Uniden - TDMA Scanner

[Dewey]

Wow :roll:cant wait for Dewey to buy that 800 then he cant rant in the GRE room instead:twisted:

Seriously we all need to take it down a notch Uniden has the Best radio's on the market period.

"WOW", don't know if that was a swing, or pun...

I said many posts back that I prefer Uniden. My opinion, which we ALL have, is that they are the better scanner manufacturer. Uniden is like "family" to me, you love them so much, you occasionally fight with them, but that is because you love them. Things not liked tend to not bother you since you don't care for them anyway. My rant is because I would hate to go GRE, only to have Uniden release something shortly afterwards. Like computers, something new is always in the wings, I just want the best bang for my buck, and I would rather that be with Uniden.

Dewey

 

[Danny6569]

Tdma

Ok this stuff is enough to drive ya nuts! its so crazy why they have to make so many different radio systems, we have apco 25, we have edacs, we have ltr, we have conventional stuff, we have opensky systems, and more, i dont know why we cant just have one simple trunking system that the whole country can run on, not saying that they could be on the same talk group ids but at least the same systems, i mean look what happened in new york during the tower bombings they couldnt even communicate with other towns and more because every ones on different stuff, its so crazy why we need all different stuff ? and now tdma to add to the headaches! if our country and states had any brains they would at least be on the same kinda system in a state anyways! here in new jersey we have one county on edacs and another county on conventional and another county on the 500 mhz trunked system and then the state police are on 800 mhz trunked systems etc etc. i hate to see it one day when one state is going to need to talk to each other locally and there all on different stuff! its just so annoying to deal with all these systems, what ever happened to going to radio shack back in the day and paying 5 bucks for a crystal and put it in and be done with it, im not saying we have to back that far but i for one liked the conventional channels a lot better at least we didnt have to worry about all this digital crap cutting out and not being able to hear half the systems like tdma and more, and i think the conv channels sound a lot better that whats out now but it is what it is, what can ya do!

 

[rdale]

Danny, all stated with trunked systems have the national mutual aid channels programmed in, so there won't be a problem.

 

[mike_s104]

Ok this stuff is enough to drive ya nuts! its so crazy why they have to make so many different radio systems, we have apco 25, we have edacs, we have ltr, we have conventional stuff, we have opensky systems, and more, i dont know why we cant just have one simple trunking system that the whole country can run on, not saying that they could be on the same talk group ids but at least the same systems, i mean look what happened in new york during the tower bombings they couldnt even communicate with other towns and more because every ones on different stuff, its so crazy why we need all different stuff ? and now tdma to add to the headaches! if our country and states had any brains they would at least be on the same kinda system in a state anyways! here in new jersey we have one county on edacs and another county on conventional and another county on the 500 mhz trunked system and then the state police are on 800 mhz trunked systems etc etc. i hate to see it one day when one state is going to need to talk to each other locally and there all on different stuff! its just so annoying to deal with all these systems, what ever happened to going to radio shack back in the day and paying 5 bucks for a crystal and put it in and be done with it, im not saying we have to back that far but i for one liked the conventional channels a lot better at least we didnt have to worry about all this digital crap cutting out and not being able to hear half the systems like tdma and more, and i think the conv channels sound a lot better that whats out now but it is what it is, what can ya do!

I think some of what you said is right. With the new systems come some new features. Some of the new features include the ability of patch radio systems together and to conventional analog freqs. I'm not sure about where you live, but around here patches are used often and most times work well (depending upon who does them).

TDMA is just an "upgraded" FDMA that will allow more traffic over a FDMA system with the same number of voice freqs. I'm sure there are numerous other differences and updates as well.

No matter what we might like, feel or what our opinions are, companies like Motorola and all the others will continue to make improvements, updates and features that the public safety radio industry wants, needs, and asks for. It will be up to Uniden and GRE to continue to make products that keep up with these systems and to provide their customers ask for and at the same time make products that will sell. It's only a matter of time before Uniden comes out with something to fit this "need".

 

[Danny6569]

Tdma

Just all a headache anymore, i just wish they would keep it more simple!

 

[mike_s104]

Wirelessly posted (Opera/9.80 (Windows Mobile; WCE; Opera Mobi/WMD-50433; U; en) Presto/2.4.13 Version/10.00)

I'm with ya on that. the more complicated the systems are the more things that can go wrong.

 

[Skypilot007]

Just all a headache anymore, i just wish they would keep it more simple!

TDMA is coming to NJSP so keep those asprin close by!

 

[Danny6569]

Tdma

TDMA is coming to NJSP so keep those asprin close by!

All of the state police are going to it when and why ? i know the system they have now i can barely pick them up where im at!

