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High power RF measurement setup - RF Cafe Forums
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| tmntRF
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Post subject: High power RF measurement setup
Posted: Thu Mar 08, 2007 10:57 am
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Joined: Thu Mar 08, 2007
10:29 am
Posts: 10 |
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Hello,
I am hoping i can get some information
and advice about taking measurements at high power.
i am thinking of a kind of RF system that is
like this:
a klystron delivering about 150kW
power to a cavity via waveguides.
in between
klystron and a circulator, i connect a directional
coupler to couple power to measure the delivered
power, and then another directional coupler between
the circulator and cavity to couple power to measure
the reflected power.
to measure reflected
power from a cavity, maybe 1 to 3kW, would i connect
an attenuator in between the cavity and reflectometer
please? or are there reflectometers that take inputs
at high power please?
I look forward to hear
of any advice or info i could use to understand
more about high power measurements, and make my
setup more realistic.
thank you for your
kind attention.
regards,
tmntRF
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sm7ovk |
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Post subject:
Posted: Mon Mar 12, 2007 4:31 am
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Joined: Thu Jan 11, 2007
12:59 pm
Posts: 16 |
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Hi,
normally you get this attenuation in
the coupler - ie if you have a coupling factor of
let say 60dB you will have a signal 60dB lower at
your measuring output. In your example 150kW is
the same as about 82dBm, with 60dB coupling you
will have 22dBm to your powermeter. If this is to
high you can easily attenuate it with a small attenuator
- or choose a higher coupling factor.
Remember
that you could be interested of a lower coupling
factor for reflected power measurement since the
reflected power, under normal conditions, is much
lower than forward power.
Regards
Jens
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tmntRF |
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Post subject:
Posted: Mon Mar 12, 2007 6:56 am
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| Captain |
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Joined: Thu Mar 08, 2007
10:29 am
Posts: 10 |
sm7ovk wrote:
Hi,
normally you get this attenuation
in the coupler - ie if you have a coupling factor
of let say 60dB you will have a signal 60dB
lower at your measuring output. In your example
150kW is the same as about 82dBm, with 60dB
coupling you will have 22dBm to your powermeter.
If this is to high you can easily attenuate
it with a small attenuator - or choose a higher
coupling factor.
Remember that you could
be interested of a lower coupling factor for
reflected power measurement since the reflected
power, under normal conditions, is much lower
than forward power.
Regards
Jens
Hi Jens, Thank you for your reply
and information. May i ask, this coupler
that you mentioned, it should be built-in inside
commercially available power meters?? Regards,
Yi
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sm7ovk |
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Post subject:
Posted: Mon Mar 12, 2007 2:18 pm
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| Captain |
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Joined: Thu Jan 11, 2007
12:59 pm
Posts: 16 |
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Hi,
no the coupler is a piece of waveguide
that you have to place in line with your existing
waveguide. You then connect your powermeter-sensor
to the coupled output of the coupler.
As you
mention the coupler for measuring output power could
be placed before the circulator and the coupler
for reflected power after the circulator - seen
from the transmitter.
You don't mention the type
of waveguide or frequency, but I'm sure that whatever
the type there are couplers to buy.
Regards
Jens
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tmntRF |
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Post subject:
Posted: Mon Apr 02, 2007 11:21 am
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Joined: Thu Mar 08, 2007
10:29 am
Posts: 10 |
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Hi Jens, how are you?
May i further ask,
does the attenuator, while attenuating the power
level to a reasonable level for monitoring, effect
the frequency of interest at all please? would a
practical attenuator introduce reactances to the
RF signal and then effects the frequency of the
signal i would like to measure please?
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sm7ovk |
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Post subject:
Posted: Mon Apr 16, 2007 2:21 pm
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Joined: Thu Jan 11, 2007
12:59 pm
Posts: 16 |
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Hi tmntRF,
no a real attenuator made for
high frequencies is purely resistive, (or at least
in theory), it'll never affect your frequency.
You will have some mismatch, ie reactance, but
most often this is so low you will not notice -
if you use an attenuator made for RF frequencies.
If you build your attenuator by yourself, it could
be different of course.
Regards
Jens
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Posted 11/12/2012
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