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Paul Hovnanian P.E.
Guest
Wed Jan 18, 2012 7:14 pm
Here's a question for all you old-timers.
I've been reading a few articles about the WWII vintage proximity (VT) fuse.
Some describe it as using the change in radiation resistance caused by the
proximity of a conductive object. Others say it worked on based on the
Doppler effect.
My vote is for radiation resistance, but I've only (briefly) examined a
poorly documented schematic of one version.
So, which is it?
--
Paul Hovnanian mailto:Paul_at_Hovnanian.com
------------------------------------------------------------------
A noble spirit embiggens the smallest man.
Ian Field
Guest
Wed Jan 18, 2012 7:44 pm
"Paul Hovnanian P.E." <paul_at_hovnanian.com> wrote in message
news:5MOdnesnDr6_kYrSnZ2dnUVZ_t-dnZ2d_at_posted.isomediainc...
Quote:
Here's a question for all you old-timers.
I've been reading a few articles about the WWII vintage proximity (VT)
fuse.
Some describe it as using the change in radiation resistance caused by the
proximity of a conductive object. Others say it worked on based on the
Doppler effect.
My vote is for radiation resistance, but I've only (briefly) examined a
poorly documented schematic of one version.
This topic came up on ABSE a few years ago when I scrounged a set of
schematics for proximity fuze.
AIUI the most common type uses constructive interference from a wave
reflected back by the target.
Usually this crosses a threshold to trigger a subminature thyratron.
Tim Wescott
Guest
Wed Jan 18, 2012 7:47 pm
On Wed, 18 Jan 2012 10:14:37 -0800, Paul Hovnanian P.E. wrote:
Quote:
Here's a question for all you old-timers.
I've been reading a few articles about the WWII vintage proximity (VT)
fuse. Some describe it as using the change in radiation resistance
caused by the proximity of a conductive object. Others say it worked on
based on the Doppler effect.
My vote is for radiation resistance, but I've only (briefly) examined a
poorly documented schematic of one version.
So, which is it?
My understanding is that it is the former, at least for the commonly used
fuses. They basically built a directional metal detector that depended
on the rotation of the missile to provide and AC component to the
detection, then they looked for that wobble in the oscillator bias.
Certainly the detailed descriptions that I've read (there was one in the
IEEE Spectrum several years ago) were consistent with the "metal
detector" idea, and had schematics that matched.
There probably _were_ fuses that were designed to use Doppler, but I
think the ones that actually worked in WWII didn't. Instead, I suspect
that the "Doppler" effect was being cited by journalists who either
didn't know what the heck the real "Doppler effect" is (and think that
_any_ change in the signal due to motion must be "Doppler"), or were
confused by later, more sophisticated fuses, or both.
--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?
Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com
Jim Yanik
Guest
Wed Jan 18, 2012 8:15 pm
"Ian Field" <gangprobing.alien_at_ntlworld.com> wrote in
news:1qERq.1406$vm5.503_at_newsfe03.ams2:
Quote:
"Paul Hovnanian P.E." <paul_at_hovnanian.com> wrote in message
news:5MOdnesnDr6_kYrSnZ2dnUVZ_t-dnZ2d_at_posted.isomediainc...
Here's a question for all you old-timers.
I've been reading a few articles about the WWII vintage proximity
(VT) fuse.
Some describe it as using the change in radiation resistance caused
by the proximity of a conductive object. Others say it worked on
based on the Doppler effect.
My vote is for radiation resistance, but I've only (briefly) examined
a poorly documented schematic of one version.
This topic came up on ABSE a few years ago when I scrounged a set of
schematics for proximity fuze.
AIUI the most common type uses constructive interference from a wave
reflected back by the target.
Usually this crosses a threshold to trigger a subminature thyratron.
Wiki has a nice article on VT fuses,but Wiki is off-line today.
--
Jim Yanik
jyanik
at
localnet
dot com
John Larkin
Guest
Wed Jan 18, 2012 8:59 pm
On Wed, 18 Jan 2012 10:14:37 -0800, "Paul Hovnanian P.E."
<paul_at_hovnanian.com> wrote:
Quote:
Here's a question for all you old-timers.
I've been reading a few articles about the WWII vintage proximity (VT) fuse.
Some describe it as using the change in radiation resistance caused by the
proximity of a conductive object. Others say it worked on based on the
Doppler effect.
My vote is for radiation resistance, but I've only (briefly) examined a
poorly documented schematic of one version.
So, which is it?
The signal detected is definitely the doppler frequency.
