Madison County Going Mototrbo
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There has been no updates of the Madison County system since it was installed in 2005. Several updates had been proposed but none acted upon. It is certainly time for an upgrade as the new digital systems have significant advantages not available in 2005. One correction to the previous post. The Gunby Communications bid for a 3 site Kenwood NexEdge VHF solution (comparable to the MCA bid for a 3 site VHF solution ) is $807,837 not $984,353... With a current Kenwood End User Rebate Promotion that was expected to start in late October but not available before the bids were to be submitted would drop the GCI proposal to approximately $767,837.. The $984,353 price was a suggested alternative for a 5 site Kenwood NexEdge UHF solution with the option to tie into the Banks County 6 site Kenwood system which would allow mobiles/portables to roam seamlessly between the two systems. As the mobiles/portables would be compatible with FleetTalk, selected units could roam anywhere in the wide area coverage and remain in contact with their home units. The UHF system was proposed as an alternative because the County purchased only enough VHF Part 22 frequencies for 3 sites. It will cost another $90,000 to purchase the additional Part 22 VHF frequencies to expand to 5 sites plus the equipment infrastructure. 3 sites will not provide adequate belt mounted portable outdoor coverage to the northern and western borders of the county. Coverage projections clearly identify the need for additional sites.
Madison County has been a unique customer for many years. In 2005, 100% of the mobiles/portables were Motorola and purchased from MCA and 100% of the infrastructure was Kenwood purchased from GCI. None of the mobile/portables had noise cancelling microphones and the mobiles had already been published by Motorola as a discontinued product. Even though the system was installed narrowband, there are still wideband units operating on the system. At no time over the past 15 years, has GCI been provided access to any Motorola mobile/portable equipment to verify setup to match the infrastructure setup. There is no reason, Kenwood and Motorola analog equipment cannot work properly together, but they must be setup to do so.
In recent months, Director Baird has made several disparaging public statements about Gunby Communications in his quest for a new Motorola radio system. Apparently prior Director David Camp, disagreed and provided a letter of recommendation addressed to the commissioners to be included with the Gunby Communications proposal.
GCI has made numerous requests to Director Baird to setup presentations with the end users to identify their needs and concerns. All have been rebuffed. At this point, my recommendation is for the BOC, Fire Depts and Cities to saddle up and purchase the MCA 3 site solution. No one seems interested in taking the time to make an honest comparative evaluation of the two technologies.
Wouldn’t moving to UHF require even more sites than VHF since UHF has a smaller coverage footprint? Other than cost savings from licensing what is the advantage for such a rural area to be on UHF frequencies?
On a related note, I feel like I knew the answer previously, but why does VHF DMR need to be on Part 22 frequencies anyway? Why not repurpose existing analog VHF public safety licenses to DMR (or NXDN for that matter)?
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The UHF solution works really well in Jackson and Banks counties that I can attest to 100%. The folks who stayed VHF have had a lot more issues than we have using 400 mhz. One thing that was out of place throughout this process by the director in every story and meeting minutes was that the MCA solution would give them mutual communications with all surrounding agencies. Banks is going to be on Nexedge, Jackson is going 800mhz P-25 type 2. Athens Clarke is P25 type 2 .... um no sir this doesn't get you there at all.
Good questions by several.. The antennas on UHF portables are more efficient than VHF portables because the UHF antennas are full 1/4 wave length. VHF antennas are coiled to shorten them.. When worn on the belt, UHF antennas are less detuned by body capacitance. UHF has better building penetration. At the tower site, a typical 9 db gain antenna UHF antenna is 20', a typical 9db gain VHF antenna is 40'. UHF has a much lower background noise floor than VHF allowing weaker signals to be detected. UHF is not subject to Tropospheric Ducting. Those are the physical determinations. Outdoor coverage with 1/4 wavelength antenna and portable at face level and nothing but trees to get through, VHF will cover a greater distance. VHF is the appropriate selection for Agriculture, Forestry, maritime, where there are wide open spaces, minimum structures involved and you can accept a less than 90% probability of successful transmission. UHF is more appropriate when you require indoor coverage and a 90% or higher probability of successful transmission.
