Someone has asked my magazine column where the name "hybrid coupler"
came from; and why do some people reserve the name "hybrid" for only
certain types of couplers?

That isn't as easy a question as it first seems. Everybody seems to talk
about "hybrids" but few authors are prepared to define exactly what it
means - much less explain why.

The following is a draft outline for my magazine article. It looks much
more authoritative than I actually feel about the subject - especially
about the origins of the term "hybrid", so I would welcome any
comments...


Hybrid is originally a biological term for a "cross-breed" that inherits
different characteristics from two different kinds of parents. The word
has then taken on a much wider sense - for example, we talk about
"hybrid road vehicles" or "hybrid analogue/digital systems".

However, a "hybrid coupler" is a much more specific term, which came
from the early days of landline telephony. Originally, a two-conductor
line could only be used in one direction at a time; but with a hybrid
coupler [Figure] at both ends, that single line can be used for full
duplex communication in both directions. An important feature is that
the coupler provides isolation between the links in opposite directions
[insert more description here, including bidirectional amplifiers].

So why was this device specifically called a "hybrid" coupler? There's
nothing particularly hybrid about the coupler, so my best guess is that
the word originally applied to the communication link - the
bidirectional offspring of two unidirectional parents. But in the
strange way that technical language evolves, "duplex" has become the
common word for a bidirectional link, while "a hybrid" has come to mean
the coupler itself. The same word has then been applied to RF couplers
that share some of the characteristics of the original telephone hybrid.

The best descriptions of RF hybrid couplers I've been able to find on
the web are in:
http://en.wikipedia.org/wiki/Power_d...ional_couplers
and:
http://www.rfcafe.com/references/ele...%20coupler.htm

In RF engineering the name "hybrid" has become attached to the 4-port
coupler in [Figure]. When ports 2, 3 and 4 are matched, the input power
at port 1 is divided equally between ports 2 and 3, with a phase shift
of 90deg between the two output ports. Since half the input power
appears at each output port, the transmission loss to each individual
port is 3dB, so this device is sometimes called 3dB coupler. The reason
why this device is called a hybrid is because of the port-to-port
isolation it provides. In the matched condition, ports 2 and 3 are
isolated from each other, and port 4 is isolated from port 1. [Add more
details of the 3dB/ 90deg/quadrature coupler configuration.]

However, the Wikipedia author(s) also point out that nowadays "any
matched 4-port with isolated arms and equal power division is called a
hybrid or hybrid coupler." This wider definition also includes 0deg
hybrids and 180deg hybrids, in addition to the original 90deg variety.
Some 3-port devices are also called hybrids because they provide
isolation between the output ports and have a 'virtual' internal 4th
port, an example being the Wilkinson 0deg power divider.

Of course, some devices that do not meet every part of the above
definition may still be called "hybrids" in practice. And a device that
offers port-to-port isolation is likely to have other names as well, eg
it may be called a "bridge". Are we confused enough yet?

Originally all these definitions were also restricted to passive linear
devices, but as op-amps get faster and faster, and move up into the RF
domain, it becomes possible to create the same port-to-port behaviour
using active devices. It is now possible to build active hybrids that
can operate up to at least 100MHz, and their advantage over
transformer-based hybrids is that they have no lower-frequency limit.
However, any hybrid still has to be a linear device.

[More to add...]



How does that look, as a first draft? I would particularly appreciate
comments on the probable history of the word "hybrid" in telephony and
electronics.





--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Ian White GM3SEK wrote:

Someone has asked my magazine column where the name "hybrid coupler"
came from; and why do some people reserve the name "hybrid" for only
certain types of couplers?

That isn't as easy a question as it first seems. Everybody seems to talk
about "hybrids" but few authors are prepared to define exactly what it
means - much less explain why.

The following is a draft outline for my magazine article. It looks much
more authoritative than I actually feel about the subject - especially
about the origins of the term "hybrid", so I would welcome any comments...


