willing I would appreciate if you could send the article as an
attachment.

Now the microstrip coupler you mention, is that what people also call a
monimatch? What are the advantages of one design over another?

regards Uwe



in article , Tom Bruhns at
wrote on 2/8/04 8:47 PM:

This has been a hot topic recently! I just scanned an ARRL article
and a section of the test equipment chapter of the RSGB VHF/UHF
Handbook to send to someone else who is interested in making a
146/440MHz SWR monitor, and I just made a couple 100MHz-6GHz detectors
for someone else who is looking at monitoring SWR at 2.5GHz.

Seems to me the simple way for most folk to do it is to make a
microstrip coupler. You can use surface-mount components for the load
and detector and RF decoupling, and they'll work quite well up into
the GHz region, from my experience. As far as RF decoupling goes, you
should be able to do an adequate job on a circuit board...once the
detector turns the RF to DC, just put shunt capacitance to ground and
series inductance in the line. Pick the inductance as you would for
other VHF work: avoid inductors with self-resonances below the freq
of interest.

You probably have already seen the ARRL article I scanned, but if
you'd like the RSGB one, I could send it. But it's almost 4 megabytes
and may take you a while to download if you have a slow connection.

Cheers,
Tom


Uwe Langmesser wrote in message
...
I have been looking at various designs of VHF SWR bridges, mainly from ARRL
sources like old QSTs and such, and I wonder if anybody here has built a
device like that.
For my experience level some of the old descriptions are just a touch to
cryptic or the design calls for parts which I can't locate (small feed thru
caps are one of those items).
I would love to discuss this with a knowledgable builder.

73 Uwe

In article , Uwe Langmesser
writes:

Now the microstrip coupler you mention, is that what people also call a
monimatch? What are the advantages of one design over another?

You might think of microstrip or stripline as "hammered flat coax." :-)

It is just a transmission line on a PCB, the characteristic impedance
dependent on trace line width, thickness of the foil, dielectric constant
of the PCB material and, to some extent, the thickness of the PCB.

Directional couplers are simply a quarter wavelength of transmission
line (coax or microstrip or stripline) that runs parallel to the main line
connecting to the antenna. The amount of coupling is dependent on
the spacing between the two lines. Their bandwidth is typically an
octave of frequency.

Typical directional coupler coupling is 20 db down from the main line.
Power is coupled mainly in one direction, from the main line to the
end closest to the coupled line's immediate end. Some power will be
coupled into that end coming in the opposite direction but that is
usually 15 to 25 db farther down. While not perfect, directional
coupling differences of about 20 db are good enough to warrant the
name "directional." Those are very common in microwave work and
from about 400 MHz and up in frequency to around 8 GHz; a quarter
wavelength at 400 MHz gets a bit long. At 20 db coupling, the load
on the coupled line can vary quite a bit without affecting the main
line. Reflections from the load can be accurately compared with
coupled energy from the source; if coupling is measured accurately
in both directions, the VSWR can be computed from amplitude
differences. If the coupled line ends have a way to measure both
amplitude and phase, the complex impedance of the load can be
computed accurately in comparison to the coupled source.

I've built directional couplers at about 1 GHz center frequency but
admit cribbing from older published data on impedances and spacings
from microwave literature. Had a somewhat stiff specification on
coupling which required a few passes at different etch masks for a
large stripline assembly of many things. Not again if I can help it. :-)

Len Anderson
retired (from regular hours) electronic engineer person

In article , Uwe Langmesser
writes:

Now the microstrip coupler you mention, is that what people also call a
monimatch? What are the advantages of one design over another?

You might think of microstrip or stripline as "hammered flat coax." :-)

It is just a transmission line on a PCB, the characteristic impedance
dependent on trace line width, thickness of the foil, dielectric constant
of the PCB material and, to some extent, the thickness of the PCB.

Directional couplers are simply a quarter wavelength of transmission
line (coax or microstrip or stripline) that runs parallel to the main line
connecting to the antenna. The amount of coupling is dependent on
the spacing between the two lines. Their bandwidth is typically an
octave of frequency.

