Copied from the UK Amateur Radio Newsgroup.

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"Joe McElvenney" wrote
Randall and Boot's cavity magnetron
didn't really come onto the scene until about 1940.

===================================

R & B's cavity magnetron was developed at Birmingham University in the
midst of the air raids on that industrial city. We can imagine R & B
having to hide under the workbench whenever a descending bomb was
heard, culminating in a loud bang and broken glass.

The ingenious device generated a peak pulse power of 50 kilowatts at
3000 MHz. Pulse repetition frequency 400 Hz. Pulse width 1
microsecond. So far as I can remember there were 6 or 8 cavities
milled into the copper block. Alternate anodes surrounding the
cathode, and close to it, were strapped together at their ends via
copper bars. The block diameter was about 2" and about 1" thick. The
magnet was a U-shape with pole-pieces which closely fitted the flat
ends round the block such that the magnetic field was parallel to the
cathode.

Because the luftwaffer in 1940/1 had more bombers than the RAF, and in
view of its potential as a war weapon, Churchill personally banned
installation in RAF aircraft in case the top-secret device should be
shot down over Germany and fall into the hands of German scientists
and engineers.

So Churchill handed the cavity magnetron to Roosevelt as a free gift
in return for 50 rusty, old, WW1 destroyers. The manufacturing
capacity of the US radio industry far exceeded that of the UK. Not to
be outdone, the Americans soon produced a 10,000 MHz version.

I first held one in my hands in 1945 by which time centimetric radar
had been installed in RAF Catalina and Sunderland flying boats on
convoy-escort duties in the Battle of the Atlantic. By 1945 German
submarine crews were on suicide missions like kamikazi pilots, only 1
U-boat in 10 returned to base.

There are more than 100,000 merchant ship and U-boat crew-members
sharing Davy Jones locker at the silent bottom of the North Atlantic
Ocean. Thus was the ferocity of the war.

Once having detected a centimetric radar beam, and being accurately
located themselves, submarine commanders preferred to remain on the
surface, uncover the guns, and fight it out, day or night.

During most of the war there had been little effect on German
industrial production by RAF raids. Many bombs fell on open fields and
sometimes killed cattle. But by 1944 RAF navigatigators had maps of
rivers and cities laid before them. More than a 1000 heavy bombers,
Lancasters, could be put into the air, night after night.

With radar they couldn't miss whole cities and individual districts.
Nevertheless on one occasion more than 100 bombers, complete with
crews, failed to return to base. Such occurrences greatly exceeded the
capacity of factories to produce them and to train aircrews.

During the last 12 months of the war, radar equipped RAF bombers
killed more German civilians than died in the concentration camps.
Hiroshima and Nagasaki, which came shortly after, were just chicken
feed. Air Marshal "Bomber" Harris was never knighted for services
rendered.

The main beneficiaries of R & B's invention of the cavity magnetron,
done amid the high-explosives and incendiaries falling on Birmingam,
have been the Japanese and other Far Eastern peoples who have
manufactured many millions of cheap, reliable, microwave ovens.

And of course the many millions of people like you and I who benefit
from daily hot meals. I detest barbiques.

There was held in the Kensington, London, Science Museum, the original
prototype of the cavity magnetron without its magnet. It was in a
securely locked mahogany and glass case and looked, as I recollect,
like a small dirty can of baked beans with things sticking out of it.
It may still be there.

Makes a change from so-called SWR meters.
----
Reg, G4FGQ.

On Sat, 24 Sep 2005 06:21:07 +0000 (UTC), "Reg Edwards"
wrote:

Makes a change from so-called SWR meters.

Ah Reggie!

Hardly, SWR was the second most considered technical hurdle in the
development of RADAR.

73's
Richard Clark, KB7QHC

Makes a change from so-called SWR meters.

Ah Reggie!

Hardly, SWR was the second most considered technical hurdle in the
development of RADAR.

73's
Richard Clark, KB7QHC

=================================

Ah Rich!, Yet again you deliberately distort my meaning in your
amusing game of 0ne-Upmanship.

For the benefit of lurkers, there's a great difference between meters
which purport to measure SWR at HF, but do no such thing and tell
lies, and probes inserted in waveguides at 3 GHz which tell the truth.
----
Reg.

On Sat, 24 Sep 2005 08:04:34 +0000 (UTC), "Reg Edwards"
wrote:


Makes a change from so-called SWR meters.

Ah Reggie!

Hardly, SWR was the second most considered technical hurdle in the
development of RADAR.

73's
Richard Clark, KB7QHC

=================================

Ah Rich!, Yet again you deliberately distort my meaning in your
amusing game of 0ne-Upmanship.

