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  1. #21
    Forum Member nmfire's Avatar
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    I must admit I haven't read all of Part 90 for obvious reasons. Never in a million years have I ever heard of school buses being licensed on public safety pool frequency. The only competition ever is between two public safety agencies. I swear you have to be the first to ever have that happen. That seems to contradict the name of the frequency pool. Typical government operation.

    I still see nothing that allows the maintenance people at a hospital to use it. The medical care people yes, but not the plumbers. Wouldn't put it past them to try...

    Regardless, you are still mistaken about the range of narrow band. I won't concede that one so easily!
    Even the burger-flippers at McDonald's probably have some McWackers.


  2. #22
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    Quote Originally Posted by nmfire View Post
    I must admit I haven't read all of Part 90 for obvious reasons. Never in a million years have I ever heard of school buses being licensed on public safety pool frequency.
    It's also common for public works operations to be on public safety pool frequencies. Drives me nuts because every little two bit town around here has a frequency licensed for their two employees to talk to each other on, making it nearly impossible for us to find an open frequency for a repeater input. It would make a lot of sense to put all of those small non-mission critical operations on one frequency and use CTCSS to multiplex them, but of course the frequency coordinators don't work that way. Any application that comes across their desk goes through the full coordination process to get them a frequency all of their own, without regard for actual usage. As an example, check out WQGQ681 - high school janitors on public safety pool frequencies.

    Andy

  3. #23
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    Quote Originally Posted by nmfire View Post
    Second of all, reducing the deviation to narrowband does not reduce the range. That is the biggest bunch of hogwash floating around about narrowbanding. It is going to go just as far as it did before. The only difference is that there is less room for audio and the noise floor remains the same. So it can sound a little more noisy a little bit sooner. Thats the only difference when it comes to voice.

    The perceived loss in "range" due to that is something like 2%.... which in all practical reality is nothing. A properly designed system with narrowband will work just as well as one in wideband. Claiming all of sudden requires more infrastructure and is some unfunded mandate is non-sense. You will not all of a sudden need a remote receiver somewhere that you didn't before.
    This isn't necessarily true in all situations. Whether a system will have reduced range after narrowbanding depends on a number of factors. The reduction in range in noise-limited systems is because of the change in the modulation index. For a brief overview, see here:

    http://www.adcommeng.com/Narrowbandi...echnicians.pdf

    Somewhere I have a much more thorough technical explanation, but I'll have to dig to find it. Need to take the wife out to dinner right now, so I'll have to look later.

    Andy

  4. #24
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    Ok I found the detailed explanation I was looking for. It's in a very long thread in the PrivateWirelessForum yahoo group started with this message:

    http://tech.groups.yahoo.com/group/P.../message/26736

    If you read through it, make sure to read the entire thread, as there are some errors that get corrected along the way. Lots of good information in there. As nmfire eluded to, the signal strengths and receiver sensitivities involved don't change when moving to narrowband, but what does change is the required signal to noise ratio to get the same recovered audio signal. This may or may not impact you depending on your system parameters and whether it's a noise limited or interference limited system (could be both depending on location of the user). Lots of good discussion/debate in that thread. Bottom line is that it's hard to predict what change you might see when moving to narrowband without doing a fairly decent engineering analysis.

    Andy

  5. #25
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    Question nbfd701

    Are some models of the HT750 model going to make the P25 switch?

  6. #26
    Forum Member nmfire's Avatar
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    Quote Originally Posted by tspivey701 View Post
    Are some models of the HT750 model going to make the P25 switch?
    Huh?

    The HT750 is a model. There are no other models of the HT750. And this discussion has nothing to do with P25. This is about narrowbanding. Two completely different things. But I'll answer both.

    The entire Waris series of radios from Motorola is analog only. This includes among other things, the 750/1250/1550 mobiles and portables. They do not and never will do P25 digital. However, they are all cable of doing narrowband.

    The only Motorola radios that will do P25 digital ("astro") are the XTS series radios. The MT1500 and PR1500 can be flash upgraded to do P25 digital as well.
    Even the burger-flippers at McDonald's probably have some McWackers.

  7. #27
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    Somthing about the school buses made me remember something. We are on 471.225 and with out the PL we can here what sounds like a bus company. It is really terrible because they use the radio like a cell phone. We have not been able to locate them.
    This space for rent

  8. #28
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    Quote Originally Posted by KyleWickman View Post
    Somthing about the school buses made me remember something. We are on 471.225 and with out the PL we can here what sounds like a bus company. It is really terrible because they use the radio like a cell phone. We have not been able to locate them.
    What's your location? It's pretty easy to do a search of the FCC database and that might help you find the source.

    Andy

  9. #29
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    Our county has school buses from another state come over our freq. We are scheduled to narrow band 2010. Hope that stops the problem. We don't know what the new freq. will be yet, because the Forestry Commission owns the repeaters and radio license. They are in the process of obtaining additional freq. that will be used when the narrow banding is done.

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