"john jardine"

But where's the non linearity for the mixing action?.


** LOL !!

Never heard of " beats " ??

Never tuned a guitar ?

What a macaroon !!!


Way I was reading it is that the reflected energy is increasing/decreasing
the radiation resistance of the aerial ...


** Nonsense.

You simply invented that notion.


So yes, constant frequency (a little pulling close on target) and R.F.
output voltage but variable L.F. anode current, as the level-control servo
loop struggles to force a constant oscillator output.


** Servo loop ?

You on drugs ??

**** off, troll.



......... Phil

On Tue, 29 May 2007 00:32:40 +0100, "john jardine"
wrote:


"John Larkin" wrote in message
.. .
On Sun, 27 May 2007 02:53:05 +0100, "john jardine"
wrote:


"Phil Allison" wrote in message
...

"john jardine"

http://www.tubedata.org/unknown_sylv..._sylvania.html


I read those patents at the bottom of the page and am still none the
wiser
about the detection method. The patents say phasing in/out
reflections
from
the aircraft, modulate the oscillator anode current at an audio
frequency
and trigger the detonator. (ie a Doppler effect but not mentioned as
such).


** That the modulation frequency is stated to drop as the shell
approaches
a
target is a dead give away for Doppler being involved. As a shell
passes
nearby a target, the relative speed and hence Doppler frequency shift
drops
to near zero.


Would have thought current variations due to that cause would be
immeasurable.


** Then you did not do much thinking.

I spent ages. About a minute!.

1. The wavelength of the radiated energy ( circa 200MHz) is many times
smaller than the wingspan of a fighter or bomber aircraft.

Yes. I assumed an infinite metal sheet.

2. The proximity for detonating the shell with effect is roughly
comparable
with the wingspan of such aircraft.

I didn't know that. I was using something like one wavelength at 100MHz
but on reflection this is too close to be of practical use.

3. Egro - an ( all metal) aircraft will be a significant reflector of
such
radiated energy when it is within range of being damaged.

It appears from the circuit arrangement that RF modulation of less than
1%
at around 100Hz would be more than enough to cause detonation.

Yes. This is the key point I missed. Oscillator 'RF modulation' as the
working mode. The oscillator tuned circuit Q being altered at an audio
rate by variable aerial loading dependant on resonant frequency,
velocity and strength of reflection. A 3.7" AA shell seems about a 250Hz
shift, which fits nicely in the audio bandpass.


No. The oscillator runs at constant frequency and amplitude. Weak RF
reflections from the target are mixed with the transmit signal. Since
the echoes are a different frequency from the transmitted signal, a
doppler beat frequency results; it can be amplified and used to fire
the thyratron. The WWII vintage fuzes, like the ones I posted, didn't
look for a change in the doppler frequency, just its presence. By the
time they detected any echo, it was time to fire the squib.

A plane, or even the surface of the earth or water (in the case of
artillery) 30 feet away wouldn't usably affect the Q of the tuned
circuit.

John


But where's the non linearity for the mixing action?.
Way I was reading it is that the reflected energy is increasing/decreasing
the radiation resistance of the aerial as the rxed reflections phase in and
out, dependant on distance from target.
Sort of like an output load resistor is being twiddled by the rxed chirp.
Hence the tuned circuit (inclusive of aerial) dynamic resistance [Q] must
also vary in a cyclic manner.
Therefore, for constant oscillations to be maintained, (oscillator prime
directive the anode current must modulate in sympathy with the prevailing
phase and strength of reflections.
So yes, constant frequency (a little pulling close on target) and R.F.
output voltage but variable L.F. anode current, as the level-control servo
loop struggles to force a constant oscillator output.
No?.

I think an adequate model is:

The transmitter tube oscillates at constant frequency. The
doppler-shifted echo is mixed with the main carrier by the
nonlinearity of the grid transfer function, resulting in a small
audio-frequency variation in plate current, just like the
oscillator-mixer tube in a cheap superhet.

The tank Q won't be significantly affected by a weak far-field echo.

John

On Thu, 24 May 2007 20:08:49 -0400, Tom Del Rosso wrote:
"Rich Grise" wrote in message
news
On Thu, 24 May 2007 14:52:55 +0000, ian field wrote:

There was a movie about that - was it the Windtalkers?

I dunno, but it was a question on "Who Wants To Be A Millionaire" -
something like, "What language was used in WWII...". The guy used
his "phone-a-friend", and almost before he was done asking the
question, the friend blurted out the answer.

I thought that was kinda cool. :-)

When we had fixed game shows in the 50s where people could answer extremely
difficult questions (because they were fed the answers) the BBC tried to
create similar shows but couldn't find people who could answer such
questions. A BBC producer asked an NBC producer how they found such smart
people. Now I'd like to know how they find such stupid people.