Typical directional coupler coupling is 20 db down from the main line.
Power is coupled mainly in one direction, from the main line to the
end closest to the coupled line's immediate end. Some power will be
coupled into that end coming in the opposite direction but that is
usually 15 to 25 db farther down. While not perfect, directional
coupling differences of about 20 db are good enough to warrant the
name "directional." Those are very common in microwave work and
from about 400 MHz and up in frequency to around 8 GHz; a quarter
wavelength at 400 MHz gets a bit long. At 20 db coupling, the load
on the coupled line can vary quite a bit without affecting the main
line. Reflections from the load can be accurately compared with
coupled energy from the source; if coupling is measured accurately
in both directions, the VSWR can be computed from amplitude
differences. If the coupled line ends have a way to measure both
amplitude and phase, the complex impedance of the load can be
computed accurately in comparison to the coupled source.

I've built directional couplers at about 1 GHz center frequency but
admit cribbing from older published data on impedances and spacings
from microwave literature. Had a somewhat stiff specification on
coupling which required a few passes at different etch masks for a
large stripline assembly of many things. Not again if I can help it. :-)

Len Anderson
retired (from regular hours) electronic engineer person

\\\ Sheesh! long post alert\\\

Hopefully not unnecessary refinements to Len's comments....



"Avery Fineman" wrote in message
...

In article , Uwe Langmesser
writes: WITH SNIPS HER & THERE...
Now the microstrip coupler you mention, is that what people also call a
monimatch? What are the advantages of one design over another?



I believe this is correct. It's been a long time, but I should look at
an old handbook to make sure I'm thinking of the right thing. I'm
thinkin' of the version where you "snake" another wire under the shield of a
piece of coax for the pickup.



Side bar: I have one of the first directional power meters, the Micro
match. It uses a resistor, yes, resistor, for the current sense rather than
the now common current transformer toroid. circa 1945 -50.





You might think of microstrip or stripline as "hammered flat coax."
:-)

The accepted terminology is "Stripline" (think "strip transmission
line") for the line with two flat ground planes on either side of the
"center conductor" which can be thought of as this flattened coax....and
"micro strip" ( I have no memory aid) for the one that is one-sided where
the "center conductor" is on the top of a PCB with a ground plane on the
bottom..




It is just a transmission line on a PCB, the characteristic impedance
dependent on trace line width, thickness of the foil, dielectric
constant
of the PCB material and, to some extent, the thickness of the PCB.

I think the PCB material (thickness & properties) has a larger
contribution to the Zo that the runner thickness...at least at the freqs I
worked at (1GHz.). Good ole' Wheeler & Sobol equations for the Zo.


Directional couplers are simply a quarter wavelength of transmission
line (coax or microstrip or stripline) that runs parallel to the main
line
connecting to the antenna.

I believe a 1/4 wave is not important here. The coupled line can do this
without such a long line. As in the coveted Bird wattmeter "slug", which
has a very short coupled line inside. For understanding just think that
when you put two "center conductors" into a coax, some power will be coupled
over to the second one from the first & visa versa. The physical
construction determines how much. I will call this added line the
"secondary" one.

A bit of the power on the main line gets sent to the coupled (Secondary)
line, but it emerges in the opposite direction--this is the "correct" end
referred to below.

So you have four connectors. Two for the main line and two for the
secondary line.


Typical directional coupler coupling is 20 db down from the main line.



This is a matter of choice by the manufacturer construction. What this
means is that the power coming out the (correct end of the) secondary line
is 20dB down (1/100 th) from the power on the main line.




While not perfect, directional
coupling differences of about 20 db are good enough to warrant the
name "directional."



This is a matter of primarily the mechanical design. The "directivity"
refers to the amount of power that gets coupled to the secondary line that
emerges out the "wrong" end--not the one we want. High or good directivity
= little coming out the wrong spigot. With 20dB of directivity, the power
emerging from the _wrong_ end of the secondary line is _another_ 20dB below
that merging out the correct end of the secondary line. So it is 40 dB down
from the main line power. And don't forget conservation of energy. All
this "coupled" power is stolen from the main line.