Some schematics, about midway down:
http://johnlarkin.yolasite.com/pics.php
John
John S
Guest
Wed Jan 18, 2012 9:31 pm
On 1/18/2012 1:59 PM, John Larkin wrote:
Quote:
On Wed, 18 Jan 2012 10:14:37 -0800, "Paul Hovnanian P.E."
paul_at_hovnanian.com> wrote:
Here's a question for all you old-timers.
I've been reading a few articles about the WWII vintage proximity (VT) fuse.
Some describe it as using the change in radiation resistance caused by the
proximity of a conductive object. Others say it worked on based on the
Doppler effect.
My vote is for radiation resistance, but I've only (briefly) examined a
poorly documented schematic of one version.
So, which is it?
The signal detected is definitely the doppler frequency.
Some schematics, about midway down:
http://johnlarkin.yolasite.com/pics.php
John
Not doppler -- proximity. So sez your schematic.
Tom Del Rosso
Guest
Wed Jan 18, 2012 10:15 pm
Jim Yanik wrote:
Quote:
Wiki has a nice article on VT fuses,but Wiki is off-line today.
Disable javascript or press the escape key as soon as the page loads, to
stop it from redirecting.
--
Reply in group, but if emailing add one more
zero, and remove the last word.
John Larkin
Guest
Wed Jan 18, 2012 10:30 pm
On Wed, 18 Jan 2012 14:31:07 -0600, John S <Sophi.2_at_invalid.org>
wrote:
Quote:
On 1/18/2012 1:59 PM, John Larkin wrote:
On Wed, 18 Jan 2012 10:14:37 -0800, "Paul Hovnanian P.E."
paul_at_hovnanian.com> wrote:
Here's a question for all you old-timers.
I've been reading a few articles about the WWII vintage proximity (VT) fuse.
Some describe it as using the change in radiation resistance caused by the
proximity of a conductive object. Others say it worked on based on the
Doppler effect.
My vote is for radiation resistance, but I've only (briefly) examined a
poorly documented schematic of one version.
So, which is it?
The signal detected is definitely the doppler frequency.
Some schematics, about midway down:
http://johnlarkin.yolasite.com/pics.php
John
Not doppler -- proximity. So sez your schematic.
"Proximity" means "near." The signal that fires the thyratron is
mathematically the doppler frequency. In as much as the shells
detonated several wavelengths (up to 100 feet stated) away from an
airplane or the ground, it's far-field RF, not some capacitive thing.
http://en.wikipedia.org/wiki/Proximity_fuze#Radio_frequency_sensing
John
John S
Guest
Wed Jan 18, 2012 11:18 pm
On 1/18/2012 3:30 PM, John Larkin wrote:
Quote:
On Wed, 18 Jan 2012 14:31:07 -0600, John S<Sophi.2_at_invalid.org
wrote:
On 1/18/2012 1:59 PM, John Larkin wrote:
On Wed, 18 Jan 2012 10:14:37 -0800, "Paul Hovnanian P.E."
paul_at_hovnanian.com> wrote:
Here's a question for all you old-timers.
I've been reading a few articles about the WWII vintage proximity (VT) fuse.
Some describe it as using the change in radiation resistance caused by the
proximity of a conductive object. Others say it worked on based on the
Doppler effect.
My vote is for radiation resistance, but I've only (briefly) examined a
poorly documented schematic of one version.
So, which is it?
The signal detected is definitely the doppler frequency.
Some schematics, about midway down:
http://johnlarkin.yolasite.com/pics.php
John
Not doppler -- proximity. So sez your schematic.
"Proximity" means "near." The signal that fires the thyratron is
mathematically the doppler frequency. In as much as the shells
detonated several wavelengths (up to 100 feet stated) away from an
airplane or the ground, it's far-field RF, not some capacitive thing.
http://en.wikipedia.org/wiki/Proximity_fuze#Radio_frequency_sensing
John
It is pointless to argue with you, John, because you are as tenacious as
a booger when it comes to "sticking" to your point even if wrong.
TTman
Guest
Wed Jan 18, 2012 11:31 pm
"John Larkin" <jjlarkin_at_highNOTlandTHIStechnologyPART.com> wrote in message
news:sudeh7tq38305hh3hnviq5s9hvmnol8rvo_at_4ax.com...
Quote:
On Wed, 18 Jan 2012 14:31:07 -0600, John S <Sophi.2_at_invalid.org
wrote:
On 1/18/2012 1:59 PM, John Larkin wrote:
On Wed, 18 Jan 2012 10:14:37 -0800, "Paul Hovnanian P.E."
paul_at_hovnanian.com> wrote:
Here's a question for all you old-timers.
I've been reading a few articles about the WWII vintage proximity (VT)
fuse.
