Having spent some 35 years with the fire service I can understand your interest in moving this project forward. There have been a number of people before you that have sort of laid down the railroad tracks that your following. However, you need to walk a careful line here and make sure your moving forward in a legal and technical fashion.
The first word of caution is that you have a station license for the fire department that has a repeater class shown on the frequencies your planning to use. You haven't mentioned this in any of your comments so far. The second concern is that you will be operating this home brew repeater in the narrow band mode come the 1st of January, 2013. Last major comment is that you have measured the deviation of the transmitter and the frequency to make sure that the radio is operating to the correct specifications for the frequency you are planning to operate on. This all requires the use of a service monitor that has been calibrated to measure both frequency and deviation.
Being that this is being used for life safety communications, you have made sure that the radios and power source are backed up in case of a prime power failure. There is nothing worse than relying on a repeater and it isn't there just when you need it the most.
I also have to support the others that have voiced their comments of relying on a mobile radio transmitter for repeater service. You can't control the amount of transmit time when the chips are down during an emergency. Radio traffic will spike way beyond your expectations and be totally out of control for maybe the first 15 to 30 minutes when this all takes place. That will cause most transmitters to max out on heat generation in just a short time.
Having said this, I noticed that you have mounted the radios inside a computer case. This may look great, but is probably the worst thing you could do for removing the transmitter heat that will be generated. You have minimal heat removal with this package.
I am not trying to be negative. But just pointing out a number of areas that seem to be on the weak side of your plans. Over the 45 years that I have been working with public safety radio systems, I have seen a bunch of red neck hook ups. Just trying to prevent yours from becoming another one.
As much as you would like to put this into action, you should take a break and step back from the project. Take a breather and evaluate what you have, what the intention is and if your going to have the desired results. You may not have the funds to work with at this point in time, but just maybe they will become available in the future. There are a number of sources for grant money in the fire service. It may take 2 years to get there, but you will be much better off using the radio equipment designed for repeater service than jack legging it with your package.
What does the fire chief think of this endeavor? He is the ultimate one that will have to answer if your repeater fails during an incident.
