PoW salvos to hit Bismarck?

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Steve Crandell
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Re: PoW salvos to hit Bismarck?

Post by Steve Crandell »

Thorsten Wahl wrote:
When the British captured their first Wuerzburg, they were not that impressed at first. They noted that the power output was only about 8kw and the receiver sensitivity and band width were relatively low. Yet when when they tested it it tracked planes to 38km, and still detected targets even when the signal to noise ratio was virtually 1:1. A couple of years later MIT/Rad LAB scientists sent them their latest findings; reporting that to attain the lowest signal to noise ratio required for detection, the band width of the receiver in megahertz should be the inverse of the pulse width in micro seconds. Sure enough the bandwidth of Wuerzburg was 1/2 megahertz and the pulse width was two micro seconds. Indeed all the German radars followed this rule (the bandwidth of the GEMA sets was adjustable).
Just to add - the german Gema Seetakt radar sets had two signal amplification units wich manipulated the incomming signals.

If the detection unit (Eingangsstufe)receives a reflected signal an oszillating unit fires a synchronised signal wich was added to the received signal so the signal strenght of the reflected return was increased without amplification of the white noise. This signal was then normally amplified and then forwarded to a second signal amplification unit(Mischstufe) amplified again and after a further amplification fed into the display device.
If you are implying that the German method described in your last paragraph is superior, that in itself wasn't necessarily any better than what anyone else used. My job in the USN was to maintain various types of receiving and recording equipment over many different frequency ranges. It was a very long time ago (in the 60s and 70s), but I can tell you that all receivers used various sequential stages of filtering and amplification to refine the signal they were trying to produce an end product from, and I'm pretty sure the Germans were not unique in that respect.
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Dave Saxton
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Re: PoW salvos to hit Bismarck?

Post by Dave Saxton »

Thorsten Wahl wrote: From New Jersey report (wich fired 18 projectiles)
range to target between 32200 and 35000 yard

Th Mark 8 operated in low speed precision scan
there was no difficulty in discerning splashes for radar spotting
Air spot was provided by CAP
Thanks for posting that Thorsten. It answered some questions I had after running across a rather detailed secondary account recently. The account read that fired was opened at 32,000 yards (29.2km) out to 35,500 yards and that air spotting was actually used throughout. Obviously it was based on the NJ reports. NJ firing only 18 rounds was probably due to several polyrods being broken off of the foretop Mk-8 by the blast from the forward turrets. The radar wasn't knocked out completely but with the damage to the antenna FC performance was probably impaired. The SGs on both battleships were knocked out by the shock of the first salvos.

One would expect slow scan speed to be used if shell splashes could be indicated at those ranges.
Entering a night sea battle is an awesome business.The enveloping darkness, hiding the enemy's.. seems a living thing, malignant and oppressive.Swishing water at the bow and stern mark an inexorable advance toward an unknown destiny.
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Dave Saxton
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Re: PoW salvos to hit Bismarck?

Post by Dave Saxton »

Steve Crandell wrote:
Thorsten Wahl wrote: Just to add - the german Gema Seetakt radar sets had two signal amplification units wich manipulated the incomming signals.

If the detection unit (Eingangsstufe)receives a reflected signal an oszillating unit fires a synchronised signal wich was added to the received signal so the signal strenght of the reflected return was increased without amplification of the white noise. This signal was then normally amplified and then forwarded to a second signal amplification unit(Mischstufe) amplified again and after a further amplification fed into the display device.
If you are implying that the German method described in your last paragraph is superior, that in itself wasn't necessarily any better than what anyone else used. My job in the USN was to maintain various types of receiving and recording equipment over many different frequency ranges. It was a very long time ago (in the 60s and 70s), but I can tell you that all receivers used various sequential stages of filtering and amplification to refine the signal they were trying to produce an end product from, and I'm pretty sure the Germans were not unique in that respect.
By the 50s -70s radars were indeed equipped with many filters and signal processing enhancement features, such as sea clutter filtering to name just one. However, what Thorsten is talking about specifically in this case was rather unique and remarkable for WWII radar. By the 50s it was fairly common among the more sophisticated designs though.

