BTDT... good luck,
Can someone point my in the right direction.. We are looking at upgrading our public safety radio system. I'm wondering if there are any tools out on the net that would show my the average signal coverage from a radio tower depending on the frequency.. currently we are in the VHF range and have a fairly large county. 8th largest in the state of Iowa with over 700 sq miles. right now we only have 2 towers and since narrow banding our coverage has suffered. One of our options is joining with a neighboring county that currently is running an 800 Mhz system. i'm curious as to how many towers we would need for complete coverage with an 800 system as apposed to how many towers we would need if we stayed with our current VHF system.
the county is Clinton County Iowa if you would like to look up the county size on the internet
Yes there are tools. However you are entering a danger zone. It's like trying to diagnose cancer by using WebMD or a Usenet newsgroup. The values and thresholds depend a lot on accuracy of supporting data - like having a terrain and clutter database, and custom antenna patterns. Being competent enough to interpret the results is another issue. You might be able to look at an X-ray and see "stuff," but a trained and experienced radiologist look at the same image and see things you don't. It's not just coverage, but timing and simulcast overlap, too.
How many sites do you need? The short answer is it's irresponsible for anyone to even guess. If anyone gives you a concrete number at this stage, either run away or tell them to have a seat in the back of a police car until everything is all over so they won't hurt themselves. I will give you a few generalizations: 700 and 800 MHz have different characteristics than VHF, as well as entirely different rules on how they can be deployed. 800 MHz can have 3 categories, each with different rules - NPSPAC, whose oversight comes from a "regional planning committee" of your peers within the state, general pool, and vacated spectrum from Sprint-Nextel (if it's available). 700 MHz also has a regional planning committee, often the same people on 800, but not always. The RPCs will review your professional engineering firm's or vendor's filings, then either approve them or specify power levels and antenna directional patterns to put the signal where you say it's needed.
You can't just put in the biggest antenna and tower at the highest location and run the most power you can get away with, like you might have been able to on VHF.
Now, you'll need to satisfy these questions - are you looking for vehicle coverage, portable coverage outside, portable coverage "on the hip" outside, portable coverage "on the hip" inside buildings? Do you have high rise construction (the building doesn't necessarily need to be 87 floors to be "high rise construction")? Do you have parking garages, tunnels, etc.? Do you have deciduous or coniferous forestation? Do you need coverage inside schools, detention facilities, and hospitals? Do you want a delivered audio quality (DAQ) of 4.0 or 3.4? Do you NEED a DAQ of 4.0 or 3.4? Everything in these questions relate back to how many sites you need. MY experience in MY system was that I had 5 VHF "Wide Pulse Astro" digital simulcast transmitter sites with 9 voting receivers. The system that replaced it was many more sites with locations shared between other counties because we specified a DAQ of 4.0, with in-building coverage where needed, and "on the hip" coverage. The overall cost for the project was in the tens of millions of dollars, and there are ongoing costs required to update firmware and devices as their technical support sunsets. Modern radio systems are not "set and forget." They're in constant tweak and update mode. You'll probably need two FTEs or a very specific maintenance agreement with a service vendor who is in a position to respond and restore (not just send a warm body out) within 4 hours of notification.
When I went through this, my group hired a consulting firm that developed a performance specification and put a performance-based bid out into the street. In essence, you don't tell the bidders how many sites you need, you tell them what you expect out of the system and then, in their response, they tell you - along with the dollar figure. Then your selection committee goes through the proposals and makes an educated choice. Another warning - the places you had for VHF may not be the places you'll end up with being proposed. Have your county attorney stand by for land acquisition, eminent domain proceedings, and lots of public (and environmental) NIMBY backlash because of newer and possibly taller towers in different locations.
Here's the bottom line: there is a delta between "want", "need", and "get."
You might want something that reaches out 40 or 50 miles a few counties in each direction. You need something that reliably and safely covers your jurisdiction and a little bit around it. You ultimately get something the taxpayers and politicians are willing to budget and stand up for. Have your facts straight, because everyone who shows up at your board meetings will be a Philadelphia lawyer and will be wearing yellow shirts with towers on them so the local media can interview them about property values, migratory birds, burial grounds, and just general "I don't like it" statements. It's all part of the deal. Expect it.
Put out a "Request for Professional Qualifications" and get a competent consultant who will direct your project. Understand that you are in control of the consultant, not the other way around. You define your needs, your consultant translates those needs to an RFP. Then, when your'e ready to move forward, you'll need to bring on a competent project manager independent of the selected vendor.
Good luck. This'll be one of the highlights of your career (and then you can "retire").