 

[W2GLD]

They are expected to make the move to all digital by the end of this year. They will not be a fully implemented TDMA system until all the radios are replaced; which given NJ's current budget crisis, this change will likely take a few years to complete. Most Troop cars and portables will be unaffected by the TDMA implementation; specialty talkgroups, outside agencies coming into the system, etc are another story...

You have some time so don't worry just yet; but rest assured, when they do go TDMA, expect 100% encryption for all police operations...

 

[Danny6569]

Tdma

Time division multiple access (TDMA) is a channel access method for shared medium networks. It allows several users to share the same frequency channel by dividing the signal into different time slots. The users transmit in rapid succession, one after the other, each using his own time slot. This allows multiple stations to share the same transmission medium (e.g. radio frequency channel) while using only a part of its channel capacity. TDMA is used in the digital 2G cellular systems such as Global System for Mobile Communications (GSM), IS-136, Personal Digital Cellular (PDC) and iDEN, and in the Digital Enhanced Cordless Telecommunications (DECT) standard for portable phones. It is also used extensively in satellite systems, combat-net radio systems, and PON networks for upstream traffic from premises to the operator. For usage of Dynamic TDMA packet mode communication, i really dont understand the advantage of this system and why anyone would want it ? saying each user has a time slot, so what happens after each user runs out of time ? and also says that multiple stations can share the same transmission ? ok so were gonna have everyone talking at once ? that really sounds like it will cause a lot of problems! i just dont get it, will someone fill me in here with this and how it works or will cause problems ?

 

[Danny6569]

Tdma

A disadvantage of TDMA systems is that they create interference at a frequency which is directly connected to the time slot length. This is the buzz which can sometimes be heard if a TDMA phone is left next to a radio or speakers.[1] Another disadvantage is that the "dead time" between time slots limits the potential bandwidth of a TDMA channel. These are implemented in part because of the difficulty in ensuring that different terminals transmit at exactly the times required. Handsets that are moving will need to constantly adjust their timings to ensure their transmission is received at precisely the right time, because as they move further from the base station, their signal will take longer to arrive. This also means that the major TDMA systems have hard limits on cell sizes in terms of range, though in practice the power levels required to receive and transmit over distances greater than the supported range would be mostly impractical anyway.

I copied this from the Wikipedia online just trying to figure this all out!

 

[MarMatthias]

Hi,

While TMDA phase 2 hasn't hit my area yet, I know it will soon and that does have me concerned. Like many here, the 396XT is a hobby for me. With that being said, I would have never paid roughly close to $600 for just a hobby. I would have bought a cheap cell phone and gotten a free app to listen to live streams here on RR and saved myself roughly $400.

My wife and I discussed the purchased (retirement does allow a lot of extras). What made the sale for us is the fact that, while she wanted me to have a hobby beside programming, we needed a reliable way to get news and information. The flooding recently in Nebraska, Iowa and outlying areas has been of great concern to anyone living here. The local news isn't always the greatest or the most reliable. I use my 396XT to also help keep my wife and I out of harm's way.

I am making this point because many people here are probably in the same situations as my wife and I, a hobby and necessity at the same time. Even though Paul (Upman) can't say anything, there is nothing stopping Uniden from making a press release.

I personally believe Uniden may have put all their eggs in the HP-1 basket and wasn't expecting the backlash of people like me that want a radio, not an mp3 player. Now Uniden has egg all over them and GRE is mopping the floor by being ahead of the game. I despise the PSR-800 simply because there is no keypad, just like the HP-1... BUT if its the only game in town, then for Uniden its game over.

I see it like this, Uniden either has to step up to the plate and say something one way or the other, or go home losers because GRE has already won the game. There are many stores in my area that actually refuse to carry the HP-1 stating that the x96XT is their best sellers. I've been told by many that the x96XT was one of the best Uniden products to date by people who have a long list of scanners they own. I personally can't say that as this is my first.

For Uniden customers, Uniden's next step will make or break them. If they stall the x96XT and focus on the HP-1, they'll hurt their market, if they continue both, they do well as long as they can stay competitive with GRE, AOR, and any others. Once Uniden is no longer competitive, all Uniden employees have to look forward to is unemployeement...

 

[Anon6083]

Time division multiple access (TDMA) is a channel access method for shared medium networks. It allows several users to share the same frequency channel by dividing the signal into different time slots. The users transmit in rapid succession, one after the other, each using his own time slot. This allows multiple stations to share the same transmission medium (e.g. radio frequency channel) while using only a part of its channel capacity. TDMA is used in the digital 2G cellular systems such as Global System for Mobile Communications (GSM), IS-136, Personal Digital Cellular (PDC) and iDEN, and in the Digital Enhanced Cordless Telecommunications (DECT) standard for portable phones. It is also used extensively in satellite systems, combat-net radio systems, and PON networks for upstream traffic from premises to the operator. For usage of Dynamic TDMA packet mode communication, i really dont understand the advantage of this system and why anyone would want it ? saying each user has a time slot, so what happens after each user runs out of time ? and also says that multiple stations can share the same transmission ? ok so were gonna have everyone talking at once ? that really sounds like it will cause a lot of problems! i just dont get it, will someone fill me in here with this and how it works or will cause problems ?

