Traffic receiver (gtm12)

Hi all, I know this is old kit these days but with our cars having built in sat navs, I keep my old Nuvi 310 for work vehicles and use the GTM12 traffic receiver to warn me of problems so that I can avoid them. However, it is now giving me no help at all. Around my home area (North Yorkshire) there is plenty of data available but as I travel south down the A1, the data disappears and is replaced with "no traffic data available". This is like this all the way down to Cambridge area and all the way back too with the exception of some sporadic entries around the Grantham (Lincolnshire) area. Can anybody help?
Many thanks in anticipation.

 

I'm was beginning to think my unit is faulty somehow but I think I may have solved it. Some time back, ( in the last 6 months or so) the power supply started to play up. Thinking nothing more of it, I just dug out my spare one. Just realised that my problems with the traffic receiver started around the same time. Reading through some old forum threads (back to 2007), it appears there was a problem with some of the power supplies, apparently it was an issue with suppression causing interference with the fm traffic signal, powered the satnav fine but interfered with traffic.
Have now repaired my dodgy power supply (just a quick solder job) so hopefully all will be well again. Find out on Tuesday.