Using 10 dB coupler for return loss measurement & 20 dB pad placement

Hello,

I have a mini-circuits ZHDC-10-63-S+. Would that work in place of a ZHDC-16-63-S+ for return loss measurement using the BB60C and USB-TG124A? The main difference between the devices seems to be 10 dB coupling vs 16 dB coupling.

Does the optional 16 dB – 32 dB attenuator with “Store 20 dB Pad” calibration apply to return loss measurements? If so where in the setup should it be placed?

Thanks,

Jeremy

Jeremy,
Your coupler will work fine. For return loss measurements, there is no reason to “store 20 dB pad” because 50 dB of dynamic range is more than enough for a return loss measurement.
For return loss measurements, if you have 3-6 dB SMA attenuators around, putting one on the TG and one on the BB can improve SWR which will make the measurements more accurate.

Thanks for the info.

For cases where accuracy is needed below -40 dB the procedure is:
1. Connect TG to SA through circuit to use as 0 dB reference.
2. Store Thru
3. Connect 20 dB attenuator between TG and circuit.
4. Store 20 dB Pad
5. Remove 20 dB attenuator, reconnect circuit. Now system is corrected for readings below -40 dB.

It’s steps 3 – 5 that weren’t entirely clear to me from the manual.

Yes, but the scalar system for return loss only has the dynamic range of your coupler’s directivity, which is less than 40 dB. So it is not recommended to “store 20 dB pad” for return loss, only insertion loss.

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