Hello to all members.
I would like your opinion about the case of measuring the 3rd order intermodulation distortion of the 8563E spectrum analyzer. In the calibration guide, pages 491-499, it is recommended to use two similar directional couplers (p/n: 0955-0098). In our case, we have only one of them (and was not able to locate a replacement model with similar specifications).
My question has to do the necessity of the second coupler. Apparently it is there for a reason (I have tried in the past, with another SA, using only one coupler and got results a little out of specs), however I cannot understand why.
Does anyone have a clue about that? Or could someone suggest a similar design (even better: an alternative method for the calibration) for the second coupler?
Thanks for your time.
I would like your opinion about the case of measuring the 3rd order intermodulation distortion of the 8563E spectrum analyzer. In the calibration guide, pages 491-499, it is recommended to use two similar directional couplers (p/n: 0955-0098). In our case, we have only one of them (and was not able to locate a replacement model with similar specifications).
My question has to do the necessity of the second coupler. Apparently it is there for a reason (I have tried in the past, with another SA, using only one coupler and got results a little out of specs), however I cannot understand why.
Does anyone have a clue about that? Or could someone suggest a similar design (even better: an alternative method for the calibration) for the second coupler?
Thanks for your time.
As for the use, it is necessary for two reasons:
1) The intermodulation of the sources can mask the intermodulation of the spectrum analyzer. So it is important to isolate the sources as much as possible. The directivity of the second coupler reduces the signal level from the first source mixing with the second source. Other possibilities are to use isolators, high-isolation combiners, narrowband filters or a combination.
2) The coupler also isolates the spectrum analyzer from any source mismatch. You can use an attenuator instead.