DF Loop Antenna - all infos

[gambla]

Hello Kaleuns,
I started with just being curious about this loop antenna on the conning tower and only found some threads discussing it's "direction finding" capabilities and/or other functionalities. I soon found it highly interesting and took a deep dive into the topic. There are a few great websites where I could gather some interesting information from.

I did the research for myself but thought why not sharing it. All credit goes to the owner of these sites and their sources !



1938:

DF Loop Antenna (HF/MF/VLF) - on Conning Tower

Used primarily for MF direction finding (surfaced) and VLF radio message reception (submerged) – secondarily for HF broadcast reception (surfaced). DF antenna was steered by hand wheel from below the counter (Radio room). Steering unit incorporated a gyro compass repeater.

• 800 mm in diameter – raised by compressed air
• Pressure-proof shielded loop antenna - null position used for direction finding
• Late war boats carried a direction sensing rod antenna mounted on the loop.

The loop antenna was designed for two maximum fields of reception and two minimum fields of reception. By rotation of the antenna on its axis operator was able to determine direction of the electromagnetic source i.e. radio-azimuth. The radio-azimuth is angle between true meridian and direction of reception of the electromagnetic (or radio) waves. Problem was because the loop antenna had two maximum fields of reception and because of that the operator could to make mistake of 180 degrees.
Solution of that problem is explained in the next chapter.




Telefunken "T 3 PL Lä 38" VLF receiver - in Radio room

• 15–33 kHz/70–1200 kHz
• Beacon MF & VLF Rec
• Size: 15 cm wide x 15 cm high x 18 cm deep
• Weight: 25 kg
• Frequency Range: 15-33 kHz/70-1,200 kHz
• Tubes: 3 RES094, 3 REO84K

1941 - 1945

In 1941 Germany declare War against USA and Russia and the war become global and now we have a real World War. At this time the submarines have to operate all over the world and the new situation need to change their strategies in many ways. The boats have now to run in a much more different patterns to hunt very far from home. Submarines with capacity to reach target all over the world and supply food, fuel and torpedos was now a must. Milk Cows was launched to solve the new demands and also a system with better communication must be built up for commanding the boats against targets around the world.

In 1942 was a new giant transmitter built up in Kalbe to solve the problem with communication. The new transmitter was called Goliath and has an enormous capacity of 1800 KW and was the strongest transmitter in the world at this time. Enigma was a cifercode for the signals to avoid reading secret info for the enemy.

In 1943 has the Transmitter in Kalbe (South of Magdeburg , Germany) begins to send signals all over the world. The system aloud the submarines to receive signals over the world and they could stand submerged and are not forced to surface to have the signals.

Position of Submarine Distance from Goliath, Depth of Sub

• North Sea 1000 km 14-24 m
• Mediterranen Sea 2300 km 12-17 m
• Bay of Biscay - Approx 30m
• Indian Occean 6000-8000 km 7-14

The subs was equipted with receivers to catch the signal from Goliath and one of this was Peiluberlagerungsempfänger Telefunken T3PLLä38 who has a five position band selector with this frequencies:

• Band 1 70 - 150 kHz
• Band 2 150 - 350 kHz
• Band 3 350 - 640 kHz
• Band 4 640 - 1200 kHz
• Band 5 15 - 33 kHz

Used on Type VIIC, IXB, XB, XXI U-boats

The technique was so interesting for the Russians so after the war that they dismantle the whole equipment at Kalbe and send it buy hundreds of railway wagons home to Russia. With help from experts (Lorentz) the Russians built it up again in Nizhny Novogorod. And still today is it used for commanding Russian Submarines (spacecraft also) around the world.



sources:
all information, pictures from these excellent sites:

http://www.uboatarchive.net
https://uboat.net
http://kriegsmarine.biz
http://www.uboatradio.com/
http://www.kriegsfunker.com
https://www.nonstopsystems.com/radio...-mil-tx-rx.htm

[Delfi]

I always assumed that was the hydrophone.

[gambla]

you're confusing it with the smaller but also rotating KDB, which was mounted on top of the bow:

"The KDB (Crystal Rotating Base Apparatus) was an improvement of the GHG in that it was rotatable and hence able to provide more accurate readings from any direction. The disadvantage however was its extreme vulnerability to depth charges."

example picture from Wikipedia: https://upload.wikimedia.org/wikiped...hydrophone.JPG

[Cyborg322]

Hi Gambla


Good stuff on the Radio side,

This may be of interest to you regarding the Hydro Gear

http://www.subsim.com/radioroom/show...=208473&page=6

Simon

[gambla]

Thank you Simon !
Very interesting thread and good work in this project.

cheers,
Steffen

[Delfi]

Originally Posted by gambla

you're confusing it with the smaller but also rotating KDB, which was mounted on top of the bow:

"The KDB (Crystal Rotating Base Apparatus) was an improvement of the GHG in that it was rotatable and hence able to provide more accurate readings from any direction. The disadvantage however was its extreme vulnerability to depth charges."

example picture from Wikipedia: https://upload.wikimedia.org/wikiped...hydrophone.JPG

That explains why the German boats can't hear anything while on the surface.