Topband: Vertical resonance/bandwidth changed

[Harry Williams]

Hi,
 I have a 65 ft base loaded vertical with 60 132 ft radials. It's fed with 300 ft of buried 52 ohm coax and it's been up for about 3 years. When I first installed and tuned it the resonant freq on 160M was around 1820. The 2:1 swr points were 1805 on the low end and 1835 on the upper end. Recently I noticed that the resonant freq has shifted to about 1830 and the 2:1 swr points are now 1805 to 1865. Any ideas on what the most likely cause is...coax....connection to radials?? I am assuming that whatever it is the antenna is not operating as efficiently as it once did. Any ideas would be appreciated.

73's
Harry
W0PIY