The GEMA radars used a master oscillation as reference for all time measurements. The pulse was formed on a small scale by the Central Impulse Geraete and the transmitter was actually a power amplifier that took the pulse formed by CIG and massively amplified it. The flanks of each pulse were marked by the CIG according to the timing of the master oscillator.

Thorsten describes that the master oscillator sent a signal (and a reference) to the receiver as well as to the indicators and that the receiver contained two zwischen or intermediate frequencies instead of the usual one. This was because the fine range or elapsed time was measured by comparison of the phase angle of the returned echo to the master oscillation. This comparison required the unique use of two IFs (ZF in German). The first mixer stage caused an intermediate frequency of 15 Mhz, and then a second IF was formed at 7 Mhz for mixing and comparison to the master reference. This comparison was determined by a precision delay circuit which placed the pips on the correct portions of the time base through phase shifts.

This unusual type of range measurement had its genesis in the first radar experiments conducted by GEMA during the early 1930s. The first experimental German radars were continuous wave. CW is like having infinite pulse width so measurement of elapsed time to measure range by timing pulses is not possible. What the GEMA engineers did was to lay a frequency modulation over the signal. By comparing the phase of the wave form of the echo to the master reference it could measure range to target. This experimental CW set tracked ships to 16 km in 1934. The method was carried over to the pulse radar designs and it featured the capability of discriminating over lapping returns to some degree.

As radar scientist and engineer Harry von Kroge wrote:
A special advantage of this GEMA method was that the resolution in range was limited only by the fine graduations of the (range measuring delay circuit) and was independent of the range (to target). The accuracy of the (fine ranging system) over long periods of time and with variations in climatic conditions, and the accuracy with which the transmitter and echo pulse were marked (by the CIG according to the master oscillation), determined the accuracy of the radar for range.
(Harry von Kroge)
Entering a night sea battle is an awesome business.The enveloping darkness, hiding the enemy's.. seems a living thing, malignant and oppressive.Swishing water at the bow and stern mark an inexorable advance toward an unknown destiny.
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Re: PoW salvos to hit Bismarck?

Post by Steve Crandell »

Bill Jurens, in his article pair of articles about fast battleship gunnery, comments that New Jersey's performance at Truk was worse than Iowa's and speculates it was because she fired three gun salvos from alternating groups from cold guns, and her use of the slow speed scan.

Iowa fired five full salvos, and her guns were already warm from a previous engagement. Her first salvo was a straddle. Her salvos were more consistent than New Jersey's, exhibiting smaller MPI errors. Unfortunately the fourth salvo was unobserved due to losing both radar and visual track, and the fifth was fired on generated course and speed. Bill claims that Iowa fired the longest ranged salvo at another ship at sea (35,700 yds) and also the longest ranged straddle.
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Re: PoW salvos to hit Bismarck?

Post by Thorsten Wahl »

Iowa fired five full salvos, and her guns were already warm from a previous engagement. Her first salvo was a straddle. Her salvos were more consistent than New Jersey's, exhibiting smaller MPI errors. Unfortunately the fourth salvo was unobserved due to losing both radar and visual track, and the fifth was fired on generated course and speed. Bill claims that Iowa fired the longest ranged salvo at another ship at sea (35,700 yds) and also the longest ranged straddle.
The first salvo was a straddle because Iowa used could gun correction. Without this correction this salvo would be short in the order of 300-500 m.
fourth and fifth salvoes were both unobserved. (Nevertherless good shooting wich shows the capabilities of USN firecontrol)

Nowaki obviously did not expect an ballistic attack at this range. Past the first 9 impacts it started maneuvering - given the flight times at this distance an destroyer could outmaneuver the firing solution relatively easy.
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Re: PoW salvos to hit Bismarck?

Post by Guest »

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The long distant firing by Iowa and New Jersey indicate nothing more than they could fire long distances - any attempt to claim wonderful accuracy is weak at best.
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