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From: Chris on 13 Apr 2010 14:58
On 13 Apr, 15:44, Rene Tschaggelar <n...(a)none.net> wrote:
> Our TWT has an anode voltage of -14kV and a
> current in the range of 60mA.
> And yes, the signal propagation of the
> electron beam matches the signal velocity
> on the helix.
> I was puzzled that there are 1400 wavelengths
> stored in the helix, while I expected much less.
>
> Rene
>
>
>
> Tim Williams wrote:
> > The point of a TWT over regular tubes is changing the paradigm on how
> > electrons do work, so that should be due to propagation of the electron beam
> > itself.
>
> > As I recall, TWTs work by shooting an electron beam (= constant velocity)
> > down a helix, where, due to spooky action and black magic, the beam turns
> > into bunches and somehow does work on the electromagnetic field.  The
> > result, gain.  The delay should be essentially the propagation of the beam.
> > Maybe with a velocity factor for the helix, or somewhat shorter for the
> > feedpoints being somewhere along it, etc.
>
> > Whatever the case, I'm guessing your anode voltage is close to 160V.
> >http://www.google.com/#q=0.5*electron+mass*(30cm%2F40ns)^2%2Felectron+charge
>
> > Tim- Hide quoted text -
>
> - Show quoted text -


Does the device to which you refer as a 'TWT' actually contain a TWT
and some filters, at least to constrain the amplitudes of harmonics
when the device is operated anywhere near to saturation? If so, the
filters will contribute to the delay.

Chris
From: Rene Tschaggelar on 18 Apr 2010 11:13
John Larkin wrote:
> On Tue, 13 Apr 2010 15:04:05 +0200, Rene Tschaggelar <none(a)none.net>
> wrote:
>
>> Since we were having a long delay in a system I
>> came to measure the delay of a traveling wave tube
>> (TWT) amplifier. The delay is in the order of 40ns,
>> which at 34.6GHz correspond to about 1380 wavelengths
>> or 13m of free space. The tube is in the order
>> of 30cm long.
>> I was aware it has two helix inside but considered
>> them to be 10 turn or so.
>
> Seems a lot. How did you measure the delay?
>
> John
>

Thanks John and Phil,

I have a CW generator and a fast switch that switches
within nanoseconds that is connected to the TWT unit,
not the tube. The unit contains whatever plus the tube.
I have no idea, whether a filter is included or not.
Even if there was a filter, it cannot contribute to the
delay as it has as bandpass a bandwidth of perhaps 2GHz.

After the unit, there is an isolator plus a directional
coupler and another directional coupler. Then a
detection diode. I measure the delay between the
control pulse of the switch and the detection diode
with a sufficiently fast scope doing a few GSample.
The pulse shapes there are sufficiently rectangular.

Rene
From: Phil Hobbs on 18 Apr 2010 13:07
Rene Tschaggelar wrote:
> John Larkin wrote:
>> On Tue, 13 Apr 2010 15:04:05 +0200, Rene Tschaggelar <none(a)none.net>
>> wrote:
>>
>>> Since we were having a long delay in a system I
>>> came to measure the delay of a traveling wave tube
>>> (TWT) amplifier. The delay is in the order of 40ns,
>>> which at 34.6GHz correspond to about 1380 wavelengths
>>> or 13m of free space. The tube is in the order
>>> of 30cm long.
>>> I was aware it has two helix inside but considered
>>> them to be 10 turn or so.
>>
>> Seems a lot. How did you measure the delay?
>>
>> John
>>
>
> Thanks John and Phil,
>
> I have a CW generator and a fast switch that switches
> within nanoseconds that is connected to the TWT unit,
> not the tube. The unit contains whatever plus the tube.
> I have no idea, whether a filter is included or not.
> Even if there was a filter, it cannot contribute to the
> delay as it has as bandpass a bandwidth of perhaps 2GHz.
>
> After the unit, there is an isolator plus a directional
> coupler and another directional coupler. Then a
> detection diode. I measure the delay between the
> control pulse of the switch and the detection diode
> with a sufficiently fast scope doing a few GSample.
> The pulse shapes there are sufficiently rectangular.
>
> Rene

Hmm. A sharp enough filter with a 2 GHz bandwidth could contribute a
couple of nanoseconds, but 40 is a stretch. Is it possible to tune the
source just a bit and measure d(phi)/d(f)?

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net
From: Jan Panteltje on 18 Apr 2010 13:20
On a sunny day (Sun, 18 Apr 2010 17:13:48 +0200) it happened Rene Tschaggelar
<none(a)none.net> wrote in <alFyn.169302$9b5.62115(a)newsfe01.iad>:

>detection diode. I measure the delay between the
>control pulse of the switch and the detection diode
>with a sufficiently fast scope doing a few GSample.
>The pulse shapes there are sufficiently rectangular.
>
>Rene

Did you take into account that the speed of the electrons in that tube is <<< c?
The turns per distance of the helix is chosen so the axial speed of
the RF signal is just below the speed of the electrons.
http://nl.wikipedia.org/wiki/Lopende-golfbuis
From: Tim Williams on 18 Apr 2010 20:19
"Jan Panteltje" <pNaonStpealmtje(a)yahoo.com> wrote in message
news:hqff0r$8sn$1(a)news.albasani.net...
> Did you take into account that the speed of the electrons in that tube is
> <<< c?
> The turns per distance of the helix is chosen so the axial speed of
> the RF signal is just below the speed of the electrons.
> http://nl.wikipedia.org/wiki/Lopende-golfbuis

Check my post from the 13th. If the total delay were due to the electron
beam, it would be powered by about 160V.

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms


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