critter449
Member
i know that the FCC assigns frequencies but i was just wondering who assigns a pl or dpl to a frequency. is it the FCC who does this and if so why are the pl or dpl tones not given on their website.
pl or dpl tones
- Thread starter critter449
- Start date
- Status
EMTLJB
Member
The FCC does not assign PL/DPL with frequencies. It is up to the user to coordinate the use of these sub-tones if they desire.
b7spectra
EMS Dispatcher
Normally, if it is done right, the customer will have researched the frequency they wish to use, as well as ascertain all the other users on the channel as well as the pl/dpl that are being used. Most actually use scanners with a pl/dpl search mode to ensure they will have a quiet channel.
critter449
Member
thanks
thank you all for your great responses to my post.
clears a lot up for me now.
thank you all for your great responses to my post.
clears a lot up for me now.
RKG
Member
A couple of other points to consider.
Some techs like to avoid PLs that are nearly a multiple of 60 Hz, on the theory that a ground hum leaking around a power supply might generate a false positive on tone test. In my neck of the woods, 131.8 is virtually a standard for PD output tones, and I've never noticed a problem.
Many techs like to avoid the higher range PLs, since the closer you get to the skirt of the high pass audio filter, the more likely it is that enough of the tone will leak past to be audible to users. This concern is valid; I like to keep below about 150 Hz.
From time to time people will debate whether lower tones take longer to be detected as valid by tone detection circuits. In theory, most such circuits require a minimum number of valid zero voltage crossings, and by definition, a PL of 198.2 crosses the zero point three times faster than a PL of 77.0. The only rigorous test I know of was conducted by some Batlabs folks a few years ago, and the conclusion was that a tone detect time of 160-200 msec was pretty consistent regardless of test tone value.
Finally, one thing to be cautious about is where a co-channel licensee is using DPL for input. I have observed that a PL-guarded system using 131.8 Hz will false on the DPL turn-off code, so that each time a high enough powered subscriber on the DPL system unkeys, the PL system will key up momentarily.
Some techs like to avoid PLs that are nearly a multiple of 60 Hz, on the theory that a ground hum leaking around a power supply might generate a false positive on tone test. In my neck of the woods, 131.8 is virtually a standard for PD output tones, and I've never noticed a problem.
Many techs like to avoid the higher range PLs, since the closer you get to the skirt of the high pass audio filter, the more likely it is that enough of the tone will leak past to be audible to users. This concern is valid; I like to keep below about 150 Hz.
From time to time people will debate whether lower tones take longer to be detected as valid by tone detection circuits. In theory, most such circuits require a minimum number of valid zero voltage crossings, and by definition, a PL of 198.2 crosses the zero point three times faster than a PL of 77.0. The only rigorous test I know of was conducted by some Batlabs folks a few years ago, and the conclusion was that a tone detect time of 160-200 msec was pretty consistent regardless of test tone value.
Finally, one thing to be cautious about is where a co-channel licensee is using DPL for input. I have observed that a PL-guarded system using 131.8 Hz will false on the DPL turn-off code, so that each time a high enough powered subscriber on the DPL system unkeys, the PL system will key up momentarily.
n1das
Member
PLs are tones. DPLs are codes, not tones.
Regarding the DPL false-decoding PL131.8, I've seen it happen in some PL decoders. It's more of a problem with PL136.5 since a DPL code is sent at 134.4 bits/sec. The "turn off" code at the end of a DPL-encoded transmission sounds like a 134.4Hz tone, causing at PL136.5 PL decoder (and sometimes 131.8) to falsely decode it as a valid PL tone. This is often referred to as the DPL kerchunk problem.
My favorite PL tones are tones in the middle of the range and I avoid using tones known to be problematic.
- I avoid all tones below 100.0 Hz due to some noise sources causing decoders to false-decode plus some false decode on adjacent tones. I've witnessed a case where a PL decoder set for 74.4Hz was false decoding on 71.9Hz and 77.0Hz tones. The higher tones don't suffer from this due to them being spaced farther apart in frequency. Some PL decoders are better than others.
- I avoid tones that are close (within +/- 2 Hz) to harmonics of 60Hz: 118.8Hz (2nd harmonic at 120.0Hz), 179.9Hz (3rd harmonic at 180.0Hz)
- I avoid 131.8Hz and 136.5Hz due to the DPL kerchunk problem.
- I avoid all tones above 167.9 due them being more audible and annoying. I've also witnessed voice frequency components falsely tripping some PL decoders set to decode the higher tones. Ever listened to 254.1Hz? It's a real screamer of a PL tone!
My favorites are: 123.0, 127.3, 141.3, 146.2, 151.4, 156.7, 162.2, 167.9. I use 141.3 as my default tone.
Good luck.
Regarding the DPL false-decoding PL131.8, I've seen it happen in some PL decoders. It's more of a problem with PL136.5 since a DPL code is sent at 134.4 bits/sec. The "turn off" code at the end of a DPL-encoded transmission sounds like a 134.4Hz tone, causing at PL136.5 PL decoder (and sometimes 131.8) to falsely decode it as a valid PL tone. This is often referred to as the DPL kerchunk problem.
My favorite PL tones are tones in the middle of the range and I avoid using tones known to be problematic.
- I avoid all tones below 100.0 Hz due to some noise sources causing decoders to false-decode plus some false decode on adjacent tones. I've witnessed a case where a PL decoder set for 74.4Hz was false decoding on 71.9Hz and 77.0Hz tones. The higher tones don't suffer from this due to them being spaced farther apart in frequency. Some PL decoders are better than others.
- I avoid tones that are close (within +/- 2 Hz) to harmonics of 60Hz: 118.8Hz (2nd harmonic at 120.0Hz), 179.9Hz (3rd harmonic at 180.0Hz)
- I avoid 131.8Hz and 136.5Hz due to the DPL kerchunk problem.
- I avoid all tones above 167.9 due them being more audible and annoying. I've also witnessed voice frequency components falsely tripping some PL decoders set to decode the higher tones. Ever listened to 254.1Hz? It's a real screamer of a PL tone!
My favorites are: 123.0, 127.3, 141.3, 146.2, 151.4, 156.7, 162.2, 167.9. I use 141.3 as my default tone.
Good luck.
Last edited:
jim202
Member
On the other hand, if you have someone using DPL and they are becoming a problem, if you use an
encode on 136.5 on their RX frequency, it will cause their receivers to mute. The game can be played
both ways.
Jim
encode on 136.5 on their RX frequency, it will cause their receivers to mute. The game can be played
both ways.
Jim
Lots of good info there, thanks for posting it.
It's nice to see reason and technical consideration put behind the decision instead of "Just make it so it different than XYZ system" and be done with it. The result of which is many people I know using PLs that you've listed as problematic, be it FRS/GMRS, HAM or public safety; and several of those have let me witness some of the issues listed above.
- Status