For the benefit of lurkers, there's a great difference between meters
which purport to measure SWR at HF, but do no such thing and tell
lies, and probes inserted in waveguides at 3 GHz which tell the truth.

Ah Reggie,

Yet again, you deliberately distort my meaning in your amusing game of
One-Downmanship.

For the benefit of lurkers, there's absolutely no difference between
meters which purport to measure SWR at any frequency. You are simply
fumbling around with one of your conceits, a troll in the lingua
franca of the Internet.

What you now describe was a flicker in time between bombs and crashing
glass that was quickly discarded as an awkward technique when RADAR
went into production. Such troglodyte methods were long gone before
you even wrapped your mitts around a magnetron.

If we pursue this with your absurd reductionist habit of arguing blind
absolutes in place of practical reality (something Lord Kelvinator
would sneer at as a foppish mannerism); then what you describe as
"probes" are measuring nothing about SWR but are doing what any probe
could accomplish: measuring a common unit of voltage, or current (and
only by inference of the actual through rectification and filtering).
The SWR only arrives by a second (or significantly more than two)
reading, and then FURTHER only after various calculations. Even then,
barring calculations (something no one does except squinty-eyed
scientists and trolls), those same METERs employed were marked in SWR.
Imagine, within very few months of RADAR emerging from the lab, SWR
METERs ruled the production line, and the field kit. And to be sure,
did they measure SWR? As much as any instrument and to your
fulminating frustration, to no obvious difference that would be
observed by Maxwell's demon (or Schrodinger's cat) craftily turned to
this mischievously scientific validation.

SWR arrived in its full glory of attention with RADAR. They were born
simultaneously and absolutely no one gave a fig before on this topic.
Further, it taught a generation of engineers the importance of
matching production designs (which had been long inbred into the AC
power production community - simply a rediscovery of a "truth" that
had never been lost). This was probably because the consequence of
SWR is so dramatic in the 100s of KW, when it occurs in the locality
of the workbench in a system as small as the span of your arms. Even
the Old Wives notice it if they, in error, try to microwave a product
wrapped in a crumpled foil such as butter is wrapped. Their startled
reaction evokes an immediate response, just as my post caused your
knee to jerk reflexively beneath your apron.

73's
Richard Clark, KB7QHC

Rich, you sure have an extensive vocabulary.

But try as I can, I can't make any sense out of your long message
about what can only be a trivial matter of your chosen ideas of
gamesmanship.

Kaput! I give up.
----
Yours, Punchinello, G4FGQ.

On Sat, 24 Sep 2005 18:07:19 +0000 (UTC), "Reg Edwards"
wrote:

But try as I can, I can't make any sense out of your long message

Ah Reggie,

As Dr. Johnson would paraphrase himself "claims of illiteracy is the
last refuge of the troll." [Not to deny that you are in plenty of
company - but you would shrug off that association.]

This is notable in that you assert:
about what can only be a trivial matter
which, of course, means you understood enough not to be able to deny
Lord Kelvinator harrumphing at your feigned attitude. It is an ill
fitted cloak.

of your chosen ideas of gamesmanship.

This is the truly amusing part, you deliberately raised two topics
(nothing had to be said about SWR meters, certainly - that injection
is your trademark invitation), and you had two respondents answering
to each of them. Even the sewer rats of Rio could see that you
considered the more interesting topic as the one that you have now
three times pursued. Such are the games being played, bucko! ;-)

C'mon, if I hadn't responded you would have been sorely disappointed
and would have had to sneer at David as an american suck-up trying to
soothe an olde codger. You need a lightning rod to keep your current
flowing and your response is the thanks I get.

You're welcome, Old Son!

73's
Richard Clark, KB7QHC

Reg Edwards wrote:

Makes a change from so-called SWR meters.

Ah Reggie!

Hardly, SWR was the second most considered technical hurdle in the
development of RADAR.

73's
Richard Clark, KB7QHC

=================================

Ah Rich!, Yet again you deliberately distort my meaning in your
amusing game of 0ne-Upmanship.

For the benefit of lurkers, there's a great difference between meters
which purport to measure SWR at HF, but do no such thing and tell
lies, and probes inserted in waveguides at 3 GHz which tell the truth.
----
Reg.

Sorry, I don't see any difference between making voltage measurements
with a directional coupler and calculating SWR through meter calibration
and making voltage measurements on a slotted line and calculating SWR
with a calculator or pencil and paper.

Best I can tell is you are saying there is no such thing as a SWR meter.

That's like saying there is no such thing as an airspeed meter in an
airplane; the meter really measures air impact pressure.

If that is your point, so what?

--
Jim Pennino

Remove .spam.sux to reply.

Jim,

To measure SWR on the line it is necessary to place the SWR meter at
the antenna end of the line. Even then it gives the correct answer
only when the line impedance is 50 ohms.

