WARNING
LONG WINDED POST BY TWO OLD FOGEYS...

Did I spell that correctly?

"Avery Fineman" wrote in message
...
In article , "Steve Nosko"
writes:

More snipping of a good post to avoid undue long length...
But I see we both are having trouble with the length, eh Len?


The accepted terminology is "Stripline" [snip] and "micro strip" ...

That's quite probably true. ..some in the RF field get over-wrought
about terminology....
Either type of physical construction makes a TEM (Transverse
ElectroMagnetic) transmission line, just like coaxial cable....

Not getting religious about it, just adding some info here & trying to
clarify/simplify the explanatin. The OP asked if the "Directional coupler"
being talked about was like the Moni-Match. I was just trying to make that
case---then, as is common here, to add a lot of stuff I felt was helpful in
explaining what I thought the OP _may_ want to know...if he/she didn't give
up on the long post hi hi


I believe a 1/4 wave is not important here.
For an octave bandwidth and even coupling it is.
...If the object to obtain a low phase error...

I didn't think the OP was asking about octave bandwidth or phase.
Perhaps I missed that.


ANY conductor running close to and parallel to a transmission line
center conductor will couple something into the coupling line.

That's the idea I was trying to point out. Like What I call the "snaked
wire" version.



Then we get into deeper detail and possibly symmantics. I'll keep my
symmantics comments to a minimum since I was simply trying to provide a
simplified comparison with the monimatch and a little info on how they work.

Typical directional coupler coupling is 20 db down from the main
line.
This is a matter of choice by the manufacturer construction.
I'll say that it is a value chosen by the users...manufacturers make
all kinds of coupler coupling values

And I meant that when a given coupling is desired, it is the physical
construction which gets you there.

...With 20 db coupling ...,
the main line is hardly affected whether the coupled line is terminated
in proper resistive value or open or shorted.

Sure. Weather or not you pull 1% of the power out, few of us will care.


name "directional."
This is a matter of primarily the mechanical design.
Mechanical AND electrical...that also influences the directivity.

Again, I was merely pointing out that good construction is necessary for
good directivity. In contrast to the "snaked" coax version which can have
highly variable performance.


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. ...

I presume you intend to mean"...from the foward _coupled_ level." ???
This is what I was trying to say.

And don't forget conservation of energy. ...
At 20 db coupling, a bad coupled line termination results in a 1%



Probably going too far for the OP's original need I guess I'm just as
guilty of adding mounds of information that he OP might not be interestred
in.

They both should have a nice (50 ohm) impedance ...
Only if that is the main line characteristic impedance being used.
That's why I put the 50 in (), just as an example. I should have left
it out, but then I figured a question of "what is 'nice'" might have
surfaced.


...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.

Sure. Again, I don't thing the OP is worried about flat freq response.
Many of us are familiar with the switched SWR meter with the pot to set the
FWD power to full scale and how that varies from band to band. We live with
it. At work, however, flat couplers are needed.
In fact, I was doing it last night. Was puzeled by the worse SWR on
teh lower bands of a high quality load. Could be... the SWR meter..
..

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.

Do you remember if you looked at the Zo of the coupled lines? I seem to
recall that in the articles, the termination of the coupled line is
considered an emperical optimization. cut-try for the value of load giving
"best" operation. I also wondered about the load seen at the end(s) where
the detectors were. Did they get a good match there. That;s going to mess
with your directivity, no? I guess you can put a good load on the main line
and just tweek for best directivity... a.k.a. lowest reading when line
matched - in BOTH directions. Seems that this is all you need to worry
about, for a ham, that is.


To make duplicates of an article's presentation requires a slavish
devotion to copying EXACTLY as described.

Again, that's where my comment about mechanigal construction came from.

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.

Won't go into detail, but high power linear amplifiers (60dB 2 tone IM)
in the 800MHz & 1800MHz range use 20 dB couplers for "Feed-Forward" IM
correction loops. Made an extensive "Backplane" with many stripline
couplers for them.


...High dielectric constant
in substrate allows making them smaller and the material insures
stability and good control in manufacture.
I have used Alumina. I also saw an article on microstrip couplers with
a complementary zig-zag pattern on the edges of the coupled lines adjacent
to each other...forget what the advantage was...I think increased coupling.


...Analog Devices log detector is
I saw that little bugger in QEX. Pretty cool!


73, Len

--
Steve N, K,9;d, c. i My email has no u's.