what is RF choke used for?

[winglj]

ferric choke

I am now doing measurement with network analyzer, somebody told me when the performance of DUT is significantly affected while my hand touching the connector, I should use RF choke... I am wondering what is RF choke and what is it used for? Any articles about that is appreciated, thanks in advanced

 

[eltonjohn]

like the name indicates is used to CHOKE or discard RF energy but allowing DC current through it.A choke is used wih a capacitor to provide the path to ground .. They are used in power supply feed lines to avoid RF getting into it!

 

[winglj]

to eltonjohn:
Thanks for your information, it make me more clear now. But I still have a detail question about the type of choke: because the choke I will use is like a coaxial cable surrounding with ferric materials.... I am not sure how it works to avoid RF currents.....

 

[rfmw]

If I understand you correctly, you have a coax cable with ferromagnetic ring(s) stuck onto it? This rings "attenuate" the RF current flowing onto the coax shield.

 

[eltonjohn]

that type of choke is more a transformer .capturing RF field and disipating it in a short circuited loop

 

[winglj]

To rfmw
Yep, that's the one you said. So do you have any online reference for that? I am just a little curious about its principle.....

 

[yibinhsieh]

RF choke is used for reducing the RF signal coupling to other blocks through the power line. For example, in power amplifier, the RF choke is necessary because the power is very large and will affect other blocks.

Yibin.

 

[winglj]

I am sorry, but I still wondering why do I need to "choke" the RF signal by using Network Analyzer? I think the RF signal (no matter goes into AUT or goes out) are used to measure the return loss or VSWR. If I choked the RF signal, then the DC current fed into Antenna can excite RF field, doesn't it?

 

[rfmw]

Hi,

Are you still refering to the use of the ferromagnetic rings-choke on the coax cable in the case of measuring the impedance/VSWR/S11 with VNA? As I said, these rings or this kind of choke prevents or attenuates the RF current flowing on the outer-side of the coax cable shield. This current can affect your measurement. That is, if you hold your antenna with the hand or a mechanical structure, you must ensure that the RF current does not flow on the coax shield. But where unavoidable, one must use these rings stuck on the cable to reduce this RF current...