They both should have a nice (50 ohm) impedance and be loaded with 50
ohms as well. The better it is constructed, the less energy is coupled onto
the coupled-line in the wrong direction. If done well, the directivity is
highest. [The secondary line can have other than 50 ohms, but common use
requires it] For the Moni-Match (snaked type) the secondary lines could be
some weird Zo and all is well if it is matched pretty well.

Snaking the extra wire into a coax is crude. I don't know what the Zo
would be, but it works ok as long as the coupled power has reasonable
directivity. Remember, the better the SWR using one of these, the worse the
accuracy, for this reason. The power coming out the wrong end of the
secondary line corrupts (adds to) the reflected power you are trying to
measure.



By the way, you can pump power into the secondary line and have some come
out the mainline as well. This is actually done for special uses.



Len Anderson
retired (from regular hours) electronic engineer person



Regards, Steve a not-so-retired person-type...Whew!
--
Steve N, K,9;d, c. i My email has no u's. Why do I do this?!?!?

\\\ Sheesh! long post alert\\\

Hopefully not unnecessary refinements to Len's comments....



"Avery Fineman" wrote in message
...

In article , Uwe Langmesser
writes: WITH SNIPS HER & THERE...
Now the microstrip coupler you mention, is that what people also call a
monimatch? What are the advantages of one design over another?



I believe this is correct. It's been a long time, but I should look at
an old handbook to make sure I'm thinking of the right thing. I'm
thinkin' of the version where you "snake" another wire under the shield of a
piece of coax for the pickup.



Side bar: I have one of the first directional power meters, the Micro
match. It uses a resistor, yes, resistor, for the current sense rather than
the now common current transformer toroid. circa 1945 -50.





You might think of microstrip or stripline as "hammered flat coax."
:-)

The accepted terminology is "Stripline" (think "strip transmission
line") for the line with two flat ground planes on either side of the
"center conductor" which can be thought of as this flattened coax....and
"micro strip" ( I have no memory aid) for the one that is one-sided where
the "center conductor" is on the top of a PCB with a ground plane on the
bottom..




It is just a transmission line on a PCB, the characteristic impedance
dependent on trace line width, thickness of the foil, dielectric
constant
of the PCB material and, to some extent, the thickness of the PCB.

I think the PCB material (thickness & properties) has a larger
contribution to the Zo that the runner thickness...at least at the freqs I
worked at (1GHz.). Good ole' Wheeler & Sobol equations for the Zo.


Directional couplers are simply a quarter wavelength of transmission
line (coax or microstrip or stripline) that runs parallel to the main
line
connecting to the antenna.

I believe a 1/4 wave is not important here. The coupled line can do this
without such a long line. As in the coveted Bird wattmeter "slug", which
has a very short coupled line inside. For understanding just think that
when you put two "center conductors" into a coax, some power will be coupled
over to the second one from the first & visa versa. The physical
construction determines how much. I will call this added line the
"secondary" one.

A bit of the power on the main line gets sent to the coupled (Secondary)
line, but it emerges in the opposite direction--this is the "correct" end
referred to below.

So you have four connectors. Two for the main line and two for the
secondary line.


Typical directional coupler coupling is 20 db down from the main line.



This is a matter of choice by the manufacturer construction. What this
means is that the power coming out the (correct end of the) secondary line
is 20dB down (1/100 th) from the power on the main line.




While not perfect, directional
coupling differences of about 20 db are good enough to warrant the
name "directional."



This is a matter of primarily the mechanical design. The "directivity"
refers to the amount of power that gets coupled to the secondary line that
emerges out the "wrong" end--not the one we want. High or good directivity
= little coming out the wrong spigot. With 20dB of directivity, the power
emerging from the _wrong_ end of the secondary line is _another_ 20dB below
that merging out the correct end of the secondary line. So it is 40 dB down
from the main line power. And don't forget conservation of energy. All
this "coupled" power is stolen from the main line.



They both should have a nice (50 ohm) impedance and be loaded with 50
ohms as well. The better it is constructed, the less energy is coupled onto
the coupled-line in the wrong direction. If done well, the directivity is
highest. [The secondary line can have other than 50 ohms, but common use
requires it] For the Moni-Match (snaked type) the secondary lines could be
some weird Zo and all is well if it is matched pretty well.

