Y did they go DPL? Newer Tech.?
DPL = Digital PL = "Definitely Prevents Losers"
I don't know why the change happened but I'll venture a few guesses:
1. More available code choices that aren't in use by other departments on the same frequencies.
2. Co-channel interference problems, particularly during band openings. BPD shares freqs with towns in VT and possibly in other neighboring states (CT & RI). VT and BPD have probably heard each other over the years during band openings. BPD and towns in VT use the same PL tone (118.8). I've heard Hartford VT PD (White River Jct VT) mention hearing BPD in the past. I know VTSP changed from PL118.8 to PL162.2 on their Mt. Ascutney (Windsor VT) repeater on 460.475 a few years ago because of problems they were having (unknown if it was due to BPD's use of 118.8).
3. PL118.8 is a VERY BAD PL tone to use. It's very close to 120.0Hz, a harmonic of 60.0Hz. Sometimes a radio operating from a power supply that isn't well filtered and regulated will have 120Hz full-wave ripple in the audio. PL decoders in receiving radios set to decode 118.8Hz can false decode on the 120Hz power supply hum.
4. Intermod problems at the repeater sites may have AC power line ripple noise in the offending signal's modulation, appearing as a power supply buzz (120Hz) in the audio, causing false decode problems (falsely decoded as 118.8).
5. DPL provides better squelch tail elimination at the end of transmissions. DPL has a "turn off" code at the end of a transmission to get rid of a squelch tail. It seems to work better than squelch tail elimination with PL. You'll notice a lot fewer long squelch tails with DPL. Overall the radio system sounds more professional with DPL.
6. Some of BPD's channels already have been using DPL. I suspect this was tried a few years ago as a solution to some of BPD's radio problems and it proved to work well enough to be worthwhile to make the change across the board. So to answer the earlier poster's question, YES it is newer tech than PL.
I've been a licensed GMRS user for several years (since 1992) and I've finally made the switch to using DPL full-time on GMRS. I've pretty much abandoned the use of PL entirely on GMRS. In urban areas, it's getting tough to find a clean PL tone to use when setting up a GMRS repeater to avoid keying up multiple repeaters on the same freq pair. I've also had to make the switch out of necessity to be able to better ignore the unlicensed "bubble pack" radio users.
I have a couple of GMRS repeaters and they now operate on DPL full time. No PLs at all! I made the change on my repeaters to help keep the riff-raff out. I've also made the switch to using DPL instead of PL on the VHF MURS freqs, like what I've done on GMRS. No more PLs for me on GMRS and MURS!
There are lots of good reasons for using DPL instead of PL. I'm not surprised at all that BPD made the switch to DPL.