Talk:High-frequency direction finding

just a remark: sigint is not for messages but for signals, so comint is sister of elint and sigint is parent

Link added to a technical paper on the WW2 Royal Navy system. Quite detailed on the history, theory, and technical limitations. —Preceding unsigned comment added by 88.109.179.110 (talk) 11:39, 3 December 2007 (UTC)

Title

Why is this article titled "High-frequency direction finding (electronics)" vs just "High-frequency direction finding" which is what our guideline Wikipedia:Article titles would suggest?

Submarine signals

There seems to be some confusion about how the German submarines sent messages. It's all in the main reference for this topic, nothing original.

1. The basic information was of a standard form: where is the convoy, where are we, what is the weather, etc. This was encoded into a short form, typically 25 characters, with numeric codes. This was intended to shorten, not hide the contents.
2. The short code was then encrypted with the Enigma machine, for security. This probably added a couple of characters (check the source).
3. The ~25-character signal was transmitted in Morse by a human operator, in about 20". There was no "burst transmission" as such, just hammering out a short message as fast as humanly possible.
4. A mechanical burst transmitter (Kurier) was in development, but never used. It, too, transmitted the signal in Morse, but with 1ms per dot, instead of about 50ms for a human. (Message speed doesn't scale exactly as dot time, it depends on dashes, inter-symbol pauses, not complicated.) Total transmission time for message encoded as above less than half a second. It simply automated the last link of the exact same chain of procedures.

It was always possible to send any non-standard information as a normal Morse message, at the risk of revealing the position. I don't know how usual (if done at all) this was.

Pol098 (talk) 17:20, 5 August 2015 (UTC)

The transmissions were also HF (see also the title of the article). CW/Morse transmissions (narrowband) were essentially a requirement because there were no other suitable modulation options. Lower frequencies require physically larger antennas (3 MHz is 100 m wavelength) and VHF is only line of sight. Glrx (talk) 17:29, 5 August 2015 (UTC)

♠I'll confess getting Kurier confused. :( I don't see a need to explain what HF is; link to it, instead.

♠There's still a lack of clarity, so I've deleted the "numbers". All code systems use numbers, to shorten messages; how the kurtz system is different needs a rewrite to clear it up. TREKphiler ^{any time you're ready, Uhura} 17:41, 5 August 2015 (UTC)

"encoding" is correct; Kurzsignale is a code; "shortening" is opaque. de:Wetterkurzschlüssel Glrx (talk) 18:08, 5 August 2015 (UTC)

"Encoding" is also opaque, because it's in addition to the use of Engima. (Let's not complicate it with ref to superencypherment, shall we?)

I agree, "shortening" isn't ideal, but the description of the process is overly complicated & ignores the fact all codes use number substitution. I'm unsure we need to go into that much detail for this page in any case. TREKphiler ^{any time you're ready, Uhura} 22:42, 5 August 2015 (UTC)

Technique v. equipment

I disagree with this edit.

Even if redundant, it is important to set up that HF/DF only worked when the target transmitted; that's why shortening the message could be an effective countermeasure. It's not clear the term and transmission are redundant: early radar was characterized as radio direction finding: omni illumination with directional detection, so the targed didn't do any transmission. The British idea for radar was inspired by reflections of broadcasts by passing planes. The notion is active versus passive direction finding.

There are several techniques of radio direction finding. See Denisowski below. A manual RDF technique physically rotates the attenna. Rotating a small, inefficient, antenna is easy to do, but difficult when the antenna gets large and ineffective for weak signals. This article's history section then explains the 1907 Bellini—Tosi goniometer (Bellini–Tosi direction finder) that used crossed antennas that were not rotated. The crossed directional antennas and goniometer do the same thing electrically as rotating a single directional antenna mechanically. An improved antenna is a crossed Adcock antenna. The Adcock antenna is an open 1919 patent, Improvements in Means for Determining the Direction of a Distant Source of Electro-magnetic Radiation. Adcock disclossed using crossed antennas and a goniometer. The Germans would be aware of the technology.

The section also describes some French work that used a rotating search coil. It's still the same RDF technique, but it is using an improved goniometer. The French destroyed their work so the Germans would not learn about it.

The article's Watson-Watt section describes Watson-Watt using crossed Adcocks in England. Instead of using a manually adjusted goniometer, Watson-Watt used a Bell Lab's oscilloscope. It wasn't the radio direction finding technique that changed, it was the use of an improved goniometer: a CRT that would resolve the angle immediately rather than a search coil that was rotated to find the angle.

BTW, goniometer article states, "The advantage to the Bellini–Tosi system is that the antennas do not move, allowing them to be built at any required size. The basic technique remains in use, although the equipment has changed dramatically." [emphasis added]

There is often a third channel antenna to sense the electric wave, but that is just a tweak and is not required for triangulation.

• http://www.denisowski.org/Articles/Denisowski%20-%20Comparison%20of%20Radio%20Direction-Finding%20Technologies.pdf Describes different RDF techniques: manual, doppler, time difference, Watson-Watt
• http://www.rdfproducts.com/wn002_apl_01.pdf More on Watson-Watt technique

Glrx (talk) 17:02, 1 September 2015 (UTC)

I'll accept different equipment. I'm not sold on the need to mention transmitting. British use of "RDF" as a covername isn't persuasive; it was meant to conceal what the set was actually doing (or describe it in a way that wasn't too revealing). TREKphiler ^{any time you're ready, Uhura} 19:48, 1 September 2015 (UTC)

Making it explicit helps understanding. It is weak, but "Early British radar sets were referred to as RDF, which is often stated was a deception. In fact, the Chain Home systems used large RDF receivers to determine directions." (direction finding) Glrx (talk) 18:13, 4 September 2015 (UTC)

That they used the RDF receivers is no surprise & no help to you; they were capturing radio signals sent out, & using the received signals to determine direction. What should they have used, having never done it before? TREKphiler ^{any time you're ready, Uhura} 21:16, 4 September 2015 (UTC)