Why Incoming Calls disconnect Broadband Router?

[#1]

Hi all,
I am new to this forum.
I am having problems with my Router disconnecting frequently.  I have narrowed it down to the cause being incoming calls in addition to normal expected occasional disconnects.  I have a long copper line from my exchange - 4.7km.  So, the broadband speed is expected to be low.
It is baffelling a lot of people including Phone and ADSL enginoeers.  I fail to undersatnd why this can happen..  Is the problem with the copper wire connections enroute to premises?  Is the problem at the exchange?    I am sure experts out there might be able to sus this out. 
Can any one help?  Help will be appreciated.
Chandu.

[#2]

I have/had this problem which seemed to be caused by the ringing not by the actual call.
Since double filtering the phone it seems to have got much better although when there is a call the upstream errors jump a bit.
One way to check is to disconnect the phone and ring in using your mobile. You can then see if the ringing causes the problem

[#3]

Thanks OldJim,
I get a number of disconnects, some during/after late night and some during the day.  The day ones have now been isolated to incoming calls and only after receiver has been lifted to answer.
I already have the NTE5 socket with BT's filtered face-plate so the router and the phone have built-in filtered sockets.  I suggested to double filtering the phone socket to the BT Telephony Engineer, but he did not like the idea.  I suppose the filtered face-plate may have developed a fault! 
I have ADSL engineer booked through PN for Monday 6th, so I better wait and see what he has to suggest and I may try the double filtering the phone socket after his visit.
I am open to more suggestions.
Thanks guys.
Chandu.

[#4]

HI chandu,
I think Jim's suggestion is definitely worthy a try. I see there is another engineer due out on Monday, so I'd be interested to see what happens there.
Jojo

[#5]

Hi Jojo,
Thanks for your input.  I have had so many disconnections lately that the DLM has relegated me to low speeds.  Yes, I will try the double filtering after the Engineer's visit.  If I do it now, it may cloud the main issue of incoming calls affecting the ADSL.  I still suspect the gremlings in the exchange - possibly my line board in the exchange!!!
Thanks for your help.
Regards
Chandu.