Conventional Vs Digital Signal Strengths

[red616]

I bit the bullet & shelled out the bucks for a digital scanner (996T) so's to be ablel to follow local PD/FD trans.

Obviously there are alot of opinions the way these new radios operate when compared to non-digital scanners.

However the one thing that blows me away is the signal strength required to hear digital trans clearly. I had no idea the difference in being able to hear analog trans & digital trans would be so different.

I can plainly hear analog trans on the 996T with no sig strength bars showing where as it's common place for 2 & 3 bar sig strength digital trans to be terrible.

After having this radio for a couple months now & reading up & trying all the "tweaks" & adjustments I wish I'd known from the start...receiving digital trans clearly requires MUCH better signal strength than analog trans.

 

[John_M]

It may require a tad bit more signal so the Vocoder can decode the signal correctly but a steady 1 bar should do it. If you are getting 2 to 3 bars worth of control channel and aren't hearing it clearly I would think either there is something wrong with your unit or the digital decode isn't set up properly (way out of wack).

 

[red616]

I doubt one bar is going to give consistently good dig sig quality.

I also doubt it's the radio as when I get good digital signal strength I get good signal quality.

 

[ampulman]

I bit the bullet & shelled out the bucks for a digital scanner (996T) so's to be ablel to follow local PD/FD trans.

Obviously there are alot of opinions the way these new radios operate when compared to non-digital scanners.

However the one thing that blows me away is the signal strength required to hear digital trans clearly. I had no idea the difference in being able to hear analog trans & digital trans would be so different.

I can plainly hear analog trans on the 996T with no sig strength bars showing where as it's common place for 2 & 3 bar sig strength digital trans to be terrible.

After having this radio for a couple months now & reading up & trying all the "tweaks" & adjustments I wish I'd known from the start...receiving digital trans clearly requires MUCH better signal strength than analog trans.

Frankly, as far as I'm concerned, digital (P25 voice) doesn't make a bit of difference to the user. Recently, I had the pleasure of being pulled over by a member of the local constabulary.

While discussing current events with the officer, her mobile sounded. The dispatcher, whose voice I recognized, was loud and clear. While I live in an adjacent town, reception sucks. I'm within 10 miles of 4 towers and the voice is crackly and I'm lucky to get one bar.

Since P25 voice can be decoded today, what is the need /benefit to switch to digital voice--certainly not security? I haven't done any tweaks or updates yet. Still undecided.

AM

 

[Patrick_]

I'd say it's one more way for the government to make money.

If it ain't broke, don't fix it... maybe I'm wrong. Any officers/dispatchers/users who made the switch know the true benefits of digital communications over the previous conventional analog systems?

I've read in some places that communications inside of buildings is better; how is that, though? I always thought the higher the frequency, the more affected by buildings the signal is.

 

[N_Jay]

. . .Since P25 voice can be decoded today, what is the need /benefit to switch to digital voice--certainly not security? I haven't done any tweaks or updates yet. Still undecided.
. . .

Narrowbanding without losing coverage.
Clearer communications at the fringe.
Increased feature set.
Open Standard Trunking.
Secure if/when they want it (open standard).
Interoperability with other agencies moving to P25 and P25 trunking.

 

[N_Jay]

I'd say it's one more way for the government to make money.

Hu?

If it ain't broke, don't fix it... maybe I'm wrong.

Many of the systems are "broke" in lots of ways.

I've read in some places that communications inside of buildings is better; how is that, though? I always thought the higher the frequency, the more affected by buildings the signal is.

Why are you mixing frequency band and digital?

 

[jrholm]

Although I don't have much personal experience with digital, friends of mine that work for agencies that have gone digital aren't very impresed. They say reception isn't any better and in some places appear worse. Also there is about a 1/2 second delay between what they are saying and when it comes out over the air. Sure the 1/2 second delay probably isn't much but it is somewhat disconcerting.....Overall most line grunts would have prefered to stay analog, at least the ones I've talked to.

 

[w8jjr]

Narrowbanding without losing coverage.
Clearer communications at the fringe.
Increased feature set.
Open Standard Trunking.
Secure if/when they want it (open standard).
Interoperability with other agencies moving to P25 and P25 trunking.

