Just wanted to update this thread a bit since the information regarding the DMR system and items that will be used for the near future were brought up in this thread previously. The county did approve the purchase of a new radio P25 Phase 2 radio system at last night's council meeting and there is a new thread
here related to that.
I wanted to clear up a few things that were mentioned earlier in this post and hopefully answer some of the questions people asked.
First, there were a couple of people that mentioned grabbing some UHF General pairs from the PW pool. This was tried multiple times and no pairs were able to be acquired due to the abundance of licensed UHF PW pairs throughout the region. There were some pairs that could be licenced but would be limited to only very small footprints in certain sections of the county. Nothing that could be used on a larger scale. Fortunately, we were able to grab the two med pairs that were available and had them licensed at multiple sites throughout the county. Being that we could only obtain these two additional pairs, it was necessary to maximize our potential with what was available. Many agencies in the county, both police and fire, already owned DMR capable equipment that they were using as their daily radio on the normal analog conventional system. This coupled with the need to maximize the limited two additional UHF pairs lead to the decision to go DMR for the alternate radio system.
I wanted to avoid any type of IP site connect with roaming if possible. With that in mind we found a viable solution in the Kenwood Kairos repeaters which allowed us to quickly deploy a 5 site DMR conventional SIMULCAST system. The Kairos repeaters in use connect to one another via IP but there is no need for roaming between pairs which eliminates the delays and safety issues that other DMR roaming type systems have the potential to create. The system provides countywide portable on street coverage on both UHF pairs. Two repeaters at each of the sites, one for each pair.
Talkgroups on the system include:
Police-A (Alternate) - Officers can quick switch to this with single button if unable to use normal analog conventional channels
Police-B - Available for full sector fail back
Police-C - Available for full sector fail back
Fire-A (Alternate) - Fire and EMS quick switch with one button if unable to use normal analog conventional channels
Fire-B
Fire-C
These channels have been used extensively over the last year since their inception and have proven to work well as an alternate not only when ducting is bad but also when there has been intentional interference on channels.
The NX-5300 radios that were purchased along side this system at the time were purchased because they could be used with all channel types that were available within Delaware County. Some of you may not know this but the TAC teams in the county run P25 conventional simplex during tactical/SWAT event so a radio that was capable of P25, DMR, and analog was needed so that officers could cary one radio and be able to access all channels needed. All MPOETC police officers in the county were issued radios with both DMR and P25 entitlements. Quick buttons on the remote speaker mic and the radio face were configured for quick access to the alternate channels in the event of ducting. Close to 2000 radios were issued out. Every single radio that left the 911 was bench tested and aligned on our Freedom R8000 service monitor. A very long process, but a process that allowed for tracking and a paper trail to go with every radio.
Questions about ducting came up previously in this thread as well and few people explained it pretty well. Our channels in UHF-T band sit on UHF TV channels 19 and 20. Be mindful that we use 25Khz and 12.5Khz channels. Each broadcast TV channel operates on almost a full 6Mhz of UHF spectrum. This is why when the conditions are right, several county channels will often experience issues at the same time.
The ducting that occurs creates issues on the repeater inputs, and is not something you would hear on the repeater outputs that you normally listen to. Take a channel like Fire Ch 1. A single transmitter with several receivers at multiple sites throughout the coverage zone. When ducting is severe, the noise floor at the receivers which is normally around -115dbm will increase and we have seen it as high as -70dbm when ducting was very severe. This means that the signal coming from the portables or mobiles must be stronger then the unwanted -70dbm signal that is making it to the receivers in order to make it in to the system and be heard. When ducting conditions are bad, you will likely hear nothing as the units are unable to get in to any receivers on the channel they are using. You may also notice a fade when listening. Signal starts strong but fades to static during transmission as the noise floor fluctuates.
Just wanted to answer some of the items that I saw perviously in the thread. I'd think anything related to the new P25 system should go in that thread if possible.
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