Snaking the extra wire into a coax is crude. I don't know what the Zo
would be, but it works ok as long as the coupled power has reasonable
directivity. Remember, the better the SWR using one of these, the worse the
accuracy, for this reason. The power coming out the wrong end of the
secondary line corrupts (adds to) the reflected power you are trying to
measure.



By the way, you can pump power into the secondary line and have some come
out the mainline as well. This is actually done for special uses.



Len Anderson
retired (from regular hours) electronic engineer person



Regards, Steve a not-so-retired person-type...Whew!
--
Steve N, K,9;d, c. i My email has no u's. Why do I do this?!?!?

50-100w at 2m....look at harry's site...sm0vpo...harry's homebrew..

there is a design there that will do you fine..even has the pcb design for
you..it works fine..i have tried it..you can make the pcb smaller if you
wish.i have used it no problems with 200w at 2m...50r line is 2.8mm with
1/16inch fibreglass pcb, so you can design your own..its not critical how
far the sense lines are away from the50r through line,( if you are just
after swr bridge) just remember to terminate each (oposite end ) with 100r
resistor..i have even hand drawn the board and it works fine too....any old
diode works too..i can here the keypads typing away saying you must use this
diode or that diode, but really use what you have..0a91's will be more
sensitive than 1n4001's but who cares at 100w???

if you are after a acturate piece of test equipment then ignore all
above..but for working easy to build, cheap, swr meter then you can not go
wrong.

n.b. see vhf/uhf dx handbook (rsgb) for similar more accurate (in power
terms atleast) swr bridges..

g0zen.
"Avery Fineman" wrote in message
...
In article , Uwe Langmesser
writes:

Now the microstrip coupler you mention, is that what people also call a
monimatch? What are the advantages of one design over another?

You might think of microstrip or stripline as "hammered flat coax."
:-)

It is just a transmission line on a PCB, the characteristic impedance
dependent on trace line width, thickness of the foil, dielectric
constant
of the PCB material and, to some extent, the thickness of the PCB.

Directional couplers are simply a quarter wavelength of transmission
line (coax or microstrip or stripline) that runs parallel to the main
line
connecting to the antenna. The amount of coupling is dependent on
the spacing between the two lines. Their bandwidth is typically an
octave of frequency.

Typical directional coupler coupling is 20 db down from the main line.
Power is coupled mainly in one direction, from the main line to the
end closest to the coupled line's immediate end. Some power will be
coupled into that end coming in the opposite direction but that is
usually 15 to 25 db farther down. While not perfect, directional
coupling differences of about 20 db are good enough to warrant the
name "directional." Those are very common in microwave work and
from about 400 MHz and up in frequency to around 8 GHz; a quarter
wavelength at 400 MHz gets a bit long. At 20 db coupling, the load
on the coupled line can vary quite a bit without affecting the main
line. Reflections from the load can be accurately compared with
coupled energy from the source; if coupling is measured accurately
in both directions, the VSWR can be computed from amplitude
differences. If the coupled line ends have a way to measure both
amplitude and phase, the complex impedance of the load can be
computed accurately in comparison to the coupled source.

I've built directional couplers at about 1 GHz center frequency but
admit cribbing from older published data on impedances and spacings
from microwave literature. Had a somewhat stiff specification on
coupling which required a few passes at different etch masks for a
large stripline assembly of many things. Not again if I can help it.
:-)

Len Anderson
retired (from regular hours) electronic engineer person

50-100w at 2m....look at harry's site...sm0vpo...harry's homebrew..

there is a design there that will do you fine..even has the pcb design for
you..it works fine..i have tried it..you can make the pcb smaller if you
wish.i have used it no problems with 200w at 2m...50r line is 2.8mm with
1/16inch fibreglass pcb, so you can design your own..its not critical how
far the sense lines are away from the50r through line,( if you are just
after swr bridge) just remember to terminate each (oposite end ) with 100r
resistor..i have even hand drawn the board and it works fine too....any old
diode works too..i can here the keypads typing away saying you must use this
diode or that diode, but really use what you have..0a91's will be more
sensitive than 1n4001's but who cares at 100w???

if you are after a acturate piece of test equipment then ignore all
above..but for working easy to build, cheap, swr meter then you can not go
wrong.

n.b. see vhf/uhf dx handbook (rsgb) for similar more accurate (in power
terms atleast) swr bridges..

g0zen.
"Avery Fineman" wrote in message
...
In article , Uwe Langmesser
writes:

Now the microstrip coupler you mention, is that what people also call a
monimatch? What are the advantages of one design over another?