They've given up on finding smart people, because they're so rare, but
the supply of stupid people seems to be infinite. )-;

Thanks,
Rich

"Rich Grise" wrote in message
news
On Thu, 24 May 2007 20:08:49 -0400, Tom Del Rosso wrote:
"Rich Grise" wrote in message
news
On Thu, 24 May 2007 14:52:55 +0000, ian field wrote:

There was a movie about that - was it the Windtalkers?

I dunno, but it was a question on "Who Wants To Be A Millionaire" -
something like, "What language was used in WWII...". The guy used
his "phone-a-friend", and almost before he was done asking the
question, the friend blurted out the answer.

I thought that was kinda cool. :-)

When we had fixed game shows in the 50s where people could answer
extremely
difficult questions (because they were fed the answers) the BBC tried to
create similar shows but couldn't find people who could answer such
questions. A BBC producer asked an NBC producer how they found such
smart
people. Now I'd like to know how they find such stupid people.

They've given up on finding smart people, because they're so rare, but
the supply of stupid people seems to be infinite. )-;

Thanks,
Rich

Is it possible that "stupid people" are better at surviving than "smart
people" ? Do you need to change your attitude? Repeat after me. "Ah don
hold much with them thar book larnins. Ah jus let mah peter tell me what to
do."

"John Larkin" wrote in
message

No. The oscillator runs at constant frequency and amplitude. Weak RF
reflections from the target are mixed with the transmit signal. Since
the echoes are a different frequency from the transmitted signal, a
doppler beat frequency results; it can be amplified and used to fire
the thyratron.

Isn't it more accurate to say that the echo has a different phase? The
frequency isn't that different because the speed is a small fraction of c.

If that's so then it isn't exactly the Doppler effect at all, but an
interference pattern - a different phenomenon.


--

Reply in group, but if emailing add another
zero, and remove the last word.

On Tue, 29 May 2007 16:10:07 -0400, "Tom Del Rosso"
wrote:

"John Larkin" wrote in
message

No. The oscillator runs at constant frequency and amplitude. Weak RF
reflections from the target are mixed with the transmit signal. Since
the echoes are a different frequency from the transmitted signal, a
doppler beat frequency results; it can be amplified and used to fire
the thyratron.

Isn't it more accurate to say that the echo has a different phase? The
frequency isn't that different because the speed is a small fraction of c.

The echo has a different phase, and the phase is constantly changing
because the shell-target distance is changing. Changing phase is
frequency. The change of frequency is a small fraction of the carrier,
as the velocity is a small fraction of c, both around 1 ppm.


If that's so then it isn't exactly the Doppler effect at all, but an
interference pattern - a different phenomenon.

Actually, it's exactly the same. The rate of change of the
interferance is the Doppler frequency.

John

"John Larkin" wrote in
message

The echo has a different phase, and the phase is constantly changing
because the shell-target distance is changing. Changing phase is
frequency. The change of frequency is a small fraction of the carrier,
as the velocity is a small fraction of c, both around 1 ppm.

Thanks John.


--

Reply in group, but if emailing add another
zero, and remove the last word.

"John Larkin" wrote in message
...
On Tue, 29 May 2007 16:10:07 -0400, "Tom Del Rosso"
wrote:

"John Larkin" wrote in
message

No. The oscillator runs at constant frequency and amplitude. Weak RF
reflections from the target are mixed with the transmit signal. Since
the echoes are a different frequency from the transmitted signal, a
doppler beat frequency results; it can be amplified and used to fire
the thyratron.

Isn't it more accurate to say that the echo has a different phase? The
frequency isn't that different because the speed is a small fraction of c.

The echo has a different phase, and the phase is constantly changing
because the shell-target distance is changing. Changing phase is
frequency. The change of frequency is a small fraction of the carrier,
as the velocity is a small fraction of c, both around 1 ppm.


If that's so then it isn't exactly the Doppler effect at all, but an
interference pattern - a different phenomenon.

Actually, it's exactly the same. The rate of change of the
interferance is the Doppler frequency.

John

Looking at the complexity around the middle tube in the T2005, presumably
this incorporates a filter network to LPF the AF signal (whether due to beat
or Doppler shift) I wondered if this stage is designed for AF regeneration
since some of the designs have gimmick or trimmer caps?

"John Larkin" wrote in
message

The echo has a different phase, and the phase is constantly changing
because the shell-target distance is changing. Changing phase is
frequency. The change of frequency is a small fraction of the carrier,
as the velocity is a small fraction of c, both around 1 ppm.

Hey, what about the effect of chaff on these things?


--

Reply in group, but if emailing add another
zero, and remove the last word.

"Tom Del Rosso"


Hey, what about the effect of chaff on these things?


** The main targets for allied AA shells with VT fuses were German V1 flying
bombs, Japanese Kamikazes and attacking torpedo bombers.

The allies were not subjected to much high level bombing in the latter part
of WW2 - they were busy carrying it out on the enemy instead. So I doubt
"chaff" (or "window" as the Poms called it ) was ever used as a decoy
against AA shells.

