[GPS_Standard] Question abt. LTC1485

[Helmut Bayerlein]

Hello @all!

Now I've ready built my GPS standard. But I have problems with the input 
circuit LTC1485. At pin 6 (A) is a digital signal of abt 4V, but no output 
signal at RO. When looking into the data sheet, I found the description of RO 
pin (output): if A>B by 200mV, RO will be high. If A<B by 200mV, RO will be low.
Because B is at ground and A is TTL level, RO will never change its level. Is 
this correct? Is this LTC1485 really necessary?

Thanks for Your help!

73 de Helmut, dc3yc