- PL/DPL INFORMATION
		- PL - CTCSS Introduction
		- DPL - DCS Introduction
		- PL/DPL Usage
		- PL/DPL Reverse Burst
		- Operator Select Multiple PL/DPL (MPL)
		- PL/DPL Programming Notes
	- Syntor X Home
	- HOME

This is an explanation of the Syntor X receiver PL/DPL, transmitter PL/DPL, reverse burst and MPL. See the PL / CTCSS page and DPL / DCS page for additional background information.

PL - CTCSS introduction:

PL is Motorola's trademark for for Continuous Tone-Coded Squelch System (CTCSS). These tones all operate below 300 Hz while the voice modulation operates from 300 Hz to 3000 Hz. These tones are not really sub-audible, except that the radio receiver filters out anything below 300 Hz. Encoded tones are sent by the transmitter and decoded tones are used by the receiver. When used, the receiver must receive the programmed tone or it will mute the audio output (i.e. the operator will not hear anything from the radio unless the programmed tone is present). There are 42 standard Electronic Industries Association CTCSS tones from 67 Hz to 254.1 Hz. The Syntor X can be programmed for all standard tones and non standard tones. You can use a formula to convert the desired tone frequency into a Syntor X 14 bit programming code so you can program a wide variety of tones. However, there are cutoff filters that make it difficult to go much above 254.1 Hz and frequencies around or below 60 Hz are not very practical (I have not even tried them). For example, some MARS operators may need a tone of 150 Hz and the Syntor X can be programmed to encode and decode this tone.

DPL - DCS introduction:

Just like PL and CTCSS, in real life DPL and DCS are the same thing, but if it isn't Motorola it isn't DPL (see trademarks at the bottom of the page). This is the reason for the mixed use of DPL and DCS in the paragraph below.

DPL is a digital code version of PL. DPL consists of a 9 bit coded value (this is 3 octal numbers, see the glossary) so there would theoretically be 512 different DPL codes. In reality if the DPL signal is electronically inverted it will appear as another different DPL code. For example when Tx DPL code normal 244 is programmed and its DPL signal is inverted, it will match Rx DPL code normal 025. Notice if a logical inversion of the 3 octal digits 244 is performed you get 533, so do not confuse an electronically inverted DPL signal with a logically inverted DPL code. Check out the DPL page for lots more information.

PL/DPL usage:

The basic premise behind PL/DPL is: stations that share the same frequency, but use different PL/DPL codes do not have to listen to each other. HAM radio operators do not have much use for this application of PL/DPL. PL/DPL is also used to protect repeater input frequencies among other uses. Basically, the transmitting station must transmit a PL/DPL code and the receiving station must use the same Rx PL/DPL code. If the PL/DPL codes do not match the receiver remains muted and the operator does not hear the transmitting station. Some multiple repeater systems use PL/DPL to select which repeaters are used. If the receiver uses carrier squelch (i.e. no PL/DPL) then all stations on the frequency are heard regardless of any transmitted PL/DPL. The "Private Line" part of the names is not to be taken literally because there is really nothing private about it when it comes to monitoring.

The designed feature of not hearing stations that do not transmit the matching PL/DPL can cause a problem. When someone does not hear any activity on a frequency they assume it is not in use and they can transmit. With receive PL/DPL the frequency can actually be in use, but the receiver does not hear it. This creates the potential problem of two or more stations unknowingly transmitting simultaneously and interfering with each other. The solution is the Syntor X accessory called the hang-up box. When the microphone is removed from the hang-up box the PL/DPL receiver squelch is disabled allowing the operator to hear everyone on the frequency. It's a natural, pick up the microphone and find out if it's really clear to transmit. Put the microphone back and the unwanted signals without matching PL/DPL disappear.

If you do not use receive PL/DPL, the hang-up box is still a very sturdy, very nice microphone hangar.

PL/DPL reverse burst:

Reverse burst only applies to radios using PL or DPL encoded receiver squelch. Reverse burst actually changes the way the transmitter operates for the benefit of the receiving station. Radios using carrier squelch do not need or benefit from reverse burst.

To understand reverse burst, first you have to understand how PL or DPL coded receiver squelch operates. The normal setup for receiver PL or DPL coded squelch is STD/STD which mutes the receiver audio and runs the squelch setting wide open (maximum noise would be heard on a frequency without any activity, except the audio is muted). This helps ensure maximum receiver sensitivity. When the radio receives a signal with a matching PL/DPL signal it will unmute the receiver audio so you can hear the signal. Since there is now a received signal present, the noise previously mentioned is absent. However, when the received signal disappears at the end of the transmission, there is a brief period of time before the receiver can detect the loss of PL or DPL and mute the audio again. This brief period of time causes a short burst of noise in the receiving radio speaker commonly called a squelch tail.

