Scharnhorst FuMB passive receiver

[minoru genda]

Reading last night about Scharnhorst final battle let me wondering. Duke of York obtained first radar contact with Scharnhorst at 1617 hours, distance 42,500 meters (46,480 yards). She didn't open fire until half an hour later when range decreased to 10,900 meters (11,920 yards). Question: Why weren't Duke of York's radar pulses detected aboard Scharnhorst during this time? By 1943 all German capital ships had FuMB passive receivers right?

Thank you.

[tommy303]

In the earlier action with the cruisers, a shell from one went through the radar office above the foretop rangefinder cupola. As well as putting the radars in the foretop out of action, the same hit probably did for the radar detectors.

[RF]

There is also the point that with so few survivors that even without that hit there may not have been any record of the transmissions being picked up, or of what action Bey would have taken if they were, particulary given the small timescale involved (half an hour).

[USS ALASKA]

Interesting question – was thrashing around (futilely as it turned out) to find some sources for this.

Questions;

What was the receive range of the FuMB?

What is the transmit freq of the DoY radar?

If they don’t overlap, then the FuMB wouldn’t have detected DoY's radar emissions. And if the FuMB could / did pick them up, then what? How many other RN vessels carried the same type radar that DoY carried? If the FuMB starts lighting up, does that always mean that something bigger and badder than you is stalking or could it be a cruiser / destroyer?

[Bgile]

Interesting question – was thrashing around (futilely as it turned out) to find some sources for this.

Questions;

What was the receive range of the FuMB?

What is the transmit freq of the DoY radar?

If they don’t overlap, then the FuMB wouldn’t have detected DoY's radar emissions. And if the FuMB could / did pick them up, then what? How many other RN vessels carried the same type radar that DoY carried? If the FuMB starts lighting up, does that always mean that something bigger and badder than you is stalking or could it be a cruiser / destroyer?

I can't answer the rest of your question, but normally an ESM receiver can pick up radar transmissions at several times the range that the radar could get an echo back.

[USS ALASKA]

Ah – my bad here. My question was poorly written. It should have ask…

"What was the receive FREQUENCY range of the FuMB?"

Not range DISTANCE but range in RECEIVE FREQ capability – once again, my bad.

[tommy303]

Scharnhorst had at least four passive devices, FuMB-1,-3,-4, and -7. Cumulatively these could detect radar emissions in the 3cm - 333cm wavelengths, however the large Timor array on the foretop range finder cupola was the most important with its all-round training.

[Bgile]

If they lost the ability to DF the signal it would be of questionable value.

[tommy303]

It probably did not help that the most important active and passive sets were concentrated in the foretop office on level 2 of the RF cupola, together with their personnel; there was an aft station occupying level 2 of the after RF cupola, but to my knowlege, it housed only active radar.

Assuming that there was at least one operating receiver on board, it would likely be picking up signals from all over, but as Steve says, without directional ability, Scharnhorst would not know she was standing into danger or that a new group of sets had come into play.

[minoru genda]

Thank you Tommy. What about hydrophones? Sound signals are picked up underwater and the receiving station should be safe below decks right? Is it possible the device was off or maybe they picked up the sound of several other ships...
It is somehow difficult to believe that Scharnhorst was taken completely by surprise by the time Duke of York opened fire, but then when I think of the night battles in Guadalcanal... well, I guess anything is possible. Another question is why did Duke of York wait for so long before opening fire and risk herself being discovered by Scharnhorst? It didn't happen but it could.

[Bgile]

Thank you Tommy. What about hydrophones? Sound signals are picked up underwater and the receiving station should be safe below decks right? Is it possible the device was off or maybe they picked up the sound of several other ships...
It is somehow difficult to believe that Scharnhorst was taken completely by surprise by the time Duke of York opened fire, but then when I think of the night battles in Guadalcanal... well, I guess anything is possible. Another question is why did Duke of York wait for so long before opening fire and risk herself being discovered by Scharnhorst? It didn't happen but it could.

Hydrophones are of inconsistent utility on ships going fast, and heavy seas reduce their efficiency quite a bit.

Duke of York waited as long as possible to open fire so it would be difficult for Scharnhorst to escape. She wanted to at least slow her down before she could get away.

[tommy303]

Steve's right. Under the prevailing conditions, Scharnhorst's speed, the fact that she was steaming into an Arctic gale, and the direction of the Duke of York battle group relative to Scharnhorst's heading probably interferred tremendously with the ability of the GHG hydrophones to detect the danger ahead. The GHG installations were such that they could not hear much coming from abaft the beam due to hull flare and self noise, and they could also not detect anything from directly ahead to about 15 degrees to either side. From course charts it looks as though the DoY battle group was in the forward dead zone. In addition, water flow noise degraded detection range until the target was nearly abeam unless Scharnhorst was moving slowly.

[Dave Saxton]

When the alarm was sounded at 4:00PM aboard the Scharnhorst, it was based on "radar contacts" toward the southwest. This was at least 17 minutes prior to the time that Duke of York made contact at a range of 42km with it's Type 273Q active search radar. Obviously the "radar contacts" the Scharnhorst based it's alarm on, were the British pulses from Duke of York or Jamaica setting off the passive radar warning recievers (radar detectors) aboard the Scharnhorst, with the range still exceeding 50km. Passive detectors can not measure range because there's no way of knowing the exact moment in time the pulse was transmitted, and range is calculated by the elasped time of the pulse's round trip. With the Scharnhorst's forward active radar having been destroyed the Germans could not know how far away the DoY group was, except a rough guess based on signal strength of the intercepted pulses.

Most likely the passive detector that sounded the alarm was a Naxos radar warning receiver for centimetric wave lengths. These had been available since May 1943. The British were probably using only the centimetric sets at that point in time. Their metric sets were air warning sets, and their decimetric sets were firecontrol sets.

The Scharnhorst probably had the Timor array removed in Oct 1943, but regardless if was still installed or not, it would have been destroyed at the same time the active foretop radar was.

The Scharnhorst also had a trainable Palau passive antenna on top of the aft rangefinder/radar hut. This was a passive detector antenna that feed intercepted signals to the Wanze automatic radar warning receiver (70cm-350cm wavelengths) and the Samos or Fanoe detector recievers. The Fanoe could automatically detect wave lengths from 20cm to 70cm.

The Bali omni-directional detector antennas would have been mounted high up on a mast or yard arm and still functional. These could have detected metric emissions at great range. Next the Sumatra antennas placed at sundry places about the superstructures could give a rough indication of direction of metric emissions.

The Scharnhorst's FuMB devices had also detected Burnette's cruiser's radar emissions early that morning, long before the Belfast detected the Scharnhorst with its Type 273 at 30km. This was the reason Bey turned around to investigate, but he failed to switch on his active radars at that point, and obviously did not have them switched on in time.