Hybrid is originally a biological term for a "cross-breed" that inherits
different characteristics from two different kinds of parents. The word
has then taken on a much wider sense - for example, we talk about
"hybrid road vehicles" or "hybrid analogue/digital systems".

However, a "hybrid coupler" is a much more specific term, which came
from the early days of landline telephony. Originally, a two-conductor
line could only be used in one direction at a time; but with a hybrid
coupler [Figure] at both ends, that single line can be used for full
duplex communication in both directions. An important feature is that
the coupler provides isolation between the links in opposite directions
[insert more description here, including bidirectional amplifiers].

So why was this device specifically called a "hybrid" coupler? There's
nothing particularly hybrid about the coupler, so my best guess is that
the word originally applied to the communication link - the
bidirectional offspring of two unidirectional parents. But in the
strange way that technical language evolves, "duplex" has become the
common word for a bidirectional link, while "a hybrid" has come to mean
the coupler itself. The same word has then been applied to RF couplers
that share some of the characteristics of the original telephone hybrid.

The best descriptions of RF hybrid couplers I've been able to find on
the web are in:
http://en.wikipedia.org/wiki/Power_d...ional_couplers
and:
http://www.rfcafe.com/references/ele...%20coupler.htm

In RF engineering the name "hybrid" has become attached to the 4-port
coupler in [Figure]. When ports 2, 3 and 4 are matched, the input power
at port 1 is divided equally between ports 2 and 3, with a phase shift
of 90deg between the two output ports. Since half the input power
appears at each output port, the transmission loss to each individual
port is 3dB, so this device is sometimes called 3dB coupler. The reason
why this device is called a hybrid is because of the port-to-port
isolation it provides. In the matched condition, ports 2 and 3 are
isolated from each other, and port 4 is isolated from port 1. [Add more
details of the 3dB/ 90deg/quadrature coupler configuration.]

However, the Wikipedia author(s) also point out that nowadays "any
matched 4-port with isolated arms and equal power division is called a
hybrid or hybrid coupler." This wider definition also includes 0deg
hybrids and 180deg hybrids, in addition to the original 90deg variety.
Some 3-port devices are also called hybrids because they provide
isolation between the output ports and have a 'virtual' internal 4th
port, an example being the Wilkinson 0deg power divider.

Of course, some devices that do not meet every part of the above
definition may still be called "hybrids" in practice. And a device that
offers port-to-port isolation is likely to have other names as well, eg
it may be called a "bridge". Are we confused enough yet?

Originally all these definitions were also restricted to passive linear
devices, but as op-amps get faster and faster, and move up into the RF
domain, it becomes possible to create the same port-to-port behaviour
using active devices. It is now possible to build active hybrids that
can operate up to at least 100MHz, and their advantage over
transformer-based hybrids is that they have no lower-frequency limit.
However, any hybrid still has to be a linear device.

[More to add...]



How does that look, as a first draft? I would particularly appreciate
comments on the probable history of the word "hybrid" in telephony and
electronics.






Hi Ian,
A hybrid coil in telephony was (is?) used to couple a 2 wire
line to a 4 wire line allowing bidirectional amplification. If you
have access to Reg's old bible _Communication Engineering_ by William
Everitt you can read an explanation of how this works starting on
page 317 (second edition).I suppose the term "hybrid" refers to
the fact that two different types of line (2 wire and 4 wire) are
involved.
From _Microwave Engineering Using Microstrip Circuits_ by
Fooks and Zakarevicius: "Hybrid couplers may be regarded as
directional couplers which can produce an equal power split
between the output ports. This definition is good in the main,
but it is possible to have hybrids with unequal power split.
Inherently, a hybrid and a directional coupler are the same type
of device. The only difference is really one of construction,
with the hybrid-line coupler historically arising out of
structures which aimed to produce equal power splitting with
good isolation, directional coupling aspects not being of
interest."
73,
Tom Donaly, KA6RUH

Ian White GM3SEK wrote:
The best descriptions of RF hybrid couplers I've been able to find on
the web are in:
http://en.wikipedia.org/wiki/Power_d...ional_couplers
and:
http://www.rfcafe.com/references/ele...%20coupler.htm
=============
Ian , tnx for the above references , they are excellent learning options.