Some describe it as using the change in radiation resistance caused by
the
proximity of a conductive object. Others say it worked on based on the
Doppler effect.
My vote is for radiation resistance, but I've only (briefly) examined a
poorly documented schematic of one version.
So, which is it?
The signal detected is definitely the doppler frequency.
Some schematics, about midway down:
http://johnlarkin.yolasite.com/pics.php
John
Not doppler -- proximity. So sez your schematic.
"Proximity" means "near." The signal that fires the thyratron is
mathematically the doppler frequency. In as much as the shells
detonated several wavelengths (up to 100 feet stated) away from an
airplane or the ground, it's far-field RF, not some capacitive thing.
http://en.wikipedia.org/wiki/Proximity_fuze#Radio_frequency_sensing
John
As I understood it, an RF wave was sent out and the reflection phase was
detcted. The phase changed as the target got ever closer, and an increasing
low frequency signal was generated by the changing phase.It was this LF that
detonated the device by way of comparison to a preset frequency.
Doppler or not, who cares.... the subject is very interesting.
John Larkin
Guest
Wed Jan 18, 2012 11:46 pm
On Wed, 18 Jan 2012 16:18:05 -0600, John S <Sophi.2_at_invalid.org>
wrote:
Quote:
On 1/18/2012 3:30 PM, John Larkin wrote:
On Wed, 18 Jan 2012 14:31:07 -0600, John S<Sophi.2_at_invalid.org
wrote:
On 1/18/2012 1:59 PM, John Larkin wrote:
On Wed, 18 Jan 2012 10:14:37 -0800, "Paul Hovnanian P.E."
paul_at_hovnanian.com> wrote:
Here's a question for all you old-timers.
I've been reading a few articles about the WWII vintage proximity (VT) fuse.
Some describe it as using the change in radiation resistance caused by the
proximity of a conductive object. Others say it worked on based on the
Doppler effect.
My vote is for radiation resistance, but I've only (briefly) examined a
poorly documented schematic of one version.
So, which is it?
The signal detected is definitely the doppler frequency.
Some schematics, about midway down:
http://johnlarkin.yolasite.com/pics.php
John
Not doppler -- proximity. So sez your schematic.
"Proximity" means "near." The signal that fires the thyratron is
mathematically the doppler frequency. In as much as the shells
detonated several wavelengths (up to 100 feet stated) away from an
airplane or the ground, it's far-field RF, not some capacitive thing.
http://en.wikipedia.org/wiki/Proximity_fuze#Radio_frequency_sensing
John
It is pointless to argue with you, John, because you are as tenacious as
a booger when it comes to "sticking" to your point even if wrong.
Well, if "proximity" is a measurable electrical effect, what is it?
John
Phil Allison
Guest
Thu Jan 19, 2012 1:14 am
"Paul Hovnanian P.E."
Quote:
Here's a question for all you old-timers.
I've been reading a few articles about the WWII vintage proximity (VT)
fuse.
Some describe it as using the change in radiation resistance caused by the
proximity of a conductive object. Others say it worked on based on the
Doppler effect.
My vote is for radiation resistance, but I've only (briefly) examined a
poorly documented schematic of one version.
So, which is it?
** A variety of VT fuses were developed during WW2 by the allies for
different jobs.
The first and main types were for fuses in AA shells and these relied on the
Doppler effect.
The basic idea stems from the fact that an AA shell that misses its target
has *zero relative speed* with that target at the point of closest approach.
So when the Doppler shift frequency drops to near zero it fires.
Fuses fitted to mortar shells detect the proximity of the ground while in a
steady vertical descent so variation Doppler shift cannot be used.
.... Phil
Paul Hovnanian P.E.
Guest
Thu Jan 19, 2012 1:18 am
TTman wrote:
Quote:
"John Larkin" <jjlarkin_at_highNOTlandTHIStechnologyPART.com> wrote in
message news:sudeh7tq38305hh3hnviq5s9hvmnol8rvo_at_4ax.com...
On Wed, 18 Jan 2012 14:31:07 -0600, John S <Sophi.2_at_invalid.org
wrote:
On 1/18/2012 1:59 PM, John Larkin wrote:
On Wed, 18 Jan 2012 10:14:37 -0800, "Paul Hovnanian P.E."
paul_at_hovnanian.com> wrote:
Here's a question for all you old-timers.
I've been reading a few articles about the WWII vintage proximity (VT)
fuse.
Some describe it as using the change in radiation resistance caused by
the
proximity of a conductive object. Others say it worked on based on the
Doppler effect.
My vote is for radiation resistance, but I've only (briefly) examined
a poorly documented schematic of one version.
So, which is it?
The signal detected is definitely the doppler frequency.