Rural UHF???
UHF is much less susceptible to co channel interference from distant transmitters. TX/RX Frequencies are always paired 5 Mhz apart. Mobiles transmit on the high freq and repeaters always transmit on the low freq. In VHF Part 90 Frequencies, your repeater input frequency will be someone's repeater transmit frequency. Part 22 frequencies are always paired very similar to Part 90 UHF frequencies. So you never have to worry about someone else base/repeater transmitting on your repeater receive freq. But, It is still VHF and subject to Tropospheric ducting. When ducting occurs mobiles from hundreds of miles away can at times be stronger into your repeater receiver than portables in your own county. UHF ducting is a very rare event. In rural areas, UHF frequencies are readily available at a much lower cost.
Repurpose existing Analog Freq's vs Part 22
If you going to the expense to purchase a trunking system you must have clear interference free frequencies, especially on the control channel. Any interference to the control channel will shut down the whole site or at a minimum cause the site to be unreliable. If you have a clear existing Part 90 analog frequency, you can sometimes get a way with using it as a traffic channel and tolerate the interference.
Habersham County tried to install their 4 site VHF DMR trunking system on Part 90 frequencies. It was a disaster. After the system was installed, they purchased 7 blocks of Part 22 frequencies estimated to be in excess of $200K.... Jackson County installed their 9 site UHF DMR trunking system on Part 90 frequencies for an estimated $8K. I'm not aware of any interference issues on the Jackson County system.
Part 22 frequencies are sold in 30Khz and 20 Khz blocks. There are only 19 30Khz blocks and 4 20 Khz blocks for any given area. Without special FCC waivers, you can get two DMR channels per 30 Khz block and 1 DMR channel per 20 Khz block. You can get four NXDN channels per 30 Khz block and 3 NXDN channels per 20 Khz block.
As it stands right now, Habersham, White, Lumpkin, Elbert, Hart and Madison have purchased all available Part 22 blocks. If Madison wants to expand their system in the future from a 3 site system they will have to purchase blocks that are already in use by Habersham, White or Lumpkin or worst case, go to the expense of simulcasting their system because there will be no Part 22 frequencies available. Simulcasting is expensive and maintenance intensive.
If your just going digital and not purchasing a trunking system, there is no reason you cannot repurpose a Part 90 frequency to DMR or NXDN and simply deal with any interference that comes along.
When you get down to actual system design for a public safety system, indoor coverage is required. Coverage designs are based upon probability of the transmission going through usually 90% is a minimum Public Safety design standard. Closing the distance between the portable and tower is the only way to address the varying amount of signal attenuation of the building materials. The more sites you have the higher the probability the call will go through. One site in the Banks County system, was specifically chosen to provide indoor coverage to the schools and government buildings. A second site to provide indoor coverage to the outlet malls in Banks Crossing. The remaining four sites chosen based upon covering the remainder of the county.
The other design considerations for a Public Safety system is redundancy and resilience. Multiple sites properly spaced will provide significant overlapping coverage. This overlapping coverage increases the probability that a portable can communicate from a specific spot. The overlapping coverage also reduces the effects of a single site failure. If a site fails, the radios will simply register to another sites.
The MCA Madison 3 site (2 tx/3 rx) VHF solution as has been described will rely on a single site in Danielsville to cover the whole northern half of the county. If that site fails, based upon coverage projections, 2/3 of the county will have no portable coverage.
Rural UHF???
UHF is much less susceptible to co channel interference from distant transmitters. TX/RX Frequencies are always paired 5 Mhz apart. Mobiles transmit on the high freq and repeaters always transmit on the low freq. In VHF Part 90 Frequencies, your repeater input frequency will be someone's repeater transmit frequency. Part 22 frequencies are always paired very similar to Part 90 UHF frequencies. So you never have to worry about someone else base/repeater transmitting on your repeater receive freq. But, It is still VHF and subject to Tropospheric ducting. When ducting occurs mobiles from hundreds of miles away can at times be stronger into your repeater receiver than portables in your own county. UHF ducting is a very rare event. In rural areas, UHF frequencies are readily available at a much lower cost.
