German VHF E Boat Emissions

Discussions about the history of the ship, technical details, etc.

Moderator: Bill Jurens

Guest

German VHF E Boat Emissions

Post by Guest »

In 1940, and up to the end of 1941, the Germans used VHF radio transmissions for plain language communication. Though the Germans would not always transmit, they left they transmitters switched on for long periods, meaning that the set would be giving off a faint but detectable signal.
Does anyone have details of the detectable range of these passive emissions from E Boats in the VHF range?
User avatar
tommy303
Senior Member
Posts: 1528
Joined: Mon Oct 18, 2004 4:19 pm
Location: Arizona
Contact:

Re: German VHF E Boat Emissions

Post by tommy303 »

VHF works on line of sight from antenna to antenna, for the most part, so even on an active transmission, range is relatively short. Picking up stray radiated emissions from a superheterodyne receiver through its antenna would be even lower due to the weakness of the source, although the Germans claimed to have had success in picking up antennae emissions from several miles.

Their shoulders held the sky suspended;
They stood and Earth's foundations stay;
What God abandoned these defended;
And saved the sum of things for pay.
A Raven

Re: German VHF E Boat Emissions

Post by A Raven »

Thank you,
I am aware of the line of sight thing, But the RN, according to an official Admiralty history of wartime radio warfare, mentions the practice of interception of such German VHF emissions from E Boats operating in the North Sea. As to interception range of active transmissions, 30 miles was about the maximum, achieved by means of airborne equipment. The first such event being in very late 1939 using an Anson aircraft off the German coast. The RN used four methods to intercept E Boat VHF active signals; shipborne, airborne, balloonborne and shore based. I make the assumption that interception of passive emissions are more difficult to pick up at any given range, but would like to know what the ranges actually were.
User avatar
Dave Saxton
Supporter
Posts: 3148
Joined: Sat Nov 27, 2004 9:02 pm
Location: Rocky Mountains USA

Re: German VHF E Boat Emissions

Post by Dave Saxton »

US submarines in the Pacific used VHF talk between ships equipment fairly freely during 1942, because it was assumed that the range was relatively short and could not be picked up beyond line of sight. However, code breakers monitoring Japanese communications learned that the Japanese were picking up some of the US submarine's chat many hundreds of miles away under some atmospheric conditions. As a result the use of VHF talk between ships among US submarines was greatly curtailed. In its place were simple two letter codes transmitted in Morse using the 10 cm SJ radar sets, which was assumed the Japanese could not pickup. (The Japanese had their own 10 cm radar sets by then, though, so that might have been a faulty assumption).

As for picking up the emissions from local oscillators of VHF receivers, this concept came up during the summer of 1943 when the Germans investigated every possibility as to how the enemy was locating their U-boats. Scientists told U-boat command that it was theoretically possible to do that provided the enemy detector had a sensitive enough receiver itself. Radar detector receivers, such as the Wanze II, and Borkum, without local oscillator emissions, replaced the Metox receiver on U-boats. Nonetheless, as a practical matter the detection of LO emissions of radio receivers was soon proved extremely unlikely unless within less than a mile away, because the typical background noise would drown out any receiver's LO emission.
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.
A Raven

Re: German VHF E Boat Emissions

Post by A Raven »

Thank you,
Re, your second paragraph; This concept etc. This practice was introduced operationally by the RN in 1941 in the North Sea area, well before the Germans were using it; the Germans conveniently leaving the on switch activated, thus allowing the interception of PASSIVE emissions.
You mentioned LO emissions. What does LO stand for.
Again, what I am seeking are the ranges at which PASSIVE VHF emissions can be intercepted.
Thank you.
User avatar
Dave Saxton
Supporter
Posts: 3148
Joined: Sat Nov 27, 2004 9:02 pm
Location: Rocky Mountains USA

Re: German VHF E Boat Emissions

Post by Dave Saxton »

Mr. Raven,

Do you mean the interception of enemy VHF transmissions or the interception of the emissions from enemy VHF radio receivers?

LO stands for Local Oscillator, which is a component of a Super Het. type radio or radar receiver.

