VOR/DME range
First one guy above posted that he could only get the SAM VOR at 60NM range at FL110.............. Get the system checked mate, your VOR unit of most likely the aircraft instalaton has a big problem, at that FL you should be getting the VOR at 100NM+
DME range is all about transmitter power and height at around the FL70 mark I can usualy get a DME station at 130-140NM provided it is not to near a major airport.
As you may know a DME station can only work 200 transmitters at a time and the weekest transmitters get pushed off the system. most modern airliners have five DME units 2 for use with the VOR/ILS and 3 to update the FMS/IRS and these usualy have a TX power in the order of 200W.
So you can so why those of you with a badly adjusted Narco DME are lucky to get DME at over 20 miles if you are near to a major airport as you are very lucky to get more than 40W TX power on a good day out of these units.
If you have a King KN64 you will get a lot better performance this unit will make 60W TX power at the very least, the KN62A and KN63 (same tx unit) will push out better than 100W so are at the top of the tree when it comes to DME range.
The King units are some of the very best bits of GA avionic kit in terms of reliability and usualy work for years without giving trouble, the more modern Narco units are not bad but need a lot more TLC if you want them to work well. If you have a Narco unit that is a bit suspect I can recomend the avionic shop at Stapleford as peope who understand these units an can get the best from the limited power avalable.