Talk:Traveling-wave tube

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[edit] Article name and spelling

First, a spelling nit: while "travelling" (two Ls) is acceptable, the more common spelling of this word is "traveling". (It's listed first in most dictionaries, and is the spelling used by all major TWT manufacturers.)

Since this article is almost exclusively dedicated to a discussion of the traveling wave tube (and not the amplifiers designed around them), I'd have preferred to see it titled "Traveling Wave Tube" without the appended "Amplifier". At least one other editor would seem to agree with me; refer to the usage note added earlier.

Anyone else care to weigh in? Engineer Bob 05:27, 21 August 2005 (UTC)

  • I agree. This article should be "Traveling Wave Tube". miterdale 14:34, 21 August 2005 (UTC)
  • Since there were no objections, the article has been moved as suggested; and the amplifier information has been moved to Traveling wave tube amplifier. I'm also cleaning up all of the redirects. Engineer Bob 23:08, 12 November 2005 (UTC)

[edit] Merge or not?

The merged article as it existed before today (covering both TWT and TWTA) had a major weakness. As we all know, a TWTA is a complex piece of electronic equipment while a TWT is the equally complex microwave tube used inside. The previous article had the TWTA title but was almost exclusively focused on TWTs. I moved the TWTA information to a separate article, allowing people to expand that article to address the finer points of EPCs and linearizers while keeping this article focused on the tube itself. Half an hour later, it's been nominated for a merge. I'm obviously not in favor; it makes about as much sense as merging the automobile and internal combustion engine articles. However, if a merge is deemed appropriate by the majority, then I believe the primary article should remain "Traveling wave tube" with a section on TWTAs. Other opinions? Engineer Bob 23:57, 12 November 2005 (UTC)

Or merging magnetron with microwave oven. Unless someone (perhaps User:The Anome) can explain why they think they should be merged, I think the merge banner can be removed. If there is a real desire for a merge then I agree that the page should be primarily about the TWT with a section on TWTA (as for the other high power vacume tubes). miterdale 13:36, 24 November 2005 (UTC)

Since no further discussion or rationale has been offered, I have removed the merge tag. Engineer Bob 06:50, 2 January 2006 (UTC)

[edit] Picture

Does the diagram actually show a TWT with a 4 stage depressed collector? Do such TWT's exist - most I came across was two stage. Suppose we could do with a paragraph on why depressed collectors are used too (might get round to it :-). miterdale 14:40, 21 August 2005 (UTC)

Hard to tell for sure -- but yes, the diagram does appear to show a 4-stage collector. I've seen as many as five collector stages in some space TWTs (where the small increase in efficiency is worth it), but radar TWTs tend to be designed with not more than 2 stages. Engineer Bob 18:29, 21 August 2005 (UTC)

The diagram shows a 4-stage collector, which is used, as Engineer Bob pointed out, when efficiency is at a premium, e.g. in space helix TWTs. --Willus 12:58, 7 July 2007 (UTC)

[edit] Bandwidth

What do we actually mean by wide bandwidth wrt TWTs? I've used pulsed coupled cavity TWTs with 50kW peak power, and 500MHz bandwidth at 9.75GHz - in my option pretty good bandwidth :-) miterdale 14:34, 21 August 2005 (UTC)

Helix TWTs have an inherently wideband structure and can easily achieve up to an octave of bandwidth (especially CW communications tubes). Coupled cavity tubes are more typically limited to 5-10% of the center frequency. Engineer Bob 18:29, 21 August 2005 (UTC)

How come the word "octave" is used to describe the bandwidth? Octaves are logaritmic units (like dB), do that doesn't really say anything about the BW, or am I just being stupid here? /Alkanen, 9 February 2007 (UTC)

The word octave actually originates in music, and corresponds to a doubling in frequency (on a musical scale it's a span of eight notes, hence the root 'oct'). For bandwidth, an octave is a range of frequencies where the upper limit is double the lower limit. For example, 4-8 GHz is an octave of bandwidth. Engineer Bob 21:04, 9 February 2007 (UTC)

[edit] Uses

I've worked on several TWT based systems (airborne surveilance, ground based surveilance/fire control, naval ECM), so don't think we should make the 'particularly in airborne fire-control radar systems' statement. Maybe a statement of why high bandwidth is useful for radar/ECM (frequency agility, narrow pulses/chirped pulses, etc.)? miterdale 14:34, 21 August 2005 (UTC)

Yes, TWTs are used in many types of radars (although many of the higher-power systems use a TWT preamp driving a crossed-field amplifier ... another article waiting to be written?) I added the 'airborne fire-control radar' note as an initial attempt to expand the 'radar' one-liner; that obviously reflects my own background, and I'd welcome additional edits in this paragraph. As for ECM applications, that probably deserves an additional paragraph of its own. Engineer Bob 18:29, 21 August 2005 (UTC)

[edit] Backward waves

Is it possible to replace the attenuation by a ferrite that acts like an isolator (circulator) ? --Arnero 06:40, 16 July 2006 (UTC)

I suppose anything is possible, but putting magnetics near the electron beam is generally a bad idea and would complicate the focusing structure. The attenuation material is commonly made of some form of RF-absorbing graphite, and many helix TWTs have a physical sever between sections so that the isolation is excellent (well over 100 dB). --Willus 12:55, 7 July 2007 (UTC)

