Question on transformer used on AD9172-FMC-EBZ and clock frequency

Hello,

AD 9172 DAC output is connected to transformer  TCM1-83X+. It is 1:1 transformer. 

DAC data sheet says that DAC output has 100 Ohm impedance. 

Should the transformer be 2:1 transformer?

What is the max DAC sampling that can be achieved in 1x bypass mode with single-link mode 20?

What is single-link mode and dual-link mode? I did not find any explanation for that.

Thanks,

Mallesh