A-6 Intruder, Any Weather, Any Time.... (1 Viewer)

Ad: This forum contains affiliate links to products on Amazon and eBay. More information in Terms and rules

That's why low pulse-repetition rates are better for long range?


For a simple, nonencoded pulse, search they are generally better. But like everything we have talked about we are only talking a simple design. By getting more complex you can get the benefits of the higher PRFs while still getting long ranges.



Because they send more pulses and ping the target more?


Yes, a higher PRF increases the average power of a return from a given target radar cross section at a given range. This means you can either track smaller targets or you are more sure to get a track on larger targets.



How does that occur?


Instead of taking a page to try and explain it how about I point you at a page from that web site that fubar57 linked.

Radar Basics



A staggered system would be like slow, fast-fast-fast, slow, fast-fast-fast?


I am talking about PRI (Pulse Repetition Interval, the reciprocal of PRF) or PRF staggers. These are the individual pulses the radar sends and their timing, pulse to pulse.


An example would be a simple, no stagger, pulsed radar sending a pulse every 2500 microseconds. A pulse happens, then 2500 usec later another pulse, then 2500 usec later another, etc. This is referred to as having a fixed PRI of 2500 usec.


A staggered system might do this: make a pulse, 2500 usec later make another pulse, 2250 usec later make a pulse, 2500 usec later another, 2250 usec later another. This 2500 / 2250 / 2500 / 2250 cycle repeats. This is called a two position 2250 / 2500 usec stagger.


And you can have multi position staggers.



What's doppler ambiguity?


fubar57's page covered that.



Because it would be overly complicated and cost an absurd amount of money to build?


Partially. Also because while it is doing one thing well it will not be able to do other things well. This is why militaries tend to have multiple radars in a system, not just one really expensive radar. While acqs are acquiring shooters can be shooting, and neither has to degrade itself in performance to do the other task.



So if there were slow speed targets you'd want to be switching routinely back and forth?


Or have the radar do it automatically as part of its normal functions.


Which means the beam goes back & forth real fast and allows you to cover some space, particularly if the computer can store some data?


Yes


T!
 
Token said:
For a simple, nonencoded pulse, search they are generally better.
Encoded means that it can determine which pulse was sent at what time?
Yes, a higher PRF increases the average power of a return from a given target radar cross section at a given range. This means you can either track smaller targets or you are more sure to get a track on larger targets.
Understood
Instead of taking a page to try and explain it how about I point you at a page from that web site that fubar57 linked.

Radar Basics
Ok
I am talking about PRI (Pulse Repetition Interval, the reciprocal of PRF) or PRF staggers. These are the individual pulses the radar sends and their timing, pulse to pulse.
Understood
A staggered system might do this: make a pulse, 2500 usec later make another pulse, 2250 usec later make a pulse, 2500 usec later another, 2250 usec later another. This 2500 / 2250 / 2500 / 2250 cycle repeats. This is called a two position 2250 / 2500 usec stagger.
Okay
Or have the radar do it automatically as part of its normal functions.
Understood
Okay
 
Fascinating for me how closely RADAR, in which I am a layman, follows ultrasonics which was my profession for many years. Token, the problem with ultrasonics and radiography is that they take a view from one angle, but used together they are complimentary and "almost" guarantee finding defects*. Using ultrasonics alone you must maximise the different angles and approaches to give a good result. In radar are systems linked to simultaneously compare results?

Ultrasonics generally uses multiples of 6dB because -6dB is a 50% reduction in signal on the screen (oscilloscope) any reason why RADAR uses 3dB

* I use defects as the commonly known word, actually ultrasonics just detects discontinuities, the specification and relevant code decide if it is in fact a "defect".

Zipper, you have a strange way to learn, asking the most detailed and involved questions in a way that only allows one word answers. Much of the theory everyone knows but do not realise it. Low frequency waves travel further, that is why fog horns have a low note. High frequencies attenuate and reflect more readily which is why a police siren in a built up area seems to come from everywhere. There is a limit to a waves reflection, a sea wave smashing a sea wall will send a wave back, it will pass a pole stuck in the beach with almost no ripples backwards. In ultrasonics the maximum detectable defect is one half of the wavelength used. There must be a similar ratio in RADAR because high frequency (centimetric) RADAR could detect a submarine conning tower whereas the lower frequency systems could only find a fully surfaced submarine.
 