You might think of microstrip or stripline as "hammered flat coax."
:-)

It is just a transmission line on a PCB, the characteristic impedance
dependent on trace line width, thickness of the foil, dielectric
constant
of the PCB material and, to some extent, the thickness of the PCB.

Directional couplers are simply a quarter wavelength of transmission
line (coax or microstrip or stripline) that runs parallel to the main
line
connecting to the antenna. The amount of coupling is dependent on
the spacing between the two lines. Their bandwidth is typically an
octave of frequency.

Typical directional coupler coupling is 20 db down from the main line.
Power is coupled mainly in one direction, from the main line to the
end closest to the coupled line's immediate end. Some power will be
coupled into that end coming in the opposite direction but that is
usually 15 to 25 db farther down. While not perfect, directional
coupling differences of about 20 db are good enough to warrant the
name "directional." Those are very common in microwave work and
from about 400 MHz and up in frequency to around 8 GHz; a quarter
wavelength at 400 MHz gets a bit long. At 20 db coupling, the load
on the coupled line can vary quite a bit without affecting the main
line. Reflections from the load can be accurately compared with
coupled energy from the source; if coupling is measured accurately
in both directions, the VSWR can be computed from amplitude
differences. If the coupled line ends have a way to measure both
amplitude and phase, the complex impedance of the load can be
computed accurately in comparison to the coupled source.

I've built directional couplers at about 1 GHz center frequency but
admit cribbing from older published data on impedances and spacings
from microwave literature. Had a somewhat stiff specification on
coupling which required a few passes at different etch masks for a
large stripline assembly of many things. Not again if I can help it.
:-)

Len Anderson
retired (from regular hours) electronic engineer person

In article , "Steve Nosko"
writes:

some snipping of a good post to avoid undue long length...

The accepted terminology is "Stripline" (think "strip transmission
line") for the line with two flat ground planes on either side of the
"center conductor" which can be thought of as this flattened coax....and
"micro strip" ( I have no memory aid) for the one that is one-sided where
the "center conductor" is on the top of a PCB with a ground plane on the
bottom..

That's quite probably true. Textbooks have the "correct" description
but some in the RF field get over-wrought about terminology and
techno-propriety. :-)

Either type of physical construction makes a TEM (Transverse
ElectroMagnetic) transmission line, just like coaxial cable.

I believe a 1/4 wave is not important here.

For an octave bandwidth and even coupling it is. Those directional
couplers show about less than +/- 1 db difference in coupling versus
frequency over that octave. If the object to obtain a low phase error
over frequency as well as magnitude, then there has to be adherence
to "traditional" shapes-configurations.

ANY conductor running close to and parallel to a transmission line
center conductor will couple something into the coupling line.
For a dual coupler arrangement in SWR checking by magnitude
alone the actual coupling values in db aren't all that important in
getting a relative reading of forward versus reverse.

Typical directional coupler coupling is 20 db down from the main line.

This is a matter of choice by the manufacturer construction. What this
means is that the power coming out the (correct end of the) secondary line
is 20dB down (1/100 th) from the power on the main line.

I'll say that it is a value chosen by the users...manufacturers make
all kinds of coupler coupling values but most seem to go to the 20 db
value because it is a compromise between coupled signal strength
and the effects on the main line from the coupled line and its varying
load impedances. With 20 db coupling (1/100th power as you noted),
the main line is hardly affected whether the coupled line is terminated
in proper resistive value or open or shorted.

While not perfect, directional
coupling differences of about 20 db are good enough to warrant the
name "directional."

This is a matter of primarily the mechanical design.

Mechanical AND electrical...that also influences the directivity.

The "directivity"
refers to the amount of power that gets coupled to the secondary line that
emerges out the "wrong" end--not the one we want.

