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Directional Coupler Ratings - RF Cafe Forums
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Below are the old forum threads, including responses to the original posts.
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Test & Measurement
Post subject: Directional Coupler Ratings Posted: Thu Feb
24, 2005 10:19 am
I'm pretty new to RF engineering
and have a question about ratings on RF directional couplers. When the
spec says something like 2W max power, does that mean only when properly
terminated, or for any port termination (like open)? I need an answer
pretty quick, please, because I need to place an order ASAP. Thanks
Post subject: Posted: Thu
Feb 24, 2005 10:59 am
The parameter of power handling
is ususally given for rpoperly terminated ports.
Post subject: Posted: Thu Feb 24, 2005
The power rating is for average power. There should also
be a rating for peak power. The power rating of a direction coupler
refers to the input signal only.
You should also have ratings for
insertion loss and tolerance (dBm and %, respectively). The directional
coupler should be specified for frequency range and coupling (GHz and
dB). Other ratings can include frequency sensitivity, directivity, VSWR
on both the main path and coupled path, coupled losss, impedance, operating
temperatures and connectors.
subject: selecting 20-dB or 30-dB directional coupler and using it...Posted:
Tue Aug 21, 2007 6:49 am
Joined: Thu Mar
08, 2007 10:29 am
Could i ask, are there procedures
that i need to take in general in order to make sure that i connect
the directional coupler to a properly terminated port please?
I intend to use a dual directional coupler to measure the reflected
and forward power into a cavity on an oscilloscope. i intend to connect
a signal generator(MO) feeding power via a power amplifier(PA) into
a cavity via a loop coupler. PA has max output power of 60W CW.
1) to ensure proper termination, am i correct to first use a VNA
to make sure that the loop coupler is matched to the cavity, and then
disconnect the VNA and feed power into the cavity with the MO and PA
please? would this be enough to ensure proper termination for the directional
2) say for example i feed in 50W from the PA,
for a 20dB directional coupler, i'll couple out about 0.5W into the
oscilloscope. having Z0=50ohms, i suppose i'll observe a V=sqrt(0.5*50)=5V
average OR 7V peak voltage waveform on the oscilloscope...
assuming my above calculation is correct, if i use a 30dB directional
coupler, 0.05W couples into the oscilloscope, i observe a V=1.6V average
voltage on oscilloscope.....
Would using a 30dB directional
coupler be too much?? i am thinking in terms of VSWR and insertion losses,
bcos i see that 30dB directional couplers have better performance than
20dB directional couplers, but then will the small voltage amplitude
on the scope be too small and consequently noise dominates the reading
on the scope.
i look forward to hear from anyone for comments
or suggestions. Thank you for your kind attention.