Last edited:
Zipper, you have a strange way to learn, asking the most detailed and involved questions in a way that only allows one word answers.
Is that bad?
Much of the theory everyone knows but do not realise it. Low frequency waves travel further, that is why fog horns have a low note. High frequencies attenuate and reflect more readily which is why a police siren in a built up area seems to come from everywhere.
Good point...
There is a limit to a waves reflection, a sea wave smashing a sea wall will send a wave back, it will pass a pole stuck in the beach with almost no ripples backwards. In ultrasonics the maximum detectable defect is one half of the wavelength used. There must be a similar ratio in RADAR because high frequency (centimetric) RADAR could detect a submarine conning tower whereas the lower frequency systems could only find a fully surfaced submarine.
Hmmm...
Fascinating for me how closely RADAR, in which I am a layman, follows ultrasonics which was my profession for many years.
Makes sense, in both cases they're both using the transmission of waves which bounce back and absorb to varying degrees.
Token, the problem with ultrasonics and radiography is that they take a view from one angle, but used together they are complimentary and "almost" guarantee finding defects*. Using ultrasonics alone you must maximise the different angles and approaches to give a good result. In radar are systems linked to simultaneously compare results?

Ultrasonics generally uses multiples of 6dB because -6dB is a 50% reduction in signal on the screen (oscilloscope) any reason why RADAR uses 3dB

* I use defects as the commonly known word, actually ultrasonics just detects discontinuities, the specification and relevant code decide if it is in fact a "defect".
Didn't know that the term was called a defect
 
Last edited:
N
Is that bad?
Yes because knowledge is a pyramid you need a broad base to reach a significant height, delving into advanced electronics, filters and radio wave transmission before even mastering the basics is impossible. In physics you usually trade a positive for a negative, having a one word answer that gives the positive does not tell you the negative you just lost.
Good point...
I had a good teacher, C.J. Abrahams pioneer of the 20dB drop sizing technique in ultrasonic testing.
Ultrasonic Examination of Circumferential Butt Welds in Pressure Piping ~ Paperback ~ C.J. Abrahams

Hmmm..
What does Hmmmm. mean? The first part is a fact anyone that has stood on a beach can verify and the second is a fact any reader of anti submarine warfare knows. Your dicing of posts means my post makes no sense and I am not the first person to say this, neither is this the first time I myself have said it.


Makes sense, in both cases they're both using the transmission of waves which bounce back and absorb to varying degrees.
They both use waves and waves share properties but they are also different. Ultrasonic waves can be shear waves, compression waves, Rayleigh or Lamb waves. In certain circumstances they can change from one mode of propagation to another and you need to know how to spot it happening. RADAR also has similar effects at low altitude, everyone knows long wave radio hugs the earth at night, it is how I listened to Radio Luxembourg in the 1970s
4 types of ultrasonic waves


Didn't know that!
Yes you did, you just didn't think about it. A photograph is a different type of test, in the visual range of the spectrum but also in two not three dimensions. Having two eyes instead of just one doesn't double our capability in sight it multiplies it by many thousands of percent.


Now, slice and dice my posts again and I will put you on ignore, I am not spending any more time cutting and pasting to make sense of your posts, and anyone reading this must go back to the previous post to make sense, it is a pain in the butt.
 
I put him on ignore long ago but then I missed all the intelligent posts so now I skim over the trash to get to the good stuff
A conversation here should be some sort of resource, there are some real experts here, I am not one, but I do know what I know on some subjects. Zipper turns every discussion into gibberish no one can follow.
 
Now, slice and dice my posts again and I will put you on ignore, I am not spending any more time cutting and pasting to make sense of your posts, and anyone reading this must go back to the previous post to make sense, it is a pain in the butt.
I didn't intend to make the post uninteligeable...
 
pbehn said:
Yes because knowledge is a pyramid you need a broad base to reach a significant height, delving into advanced electronics, filters and radio wave transmission before even mastering the basics is impossible. In physics you usually trade a positive for a negative, having a one word answer that gives the positive does not tell you the negative you just lost.
Token did a pretty good job and I've learned quite a lot, actually.
What does Hmmmm. mean? The first part is a fact anyone that has stood on a beach can verify and the second is a fact any reader of anti submarine warfare knows.
I found it fascinating
 
Token did a pretty good job and I've learned quite a lot, actually.
I found it fascinating
You didn't because you have not learned about attenuation or reflection, you have learned just enough to use some words and quote out of context.
 
to quote your post gives this

Is that bad?
Good point...
Hmmm...
Makes sense, in both cases they're both using the transmission of waves which bounce back and absorb to varying degrees.
Didn't know that the term was called a defect
I am not sorting this jibberish out any more especially since you are editing it.
 