"Directivity" values are the sum of forward coupling and reverse
coupling. If a coupler has 20 db coupling and the directivity is
45 db, the reverse coupling is down 25 db. [numerical example
only] "Single" couplers have only 3 ports. "Duals" have 4.

from the main line power. And don't forget conservation of energy. All
this "coupled" power is stolen from the main line.

At 20 db coupling, a bad coupled line termination results in a 1%
change of the main line power level. Small value, hard to measure
or hard to see on a meter.

They both should have a nice (50 ohm) impedance and be loaded with 50
ohms as well.

Only if that is the main line characteristic impedance being used. The
TV cable folks work with 75 Ohm Zo and have couplers for that main
line with no problem.

requires it] For the Moni-Match (snaked type) the secondary lines could be
some weird Zo and all is well if it is matched pretty well.

But...the amount of coupling CAN vary considerably with frequency
even though direction of coupling has an good relative agreement.
I'll base that on measuring the "snaked-through-the-large-coax" kind
(two different versions) intended for higher HF bands that had about
15 db difference between the two of them AND had quite a variation
in coupling over frequency. Did that about 40 years ago and didn't
get to keep the notes. Did the same with a rigid copper pipe coax
section having a slot for insertion of a coupling line about 30 years
ago and it was more even in coupling over high HF and reproducible
(based on the same measurement set-ups used by another to check
duplicates shortly thereafter).

To make duplicates of an article's presentation requires a slavish
devotion to copying EXACTLY as described. It's not a case of just
snaking it through the coax, running alongside the outer conductor
braid...which can result in a remarkable variance from the original due
to coax flexibility. With all the available copper piping in many sizes
in home repair stores, the choice of spending a bit more time rather
with a piece of flexible coax will be far more worth it in the long run.

By the way, you can pump power into the secondary line and have some come
out the mainline as well. This is actually done for special uses.

3 db couplers, also known as "hybrid couplers." Very good for making
wideband push-pull or push-push amplifiers out of modular amplifiers.

I'll just add that some directional couplers, both single and dual, are
made with double-sided PCB material, the coupled line on one side,
the main line on the other. Those seem to be good (as products) only
to about 4 GHz or so due to variation in dielectric constant and board
thickness variation. The tiny versions of the last decade use "hard"
substrates of ceramic, etc., and the so-called "blue line" of co-fired
construction from Mini-Circuits is an example. High dielectric constant
in substrate allows making them smaller and the material insures
stability and good control in manufacture.

Once something to be used for measurement is done, there is no
guarantee that it will work as planned. Separate testing needs to be
done to prove it out. That requires measurement with accuracy of
power levels of large dynamic range. The microcontroller display
power meter using an Analog Devices log detector is excellent for
that purpose, dynamic range as large as the basic log detector's
specs. Those seem to be popular in Denmark and Germany according
to the number of ham websites and commentary and photos therefrom.
Search under "power meter" and ignore the commercial hits to find
several ham sites having such homebuilt meters.

Len Anderson
retired (from regular hours) electronic engineer person

In article , "Steve Nosko"
writes:

some snipping of a good post to avoid undue long length...

The accepted terminology is "Stripline" (think "strip transmission
line") for the line with two flat ground planes on either side of the
"center conductor" which can be thought of as this flattened coax....and
"micro strip" ( I have no memory aid) for the one that is one-sided where
the "center conductor" is on the top of a PCB with a ground plane on the
bottom..

That's quite probably true. Textbooks have the "correct" description
but some in the RF field get over-wrought about terminology and
techno-propriety. :-)

Either type of physical construction makes a TEM (Transverse
ElectroMagnetic) transmission line, just like coaxial cable.

I believe a 1/4 wave is not important here.

For an octave bandwidth and even coupling it is. Those directional
couplers show about less than +/- 1 db difference in coupling versus
frequency over that octave. If the object to obtain a low phase error
over frequency as well as magnitude, then there has to be adherence
to "traditional" shapes-configurations.

ANY conductor running close to and parallel to a transmission line
center conductor will couple something into the coupling line.
For a dual coupler arrangement in SWR checking by magnitude
alone the actual coupling values in db aren't all that important in
getting a relative reading of forward versus reverse.

Typical directional coupler coupling is 20 db down from the main line.

