Amplitude imbalance between I and Q in a demod board, AS11, with the new 90 deg splitter was measured.
It shows roughly 10% amplitude imbalance when the LO power is in a range from 0 to 5 dBm. Not so bad.
With the handmade coil there used to be a huge imbalance (either I or Q goes to zero volt while the other keeps about 1 V rms) as the LO power decreases.
But with the new 90 deg splitter now there are no more such a huge imbalance.
The remaining 10 % imbalance possibly comes from the fact that we are using ERA-5 in each I and Q path. They may have such gain imbalance of 10%.
We should check the ERA-5 gains so that we can confidently say ERA-5 causes the amplitude imbalance.
Then our plan replacing the ERA-5s (see here) will sound more reasonable.

Quote from #4555 |
The new 90 deg splitter works better.
I will also measure amplitude unbalances between I and Q.
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