I'm sure you know this, but for any readers which may not: A super het. radio receiver mixes a second radio frequency close in frequency to the incoming radio wave frequency. The LO creates this second frequency. This is then used to create a intermediate frequency (or IF) that can be better processed and amplified by the receiver into usable data than the incoming radio wave frequency.

The wave form emitted by the receiver's LO may be picked up over a very short distance. An example of this, is the State of Virginia had a law that motorists may not use radar detectors to warn them of police radar and radar camera traps. The police in Va were issued radar detector detectors, which detected the LO emissions of the radar detector if switched on. The range of detection of LO emissions was only about 500 yards.
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.
User avatar
tommy303
Senior Member
Posts: 1528
Joined: Mon Oct 18, 2004 4:19 pm
Location: Arizona
Contact:

Re: German VHF E Boat Emissions

Post by tommy303 »

The passive emissions given off by a VHF superheterodyne receiver local oscillator (LO) through the antenna are known as spurious emissions. The range at which these are detectable depends on a wide number of factors, not the least of which would be time of day, air temperatures, weather, type of antenna, quality and nature of shielding, direction finder operator experience, number of LOs that are switched on, and self noise generated by listening station. A convoy, with forty or fifty LO's turned on would be extremely noisy as opposed to a small group of S-Boats. Vessels with older mast to mast arials and older sets were very noisy indeed. U-boat crews claimed to be able to pick up and DF on spurious emissions generated by a convoy at up to 100nm under ideal conditions at night. Such a range would be a rarity and would not normally be achievable under most conditions and might in any event be intermittent at best. I am sure most people have experienced being able to occasionally receive a distant AM or FM broadcast at distances that far exceed the normal. Under normal night time conditions, I would expect an airplane to generate a high amount of noise from its own electronics and ignition systems, which would mask the LO spurious emissions by causing static on the receiver until the range was quite close--perhaps a couple of miles.

Their shoulders held the sky suspended;
They stood and Earth's foundations stay;
What God abandoned these defended;
And saved the sum of things for pay.
A Raven

Re: German VHF E Boat Emissions

Post by A Raven »

Re Mr Sexton's message of the 20th,
I mean the interception of EMISSIONS from VHF sets when they were left switched on, but not transmitting.

Re Mr Tommy's message of the 20th,
In historical context:

The use by the RN, of shipborne transmission of VHF signals in 1939 to the middle of 1941, was just about ZERO. VHF transmitters began to be fitted to RN ships around mid 1941. One of the first RN ships to be fitted with a VHF transmitter was the cruiser Hermione.

First interception of enemy VHF TRANSMISSIONS was in late 1939 by an aircraft (Anson type).

Followed by more interceptions of enemy E boat VHF TRANSMISSIONS in the following year by airborne. balloonborne and shore based equipments.

First shipborne interceptions of enemy E Boat VHF Transmissions, (headache) in April 1941 by a Hunt class destroyer of Nore Command.

First shipborne D/fing of enemy E boat VHF TRANSMISSIONS in mid 1941 using a lash-up/jerry rig arrangement of two wire dipoles on a Hunt class destroyer. Only partially successful.

First shipborne interception of Italian MTB VHF TRANSMISSIONS was by the destroyer Maori during operation 'Substance'.

First fit of successful purpose built shipborne VHF intercept/D/fing equipment in the RN was on the quarterdeck of the battleship Queen Elizabeth in 1943. Removed after a brief period.

In the latter part of 1941, the first interception of enemy E Boat VHF EMISSIONS. Exact date unknown. By airborne or shipborne is unknown to me at this time.

Admiralty contemporary documents do NOT use the term LO, only transmissions and emissions.