This is a matter of choice by the manufacturer construction. What this
means is that the power coming out the (correct end of the) secondary line
is 20dB down (1/100 th) from the power on the main line.

I'll say that it is a value chosen by the users...manufacturers make
all kinds of coupler coupling values but most seem to go to the 20 db
value because it is a compromise between coupled signal strength
and the effects on the main line from the coupled line and its varying
load impedances. With 20 db coupling (1/100th power as you noted),
the main line is hardly affected whether the coupled line is terminated
in proper resistive value or open or shorted.

While not perfect, directional
coupling differences of about 20 db are good enough to warrant the
name "directional."

This is a matter of primarily the mechanical design.

Mechanical AND electrical...that also influences the directivity.

The "directivity"
refers to the amount of power that gets coupled to the secondary line that
emerges out the "wrong" end--not the one we want.

"Directivity" values are the sum of forward coupling and reverse
coupling. If a coupler has 20 db coupling and the directivity is
45 db, the reverse coupling is down 25 db. [numerical example
only] "Single" couplers have only 3 ports. "Duals" have 4.

from the main line power. And don't forget conservation of energy. All
this "coupled" power is stolen from the main line.

At 20 db coupling, a bad coupled line termination results in a 1%
change of the main line power level. Small value, hard to measure
or hard to see on a meter.

They both should have a nice (50 ohm) impedance and be loaded with 50
ohms as well.

Only if that is the main line characteristic impedance being used. The
TV cable folks work with 75 Ohm Zo and have couplers for that main
line with no problem.

requires it] For the Moni-Match (snaked type) the secondary lines could be
some weird Zo and all is well if it is matched pretty well.

But...the amount of coupling CAN vary considerably with frequency
even though direction of coupling has an good relative agreement.
I'll base that on measuring the "snaked-through-the-large-coax" kind
(two different versions) intended for higher HF bands that had about
15 db difference between the two of them AND had quite a variation
in coupling over frequency. Did that about 40 years ago and didn't
get to keep the notes. Did the same with a rigid copper pipe coax
section having a slot for insertion of a coupling line about 30 years
ago and it was more even in coupling over high HF and reproducible
(based on the same measurement set-ups used by another to check
duplicates shortly thereafter).

To make duplicates of an article's presentation requires a slavish
devotion to copying EXACTLY as described. It's not a case of just
snaking it through the coax, running alongside the outer conductor
braid...which can result in a remarkable variance from the original due
to coax flexibility. With all the available copper piping in many sizes
in home repair stores, the choice of spending a bit more time rather
with a piece of flexible coax will be far more worth it in the long run.

By the way, you can pump power into the secondary line and have some come
out the mainline as well. This is actually done for special uses.

3 db couplers, also known as "hybrid couplers." Very good for making
wideband push-pull or push-push amplifiers out of modular amplifiers.

I'll just add that some directional couplers, both single and dual, are
made with double-sided PCB material, the coupled line on one side,
the main line on the other. Those seem to be good (as products) only
to about 4 GHz or so due to variation in dielectric constant and board
thickness variation. The tiny versions of the last decade use "hard"
substrates of ceramic, etc., and the so-called "blue line" of co-fired
construction from Mini-Circuits is an example. High dielectric constant
in substrate allows making them smaller and the material insures
stability and good control in manufacture.

Once something to be used for measurement is done, there is no
guarantee that it will work as planned. Separate testing needs to be
done to prove it out. That requires measurement with accuracy of
power levels of large dynamic range. The microcontroller display
power meter using an Analog Devices log detector is excellent for
that purpose, dynamic range as large as the basic log detector's
specs. Those seem to be popular in Denmark and Germany according
to the number of ham websites and commentary and photos therefrom.
Search under "power meter" and ignore the commercial hits to find
several ham sites having such homebuilt meters.

Len Anderson
retired (from regular hours) electronic engineer person

"Steve Nosko" wrote in message ...

Side bar: I have one of the first directional power meters, the Micro
match. It uses a resistor, yes, resistor, for the current sense rather than
the now common current transformer toroid. circa 1945 -50.