But the SWR meter is always placed immediately adjacent to the
transmitter. Whatever the meter indicates it is not SWR because there
is no line on which to measure it. The meter is telling lies.

The meter indicates only whether or not the transmitter is loaded with
a resistance of 50 ohms. Which is ALL you want to know. It tells you
nothing more and nothing less.

This is, of course, a very valuable function of the instrument. But
it is NOT behaving as an SWR meter. Its name should be changed to
Transmitter Loading Indicator (TLI).

To use the name "SWR meter" and to imagine it is actually measuring an
SWR is seriously misleading and is a source of confusion about what is
really going on.

It is why there are perpetual arguments and misunderstandings about
SWR, tuners and related matters on this newsgroup and in every other
place.

Change the name to TLI, which is what it really does. Novices will not
be lead astray, clear thinking will prevail, false ideas will not take
root to remain embedded for the remainder of one's radio career.

Air pressure indicators instead of airspeedometers are OK because air
pressure actually exists.

SWR meters are NOT OK because there is no line for SWR to exist on.
(At least not where the meter is imagined or supposed to measure it.)

Makes a change from cavity magnetrons.
----
Reg.

On Sun, 25 Sep 2005 03:44:00 +0000 (UTC), "Reg Edwards"
wrote:

Ah, Reggie, and Richie----

You two ought to go on the road together--your humor beats Bob Hope's hands
down. You'd have em laughing their guts out in the aisles!

Walt, W2DU

Reg Edwards wrote:
Jim,

To measure SWR on the line it is necessary to place the SWR meter at
the antenna end of the line. Even then it gives the correct answer
only when the line impedance is 50 ohms.

Well, duh.

Anyone that doesn't know that SWR is with reference to a stated
impedance or that SWR is influenced by the characteristics of a
real transmission line just isn't paying attention.

But the SWR meter is always placed immediately adjacent to the
transmitter. Whatever the meter indicates it is not SWR because there
is no line on which to measure it. The meter is telling lies.

Errr, no, the meter is telling what it sees at the point of measurement.

If the measurer is so opaque that he/she doesn't take line influences
into account, it is hardly the fault of the measuring instrument that
what is reported is not the SWR of the antenna at the specified
impedance.

The meter indicates only whether or not the transmitter is loaded with
a resistance of 50 ohms. Which is ALL you want to know. It tells you
nothing more and nothing less.

Basically true given the stated conditions, and all that is probably
of interest for the average ham.

This is, of course, a very valuable function of the instrument. But
it is NOT behaving as an SWR meter. Its name should be changed to
Transmitter Loading Indicator (TLI).

Uttern nonsense; the instrument is still behaving as a SWR meter but
the user is not applying it per spec and not correcting measurement
error caused by line position.

By this logic we have a lot of names to change. For starters:

PAM has to change the name of their cooking spray to: Teenage looser
get high in a can.

Screwdriver manufacturers have to change the name of their product
to: General prying instrument and paint can lid removal tool.

You may add others.

To use the name "SWR meter" and to imagine it is actually measuring an
SWR is seriously misleading and is a source of confusion about what is
really going on.

Nonsense, the meter is always measuring SWR but the user is obviously
not measuring the SWR that would be seen at the end of the line.

You can't fault the instrument for it's misuse by the ignorant.

What would you call a low impedance voltmeter used by some nimrod
to measure voltage in a high impedance circuit?

It is why there are perpetual arguments and misunderstandings about
SWR, tuners and related matters on this newsgroup and in every other
place.

That is probably true since most people are opaque as to what goes
on on a real transmission line, but not everyone is.

Change the name to TLI, which is what it really does. Novices will not
be lead astray, clear thinking will prevail, false ideas will not take
root to remain embedded for the remainder of one's radio career.

Clear thinking would demand that the influences of a real line on the
observered SWR at an arbitrary point be explained.

Air pressure indicators instead of airspeedometers are OK because air
pressure actually exists.

Non sequitur; SWR actually exists. Getting an accurate measurment is
another issue and a matter of education.

SWR meters are NOT OK because there is no line for SWR to exist on.
(At least not where the meter is imagined or supposed to measure it.)

Nonsense.

Makes a change from cavity magnetrons.

More nonsense and not even a sentence.

About the only difference between microwave and HF is that it is a lot
easier to build a line, i.e. waveguide, that approximates a theoretical
ideal lossless transmission line for reasonable distances at microwave
than it is to build lossless coax as commonly used at HF.

All the theory remains the same.

Personally, I have never had any problem with understanding what it is
that a SWR meter displays.

----
Reg.



--
Jim Pennino

Remove .spam.sux to reply.