Reverse burst causes the transmitting station to go through a special process every time the transmission ends. When the transmitting station releases the PTT the transmitter will still transmit for about 180 milliseconds. During this 180 ms time, a transmitted PL signal phase will be abruptly changed by 120 degrees (other radio manufactures use an incompatible 180 degree phase shift). A transmitted DPL signal will be changed to a special tone around 130 Hz that does not match the programmed receiver DPL. This gives the receiver time to decode and recognize the loss of a valid PL or DPL and mute the receiver audio before the transmitted signal disappears, which is while the receiver is still quiet. This eliminates the squelch tail noise burst in the receiver speaker.

The reason for using a phase shift for the PL reverse burst probably came about because in the old days mechanical resonate reeds (called Vibrasponders) were used to detect PL tones. The sudden PL signal phase shift of the resonate frequency PL signal would more quickly reduce the vibrations of the reed, rather than letting the vibrations wind down on their own as in if the resonate frequency PL signal was simply changed to a non-resonate frequency or removed. Without the reverse burst phase shift, the old Vibrasponder PL squelch would probably not close very quickly.

The different PL reverse burst phase shift used by Motorola as compared to other manufactures is why Motorola PL reverse burst usually does not work with other brands and why their CTCSS reverse burst usually does not work with Motorola radios. Keep in mind that PL and CTCSS do work together, the reverse burst is the only thing that can be incompatible. DPL reverse burst is compatible with other manufactures DCS reverse burst.

The effect of loosing the squelch tail is very pleasant to the ears of the human receiver.

On radios equipped with DVP the reverse burst is turned off when transmitting encrypted audio and turned on when transmitting normal voice. The optional HLN4425A or HLN5008A DVP Interface Board (located on the Personality Board) takes over direct control of enabling / disabling the reverse burst.

Non-DVP radios install Personality Board jumper JU2 to enable reverse burst. For packet data radios JU2 should be removed to ensure rapid switching between transmit and receive.

Operator select multiple PL/DPL (MPL):

A PL/DPL option is the System 90*s operator select multiple PL/DPL control head (MPL). This external control head allows the operator to select up to 8 PL/DPL receive and/or transmit MPL codes or use the PL/DPL code already programmed for the mode (via the MPL OFF button). Any mode that is programmed to use this control head may use one of the 8 selected PL/DPL codes. There can be separate control head boards for receive PL/DPL (decode) and transmit PL/DPL (encode), or a single control head board can be jumpered to do both receive and transmit PL/DPL (decode and encode). The EEPROM normally uses 512 bytes to store up to 32 modes of information while the EEPROM actually has 1024 bytes of addressable storage space. The codes selected by the System 90*s operator select multiple PL/DPL interface are stored in the portion of the EEPROM that is not used for mode storage. The jumpers on the control head MPL board must be set to match the address where these MPL codes are stored. The MPL codes stored at these addresses are programmed using bytes 4,5,6 and 7 exactly like they would be programmed for any regular mode. Any mode can select transmit or receive MPL and its Squelch Type (see table below). There is a OFF button on the MPL control head that is used to turn MPL on or off. When MPL is turned off the modes will use the PL/DPL programmed for that mode instead of the MPL PL/DPL.

Another project is to show a modification for the 8 mode System 90*s operator select multiple PL/DPL control head (MPL) that will convert it to a 32 mode MPL.

For each mode in the radio (up to 32 modes maximum) there is receiver and transmitter PL/DPL information programmed into the EEPROM. The receiver PL/DPL is used to control the receiver squelch opening when a matching PL/DPL signal is received. The transmitter PL/DPL sends the programmed PL/DPL signal along with the transmitted audio. Radios equipped with DVP automatically disable the PL/DPL modulation path when transmitting data (i.e. encrypted voice). In this case PL/DPL is disabled because the DVP data and PL/DPL share some of the same bandwidth and would interfere with each other. Normal voice transmissions are above 300 Hz and PL/DPL is below 300 Hz so they do not interfere with each other.

PL/DPL programming notes:

The Syntor X code plug bit map can be programmed for the desired receiver PL/DPL and transmitter PL/DPL. Each mode (up to 32 maximum) must be individually programmed. This discussion will be for a single mode (the other modes program the same way). MPL PL/DPL codes are programmed into bytes 4, 5, 6 and 7 as described below, but they are not stored with any other mode information.