Frank KN6WH /GM0CSZ

Hi Ian,

Hybrid in biological terms I believe means that it can not reproduce
itself. Plants from Hybrid seeds can only be grown from the original
seeds.
I would guess that the relationship to the hybrid coil would have to
do with the isolation between ports,,, can't be reproduced from port
to port only from the original or single port.

73
Gary K4FMX

On Wed, 31 Jan 2007 15:08:53 +0000, Ian White GM3SEK
wrote:


Someone has asked my magazine column where the name "hybrid coupler"
came from; and why do some people reserve the name "hybrid" for only
certain types of couplers?

That isn't as easy a question as it first seems. Everybody seems to talk
about "hybrids" but few authors are prepared to define exactly what it
means - much less explain why.

The following is a draft outline for my magazine article. It looks much
more authoritative than I actually feel about the subject - especially
about the origins of the term "hybrid", so I would welcome any
comments...


Hybrid is originally a biological term for a "cross-breed" that inherits
different characteristics from two different kinds of parents. The word
has then taken on a much wider sense - for example, we talk about
"hybrid road vehicles" or "hybrid analogue/digital systems".

However, a "hybrid coupler" is a much more specific term, which came
from the early days of landline telephony. Originally, a two-conductor
line could only be used in one direction at a time; but with a hybrid
coupler [Figure] at both ends, that single line can be used for full
duplex communication in both directions. An important feature is that
the coupler provides isolation between the links in opposite directions
[insert more description here, including bidirectional amplifiers].

So why was this device specifically called a "hybrid" coupler? There's
nothing particularly hybrid about the coupler, so my best guess is that
the word originally applied to the communication link - the
bidirectional offspring of two unidirectional parents. But in the
strange way that technical language evolves, "duplex" has become the
common word for a bidirectional link, while "a hybrid" has come to mean
the coupler itself. The same word has then been applied to RF couplers
that share some of the characteristics of the original telephone hybrid.

The best descriptions of RF hybrid couplers I've been able to find on
the web are in:
http://en.wikipedia.org/wiki/Power_d...ional_couplers
and:
http://www.rfcafe.com/references/ele...%20coupler.htm

In RF engineering the name "hybrid" has become attached to the 4-port
coupler in [Figure]. When ports 2, 3 and 4 are matched, the input power
at port 1 is divided equally between ports 2 and 3, with a phase shift
of 90deg between the two output ports. Since half the input power
appears at each output port, the transmission loss to each individual
port is 3dB, so this device is sometimes called 3dB coupler. The reason
why this device is called a hybrid is because of the port-to-port
isolation it provides. In the matched condition, ports 2 and 3 are
isolated from each other, and port 4 is isolated from port 1. [Add more
details of the 3dB/ 90deg/quadrature coupler configuration.]

However, the Wikipedia author(s) also point out that nowadays "any
matched 4-port with isolated arms and equal power division is called a
hybrid or hybrid coupler." This wider definition also includes 0deg
hybrids and 180deg hybrids, in addition to the original 90deg variety.
Some 3-port devices are also called hybrids because they provide
isolation between the output ports and have a 'virtual' internal 4th
port, an example being the Wilkinson 0deg power divider.

Of course, some devices that do not meet every part of the above
definition may still be called "hybrids" in practice. And a device that
offers port-to-port isolation is likely to have other names as well, eg
it may be called a "bridge". Are we confused enough yet?

Originally all these definitions were also restricted to passive linear
devices, but as op-amps get faster and faster, and move up into the RF
domain, it becomes possible to create the same port-to-port behaviour
using active devices. It is now possible to build active hybrids that
can operate up to at least 100MHz, and their advantage over
transformer-based hybrids is that they have no lower-frequency limit.
However, any hybrid still has to be a linear device.