And the best two

Thats what manufactures are making and fcc is pushing everyone to digital.
Even your tv

 

[n1das]

Although I don't have much personal experience with digital, friends of mine that work for agencies that have gone digital aren't very impresed. They say reception isn't any better and in some places appear worse. Also there is about a 1/2 second delay between what they are saying and when it comes out over the air. Sure the 1/2 second delay probably isn't much but it is somewhat disconcerting .....Overall most line grunts would have prefered to stay analog, at least the ones I've talked to.

The delayed digital audio also means a cop's radio is no longer faster than a bullet with his name on it.

In certain life/death situations where timing of communications between officers is critical in order to prevent loss of life (like in a hostage standoff/SWAT situation for example), the digital audio delay may be unacceptable, resulting in officers not hearing critical commands in time. An officer yells "Duck!" to other officers to dodge gunfire from a perp and the officers hear the digitally delayed version of it 1/2 second later instead of hearing it in real time.

 

[Sonar]

I'd say it's one more way for the government to make money.

Um...don't you mean for the radio supplier and radio manufacturer to make more money?

The government ends up spending more money to upgrade.

 

[SAR923]

Having used both digital and analog systems, I will say that digital is far superior with good signal strength and a system set up by someone who knows what they are doing. What bothered me as a peace officer is digital is either all or nothing. It's clear as day or nothing but noise - or even worse, no signal at all. With analog, you could have a very weak signal and still be able to copy the gist of the message, particularly if an officer was in trouble. The tone of voice was often enough to know what was going on. I know that everything will eventually be digital but I wish there was some kind of analog fall-back when digital signal just doesn't get decoded.

 

[n4voxgill]

a lot of information on this subject in this thread

http://www.radioreference.com/forums/showthread.php?t=71187

 

[loumaag]

I bit the bullet & shelled out the bucks for a digital scanner (996T) so's to be ablel to follow local PD/FD trans.

Obviously there are alot of opinions the way these new radios operate when compared to non-digital scanners.

However the one thing that blows me away is the signal strength required to hear digital trans clearly. I had no idea the difference in being able to hear analog trans & digital trans would be so different.

I can plainly hear analog trans on the 996T with no sig strength bars showing where as it's common place for 2 & 3 bar sig strength digital trans to be terrible.

After having this radio for a couple months now & reading up & trying all the "tweaks" & adjustments I wish I'd known from the start...receiving digital trans clearly requires MUCH better signal strength than analog trans.

You are correct, there are a lot of opinions; then there are facts. Fact--at the same signal strength, same band, a digital signal will be clearer at the fringe then an analog signal. It sounds as if your scanner is out of whack or you are not giving all the information.

Since P25 voice can be decoded today, what is the need /benefit to switch to digital voice--certainly not security?

See the above answer and despite what the "straw vote" has to say, digital is superior to analog in an apples-to-apples comparison.

...there is about a 1/2 second delay between what they are saying and when it comes out over the air. ...

Again, we are not given the whole story here. A digital signal generated from the radio gets the audio from the mike, just like an analog radio. The conversion to digital signal is done at the speed of light, there is no perceptible delay between the voice and the signal leaving the radio antenna. Now, delay does happen in the networks, especially of large trunked systems; however, that has nothing to do with digital or analog. Kind of like the difference between talking on a digital "cell" phone and digital "direct connect". With direct connect (non-network) there is no delay, on the cell network there is, but that same delay existed on analog cell networks (and large trunked systems) also.

Thats what manufactures are making and fcc is pushing everyone to digital.
Even your tv

The reason the "push" is on, is that it works better...especially TV.

 

[red616]

You are correct, there are a lot of opinions; then there are facts. Fact--at the same signal strength, same band, a digital signal will be clearer at the fringe then an analog signal.


What a silly statement. Now that's a fact.

What's the "strength" ? How far is the "fringe" ?

 

[CCHLLM]

Since I don't own a scanner, all I can base my experience on in the digital vs analog battle is the use of Motorola bases, portables, and mobiles. As a comm tech with nearly 40 years experience and an active part in the NC VIPER project, I see nothing silly at all about loumaag's post, but maybe I missed your point. If you mean the "fringe" of digital vs the "fringe" of analog, you're exactly right, they're different. But all theory aside, actual observation says that if you're well into the fringes of analog, you're also into the fringes of digital.

All other factors being equal, digital audio comes through reliably at significantly lower signal levels than analog, though as far as "fidelity" is concerned, analog usually has it hands down when there's enough signal. At full strength, there's only the characteristic digital vs analog "sound" to argue about. Since a direct comparison of analog vs digital can be made over VIPER on the same sites, I can say the reliable readable audio range on a given site is something like 10-15% on the move, and usually more if the mobile or portable is stationary.

