On 31 May 2006 15:31:11 -0700, "K7ITM" wrote:

In the last paragraph you quoted, there is what I consider a mistake
that can lead to misunderstanding of how things work. It suggests that
each cavity is an oscillator. The cavities are no more oscillators
than a bottle.

Hi Tom,

I defer to the author's explanation, and the nature of writing for a
wide audience. This group would be such an example.

The author mentions, in portions not quoted, that the electron
beam/current/what-have-you streams at a grazing angle along the arc of
the inside of the plate, crossing these openings. The cavities are,
then, parallel plate loads.

It stands to reason, on the other hand, that there is only one output
from ostensibly one cavity whose fields are sharing the passing stream
of electrons that is also resonating. In fact, this operation (also
described by the author) led to understanding and development of the
Klystron tube and other traveling wave amplifiers.

73's
Richard Clark, KB7QHC

Richard,

Randall & Boot's original magnetron used to be displayed in the
London, England, Science Museum. It was all by itself in a very
large, securely locked glass case. No magnet. I don't know whether it
is still there.

It lay there, all forlorn, hardly noticed, about the same
insignificant size as a small, half-size, rusty can of baked beans.

My sentiments lie with R and B, slaving away in the laboratory at
Birmingham University while the Luftwaffer rained down bombs and
incendiaries on the city. At the time, the top-secret goings-on were
unknown to me, and I spent my time in a corrugated-iron air raid
shelter in the back garden just a few miles down the road.

A few years later, having joined the RAF as a Radar technician, I had
the pleasure of holding a production model in one hand and the magnet
in the other. At the other end of the workshop bench a parabolic dish
rotated once every two seconds. It is not true that a 50 kW peak pulse
power at 3000 Mhz sterilises one's reproductive organs. I have
fathered 5 children.

It was left to the Japanese to populate the World's kitchens with
microwave ovens. Beyond the first, no magnetron has ever been made in
the industrial city of Birmingham, England. But they don't make many
motor cars there any more either.

Reg, G4FGQ wrote:
"It was left to the Japanese to populate the World`s kitchens with
microwave ovens."

The Japanese proved adept at improving and producing high quality
technical products. Japanese didn`t market the first microwave oven.
Raytheon introduced its "Radar Range" soon after WW-2 ended. Japanese
copies were innovative, reliable, and cheap, so they won instant
acceptance worldwide.

The magnetron has been called the best import ever from Britain and I
think that comparison even included Bob Hope and Liz Taylor. At the time
of the magnetron gift to the U.S., British war production was already
bursting at the seams and the U.S. was well advanced in radar and had a
few tricks up its sleeve to improve the British gear.
I`ve noticed early British airborne radar using yagi antennas. That
seemed quaint to me.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:

At the time
of the magnetron gift to the U.S., British war production was already
bursting at the seams and the U.S. was well advanced in radar and had a
few tricks up its sleeve to improve the British gear.

All the major powers were well advanced in radar at the time. All the
ideas were already in place, and engineers everywhere were starting to
put them together. However, as Reg points out, freedom from bombing
raids is a wonderful aid to creativity.

The USA developed ways to mass-produce the magnetron, notably a method
of building up the cavity from laminations rather than needing to have a
skilled machinist mill it out from solid (and before Roy gets a word in,
they fixed the oil leaks too).

I`ve noticed early British airborne radar using yagi antennas. That
seemed quaint to me.

Those were the phased arrays for the earlier VHF radar, and consisted of
two or four two-element yagis clustered around the nose (of a
two-engined aircraft, obviously). This gave a fairly good
forward-looking capability. Both sides did much the same, and given the
relatively long wavelength, it's hard to think how better to do it.

The huge benefit of the magnetron was that it operated at much shorter
wavelengths, which frees up the antenna design and provides much better
spatial resolution - witness the downward-looking "H2S" radar which was
the magnetron's first major deployment.


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

"Ian White GM3SEK" wrote in message
...


Those were the phased arrays for the earlier VHF radar, and consisted of
two or four two-element yagis clustered around the nose (of a
two-engined aircraft, obviously). This gave a fairly good
forward-looking capability. Both sides did much the same, and given the
relatively long wavelength, it's hard to think how better to do it.

The huge benefit of the magnetron was that it operated at much shorter
wavelengths, which frees up the antenna design and provides much better
spatial resolution - witness the downward-looking "H2S" radar which was
the magnetron's first major deployment.

The VHF radars were still around into the late 1970's, maybe beyond. The US
Navy had them on carriers for air search. I think the nomenclature was
AN/SPS-29 and/or AN/SPS-37. The one I recall was in the 218 - 220 MHz and
it was hell on TV channel 13! The antenna was referred to as a bedspring
array; the rectangular framework for the dipole radiating elements resembled
a giant bedspring.

Sal M. Onella wrote:

"Ian White GM3SEK" wrote in message
...


Those were the phased arrays for the earlier VHF radar, and consisted of
two or four two-element yagis clustered around the nose (of a
two-engined aircraft, obviously). This gave a fairly good
forward-looking capability. Both sides did much the same, and given the
relatively long wavelength, it's hard to think how better to do it.

The huge benefit of the magnetron was that it operated at much shorter
wavelengths, which frees up the antenna design and provides much better
spatial resolution - witness the downward-looking "H2S" radar which was
the magnetron's first major deployment.

The VHF radars were still around into the late 1970's, maybe beyond. The US
Navy had them on carriers for air search. I think the nomenclature was
AN/SPS-29 and/or AN/SPS-37. The one I recall was in the 218 - 220 MHz and
it was hell on TV channel 13! The antenna was referred to as a bedspring
array; the rectangular framework for the dipole radiating elements resembled
a giant bedspring.


Sure, but none of those would fly very well. The discussion was really
about airborne radar, where there are tough limits on antenna size.


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

Back in the early 70's I got a pair of magetron magnets that came out
of old airborne radio set - can't remember the nomenclature - that the
USAF converted into a weather radio. They were quite large and strong,
and 'U' shaped. Someone swiped them in a move. Anybody know where I
might find a set? Google and eBay haven't turned up anything.

Ian, GM3SEK wrote:
"Sure, but none of those (bedapring antenna arrays) would fly very
well."

It`s been a long time now but I believe investigation showed the army`s
new radar (earthborne) got good echos from the approaching Japanese
arircraft on December 7, 1941, but the top brass rejected the reports in
disbelief of either the new equipment or the audacity of the Japanese
Navy. That attack changed naval warfare forever. Lot more respect for
both aircraft and radar ever since.

Best regards, Richard Harrison, KB5WZI