Some schematics, about midway down:
http://johnlarkin.yolasite.com/pics.php
John
Not doppler -- proximity. So sez your schematic.
"Proximity" means "near." The signal that fires the thyratron is
mathematically the doppler frequency. In as much as the shells
detonated several wavelengths (up to 100 feet stated) away from an
airplane or the ground, it's far-field RF, not some capacitive thing.
http://en.wikipedia.org/wiki/Proximity_fuze#Radio_frequency_sensing
John
As I understood it, an RF wave was sent out and the reflection phase was
detcted. The phase changed as the target got ever closer, and an
increasing low frequency signal was generated by the changing phase.It was
this LF that detonated the device by way of comparison to a preset
frequency. Doppler or not, who cares.... the subject is very interesting.
It is detecting the amplitude of the frequency difference between the signal
and Doppler shifted reflected wave. The range of the device indicates that
it operates in the far field (more than a couple of wavelengths by the
classic definition of far field). But the classic definition of far field
is where the target's absorption or reflection of the signal has no effect
on the transmitter. This is clearly not the case with the VT fuse.
True Doppler radar (weather radar, for example) doesn't look at the radiated
power change. It simply compares the generated and detected frequencies. In
fact, in some forms of radar, transmitted the pulse (or chirp) is turned
off by the time the return signal arrives (so as not to swamp the receive
stage).
--
Paul Hovnanian mailto:Paul_at_Hovnanian.com
------------------------------------------------------------------
If Mama Cass had just split that ham sandwich with Karen Carpenter,
they'd both be alive today.
P E Schoen
Guest
Thu Jan 19, 2012 1:26 am
"Tom Del Rosso" wrote in message news:jf7cr1$ouq$1_at_dont-email.me...
Quote:
Disable javascript or press the escape key as soon as the page
loads, to stop it from redirecting.
The information is still there, if you look at the HTML source. The ESC key
did not work for me. But I copy/pasted the body of the HTML into a blank
document, and added the following so the images would show up:
<head>
<BASE href="http://en.wikipedia.com/">
</head>
Works a charm.
Paul
John Larkin
Guest
Thu Jan 19, 2012 1:28 am
On Wed, 18 Jan 2012 16:18:34 -0800, "Paul Hovnanian P.E."
<paul_at_hovnanian.com> wrote:
Quote:
TTman wrote:
"John Larkin" <jjlarkin_at_highNOTlandTHIStechnologyPART.com> wrote in
message news:sudeh7tq38305hh3hnviq5s9hvmnol8rvo_at_4ax.com...
On Wed, 18 Jan 2012 14:31:07 -0600, John S <Sophi.2_at_invalid.org
wrote:
On 1/18/2012 1:59 PM, John Larkin wrote:
On Wed, 18 Jan 2012 10:14:37 -0800, "Paul Hovnanian P.E."
paul_at_hovnanian.com> wrote:
Here's a question for all you old-timers.
I've been reading a few articles about the WWII vintage proximity (VT)
fuse.
Some describe it as using the change in radiation resistance caused by
the
proximity of a conductive object. Others say it worked on based on the
Doppler effect.
My vote is for radiation resistance, but I've only (briefly) examined
a poorly documented schematic of one version.
So, which is it?
The signal detected is definitely the doppler frequency.
Some schematics, about midway down:
http://johnlarkin.yolasite.com/pics.php
John
Not doppler -- proximity. So sez your schematic.
"Proximity" means "near." The signal that fires the thyratron is
mathematically the doppler frequency. In as much as the shells
detonated several wavelengths (up to 100 feet stated) away from an
airplane or the ground, it's far-field RF, not some capacitive thing.
http://en.wikipedia.org/wiki/Proximity_fuze#Radio_frequency_sensing
John
As I understood it, an RF wave was sent out and the reflection phase was
detcted. The phase changed as the target got ever closer, and an
increasing low frequency signal was generated by the changing phase.It was
this LF that detonated the device by way of comparison to a preset
frequency. Doppler or not, who cares.... the subject is very interesting.
It is detecting the amplitude of the frequency difference between the signal
and Doppler shifted reflected wave. The range of the device indicates that
it operates in the far field (more than a couple of wavelengths by the
classic definition of far field). But the classic definition of far field
is where the target's absorption or reflection of the signal has no effect
on the transmitter. This is clearly not the case with the VT fuse.
They call the first tube a "reaction detector." It's just an RF
oscillator/transmitter that acts as its own receive detector, sort of
like the oscillator/mixer in the front end of an old AM radio.
There's an active filter gain stage downstream of the
oscillator/detector, then the squib thyratron. Pretty impressive for
three low-transconductance gadgets.
John
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