Nor is it likely any axis forces were aware of the VT fuse's existence or
its mode of operation since the allies were most careful that none ever fell
into their hands.

Probably it would have done nothing to fool a VT fuse anyway.



........ Phil

Tom Del Rosso wrote:
"John Larkin" wrote in
message
The echo has a different phase, and the phase is constantly changing
because the shell-target distance is changing. Changing phase is
frequency. The change of frequency is a small fraction of the carrier,
as the velocity is a small fraction of c, both around 1 ppm.

Hey, what about the effect of chaff on these things?

It's called a countermeasure. Prox fuses are one of the reasons
chaff is deployed.

"Chuck Harris"

It's called a countermeasure. Prox fuses are one of the reasons
chaff is deployed.


** Certainly not in WW2 from an aircraft.

There was a much more effective countermeasure possible - a simple sweep
frequency radio jammer.

Google it .



........ Phil

On Sat, 2 Jun 2007 17:27:03 +1000, "Phil Allison"
wrote:


"Tom Del Rosso"


Hey, what about the effect of chaff on these things?


** The main targets for allied AA shells with VT fuses were German V1 flying
bombs, Japanese Kamikazes and attacking torpedo bombers.

Prox fuzes in artillery were very effective late in the European war;
Patton gave them a lot of credit for speeding him into Germany, and
the prox fuze was instrumental in stopping The Bulge. Regular
artillery would tend to bury itself in the ground, and foxholes were a
useful defense. Prox shells could be set to detonate 30 feet above the
ground, spraying shrapnel downward. It was devastating to troops. I
have a photo in one of my books of a test, with wooden boards
representing soldiers, with every board within 30 meters penetrated or
shredded.

The prox shells was used against land forces only late in the war when
it was felt that the Germans were going to lose and didn't have time
to copy them.

John

On Sat, 02 Jun 2007 07:46:33 -0700, John Larkin wrote:

On Sat, 2 Jun 2007 17:27:03 +1000, "Phil Allison"
wrote:


"Tom Del Rosso"


Hey, what about the effect of chaff on these things?


** The main targets for allied AA shells with VT fuses were German V1 flying
bombs, Japanese Kamikazes and attacking torpedo bombers.

Prox fuzes in artillery were very effective late in the European war;
Patton gave them a lot of credit for speeding him into Germany, and
the prox fuze was instrumental in stopping The Bulge. Regular
artillery would tend to bury itself in the ground, and foxholes were a
useful defense. Prox shells could be set to detonate 30 feet above the
ground, spraying shrapnel downward. It was devastating to troops. I
have a photo in one of my books of a test, with wooden boards
representing soldiers, with every board within 30 meters penetrated or
shredded.

The prox shells was used against land forces only late in the war when
it was felt that the Germans were going to lose and didn't have time
to copy them.

You don't really need a proximity fuze in surface-to-surface artillery. A
mechanical time fuze, like the first AA fuzes, can be set to fire a few
yards above the ground if you know the elevation of the target. Both
sides used this "time fire."

On Sat, 02 Jun 2007 13:06:12 -0400, "Stephen J. Rush"
wrote:

On Sat, 02 Jun 2007 07:46:33 -0700, John Larkin wrote:

On Sat, 2 Jun 2007 17:27:03 +1000, "Phil Allison"
wrote:


"Tom Del Rosso"


Hey, what about the effect of chaff on these things?


** The main targets for allied AA shells with VT fuses were German V1 flying
bombs, Japanese Kamikazes and attacking torpedo bombers.

Prox fuzes in artillery were very effective late in the European war;
Patton gave them a lot of credit for speeding him into Germany, and
the prox fuze was instrumental in stopping The Bulge. Regular
artillery would tend to bury itself in the ground, and foxholes were a
useful defense. Prox shells could be set to detonate 30 feet above the
ground, spraying shrapnel downward. It was devastating to troops. I
have a photo in one of my books of a test, with wooden boards
representing soldiers, with every board within 30 meters penetrated or
shredded.

The prox shells was used against land forces only late in the war when
it was felt that the Germans were going to lose and didn't have time
to copy them.

You don't really need a proximity fuze in surface-to-surface artillery. A
mechanical time fuze, like the first AA fuzes, can be set to fire a few
yards above the ground if you know the elevation of the target. Both
sides used this "time fire."

The "few yards" thing doesn't compute.

Effectiveness against ground forces peaks rather sharply at a burst
height of just about 10 meters. If a shell is traveling a couple of
hundred meters per second, critical timing accuracy will be in the
milliseconds, out of seconds of flight. That just can't be done with
fixed timers, especially given changes in propellant charge, wind, and
elevation. In the Battle of the Bulge and later action, after the prox
fuses were released for land use in Europe, 10-meter high bursts were
being achieved at ranges of 15 miles, day and night. See Baldwin, pp
280-281.


John