common mode rejection graph of 1:1 RF transformers

[robismyname]

I measured the CMRR of a group of like transformers and recognized that some of the transformer plots are different. My question is which plot shows the best transformer and which plot shows the worst transformer ad why?

 

[BigBoss]

While blue one has approx. -22dB isolation, the purple one shows -15dB isolation at the frequency ( at red line ).But other parameters should be examined too.( Insetion loss,Port Phases etc.)

 

[FvM]

It looks like the frequency has been extended considerably beyond the useful transformer frequency range, in so far the upper part is probably meaningless. Assuming a simple single ended measurement setup, the inter winding capcitance is apparently varies by a factor of two. In case of doubt we would prefer the transformers with lower capacitance.

 

[chuckey]

CMRR is a dubious term to use on transformers. It means that if the voltages on two terminals are in phase what is the loss compared to if they are anti phase.
A precision centre tapped RF transformer might have a 40 dB balance.
What do you mean by CMRR and how are you measuring it?
Frank

 

[FvM]

CMRR is a dubious term to use on transformers.

At least not well defined. I confess that I was only concluding about the measurement setup from the curves. Although I'm almost sure how they were obtained, I should have said: the curves are pointless without showing the measurement circuit.