Benefits of digital VS analog

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NHdave
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Benefits of digital VS analog

#1 Post by NHdave » 30 Jul 2014 19:46

I've been scanning for almost 35 years but I'm a layperson when it comes to radio systems and their function. All I have in range is conventional analog and digital, never had to deal with trunking or anything out of the ordinary. I thought digital was supposed to improve reliability and range yet I constantly hear dispatch telling officers to repeat because they went "digital" (I assume they mean garbled) during their transmission. Also Exeter NH went back to analog after having issues with their digital system a few years back and are still there. Is it one of those things that was better on paper?

If it's that much better why haven't fire and EMS switched over when the police in the same towns have?
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MaineRadioMan
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#2 Post by MaineRadioMan » 30 Jul 2014 20:13

Im the same as you DaVE. I like the term you used LayPerson..
Up on a huge hill with a tower 100ft in the air!

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jmarcel66
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#3 Post by jmarcel66 » 30 Jul 2014 20:52

Fire hasn't switched over mainly because most departments still utilize "two-tone" paging to alert members and stations. FD's extensively use minitor style pagers and currently, they are not digital capable. So at the minimum they need analog to dispatch. In addition, it is recommended that Fireground operations operate in analog due to how digital translates noise, especially background noise. After that, plain ole'reliability.

Digital changes everything to data (1's and 0's), then pushes those over the airwaves. If any of those 1's or 0's drop out due to signal strength, the radio will drop the message completely and require re-capture to continue. There is no such thing at "White Noise" in digital. This was a major problem early on; but has gotten better as radios get better with compensating for that issue. An advantage is longer ID's on radios (analog MDC, etc usually limited to 4 Characters). In theory, digital can mix data (Computers, etc) and voice; but typically it doesn't seem to do well. NHSP does have their MDT's attached to the radios and does voice and data on their troop frequencies. P25 encryption is easier to attain and use than analog encryption. But I've heard many cases where that isn't working as planned.

Systems like DMR and Nxdn show some promise as they increase capability. But they are for business, not public safety. I don't see P25 offering anything exciting over Analog with MDC capability.
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Concord, NH Fire Alarm

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#4 Post by MaineRadioMan » 30 Jul 2014 22:06

Thanks John!!!
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#5 Post by cdgordon » 30 Jul 2014 23:26

P25 Phase II conventional will add a second slot to each frequency when it happens.
As often happens, many radio systems have issues. Inadequate coverage due to poor design, power reduction, antenna height, topography, cost and many times a combination of many factors. With analog, the conditions become marginal with static over the conversation. Digital has an advantage where the signal seems clear to the end user until the error correction cannot overcome the amount of dropped 1's & 0's and the voice cannot be recovered enough to hear a message.

chris

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NHdave
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#6 Post by NHdave » 31 Jul 2014 06:55

Thanks John & Chris, appreciate the feedback!
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#7 Post by ScanBoston » 31 Jul 2014 08:30

I'm not going to get into the Fire thing cause thats just a mess....

But P25 and all the digital formats are here for one reason and one reason only. To improve range, and intelligibility with narrowbanding. If you take a 25 KHz voice channel and cut it in half to create two 12.5KHz like was done in the first phase of rebanding you're also bring down the deviation to 2.5Khz. This gives you a very limited signal to noise ratio making the radios much harder to understand. You have probably said to yourself why do FRS radios sound so muffled. You also lose range as you fall into noise earlier. That's why the Association of Police Chiefs and the Federal Government tried to come up with a digital standard to fix this called Project 25. This is the same thing the manufacturers are trying to do less expensively with DMR, NXDN etc. Now the FCC's rebanding plan is a two step operation. Though the drop dead date for the second phase has not been set yet it will happen and the next phase splits the channels again giving us 6.25KHz voice channels. Now at this point I'd like to see the Fire Departments try to stay analog : ). Anyways everything will be digital by then and that is why many of the police were waiting for P25 phase two equipment to be released at their infrastructure level. P25 phase one radios can still be used till that drop dead date as these system are backward compatible but I'd say there will be no analog after that.

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