Fluctuating broadband speeds?

Why does bt broadband connection speeds fluctuate so much,i mean one second its 5,00kbps then a few minutes later its droped to 2,800kbps i still have my bt voyager 205,if i use this instead of my home hub will there be any problems,the hub resets when it wants to i had the voyager for over 18 months and it never played up once,but the home hub is a daily problem any advice on a decent adsl router modem cheers
Answer
I use bt broadband as well - there are reasons why fluctuation can occur 1.exchange distance between you and your server 2.bad weather 3.simutaneous logging to server etc.having said that try moving the hub a little bit, it might help.