I said this before and I'll say it again:
Zipper, come back when you've done your homework! You need to learn a little on your own so you can carry on an informed intelligent discussion instead of this incessant "picking everybody's brains". We know you can do it; you did it on SAC history and bombing tactics, and there you actually talked sense. Instead of collecting disconnected factoids, try to build a coherent body of knowledge about whatever topic you're pursuing at the moment. This means studying multiple sources, assessing the reliability of each, reconciling apparent inconsistencies in the data, and coming up with an informed interpretation that you can communicate clearly to others. For those of limited experience, that can seem daunting, but many here, through education, age and experience, make it seem easy. Good luck!
Cheers,
Wes
 
You didn't because you have not learned about attenuation or reflection, you have learned just enough to use some words and quote out of context.
I did compared to what I knew before: As for making jibberish, I was under the impression your objection was that I quoted out of sequence, not that I responded line by line.

XBe02Drvr said:
Zipper, come back when you've done your homework! You need to learn a little on your own so you can carry on an informed intelligent discussion instead of this incessant "picking everybody's brains". We know you can do it; you did it on SAC history and bombing tactics, and there you actually talked sense. Instead of collecting disconnected factoids, try to build a coherent body of knowledge about whatever topic you're pursuing at the moment.
I'll read the stuff Fubar57 wrote and the other links, but I'm not entirely sure where else I'd find much, unless you would prefer I just sent Token some PM's?

BTW: As for the limited experience, that is one reason why I would be inclined to pick the brains of those more knowledgeable than myself.
 
I did compared to what I knew before: As for making jibberish, I was under the impression your objection was that I quoted out of sequence, not that I responded line by line.

I'll read the stuff Fubar57 wrote and the other links, but I'm not entirely sure where else I'd find much, unless you would prefer I just sent Token some PM's?

BTW: As for the limited experience, that is one reason why I would be inclined to pick the brains of those more knowledgeable than myself.
GOOD GOD MAN!! There are people on here who've trained and studied and worked a lifetime to acquire their knowledge and experience. So far they've been amazingly patient with you, but do you think they'll have the time and inclination to spoon-feed your kindergarten lessons forever? You need to put in a little effort on your own behalf. There's a world of information out there on the internet, in libraries and bookstores, and potentially on your own bookshelf. Go get it.
Cheers,
Wes
 
Zipper, I will give you a small example. Post number 33 has a schematic beam diagram. It mentions 3dB. What do you understand by 3dB? Most people see a decibel as a unit in the way pounds, kilos and feet and inches are units. It is not, it is a means to compare two values on a logarithmic scale. When people say a rock concert is 110dB they rely on the instrument being set at a base level that has no sound but where do you find that place at a rock concert. This was a problem in my youth at race meetings, the people testing the exhaust noise couldn't find anywhere to set the base level on the circuit and calibrating it off circuit meant it couldn't be switched off and the batteries died.
In fact if you find a place with absolutely no sound you start to go slightly gaga, after 10 minutes you hear your heart beating and blood flow in your ears.
Here is what wiki has to say on decibels
Decibel - Wikipedia
All modern ultrasonic sets have a "gain" (sound volume) control which appears to increase the signal strength as you increase the value, like a music system does. This is done to make it easy for the operator in fact the reverse is happening, as you increase the value on the dial you are decreasing the electronic attenuation within the system. The first sets I saw were from the 1950s and 1960s and didn't have a "gain" control they had an attenuation control which did exactly the same thing but in reverse. To increase the signal height you removed dB. RADAR systems must be the same/similar because it is fundamental physics.

Again post 33 has a schematic representation of a beam, ultrasonic beams are similar, in fact water waves are similar too. However in practice the lobes are not beautiful symmetrical curves they are raggy and irregular, with no guarantee that the centre of beam intensity actually goes in a perfectly straight line, or loses strength in accordance with inverse square laws.

To sum up, it is complicated both in theory and practice, if it wasn't complicated we could all knock up a military RADAR in the garage like a bird nesting box.
 
Last edited:
Fascinating for me how closely RADAR, in which I am a layman, follows ultrasonics which was my profession for many years. Token, the problem with ultrasonics and radiography is that they take a view from one angle, but used together they are complimentary and "almost" guarantee finding defects*. Using ultrasonics alone you must maximise the different angles and approaches to give a good result. In radar are systems linked to simultaneously compare results?