[edit] The never-mentioned acronym: TWAT

Early in my career I learned this was once referred to as a TWAT (convencient pronunciation of TWT, but also for Traveling Wave Amplifier Tube), and I confirmed this with older engineers who had been employed in the 1950s. Older microwave engineers I have talked to all seem to know this term, but one never sees it in print for obvious reasons, especially in these modern times when the engineering profession isn't almost exclusively male. I think this historical tidbit deserves a mention. -Axlq 05:51, 14 December 2006 (UTC)

It might deserve a mention if you could find it in print. In the 33 years that I knew John Pierce, he only used TWT and TWTA. I never heard TWAT (or not in that context, I mean). It's probably just a way to pronounce TWT. Dicklyon 05:57, 14 December 2006 (UTC)
That's the problem, it's one of those terms that occur in conversation and informal reports, but generally not in print. In the 22 years I've been in the radar cross section measurement business, I've seen and heard it called TWAT (in informal contexts) as well as TWT. It's like the mnemonic to remember the resistor color code; the really memorable version doesn't appear in any textbook.
However, after some searching, I actually did find a few references for TWAT:
I think it's valid to include. -Axlq 06:19, 14 December 2006 (UTC)

I'd support including the alternate acronym, but only a quick mention -- for example:

"The device has also occasionally been referred to as a traveling wave amplifier tube, or TWAT."

-- Engineer Bob 09:16, 14 December 2006 (UTC)

That'd be fine if you cite a source. Dicklyon 17:08, 14 December 2006 (UTC)
The acronym definition on fas.org or the patent I cited above aren't enough? =Axlq 03:36, 15 December 2006 (UTC)
Seems OK. Cite one or both. Dicklyon 04:37, 15 December 2006 (UTC)

Axlq, thanks for finally just putting the acronym instead of beating around the bush. Dicklyon 07:54, 19 December 2006 (UTC)

I think all of us who were contributing to that sentence were beating around the bush. I finally realized something I read in a policy somewhere, "Wikipedia is not censored." So be it. -Axlq 15:28, 19 December 2006 (UTC)

[edit] The difference between a klystron and a TWT

I just read this article after eading the klystron article because I would like to familiarize my-self with those two types of RF amplifiers. I sit back with some open questions are reading them

  1. I have the impression that if you take a klystron and add a helix wire you have (conceptually) a TWT. Is that correct understood from a birds eye perspective?
  2. The concept of the klystron (1939) was developed before the TWT (WWII). Would it be fair to consider a TWT as a refinement of the klystron?
  3. The helix wire makes thwe RF signal propagate with the same speed as the electron beam along the tube. Is this what makes the TWT so widebanded?

I do not know what the answers of these questions are, but I think it could be helpfull to add some comparative remarks to klystron (and possibly other types of RF amplifiers that I have yet to learn about) in this article as it helps the reader to navigate and relate the different kinds of amplifiers to each other. -- Slaunger 13:25, 30 October 2007 (UTC)

In all fairness I should mention that reference is made to the klystron, but I think the some comparative remarks should be moved up in the more introductory text and perhaps be elaborated a little. -- Slaunger 07:41, 31 October 2007 (UTC)

[edit] Solenoid coil or permenant magnet

64.209.156.12 substantially removed the following:

"A solenoid coil wrapped around the tube creates a magnetic field which focuses the electrons into a beam, which then passes down the middle of a wire helix that stretches the length of the tube, finally striking a collector at the other end. (In lower-power devices, the solenoid coil can be replaced by permanent magnets.)"

This was substantially replaced with:

A magnetic containment field around the tube focuses the electrons into a beam, which then passes down the middle of a wire helix that stretches from the RF input to the RF output, The electron beam finally striking a collector at the other end. (rem, lower power is not an absolute value and is therefore meaningless)

I think the original was appropriate in the article. Nevertheless, the comment about low power being meaningless is a comment about the article which should have been put on the discussion page, not in the article itself. I removed it. Rsduhamel 21:00, 4 December 2007 (UTC)

I think the original was appropriate, too. The new version removes important information about typical focusing structures in TWTs in favor of something more generic. "Lower power" was not meaningless, as most PPM-focused TWTs (tens to hundreds of watts, but largely dependent on frequency) are indeed "lower power" than most solenoid-focused TWTs (multi-kilowatt, again with lots of wiggle room). Because solenoids require a power source, are heavy, and frequently require cooling, they are typically used only when the beam cannot be adequately focused by a PPM stack, and that typically occurs as beam current (and hence beam power and RF power) increases. At some point, this should be reverted--maybe not exactly to what it was, but with information about solenoids vs. PPM again. I can do it at some point. Willus (talk) 18:52, 8 May 2008 (UTC)

[edit] Merge from TWTA into TWT

In Nov. 2005, when there was a consensus to change title from traveling wave tube amplifier to traveling wave tube, Engineer Bob did that, but then also, without any prior suggestion or comment, took out the TWTA bits and made a new article that has remained unreferenced and nearly orphan. I propose we merge it back in as a section or two. Dicklyon (talk) 21:33, 6 January 2008 (UTC)

Done; improvements are invited. Dicklyon (talk) 07:45, 15 January 2008 (UTC)
Sorry for the delay; I haven't logged in here in several weeks. The re-merge was nicely done, and I concur with the end result. -- Engineer Bob (talk) 03:43, 29 January 2008 (UTC)