1944 H2D Pulsed Doppler Radar - True or Misidentified?

[GUNDAM123dx]

In the book Echoes of War: The Story of H2S Radar, there's some information about H2D radar tested in 1944. H2D is (in the book) said to be a Pulsed Doppler version of H2S series.

However WW2 magnetron could only give random coherent signal. It seems impossible for ww2 tech to achieve any kind of "all coherent" which is a basic requirement for what we nowadays call "Pulse Doppler".
Some radar devices used Doppler effect in ww2 such as Fakir and Tastlaus (German), but these were not "Pulsed Doppler"/"Pulse Doppler".
Klystrons can produce coherent signals, and there are klystron versions of H2S radar according to the book. However, according to Merrill I. Skolnik, there was not any Pulse Doppler radar in ww2 - PD was a 1970s tech. (Edited: I mean, mature application of PD was a 1970s tech.)
The author of the book Bernard Lovell was one of the key persons in H2S project so these claims in his book should hardly be wrong.
So maybe the meanings of the "Pulse Doppler" are different? (1940s, 1970s, nowadays)
TNA documents AVIA 7/2514 and AIR 20/877 are about H2D trials so there may be more details but I'm not in the UK.

 

[WATU]

Not my own area of expertise but a more knowledgeable friend said that TRE did do research with a model of H2S primarily to detect tanks. He confirmed that the magnetron signal would jump about a bit. However at short ranges with a persistent CRT display this would not disturb the observer.

 

[Zipper730]

That's a fascinating development.

 

[Token]

In the book Echoes of War: The Story of H2S Radar, there's some information about H2D radar tested in 1944. H2D is (in the book) said to be a Pulsed Doppler version of H2S series.
View attachment 676882
View attachment 676883
However WW2 magnetron could only give random coherent signal. It seems impossible for ww2 tech to achieve any kind of "all coherent" which is a basic requirement for what we nowadays call "Pulse Doppler".
Some radar devices used Doppler effect in ww2 such as Fakir and Tastlaus (German), but these were not "Pulsed Doppler"/"Pulse Doppler".
Klystrons can produce coherent signals, and there are klystron versions of H2S radar according to the book. However, according to Merrill I. Skolnik, there was not any Pulse Doppler radar in ww2 - PD was a 1970s tech.
The author of the book Bernard Lovell was one of the key persons in H2S project so these claims in his book should hardly be wrong.
So maybe the meanings of the "Pulse Doppler" are different? (1940s, 1970s, nowadays)
TNA documents AVIA 7/2514 and AIR 20/877 are about H2D trials so there may be more details but I'm not in the UK.

Below is my take on what you are seeing. Keep in mind I have very little knowledge of the H2S specifically, but this thread has piqued my curiosity, and I will endeavor to educate myself on the subject.

The book you quote was written in the late 1980's I think. By that time the term "Pulse Doppler radar" was in common use. Maybe it is a case of applying a later term to a technique that existed at an earlier time, but was not yet referenced using that same later term. I would say this technology being experimented with in WW II is very possible if there were, indeed, Klystron versions of the H2S.

From publications of the period it is pretty evident that the technology behind what we now call "Pulsed Doppler" was well enough understood before the end of the war to produce a system using that technique. I will go to my old standby, the MIT Radiation Laboratory Series, published in 1947. For those not familiar, this is a 28 volume set published immediately after WW II, documenting the state of knowledge, with regards to radar technologies, at the time of publication. In the spirit of the everlasting peace just won, things heavily classified just 18 months previously were freely published. Because, you know, we would never have a war again or anything..... And yes, at least 10 sets were delivered to the Soviet Embassy in Washington DC.

A search through these publications shows that the term "Pulse Doppler" is never used in the body of the text. However, the technique is defined without that specific name, and the name is indirectly referenced in a footnote.

The index (Volume 28) contains a reference (page 45) to "Doppler, pulsed, 20 20". This indicates the subject is covered in Volume 20, starting on page 20.

Volume 20 is "Electronic Time Measurements". Page 20, section 2.9, discusses "Pulse Systems - Externally-coherent Echo Interference". How to measure and detect moving targets on the ground, via Doppler detection of the radial velocity, is discussed in detail over the next few pages. While they do not talk about any specific hardware, from the text it is obvious that they had been doing a good bit of work in this area, using terms like "were able to detect vehicle motions of under 5 MPH" and similar. It also contains a footnote referencing another document, "Pulse Doppler with Reference to Ground Speed Indication", RL Group Report, March 30, 1944. Note the use of "Pulse Doppler" in that reference.

Volume 19 is "Waveforms" and goes into all the detail needed to do a PD radar, including the specifics of phase detection and storage.

Re Skolnik saying that there was no PD radar in WW II, and that it was a 1970's technology, can you be specific where this is said? I am pretty sure modern PD radars go at least back to the 1960's, if not the late 1950's. Most of the time I hear of the AN/DPN-53 (in the IM-99B missile) as the "first production PD airborne radar" and that goes back to the late 1950's. I have pictures from BOMARC testing in the early 1960's on my office wall. But I also know (well, have been told) that onesies and twosies PD systems predate the AN/DPN-53.