Audio delay and audio lag are two different things, and are determined by several factors. Audio delay is an intentional audio lag used to give the system audio processing time to delete certain undesirable factors in the receiver audio before it gets repeated, usually about a 1/4 second or less. Audio lag is what happens because of the multi-step audio processing required by the system. How much lag depends upon how many steps and media it has to pass through.

Newer radios capable of both formats usually process the audio through digital protocols no matter which platform it's utilizing, resulting in audio lag. Add in processing through multiple steps such as links, comparators, interface modules, and repeated audio processing, etc., and audio lag is inevitable.

And while we're at it, when you add the all-hallowed VoIP to the mix, there's even more delay, regardless of whether it's analog or digital at the point of origin. This was one of the largest problems encountered in the evolution of VoIP connections.

 

[loumaag]

I fixed your incorrect use of the quote function.

You are correct, there are a lot of opinions; then there are facts. Fact--at the same signal strength, same band, a digital signal will be clearer at the fringe then an analog signal.

What a silly statement. Now that's a fact.

What's the "strength" ? How far is the "fringe" ?

Silly?
Apparently your knowledge of radio principles leave some doubt as to your statements earlier.

I didn't say "strength", I said "at the same signal strength", which would indicate the actual strength is not relevant as long as it was the same.

Finge is a common enough term used in radio, but since you were too lazy to even look any definition up, you are welcome to use this one:
http://www.yourdictionary.com/ahd/f/f0329700.html

Suppose you read wx4cbh's reply and I will bow to his experience as being more than mine; however, I don't see a lot of difference in what he says and what I said.

 

[studgeman]

That is one of the best most comprehensive posts I have seen in a long time on this board! Thank you so much for you ACTUAL, REAL LIFE, EXPERT opinion! As anyone who works on radio enough, you really dont know how it will perform untill it is on the air.

One thing that no one has mentioned, is multi-pathing and other interference. Depending on the P25 modulation type CPQSK or C4FM you will have differnt performance. CPQSK is more resistant to multipathing, that is why you see it prevelent in simulcast systems. With C4FM modulations, Digital is can have problems over analog in a multipath environment. That might explain the original posters problem.

Side note about delay. You will find the delay is more extreme in the new XTS series radios in Analog mode than in Digital. approx .35 seconds in analog and about .25 seconds in digital. Analog in the new radios has extra processing time. Delay being defined as a simplex communication from the time one person speaks into a radio to the time it comes out the speaker on the reciever radio.

The human ear can descern delay over about .13 seconds. Over .3 it sounds like an echo.

 

[DonS]

...there is about a 1/2 second delay between what they are saying and when it comes out over the air. ...

Again, we are not given the whole story here. A digital signal generated from the radio gets the audio from the mike, just like an analog radio. The conversion to digital signal is done at the speed of light, there is no perceptible delay between the voice and the signal leaving the radio antenna.

Not quite. In non-digital, the analog voice signal from the mic is merely used to modulate a carrier and is essentially transmitted immediately. There's certainly a delay between microphone and antenna, but it's probably measured in (at most) tens of mS.

In digital, that same analog voice signal from the mic must be sampled and converted to digital values. It must then be compressed (e.g. IMBE), then converted to the appropriate data format (e.g. CQPSK, C4FM). That data is finally used to "modulate" the carrier. Those additional steps all take time - time that can be significant depending on the actual implementation. At the receiving end, the reverse process must be performed == more time. I wouldn't doubt 1/2 second of "extra" time for the digital process, from transmitter's microphone to receiver's speaker, everything else in the network being equal.

A more extreme example would be a DVR, like TiVo. Two televisions, one connected directly to an antenna and the other with a TiVo between it and the antenna, represents a similar situation and will exhibit similar behavior. The TiVo-connected TV, since it's doing an analog/digital conversion, compression, decompression, and digital/analog conversion ("extra" steps not performed by the directly-connected TV), will look and sound like it's "delayed" for a second or so.

 

[red616]

Suppose you read wx4cbh's reply and I will bow to his experience as being more than mine; however, I don't see a lot of difference in what he says and what I said.

I see...you put alot of stock into someone's post who does not even own a scanner.

That make's about as much sense as your 1st post on this subject. Then again maybe you do not own a 996T ??

Sorry...you are zero for two.