Not really all that uncommon. A Wheatstone bridge works fine for
monitoring SWR, and transformer-coupled versions of essentially a
Wheatstone bridge are commonly used in S-parameter test sets used with
network analyzers. Nice for flat response over lots of octaves, if
you are verrrry careful about the construction.


You might think of microstrip or stripline as "hammered flat coax."
:-)

The accepted terminology is "Stripline" (think "strip transmission
line") for the line with two flat ground planes on either side of the
"center conductor" which can be thought of as this flattened coax....and
"micro strip" ( I have no memory aid) for the one that is one-sided where
the "center conductor" is on the top of a PCB with a ground plane on the
bottom..

(And though stripline is true TEM, microstrip is quasi-TEM because of
the different dielectric above and below the microstrip.)

It is just a transmission line on a PCB, the characteristic impedance
dependent on trace line width, thickness of the foil, dielectric
constant
of the PCB material and, to some extent, the thickness of the PCB.

I think the PCB material (thickness & properties) has a larger
contribution to the Zo that the runner thickness...at least at the freqs I
worked at (1GHz.). Good ole' Wheeler & Sobol equations for the Zo.

Yep, by far. The free "RFSim99" program will help with the dimensions
for five different kinds of couplers, you pick the coupling, including
stripline and microstrip. The one thing it fails to mention is the
1/4 wave line length for the given coupling.


Directional couplers are simply a quarter wavelength of transmission
line (coax or microstrip or stripline) that runs parallel to the main
line
connecting to the antenna.

I believe a 1/4 wave is not important here.

Right...but beware of NULLS in the response at integer multiples of
1/2 wavelength, and the response returns to the same value at 3/4 wave
as it was at 1/4 wave. They are broadly rounded peaks, as Len says
useful over perhaps an octave for non-precision power measurements.
This can be used to advantage for a 146-440MHz coupler: make it 1/4
wave at 146, and it will respond fine at 3/4 wave at 440. But 1/4
wave (even with the 0.5 VF of glass-epoxy circuit board mtrl) is a bit
long. But...you can fold that in a "U" and get it down to ten inches
or so board length.

For broader bandwidth, it's common to make the stripline or microstrip
in three (or five, or...) sections with varying coupling. The center
section is highest coupling, and the outer sections are lower. You
can find design info on the web about this. The broadening is quite
significant.

....
Typical directional coupler coupling is 20 db down from the main line.

This is a matter of choice by the manufacturer construction. What this
means is that the power coming out the (correct end of the) secondary line
is 20dB down (1/100 th) from the power on the main line.

In fact, -20dB with 100 watts input gives you a WATT at the "FWD"
output, which is WAY more than I want to deal with! Simple diode
detectors let me "see" down to -50dBm, so even a milliwatt is really
more than I need. Even with 10mW of excitation, a -30dB coupler is
quite useful. DESIGN the coupler to give you what you want at the
output!


While not perfect, directional
coupling differences of about 20 db are good enough to warrant the
name "directional."

This is a matter of primarily the mechanical design.

AND the loading on the "other" end of the coupled line. Steve touched
on this, but I think it deserves more emphasis. Consider: if you have
a -20dB coupler and 100 watts forward and zero return on the "through"
line, you have a watt trying to come out the "forward" coupled port.
If you don't terminate that perfectly, some of that watt goes back the
other way, and spoils the directionality. SO...if you screwed up the
trace width (perhaps because you didn't know the dielectric constant
or thickness of the board material exactly, or your etching wasn't
perfect), you can still adjust for very nearly perfect directivity by
adjusting the load on the coupled line. This is also why it's good,
especially at microwaves, to NOT try to use two detectors on opposite
ends of the same coupled line, because the detectors are more
difficult to have be really good resistances and not introduce
parasitic reactance. One way to make the load adjustable (assuming
low enough coupled power that you can use SMT resistors) would be to
provide pads for multiple termination resistors (two or three) and use
a parallel combination that gives you just the right termination.
This assumes you have a really good load (including any line and
fittings) you can put on the through-line to insure near-zero
reflections there! Calibration-quality loads for GHz frequencies are
NOT cheap, and garden-variety coax is practically guaranteed to NOT be
50 ohms exactly. (45-55 is about the best reasonable expectation you
should have for RG-58.)

....

Cheers,
Tom