First and foremost, understand that the PRN System itself is not a club or organization, therefore there are no members, no monetary dues, no application fee, no elected officers and no by-laws. Instead, the network is made up of independent, privately owned repeaters. These repeater owners have linked together to help create a network because they believe in the same idea: that having a wide-area linked digital radio system can be fun. Even though the repeaters are linked, the individual repeater owner retains full ownership of their repeater(s) and may decide at any time, without prior warning, who may use them and who may not. Per FCC regulations 97.205(e), “Limiting the use of a repeater to only certain user stations is permissible.” While this type of action is rare in the Amateur Radio world, there may be times when it is necessary. For example, it may be used where jamming is an issue. By using any repeater on the PRN System, you agree to these statements. Remember, since the repeaters are linked, if you violate FCC rules on one repeater, you may be doing it on every repeater!! Therefore, if you do not agree to these statements, that is absolutely your choice, and the repeater owners simply ask that you not use the system.
Below you will find some of the questions we hear the most.
1) Do I need to buy a Motorola radio to use the system?
No. You may use any portable or mobile radio that conforms to the DMR Tier 2 standard. We highly recommend only using Motorola, Kenwood or Tait, as they fully support the protocol. But you may use a Chinese radio (TYT, Anytone, etc) as long as the radio does not interfere with the other time slot. How can you tell if it is interfering with the other time slot? You can use echo test to hear if you have a flutter on your signal, or ask someone on the air if they hear a flutter or chopping. This is an indicator that your timing is off and the radio is bad. There is no fix.
2) What about if I want to add a repeater to the system, does it have to be a Motorola?
Due to the connection required between the repeaters, all of our repeaters must be Motorola. So if you are interested in joining the network as a repeater owner you must get a Motorola.
3) I am used to channels being individual frequencies, so what are talkgroup and zones?
Channels and talkgroups can be thought of as the same. The word ‘talkgroup’ will usually be heard in a commercial and public safety environment. When you turn the channel knob on the top of your radio, and let’s say for example that the screen changes from Raleigh PRN to Raleigh Chat 1, you are simply changing the talkgroup that your radio is going to try to talk to or listen for. You are still on the same frequency, which is sometimes why we can’t think of channels as frequencies in the digital world. But, when you are turning that knob, you are just telling the radio to only listen for and talk to other users in the same group, therefore it is a talkgroup.
Zones, on the other hand, are just memory banks. In the generic code plugs on the web site we have set up each repeater to be in a separate Zone, but there is no reason you could not place three repeaters in the same Zone, for example, other than you may be physically limited to 16 channels per Zone in some radios. Some people create a Travel zone and place the PRN talkgroup for each repeater in that Zone, so they just have to turn the knob to move to the next repeater on their route.
4) What does the Last Heard list tell me?
The Last Heard list can be used to see activity on the network. It will show you who is talking, and what talkgroup they are talking on. It will also show a Received Signal Strength Indicator (RSSI), which you can use to judge how well you are being received by the repeater. Lower numbers are better, so a -65 dBm is better than a -75 dBm. If you are above -105 dBm, you are probably (but not always!) having a hard time getting into the repeater and are probably suffering from packet loss. If you are keying up to see what your RSSI is, please do it on the repeater local talkgroup. That way you are not keying up all of the repeaters just to see how well your repeater is hearing you.
5) What is the deal with the XPR2500, XPR4350 and XPR3500 radios?
These radios have limited space, and we have exceeded the number of repeaters that you could possibly put in them and have full functionality. For example, the 2500 and 3500 radios only have 8 zones of 16 channels in each zone. We currently use 5 channels per repeater. So, even if you put two repeaters per zone with all of the possible talkgroups for each one, you would still not have enough room. The 4350 is even worse, it only has 2 zones of 16 channels.
6) Is the PRN System the same as the DMR-MARC system?
No, these are two different linked networks. In the DMR realm, several repeater owners have come together and built networks that cover different areas of the world. Just an example of some of these networks are DCI, NorCal, PRN, DMR-IL, GeorgiaDMR and MIT. These groups have agreed to use DMR-MARC as the central registration point and therefore DMR-MARC handles the ID numbers for the radios. Regardless, if you have any question about a repeater in a certain area, you should contact the network administrators or repeater owners who are responsible for that area, and not ask DMR-MARC unless it is a DMR-MARC repeater.
7) Can I use a RF amplifier on the PRN system?
As a general rule, no. The amplifier for a subscriber radio (handheld and mobile radios) must be TDMA compliant. There are no analog amplifiers that meet the TDMA specification without highly modifying the internal components.
It is important to remember that TDMA uses two time slots, and that each time slot is only transmitting for approximately 30 milliseconds. The amplifier ramp up and ramp down times allowed via the specification are only 1.5 milliseconds. Not only that, the ramp up time is also used to account for the speed of light delay for distant stations. So to put it all together, the radio has to energize the amplifier and the radiation has to get from your antenna to the repeater in 1.5 milliseconds, the radio then sends a 27.5 millisecond payload (your voice traffic), and lastly the radio must shut down the amplifier and stop transmitting in another 1.5 milliseconds so it does not overlap the next time slot. Analog radios and amplifiers do not have these same stringent requirements, and so they may not shut off in time, and you will be harming the next time slot. There are, of course, other issues that are too complicated to discuss in this area, but we invite everyone to read about the open DMR specification. If you choose to want to know more, the entire specification can be found on the ETSI web site at the following link.