Although I am likewise troubled by the industry choice to move to TDMA, it is a viable alternative. Many phone systems like those that rely on the T1 specification use TDMA so that a single medium can service multiple channels (24, if memory serves) in a single frequency allocation. In telecommunications, despite having access to the entire spectrum accross the line, certain frequencies are better suited to the human voice (T1 samples voice at approximately 8KHz, though there is some drift as you aluded to). The advantage, therefore, of using TDMA as an industry standard is the attractiveness of the consolidation of frequency allocations that system owners must purchase.

The use of time-slotting (the principle of TDMA) doesn't really limit how long a station can transmit; rather, it affects the quality of the transmission (at face value, this doesn't seem intuitive at all, but it is the case). The is achieved by the afore-mentioned sampling rate of 8KHz. If each channel is only sampled at 8KHz but the system is operating at a frequency that is a magnitude greater than that of the sampling rate (say, >800MHz), you can clearly fit multiple parallel channels into a single cycle across the medium. This is the fundamental mechanic of TDMA.

Contention over a particular channel is an interesting issue, and one cannot authoritatively say how this will be handled by industry manufacturers. Similar to current trunked systems, each of the N channels available in a TDMA system will have to be dynamically allocated to a subscribed radio as each one attempts to key up (there are still only N channels available in any given TDMA system, with N varying by bandwidth and voice quality, and N is typically substantially less than the number of talkgroups on a system). TDMA systems have a number of possible techniques for achieveing trunked channel management for channel allocation such as the use of Robbed Bit Signaling or Out of Band Signaling so that a radio and a system may exchange service information while voice communication is ongoing.

 

[Anon6083]

...

You have some time so don't worry just yet; but rest assured, when they do go TDMA, expect 100% encryption for all police operations...

Is this something that you can truly be confident in saying? I'm just interested in what the indications are that 100% of consuming agencies will utilize voice encryption after the transition to TDMA. My speculation is not one of disbelief, necessarily, but rather a lack of understanding/awaredness.

 

[W2SJW]

You have some time so don't worry just yet; but rest assured, when they do go TDMA, expect 100% encryption for all police operations...

I'm going to have to refute that for now, as i know the man who represents Moto at the admin level for this upgrade, and has said nothing to me about that yet.

DOT will be the first that goes TDMA as a test-bed. It will be full 'Phase-II', not X2, and will be on 700MHz.

I promise to find out more this week, as I have to program a D-STAR radio for him & show him how it's done. We should probably take this discussion further over in the NJ forum... :wink:

 

[Danny6569]

Tdma

Thanks nbuuck for youre help even though i still have no idea really how it works, it sounds like a lot of technical headaches that really dont sound any better than what a trunked digital system can do now, we have a 500 mhz trunked digital system that they put in here about 9 years ago and i know there not gonna change ours anytime soon with all the money they spent on it, and it works ok, i just dont see the advantage of this tdma system over any other trunked digital system out there now ? i mean without getting too technical how is it gonna be better or help out in any way compared to digital trunked systems out now ? other than not being able to pick it up on scanners yet because its a new system i dont see what purpose it even serves ? or is it not going to be any different that whats out now its just a different system that towns wanna change too because its newer ? i just dont get it

 

[Anon6083]

Thanks nbuuck for youre help even though i still have no idea really how it works, it sounds like a lot of technical headaches that really dont sound any better than what a trunked digital system can do now, we have a 500 mhz trunked digital system that they put in here about 9 years ago and i know there not gonna change ours anytime soon with all the money they spent on it, and it works ok, i just dont see the advantage of this tdma system over any other trunked digital system out there now ? i mean without getting too technical how is it gonna be better or help out in any way compared to digital trunked systems out now ? other than not being able to pick it up on scanners yet because its a new system i dont see what purpose it even serves ? or is it not going to be any different that whats out now its just a different system that towns wanna change too because its newer ? i just dont get it

TDMA can operate using fewer frequencies while supporting the same/more system usage, possibly at the cost of voice quality.

 

[kikito]

My opinion, which we ALL have....

Uh, NO, we do NOT ALL have that opinion. In fact, lately I've been having more issues with screen contrast, button labels rubbing off, etc. on my last two Unidens than with my last two GREs.