Repurpose existing Analog Freq's vs Part 22
If you going to the expense to purchase a trunking system you must have clear interference free frequencies, especially on the control channel. Any interference to the control channel will shut down the whole site or at a minimum cause the site to be unreliable. If you have a clear existing Part 90 analog frequency, you can sometimes get a way with using it as a traffic channel and tolerate the interference.
Habersham County tried to install their 4 site VHF DMR trunking system on Part 90 frequencies. It was a disaster. After the system was installed, they purchased 7 blocks of Part 22 frequencies estimated to be in excess of $200K.... Jackson County installed their 9 site UHF DMR trunking system on Part 90 frequencies for an estimated $8K. I'm not aware of any interference issues on the Jackson County system.
Part 22 frequencies are sold in 30Khz and 20 Khz blocks. There are only 19 30Khz blocks and 4 20 Khz blocks for any given area. Without special FCC waivers, you can get two DMR channels per 30 Khz block and 1 DMR channel per 20 Khz block. You can get four NXDN channels per 30 Khz block and 3 NXDN channels per 20 Khz block.
As it stands right now, Habersham, White, Lumpkin, Elbert, Hart and Madison have purchased all available Part 22 blocks. If Madison wants to expand their system in the future from a 3 site system they will have to purchase blocks that are already in use by Habersham, White or Lumpkin or worst case, go to the expense of simulcasting their system because there will be no Part 22 frequencies available. Simulcasting is expensive and maintenance intensive.
If your just going digital and not purchasing a trunking system, there is no reason you cannot repurpose a Part 90 frequency to DMR or NXDN and simply deal with any interference that comes along.
When you get down to actual system design for a public safety system, indoor coverage is required. Coverage designs are based upon probability of the transmission going through usually 90% is a minimum Public Safety design standard. Closing the distance between the portable and tower is the only way to address the varying amount of signal attenuation of the building materials. The more sites you have the higher the probability the call will go through. One site in the Banks County system, was specifically chosen to provide indoor coverage to the schools and government buildings. A second site to provide indoor coverage to the outlet malls in Banks Crossing. The remaining four sites chosen based upon covering the remainder of the county.
The other design considerations for a Public Safety system is redundancy and resilience. Multiple sites properly spaced will provide significant overlapping coverage. This overlapping coverage increases the probability that a portable can communicate from a specific spot. The overlapping coverage also reduces the effects of a single site failure. If a site fails, the radios will simply register to another sites.
The MCA Madison 3 site (2 tx/3 rx) VHF solution as has been described will rely on a single site in Danielsville to cover the whole northern half of the county. If that site fails, based upon coverage projections, 2/3 of the county will have no portable coverage.
In Georgia, when rural counties started installing public safety radio systems some 50 years ago, they all went VHF. At the time UHF receiver specs where horrible compared to VHF receiver specs. UHF radios cost about 15% more than VHF radios. At the time it was a no brainer to go VHF. In the years that followed most counties added an additional repeater here or there or maybe installed a voted repeater system to improve portable coverage, but there were already 100's of VHF analog radios in service that would work with the upgrades. So even with the narrowband mandate in 2013 most everyone maximized their investments and stayed VHF. VHF/UHF radio specs today are equal and significantly better than they were as little as 20 years ago.
Now that counties are going digital, everything must be replaced. Pricing for VHF and UHF equipment is the same. The receiver specifications are the same. There a numerous interoperability products/methods to allow non compatible radios to talk to each other. Today It makes no sense now to stay VHF and deal with the inherent interference.
Now that counties are going digital, everything must be replaced. Pricing for VHF and UHF equipment is the same. The receiver specifications are the same. There a numerous interoperability products/methods to allow non compatible radios to talk to each other. Today It makes no sense now to stay VHF and deal with the inherent interference.
Excellent explanation! Thank you for taking the time to educate us on the benefits of UHF.
