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Electronics => RF, Microwave, Ham Radio => Topic started by: CopperCone on September 16, 2017, 02:24:41 am

Title: does a directional coupler need to be terminated to work right?
Post by: CopperCone on September 16, 2017, 02:24:41 am

If you have a directional coupler, does it need to be terminated to 50 ohms? Can you leave it floating when sampling is not being done?

or I found it

http://www.scte.org/TechnicalColumns/10-11-01%20why%20use%20terminators.pdf (http://www.scte.org/TechnicalColumns/10-11-01%20why%20use%20terminators.pdf)

Spigot and feeder were not terms I was familiar with before, but it makes sense.

Title: Re: does a directional coupler need to be terminated to work right?
Post by: KE5FX on September 16, 2017, 04:35:07 am

This:

https://www.microwaves101.com/encyclopedias/directional-couplers (https://www.microwaves101.com/encyclopedias/directional-couplers)

... is a good summary of the operation and theory behind couplers.

Title: Re: does a directional coupler need to be terminated to work right?
Post by: bjcuizon on September 16, 2017, 05:15:58 am

Sometimes they are already internally terminated like the one shown here: (and watch this video too for basics of directional couplers)
https://www.youtube.com/watch?v=iBK9ZIx9YaY (https://www.youtube.com/watch?v=iBK9ZIx9YaY)

Title: Re: does a directional coupler need to be terminated to work right?
Post by: bjcuizon on September 16, 2017, 05:23:39 am

Here's another video of The Signal Path. It is about microwave components in general but I linked it to the part where he talks about directional couplers.
https://youtu.be/6kwamCh1QkE?t=28m51s (https://youtu.be/6kwamCh1QkE?t=28m51s)

Title: Re: does a directional coupler need to be terminated to work right?
Post by: Antonio84e on September 24, 2017, 04:41:50 pm

If you have a 3port directional coupler and you are not using the coupling port, it's better to terminate it with a 50 ohm load for various reasons:
1. Depending on the coupling value, the higher this is (4dB for example), the coupled signal will reflect and couple back to the main line worsening the performance in terms of IL, VSWR, etc.
2. most of the coupled signal will reflect if the output port is not terminated and then this will couple back to the main line but most (depending on the coupling value) will go to the internal load. You may need to derate the input power in order not to damage the internal load.