 

[Raccon]

Although I am likewise troubled by the industry choice to move to TDMA, it is a viable alternative. Many phone systems like those that rely on the T1 specification use TDMA so that a single medium can service multiple channels (24, if memory serves) in a single frequency allocation. In telecommunications, despite having access to the entire spectrum accross the line, certain frequencies are better suited to the human voice (T1 samples voice at approximately 8KHz, though there is some drift as you aluded to). The advantage, therefore, of using TDMA as an industry standard is the attractiveness of the consolidation of frequency allocations that system owners must purchase.

Not sure if I understand that correctly but the carrier frequency has no direct relation to the sampling frequency of the voice. Human voice is in the area of 300-3400Hz, and according to the Nyquist–Shannon sampling theorem double of the highest frequency should be used. So they rounded up to 4kHz and hence the sampling frequency came to be 8kHz. In addition you need to know the sampling resolution, which at 8 bit gives you then one 64kbit/s PCM timeslot (1 DS0 in a T1 link).

The use of time-slotting (the principle of TDMA) doesn't really limit how long a station can transmit; rather, it affects the quality of the transmission (at face value, this doesn't seem intuitive at all, but it is the case). The is achieved by the afore-mentioned sampling rate of 8KHz.

Digital trunking systems typically have a very limited channel bandwidth and therefore use vocoders to compress the data stream, some down to 2 kbps, which has the biggest effect on the voice quality. An uncompressed signal sampled at 8 kHz would sound just fine, even it's transmitted by using TDMA.

If each channel is only sampled at 8KHz but the system is operating at a frequency that is a magnitude greater than that of the sampling rate (say, >800MHz), you can clearly fit multiple parallel channels into a single cycle across the medium. This is the fundamental mechanic of TDMA.

You are confusing the carrier frequency (e.g. 800MHz) with the carrier bandwidth (e.g. 25kHz for TETRA = 4-slot TDMA). The sampling rate (8 kHz) is only indirectly related.

Contention over a particular channel is an interesting issue, and one cannot authoritatively say how this will be handled by industry manufacturers. Similar to current trunked systems, each of the N channels available in a TDMA system will have to be dynamically allocated to a subscribed radio as each one attempts to key up ...

Not entirely correct unless the radio is in a private call, else the channel (timeslot) is allocated for the entire group, i.e. all radios that are listening to or which transmit in that group under the coverage of the same station will use the same timeslot.

 

[Anon6083]

Not sure if I understand that correctly but the carrier frequency has no direct relation to the sampling frequency of the voice. Human voice is in the area of 300-3400Hz, and according to the Nyquist–Shannon sampling theorem double of the highest frequency should be used. So they rounded up to 4kHz and hence the sampling frequency came to be 8kHz. In addition you need to know the sampling resolution, which at 8 bit gives you then one 64kbit/s PCM timeslot (1 DS0 in a T1 link).

Right, I'm not really trying to imply what you're trying to refute. Much of that was an attempt at simplification for the sake of someone who is expressing confusion about how TDMA works. The entire goal was to relate some existing concepts with how an RF system might use TDMA.

Digital trunking systems typically have a very limited channel bandwidth and therefore use vocoders to compress the data stream, some down to 2 kbps, which has the biggest effect on the voice quality. An uncompressed signal sampled at 8 kHz would sound just fine, even it's transmitted by using TDMA.

Right, I'm not saying that the quality would be beneath acceptable standards. Rather, the goal was to note that something has to be sacrificed in order to achieve concurrent channels, and quality - though perhaps not discernible - is that sacrifice.

You are confusing the carrier frequency (e.g. 800MHz) with the carrier bandwidth (e.g. 25kHz for TETRA = 4-slot TDMA). The sampling rate (8 kHz) is only indirectly related.

Not trying to get into a spitting match, but I wasn't trying to equate them; I do recognize the difference. I think my response to your first correction will probably apply to this point as well, as this was an effort in simplification, not exhaustive elaboration. You're completely correct, though it is worth noting that both the channel bandwidth and sampling rate are an order of magnitude smaller than the carrier; I still maintain that this is what facilitates multiple concurrent voice channels on a single carrier (which is again where my perhaps imprecise references to T1 relate).

Not entirely correct unless the radio is in a private call, else the channel (timeslot) is allocated for the entire group, i.e. all radios that are listening to or which transmit in that group under the coverage of the same station will use the same timeslot.

That's one take on how it could be done. I cautioned against your perspective because you are saying that one technique is the exclusive technique for this problem, which I believe is an unfair generalization; one that may be inaccurate.



All in all, you're correct in those areas where you replied, and I'm not really looking to get into a drawn out back and forth about these items. I hope I've made it more clear what I was trying to accomplish when responding to someone who was unfamiliar with the topic at hand.