It appears that Jenkins Co. can access the Screven Co. system; not sure about the reverse.
As far as I know, Burke Co. has zero interoperablility with other agencies. This is excluding the fire trucks which still have VHF radios so maybe they can communicate with Forestry or Jefferson Co. fire departments (although that is highly unlikely).
You would think that Jenkins, Screven and Burke would be sharing towers. I don't know if the counties own their systems or if they are possibly subscribers on a commercial system.
It appears that Jenkins Co. can access the Screven Co. system; not sure about the reverse.
As far as I know, Burke Co. has zero interoperablility with other agencies. This is excluding the fire trucks which still have VHF radios so maybe they can communicate with Forestry or Jefferson Co. fire departments (although that is highly unlikely).
You would think that Jenkins, Screven and Burke would be sharing towers. I don't know if the counties own their systems or if they are possibly subscribers on a commercial system.
Demonstrating the benefits of a multi-site public safety communications system can be easily done a 10 minute video presentation showing how the individual coverage projections of each site work together to not only expand coverage area but to improve the probability of transmission going through and overall reliability of the system. If anyone is interested, I will be glad to setup a webinar to show a couple of our designs.
twotoejoe
Member
I haven't heard anything and nothing in the local media. Last time talked with the Sheriff he had no idea, just probably a 800 system.
I read in their BOC meetings a few months back that they are looking into Southern Linc as a backup system but no mention of P25. SPLOST funds don't appear as soon as it is passed since it only authorizes the county to impose an additional 1% sales tax and it takes the duration of the cycle in order for the funds to fully collect which is either 5 or 6 years depending on how it was structured. Some counties decide to pursue SPLOST or general obligation bonds which is essentially a loan that provides projected funds to be available immediately. These are risky since overall SPLOST revenue is only a projection and not guaranteed and is strongly dependent on the status of the local economy. Bonds will require a BOC vote and no recent minutes have mentioned it. I can't see a bond passing any time soon due to the current political environment and economic uncertainty. I don't think we will see anything happen until they either pursue bonds or the cycle completes.
For those in the area, they have 5 Part 22 licenses for 3 pairs of frequency ranges. They are WRHU723, WRHU724, WRHU725, WRHU726, and WRHU727. The receive ranges are 152.165-152.195, 152.230-152.250, and 152.830-152.850. I wonder if they plan on encrypting fire dispatch. That would be pointless considering they will have to permanently patch it to analog in order to page their firefighters.
Does anyone know how the Madison county Mototrbo trunking system was ultimately built out. I've heard three site receive with two site transmit. I understand there is already plans to add a fourth receive site. The fourth site being somewhere on the north end of the county.
Radios signals ride troposphere ducts well into the microwave range. Have worked the northern US on 432 from Georgia many times.
Amateur UHF Tropo communications generally involves using high gain, highly directional UHF antenna arrays with moderate/high power on simplex SSB with very good rx sensitivity on both ends. Almost always fixed point to point operation. Not mobile...SSB with good receiver filtering supports receive levels down to -140/145 much better RX sensitivity than typical FM repeater receiver which is around -120/125. I'll concede UHF ducting occurs. Not near as often as VHF ducting. However, the general point was in LMR with UHF paired frequencies and UHF mobiles/portables with their low power and low gain omni antennas, UHF systems rarely experience the interference that is well known with VHF systems. Microwave ducting above 500Mhz is an extremely rare occurrence.
Agree with most of that post. But microwave ducting occurs a lot. Not only on the earth's surface, but at different levels of the atmosphere. The US military uses recent rawinsonde launches to plot a detailed skew-t chart that not only shows the current ducts but which levels of elevation they occur.
Not a factor though in a county like Madison. (elevation wise)
73
Jim
Just curious if anyone has any updates on the Madison County TRBO system and how it is working. Noticed back in the fall, the county had put in a TRBO receive site at the Poca Tower using a microwave link installed as part of the old analog system back in 2005. The MCA proposal for the new system did show a need for a site at Poca. The GCI proposal demonstrated a need for a site at Poca and the NE corner of the county for reliable portable talkback
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