• Receive PL/DPL can be disabled by setting byte 7, bit 6 to "DPL Code" and bit 5 to "DPL Disable". Transmit PL/DPL can be disabled by setting the same bits in byte 5.
• The System 90*s operator select multiple PL/DPL control head (MPL) may be enabled for decode (receive) use by setting Byte 7, bit 7 to "MPL Operator Select". The encode (transmit) can be enabled by setting the same bit on byte 5. Make sure you have the System 90*s MPL control head if you program MPL.
• Receive PL/DPL codes also require setting the squelch type, byte A bits 5 and 6. Here is a table of the 3 squelch types:

  SQUELCH TYPE

  STD/STD

  AND/STD

  AND/OR

• The STD/STD squelch type guarantees the best receiver sensitivity possible. AND/STD is not used in the factory PL/DPL programming. AND/OR is a special squelch type used when distant, weak, unwanted signals with the correct PL/DPL are causing the receiver squelch to open. AND/OR uses the squelch potentiometer on the control head to reduce the receiver sensitivity and eliminate the weak signals. When carrier squelch is programmed (i.e. receiver PL/DPL is disabled) it does not seem to matter which squelch type is chosen, except when the decode (receive) "MPL Operator Select" bit is set, then it does matter. Any MPL codes selected from a mode will use the squelch type programmed for that mode.
• Previously, the difference between an electronically inverted DPL signal and a logically inverted DPL code was pointed out. The reason for this is the DPL codes are logically inverted before they are stored in the EEPROM (i.e. DPL code 244 is stored in the EEPROM as 533). A normal DPL signal or an electronically inverted DPL signal can be programmed with bit 7 of byte 4 or byte 6. So you should not confuse the two different types of inversions.
• To program a transmit DPL code, first look up a DPL code from "Tx and Rx DPL Codes" table at http://home.xnet.com/~pakman/syntor/syntorx.htm. Logically invert the selected DPL code and put it in an ABC form (i.e. code DPL code 306 logically inverted is 471, so A=4, B=7, C=1). Then put the binary value for 4 into byte 5, bits 3 and 4 and byte 4 bit 0, the binary value for 7 in byte 4 bits 1, 2 and 3, the binary value for 1 in byte 4 bits 4, 5 and 6. Decide if you want it to be a normal or inverted signal and set byte 4 bit 7. Then set byte 5 bit 6 to "DPL Code" and Byte 5 bit 5 to "DPL Enable". Lastly set byte 5 bit 7 to use the MPL control head or not. It works exactly the same for receive DPL codes except bytes 6 and 7 are used instead of bytes 4 and 5.
• When an electronically inverted DPL signal is programmed it can also be decoded and recognized by its corresponding normal DPL signal (i.e. a Tx DPL 244 inverted signal can be decoded as Rx DPL normal signal 025 or Tx DPL 025 inverted signal can be decoded as Rx DPL normal signal 244). See the "Tx and Rx DPL Codes" table at http://home.xnet.com/~pakman/syntor/syntorx.htm for a list of DPL normal codes and their corresponding inverted signal values. Of course a DPL inverted signal can always be received as the same inverted signal (i.e. Tx DPL 244 inverted signal can be decoded as Rx DPL inverted signal 244) just like DPL normal signals can match.
• To program a PL tone just pick a ready to use code from the table. You may want to change the MPL operator select bit to use the System 90*s control head. The supplied formulas can also be used to make custom PL tones. If you use a formula to calculate the PL code, take note that the PL bits are also logically inverted and then the two bytes of the 16 bit integer are swapped before they are saved in the EEPROM. To double check your PL tone calculation just use the formula for a standard tone and your result should match what is in the table.
• If you program the MPL operator select bit and do not have the System 90*s MPL control head installed, the radio will be stuck in MPL mode. Even worse, because the radio reads incorrect data when the control head is missing it will probably not have any PL at all for any programmed MPL modes.
• My limited testing has shown the PL bandwidth is about 4 Hz wide (+ 2 Hz and - 2 Hz from the programmed tone frequency), however, only 1 Hz (+ .5 and - .5 from the programmed tone frequency) of this is reliable enough to be usable. When programming your own PL tones be aware that other PL tones within about 2 Hz of your tone may open your squelch, although the squelch may open intermittently further than about .5 Hz away from your tone.

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PL, Private Line, DPL, Digital Private Line, Vibrasponder, MPL, Talkaround, MDC-600, MDC-1200, MVS-20, Securenet, Smartnet, Privacy Plus, Trunked X2, Trunked X3, Touch Code, Quick Call II, Channel Scan, Talkback Scan, System 90, System 90*s, Systems 9000, Mitrek, Micor, Spectra, MataTrac, Syntor, Syntor X, Syntor X 9000 and Syntor X 9000E are trademarks of Motorola Inc.