I HOPE that this clears things up, and still no emission pick-up ranges.
User avatar
Dave Saxton
Supporter
Posts: 3148
Joined: Sat Nov 27, 2004 9:02 pm
Location: Rocky Mountains USA

Re: German VHF E Boat Emissions

Post by Dave Saxton »

Louis Brown gives a range that the Germans found of picking up Metox receiver emissions (which would be a VHF band receiver) from an airborne platform as 80 km:
the most puzzling aspect of the entire local oscillator affair is that it had been proposed by none other than Wilhelm Runge, sent in July from his technical exile at Telefunken to examine the failure of the Metox receivers. He suggested the local oscillator as a homing signal for patrol aircraft and detected it in an airplane at a distance of 80 km. .... (pg 342)
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.
A Raven

Re: German VHF E Boat Emissions

Post by A Raven »

Thank you,
80 km appears to be on the high side, but if Brown's statement is from an official document, (does he give a specific source ?), then I will accept. Possible that the range stated (80km)would be from a high flying aircraft.
Although the Germans ceased using VHF transmissions by the end of 1941 in the combat area (the UK East Coast), they continued to transmit upon leaving harbor, thus giving the RN ample time to get ready. I believe, but cannot be certain, that the Germans continued this practice throughout the war.
User avatar
Dave Saxton
Supporter
Posts: 3148
Joined: Sat Nov 27, 2004 9:02 pm
Location: Rocky Mountains USA

Re: German VHF E Boat Emissions

Post by Dave Saxton »

I'm skeptical of this range as well, at least on a consistent basis. 80 km was about the max range that Naxos T could pickup high power S and X band Transmissions, much less LO emissions.

He cites Alfred Price and Frank Reuters. These would be secondary sources and not official documents.
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.
User avatar
Dave Saxton
Supporter
Posts: 3148
Joined: Sat Nov 27, 2004 9:02 pm
Location: Rocky Mountains USA

Re: German VHF E Boat Emissions

Post by Dave Saxton »

The German documents literature does allude to possibility that the Metox LO emissions were being used by the enemy to home in on German ships and submarines, so that the Wanze 2 and the Borkum were deployed to provide radar detectors covering the metric wavelengths in place of the Metox. However no ranges are given in the documents. The German documents I have access to also describe in much detail the operations of S-Boats, but once again no ranges of possible LO emissions from VHF equipment are specified or discussed (unless I missed it because of my limited German language skills or I don't have access to the necessary documents.)

The German S-Boats had to still monitor radio frequencies post 1941, even if they didn't transmit, while operating, because of the tactics they used. The Germans surveyed the operational areas with coastal radar and then directed the S-boats (also destroyers and TBs) from ashore much like ground control intercept of aircraft. One has to consider that they shielded their LO emissions or reduced the signal strength of such emissions post 1941? The Germans also had UHF equipment they could have used which may not have been monitored.
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.
A Raven

Re: German VHF E Boat Emissions

Post by A Raven »

Re your first two lines,
The RN were aware that the germans believed that the RN were listening to these emissions, but as you probably know, this was not the case. This false belief added a full year of tactical advantage to the RN in the North Atlantic.

On UHF. The Germans did use, but on a very limited and experimental basis. In one of the post war British intelligence papers, there is mention of television for operational purposes, but it does not go into details.

On the RN side, work progressed slowly with UHF, however by the latter half of 1944, two of the large fleet carriers, ( I have temporarily forgotten the names), were each fitted with television receivers and transmitters. These two vessels deployed to the Pacific Fleet where they saw action against the Japanese. Work also progressed with UHF radio fits, but there was no large scale fitting before wars end.
The use of television by RN ships in the war is very little written about.
As to USN vessels fitted with television during the war, I cannot comment.
A Raven

Re: German VHF E Boat Emissions

Post by A Raven »

Re Mr Saxton's note of the 22 March.

It relates to the torpedo trials of a German raider 'Schiff 45', and comes from an official RN intelligence history.

"By a freak of wireless interception similar to that which enabled us to listen in to the final stages of Luetzow's working up in the Baltic in June 1941, VHF traffic from a raider working up her torpedo armament in the Gulf of Danzig was heard by stations in the Harwich and Dover arrears........"

The item does not state exactly where in the Gulf of Danzig the ship was, but it's well over one hundred miles from Harwich and Dover. I give this as a specific example of VHF interception under abnormal weather conditions.
User avatar
Dave Saxton
Supporter
Posts: 3148
Joined: Sat Nov 27, 2004 9:02 pm
Location: Rocky Mountains USA

Re: German VHF E Boat Emissions

Post by Dave Saxton »

This correlates with the Japanese ability to intercept the VHF transmissions of US submarines in certain conditions.
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.
Post Reply