A thought. There are a couple of definitions for "Pulse Doppler". In more recent times it has generally defined a high or very high PRF radar with high range ambiguity and low Doppler ambiguity. Prior to that the definition did not include a description of the PRF rate. By a definition that includes that high or very high PRF (with high range ambiguity) caveat, it is probable that nothing we would call PD did exist in WW II, even if the basic technique was actually in use in a limited way.

T!

 

[Zipper730]

From publications of the period it is pretty evident that the technology behind what we now call "Pulsed Doppler" was well enough understood before the end of the war to produce a system using that technique.

Yeah, plus it didn't appear that they were trying to lock onto the train -- just merely detect it by ignoring things that don't move relative to the plane (while I could be wrong - I figure the idea would be that bomber crews would compute lead in some way prior to release and plant the bombs on target that way).

I will go to my old standby, the MIT Radiation Laboratory Series, published in 1947.

It appears the entire database has been converted to PDF format.

 

[GUNDAM123dx]

Re Skolnik saying that there was no PD radar in WW II, and that it was a 1970's technology

About the second sentence - "1970s", that's my addition: I mean mature application of PD was a 1970s thing. Not from Skolnik.
The first sentence : "Yet in WWII, none of these pulse radar applications used doppler." from Radar Handbook third edition, chapter 1.3 > The Doppler Shift in Radar. Skolnik

 

[Geoffrey Sinclair]

I did not take a copy of AVIA 7/3632 \ H2S Doppler Applications \ H2D, My summary of the file is Doppler set tried in air and on ground in 1944 to track ground targets, "anti clutter", then for wind drift for an aircraft, then AA trials from May 45.

 

[Token]

About the second sentence - "1970s", that's my addition: I mean mature application of PD was a 1970s thing. Not from Skolnik.
The first sentence : "Yet in WWII, none of these pulse radar applications used doppler." from Radar Handbook third edition, chapter 1.3 > The Doppler Shift in Radar. Skolnik

Possibly he meant that such systems were not in use in large numbers or with major fielded systems. Or maybe he just made a mistake, either on his own or one of the editors / contributors of the Handbook. It is pretty clear from references that the basic technologies involved were understood before the end of the conflict, and that, at least in small numbers, such systems (pulsed radar systems leveraging Doppler components of the returned signal) had been tested.

T!

 

[yosimitesam]

I did not take a copy of AVIA 7/3632 \ H2S Doppler Applications \ H2D, My summary of the file is Doppler set tried in air and on ground in 1944 to track ground targets, "anti clutter", then for wind drift for an aircraft, then AA trials from May 45.

In late WWII, some ground radars (early warning) were experimentally fitted with "MTI" (moving target indicator) which is doppler. But because magnetrons are phase non-coherent, the PD wasn't invented yet. I think PD radar needs phase coherence and thus requires klystrons or TWT's (True? or False?). I discovered this when trying to read up on "mercury delay lines" which were used in MTI to delay (store) a received pulse so that the next pulse could be electronically 'subtracted' from the first, and this would only show things moving toward or away from the unit. The electronic "pulse" was converted into a "sound wave" which was sent down the mercury tube for the delay (equal to the PRF), and then converted back into an electric voltage at the end! I found this interesting, at the time, for some reason. It still amazes me what they accomplished in the vacuum tube era.

 

[Token]

In late WWII, some ground radars (early warning) were experimentally fitted with "MTI" (moving target indicator) which is doppler. But because magnetrons are phase non-coherent, the PD wasn't invented yet. I think PD radar needs phase coherence and thus requires klystrons or TWT's (True? or False?).

It is true that magnetron systems typically are not phase coherent on transmit. There are ways to make that happen (such as pumping the magnetron), but probably nothing implemented during WW II. However, magnetron systems can be coherent on receive, which would allow Doppler based MTI functionality. And this technique was understood before the end of WW II.


Basically, you sample the transmitted pulse from the magnetron and you phase lock an oscillator to that signal. You then use this COHO (COHerent Oscillator) as your receiver LO, and so the received signal for the next echo return is phase locked to the last magnetron pulse sent.


Traditional PD radar may require phase coherence, but phase coherence does not require a TWT or Klystron. Those are pretty typical in radar application today, but any PA (Power Amplifier) technology that supports the frequency of operation can be used, such as a radial beam tetrode, power triode, or pentode.


Prior to the development of the magnetron many radars used PAs that would support phase coherence. The introduction of the magnetron was a step backwards in this respect, but well worth it in most other ways, with its more compact footprint for a given power output and frequency. The very amplifier technologies that were limiting radar upper frequency limits and power levels would have made PD applications possible.


That is an important take away here. Early radars, prior to magnetrons, were often prime candidates to be what we now call coherent radars. Some of them were MOPAs (Master Oscillator Power Amplifiers) and fully coherent.

I discovered this when trying to read up on "mercury delay lines" which were used in MTI to delay (store) a received pulse so that the next pulse could be electronically 'subtracted' from the first, and this would only show things moving toward or away from the unit. The electronic "pulse" was converted into a "sound wave" which was sent down the mercury tube for the delay (equal to the PRF), and then converted back into an electric voltage at the end! I found this interesting, at the time, for some reason. It still amazes me what they accomplished in the vacuum tube era.

The use of delay lines, as you describe, are typical in non-coherent MTI radar applications. You might also look at the storage tube style MTI's.

T!