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transmission line tap

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aloishis89

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Do surface mount RF taps exist? I'm trying to figure out how to be able to observe my signal through several RF stages. I feel like it's a bad idea to try to just put connectors in series with a transmission line though.
 

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Depending on the frequency you are working on; in low frequencies (~100 MHz) there is no problem with additional small (1-2 cm) stubs, but at high frequencies (~1GHz) stub length must be as small as possible to reduce its effect on frequency response. also it is possible to use series jumpers with stubs which could be made by 0 ohm 0603 resistors. also you could use another jumper to disconnect the next stage.
Also you could simulate loading effect of the stub/connectors with ADS or MW office and optimize or compensate its frequency response.

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Depending on the frequency you are working on; in low frequencies (~100 MHz) there is no problem with additional small (1-2 cm) stubs, but at high frequencies (~1GHz) stub length must be as small as possible to reduce its effect on frequency response. also it is possible to use series jumpers with stubs which could be made by 0 ohm 0603 resistors. also you could use another jumper to disconnect the next stage.
Also you could simulate loading effect of the stub/connectors with ADS or MW office and optimize or compensate its frequency response.

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To "tap" a RF line with a nominal 50 or 75-Ohm impedance, the only acceptable method is to use a directional coupler inserted in the line. A good coupler is well matched so it does not cause any mismatch. Use more than 10 dB coupling loss, and make sure tat the coupled output is terminated in 50 (75) Ohms.

Any other way of "tapping", capacitive or inductive probe, causes a mismatch on the line and can gravely disturb the components and the system. The higher the frequency, the worse the mismatch effect.
 

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A resistive 500 or 1000 ohm probe can be an acceptable compromise in many cases.
 

FvM

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1 or 2 GHz can work with homemade probes, I think. Agilent is specifying 6 GHz bandwidth for their passive probe. 0.25 pF input capacitance makes the probe purely resistive to > 1 GHz.
 

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aloishis89

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To "tap" a RF line with a nominal 50 or 75-Ohm impedance, the only acceptable method is to use a directional coupler inserted in the line. A good coupler is well matched so it does not cause any mismatch. Use more than 10 dB coupling loss, and make sure tat the coupled output is terminated in 50 (75) Ohms.

Any other way of "tapping", capacitive or inductive probe, causes a mismatch on the line and can gravely disturb the components and the system. The higher the frequency, the worse the mismatch effect.
So do you think it would be better to make a stripline directional coupler next to the transmission lines I'd like to tap or use one like this: http://www.minicircuits.com/pdfs/ADC-10-4.pdf
If I used the one from minicircuits, I'd have to figure out a way to make it removable (ie leave it unpopulated) without disturbing the normal operation of the circuit.
 

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