[More to add...]



How does that look, as a first draft? I would particularly appreciate
comments on the probable history of the word "hybrid" in telephony and
electronics.

From: "Tom Donaly" on Wed, Jan 31 2007 6:05 pm

Ian White GM3SEK wrote:

Someone has asked my magazine column where the name "hybrid coupler"
came from; and why do some people reserve the name "hybrid" for only
certain types of couplers?

That isn't as easy a question as it first seems. Everybody seems to talk
about "hybrids" but few authors are prepared to define exactly what it
means - much less explain why.

The following is a draft outline for my magazine article. It looks much
more authoritative than I actually feel about the subject - especially
about the origins of the term "hybrid", so I would welcome any comments...
...
Hi Ian,
A hybrid coil in telephony was (is?) used to couple a 2 wire
line to a 4 wire line allowing bidirectional amplification. If you
have access to Reg's old bible _Communication Engineering_ by William
Everitt you can read an explanation of how this works starting on
page 317 (second edition).I suppose the term "hybrid" refers to
the fact that two different types of line (2 wire and 4 wire) are
involved.

Hello Ian and Tom,
The mention of "Communication Engineering" by William Littell
Everitt sparked my interest since it has prime occupancy on my
Basics bookshelf space (the book and I were "born" in the same
year...:-)
Going into the etymology of *ALL* "hybrids" in communications
will probably focus not on "radio" but the common telephone
handset and the long-distance, wired telephone system courtesy
of remarkable innovation by the American Telephone and Telegraph
laboratories. Note: I'm not waving a flag for "Americanism"
only that the AT&T system grew to be huge early-on and also
engineered for rather incredible longevity and good performance.
The common telephone set made here by the MILLIONs between
the 1930s and 1970s period all had a "hybrid transformer" as its
basic "coupler" to the telephone line, here a 2-wire balanced-
pair to the central office. Mouthpiece and earpiece were
actually isolated by this "hybrid" with a controlled leak-
through to the earpiece for "sidetone" (a term that came from
telephony as well). In addition, the "hybrid" coupled or
isolated the 40 VDC (give or take) always present on our
telephone lines and the 20 Hz Ring signal (with/without the
hook switch cut-out). Added to that were a (somewhat) primitive
"ALC" using thermistors-varistors to keep loud talkers from
blasting ears of other users. Rather complex arrangement but
very simple in terms of parts, rugged, long-lasting (better
than 30 years life), and cost effective.
It would seem that the POTS hybrid scheme grew out of
long-distance lines' repeater stations where two amplifiers
were needed to boost signal strength both ways...AND provide
a DC path for lots of different telco service needs. The
concept of linearity through negative feedback was a direct
result of "long-lines" repeater needs. A long-lines repeater
"hybrid" seems to have evolved from the already-existing
bridge circuit used for measurement of passive components.
I say "seems" because both repeater hybrid and measurement
bridges are configured for balance and "separation" of the
components' characteristics. All of that took place at
"audio" frequencies (under 15 KHz), including frequency-
multiplexed SSB voice channels. Yes, "SSB" was pioneered
by the various telephone companies in the world, on wire
lines first, then on "radio." :-)
