Thanks, I guess I'll have to examine it carefully next time I pull it down.It could be as simple as a loose screw. Honestly you will not figure it out until you look at the antenna physically.
Unfortunately, I don't think that's the case. My Diamond is now being outperformed on low band by a ham antenna.(2 meters/70 centimeters)That same antenna was performing a lot worse than the discone right after I put it up. I should have also mentioned in my original statement that the agencies I was listening to were local.Perhaps when you installed the antenna, the band was open and then it closed on you.
Just a thought.
I have done some experimentation with the D130 on low band. First, this antenna is not a discone on low band - it is a sort of base loaded ground plane. As was pointed out by prcguy, it tunes up at about 50Mhz and can be trimmed to work a little higher in the six meter band. The bandwidth is very narrow on low band - maybe about 4Mhz at the most. Here in California the main low band system is the CHP. They use frequencies from 39Mhz to 45Mhz with most of the activity around 42Mhz. The stock D130 is useless at these frequencies and the SWR is extremely high. I replaced the stock whip with one that is 48 inches long. The antenna is now resonant at about 42.5Mhz and does a good (not excellent) job with CHP. You don't say what portion of the low band you listen to, but a longer whip may be the solution.
The whip is 0.10 inch. They can be obtained from many radio supply outlets in various lengths.
I am considering building a 42Mhz j-pole. Rather long, but I think it will be effective. I had a 42Mhz ground plane for a while and it worked very well.