Not 100% sure I understand the question.


Are you asking if radar systems can work together, sensor fusion with each one looking at the problem from different angles and using different techniques, to enhance probability of detection?


If so the answer is yes. Different radars are better at detecting different kinds of target, high speed vs low speed, small aircraft vs large aircraft, high altitude vs low altitude, long range vs short range, etc. One radar may be able to do it all, but seldom will that radar do it (whatever aspect "it" is) as well as an optimized design for a specific task. By interleaving these capabilities as part of an Integrated Air Defense System you can leverage the strengths of the various systems to optimize detection.


Or rather are you asking if a single radar, when viewing an area from varying angles and integrating the result, will detect more detail?


If so the answer is yes, this is the basic premise of Synthetic Aperture Radar.


Ultrasonics generally uses multiples of 6dB because -6dB is a 50% reduction in signal on the screen (oscilloscope) any reason why RADAR uses 3dB


Voltage vs power.


On an oscope an amplitude change of 2x is twice the voltage. For a given impedance twice the voltage is 4 times the power, or 6 dB. P=V^2/R For example 2 Volts into a 50 Ohm load yields 0.08 Watts. 4 Volts, twice the voltage or amplitude on an oscope, into the same 50 Ohm load yields 0.32 Watts.


But twice the power is 3 dB. In the radar world, when discussing the signal, we deal with power and not voltage.



Low frequency waves travel further, that is why fog horns have a low note. High frequencies attenuate and reflect more readily which is why a police siren in a built up area seems to come from everywhere. There is a limit to a waves reflection, a sea wave smashing a sea wall will send a wave back, it will pass a pole stuck in the beach with almost no ripples backwards. In ultrasonics the maximum detectable defect is one half of the wavelength used. There must be a similar ratio in RADAR because high frequency (centimetric) RADAR could detect a submarine conning tower whereas the lower frequency systems could only find a fully surfaced submarine.


In RF you can detect very small targets by comparison to the wavelength. I started to write up a description of RCS (Radar Cross Section, the reflectivity of an item in the direction of the radar trying to detect it) in various regions, Optical, Mie, and Rayleigh, for various shapes, and realized that it cannot be simplified enough to do it justice in such a post.


Reflectivity is very shape dependent, even for small features. However it, reflectivity, does get small pretty quick when the size of the feature is less than about half a wavelength. At 0.1 wavelength you can detect it, but it is going to be a weak return that you must deal with somehow. Shape, orientation, etc, become very important.


The relatively early example you are talking about, conning tower detection of a partially submerged submarine vs a fully surfaced sub, has to do as much with the processing technology of the day as it does with wavelength vs target physical size. I assume you are talking about things like the VHF frequency ASV-1 and ASV-2 vs 3 GHz frequency ASV-3 and APS-2?


As I said above, you can detect targets that are quite small compared to wavelength, however RCS is tied to size, shape, surface material, and varies with wavelength.


Just as an example, don't take the numbers too seriously, but here are some indications of the issues with conning tower detection. Lets do a simplistic model of a Type VIIC conning tower viewed from head on.


From this view it presented a shape similar to a cylinder 11 feet tall and 6 feet wide (cylinders are easier to model than the side view of the conning tower would be). The RCS for our notional conning tower at the 175 MHz frequency of the ASV-2 would be about 29.4 dBsm. For a 3 GHz APS-2 it would be about 51.7 dBsm. The 3 GHz radar will receive a return roughly 170 times larger than the 175 Mhz radar. This is made MUCH worse by the fact the ASV-2 has a very wide, by comparison to the APS-2, beam, meaning that small target has to be detected in a very large area of clutter. So the later 3 GHz radar illuminated a smaller area (tighter beam) and had a much larger return to look for in that smaller area. The technology of the day simply did not allow detection of such a small target in the sea return. If that 29.4 dBsm target had been in blue sky it is certain the ASV-2 could have detected it.


Note that in WW II even the 3 GHz radars could not detect periscopes on the surface.


T!
 
Great post Token, I reply to one point to acknowledge, the rest takes me back to theory I learned 40 years ago and rarely used, I will think and reply further, if only to stop wasting time
Note that in WW II even the 3 GHz radars could not detect periscopes on the surface.
T!
I was struggling with the words when I wrote it to avoid confusion but didn't manage it. Submarine commanders realised they were visible to RADAR while fully surfaced, they then went to being partially submerged, just the conning tower above water. With centimetric RADAR just the conning tower could be detected.
 

Users who are viewing this thread

Back