Segue to World War II and some massive head-scratching
on both sides. "Radio" folks of older days may have
encountered a "Magic-T" in waveguide, particularly at X-Band
(3 cm or 8 to 12 GHz). A Magic-T is really a hybrid
transformer equivalent, RF energy coming into a common port
(inbound) is relatively isolated from RF energy into a 3rd
port intended to go outbound. The fourth port is generally
terminated in a resistive load for broadband balance but
can also be used as a bidirectional port. "Isolation" is
a result of good directional balance, a term that became
common in the microwave field after WW2 and Isolators and
Circulators came into being. Note: A "circulator"
performs the same function as the old Magic-T but has a
greater production yield, generally more compact.
The "rat-race hybrid" of all-coaxial lines probably
evolved out of the Magic-T as a semi-broadband hybrid
transformer but at RF lower than microwaves. It had
limited use until Stripline and Microstrip was innovated.
Most Rat-Races are still rather narrowband and incapable
of working to octave bandwidths common to microwaves.
With Stripline a whole vast array of "flat" configurations
were innovated but all based on basic transmission line
properties...including all the filter structures built
entirely on PCBs.
Broad-banding at RF also had to wait for better
powdered-iron and ferrite materials' better characteristics
that came about after WW2. One offshoot of that was the
broadband RF transformer that could have double decade
bandwidth. Such RF transformers could be configured very
much like the old POTS hybrid transformers. :-) Variants
of those appeared in HF through UHF solid-state power
amplifiers and "hot plug swapping" RF power amplifiers
composed of many modules, each relatively isolated from
one another. Does anyone working at RF not know about
the "balun?" [broadband impedance-changing/isolating
transformer]
It is my opinion that many, many terms became a sort
of jargon or "tech-speak" for the simple reason of the
names being short yet familiar to all working with a
particular field. For example, it is much easier to say
and pronounce "flip-flop" than the formal name of "Eccles-
Jordan Bistable Multivibrator." :-) Folks in radio say
"mike" for microphone or for microfarads of capacitance;
what they are talking about does a subtle unconscious
separation and ordering of the incoming information.
There isn't much confusion about such jargon even if
discussing 'condenser microphones.' :-)
Sometimes the jargon becomes over-used. I use the
term "Wilkinson Power Divider" [or "Power Splitter"]
for a familiar Stripline structure, yet I've heard and
seen it described as a "Wilkinson Hybrid." While it is
on the grey area of veddy proper useage, most RF folks
know what either is. Editors writing for a large,
unknown-technical-smarts-set readership do, understand-
ably, get a bit under stress trying to Explain It All.
[been there, done that, got a few T-shirts...:-) ]
I would trace "hybrid" in electronics all the way
back to the guy that invented the "Wheatstone Bridge."
Wheatstone spoke and wrote about that clever thing so
much that His name got stuck on the configuration, the
real inventor's name got rather lost. Balance and
isolation were essential there...and balance and
isolation was necessary in the telephone "hybrid."
Millions of telephone "hybrids" later, the jargon
happened. The "hybrid" essential principles were
applied to other fields within electronics and the
rest is slightly confused history...:-)

