hi i am radio amateur at 160m. the problem is that when i operate my transmitter the transmitter create interference to the telephone.
i am thinking to put a circuit at telephon's line. My first thought is to put capacitors (10nf) which will ground the r.f. signal what do you think about this. Do you have any better proposition? some one tell me to put one adsl filter.

 

Caps are always a start but in your case may not be enough. You're operating around 1.875 MHz so DSL filters might be useful as they're basically a crude low pass filter used to block the individual phones from attenuating the DSL carrier. Easy enough to snag some free ones from your local telephone carrier to try.

With standard ADSL (annex A), the band from 26.000 kHz to 137.825 kHz is used for upstream communication, while 138 kHz – 1104 kHz is used for downstream communication.

 

I'd try the ADSL filters first. They should get rid of much of it.

 

Not sure where you are but in Australia it is illegal to put anything that hasn't been approved on to a phone line.