Cheers,

wrote in message ......

Many thanks for a fascinating post, Len.

John A

On Feb 2, 1:23?am, "John A" wrote:
wrote in message ......

Many thanks for a fascinating post, Len.

John A

Thank you, but most of the thanks should go to a
gentleman at the Signal School that was in Fort
Monmouth, NJ, back in 1952. He had spent a lot
of his work time at Bell Labs. My MOS was
Microwave Radio Relay in the Army and had to
encompass comms techniques from landline
telephone through radio at VHF to microwaves.
Even more to a couple of GE technical reps who
oversaw the installation of 24-voice-channel 1.8
GHz radio relay terminals in Japan '54 to '56.
They had the knowledge at their mind's finger-
tips and infused a number of us back then with
some indelible information. :-)

If you wish to see a bit more of 50-year-old
military communications, download:

http://sujan.hallikainen.org/Broadca...s/My3Years.pdf

It's about 6 MB and takes about 20 minutes on a
dial-up connection. Hal has a lot of information
collected there, not all of it on broadcasting.

On Feb 2, 2:17 pm, "
wrote:
On Feb 2, 1:23?am, "John A" wrote:

wrote in message ......

Many thanks for a fascinating post, Len.

John A

Thank you, but most of the thanks should go to a
gentleman at the Signal School that was in Fort
Monmouth, NJ, back in 1952. He had spent a lot
of his work time at Bell Labs. My MOS was
Microwave Radio Relay in the Army and had to
encompass comms techniques from landline
telephone through radio at VHF to microwaves.
Even more to a couple of GE technical reps who
oversaw the installation of 24-voice-channel 1.8
GHz radio relay terminals in Japan '54 to '56.
They had the knowledge at their mind's finger-
tips and infused a number of us back then with
some indelible information. :-)

If you wish to see a bit more of 50-year-old
military communications, download:

http://sujan.hallikainen.org/Broadca...s/My3Years.pdf

It's about 6 MB and takes about 20 minutes on a
dial-up connection. Hal has a lot of information
collected there, not all of it on broadcasting.




As is so often the case with word/phrase etymology, origins are
sometimes cloudy. The wikipedia article alludes to this. But I
believe the key is that the two outputs are equal in a so-called
"hybrid". You might simply tell your readers in summary that the
issue is unclear, and that you gave it the best shot anyone reasonably
can.

Thanks for all the interesting replies - particularly Len's long
historical narrative - and please accept my apologies for not responding
immediately. The magazine article took a different course from the one
that I'd anticipated, and thus took much longer to write.

After all the research and reminiscence, though, we still aren't much
closer to understanding why some old-time telephone engineer named this
circuit a "hybrid" . We can only speculate that, before finding his true
vocation with Ma Bell, he had failed both English and Genetics.

In the end it seemed more important to concentrate on the defining
characteristics of a modern "RF hybrid", which are coupling between some
of its ports (usually equal power division), and at the same time,
isolation between other ports. Even that is more of a loose consensus
than a firm definition, of course.

Anyhow, the article eventually started with a fairly detailed
description of the telephone hybrid (which also explains why a hybrid
can sometimes be called a bridge instead) and then wandered onward to
identify a few RF hybrids and describe some useful applications of RF
hybrids; by which point, I had used up my two pages.

Thanks again to everyone who contributed - it certainly helped to
straighten out my thinking on what had originally seemed such an
innocent little question.


--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

On Feb 13, 6:47�am, Ian White GM3SEK wrote:
Thanks for all the interesting replies - particularly Len's long
historical narrative - and please accept my apologies for not responding
immediately. The magazine article took a different course from the one
that I'd anticipated, and thus took much longer to write.

After all the research and reminiscence, though, we still aren't much
closer to understanding why some old-time telephone engineer named this
circuit a "hybrid" . We can only speculate that, before finding his true
vocation with Ma Bell, he had failed both English and Genetics.

In the end it seemed more important to concentrate on the defining
characteristics of a modern "RF hybrid", which are coupling between some
of its ports (usually equal power division), and at the same time,
isolation between other ports. Even that is more of a loose consensus
than a firm definition, of course.

Anyhow, the article eventually started with a fairly detailed
description of the telephone hybrid (which also explains why a hybrid
can sometimes be called a bridge instead) and then wandered onward to
identify a few RF hybrids and describe some useful applications of RF
hybrids; by which point, I had used up my two pages.

Thanks again to everyone who contributed - it certainly helped to
straighten out my thinking on what had originally seemed such an
innocent little question.

--

73 from Ian GM3SEK * * * * 'In Practice' columnist for RadCom (RSGB)http://www.ifwtech.co.uk/g3sek

Heh heh heh, the etymological problems can be furthered
by looking at other terms in all of electronics and how they
came to be known. :-) Sometimes we just have to plain
accept common terms rather than buy industrial-strength
aspirin quantities to ease the ensuing headaches. "English"
(our supposed 'common' language) has, like most other
languages in Yurp, grown, adopted, changed, mangled,
seasoned, and baked thoroughly by common folk for
centuries in daily use. The only "correct" use seems to
be that authorized by our school teachers... :-)

How about posting in here when the publishing schedule
is firm about which issue the article will appear in? [he
said, mangling sentence structure] Might be a fun future
topic for discussion? :-)