Batboard

Been looking over the following info on Nextel's Direct Talk on the Nextel site and have a few questions.
It states that Direct Talk is an off-network, short range communication system using 10 frequencies in the 900mHz range and 15 codes.

http://support.sprint.com/doc/sp4144.xm ... irect_Talk

--Does anyone know the exact frequencies and codes they use?

--Are they "in the clear"?

--Would the proper Nextel instrument continue to work in Direct Talk after it was deactivated (or never activated) from
the system?

--Would it be possible to program a 900 mHz radio to communicate with a Nextel instrument in Direct Talk?

--Does anyone know the exact frequencies and codes they use?

It is spread spectrum.

--Are they "in the clear"?

They are not encrypted

--Would the proper Nextel instrument continue to work in Direct Talk after it was deactivated (or never activated) from
the system?

Yes, when you are in the DT mode you are off the system. (No dispatch, or interconnect when in DT mode)

--Would it be possible to program a 900 MHz radio to communicate with a Nextel instrument in Direct Talk?

No.

just an FYI here


i was recently in the bahamas (nassau) - and of course, they have no "nextel" network (sprint did work tho - on roaming)

i was able to talk FROM THE *INSIDE* OF THE CRUISE SHIP to our party while they were ashore - well over 1/4 mile and thru the steel hull of the ship.

also - the DT feature worked VERY VERY WELL onboard the vessel.... forward to stern...... i was - quite frankly - VERY impressed.




doug

--Would the proper Nextel instrument continue to work in Direct Talk after it was deactivated (or never activated) from
the system?

We have had some discussion about this recently on Howardforums as well.

http://www.howardforums.com/showthread.php?t=1174220

Anyway, my experience with regards to the never activated SIM card is has to have been activated at some point. When I used a pair of i325s for the first time on Direct Talk I could not get the one with the "virgin" SIM card to work. To make it work I switched service from the old SIM card to the new SIM card, and then back. Then both units were able to communicate with each other. I actually think that in some respect this is a better option for some people than cheap over the counter FRS or GMRS radios that are available at Wal-Mart. First off, it is pretty unlikely that the neighbor kid will be creating intentional interference on Direct Talk. Second off, a Nextel without service will still be able to call 911 in an emergency in areas that you are able to access Nextel sites. Third, a Nextel probably blends into the community a little bit better than a FRS radio. One other thing about Direct Talk, unlike analog conventional modulation on FRS/GMRS, if you transmit and no other unit receives the signal, you still get the "User Not Available". Also, one of the "kings" of Direct Talk range is the i325. It has a fixed antenna. Not everyone is going to like a fixed antenna because it can be kind of unwieldy, but it will give pretty darn good simplex range.

I have a Motorola i580 and the "MotoTalk" as they call it, and you need to have a SIM card that's at least valid. It doesn't have to be activated, it just has to be a real SIM. That is, a blank SIM that came with my replacement phone works just fine, as does an older SIM from a de-activated account.

batdude wrote:i was recently in the bahamas (nassau) - and of course, they have no "nextel" network (sprint did work tho - on roaming)

I'm guessing you upgraded to one of the new Buzz ic-series phones? We got 'em at work, but I'm holding off upgrading my personal line until they've seen a few months of field use.

Now here's the million-dollar question: Nextel Direct Talk and the DTR-series radios use very similar -if not identical- technology in the same band. Anyone got a Direct Talk-capable phone and a DTR radio that wants to see if they'll talk to each other?

[quote="motorola_otaku]

Now here's the million-dollar question: Nextel Direct Talk and the DTR-series radios use very similar -if not identical- technology in the same band. Anyone got a Direct Talk-capable phone and a DTR radio that wants to see if they'll talk to each other?[/quote]


I have tried, it did not work. If they had the same "codes" they would.

Jim

n7maq wrote:

Now here's the million-dollar question: Nextel Direct Talk and the DTR-series radios use very similar -if not identical- technology in the same band. Anyone got a Direct Talk-capable phone and a DTR radio that wants to see if they'll talk to each other?

I have tried, it did not work. If they had the same "codes" they would.

Jim
n7maq

I've wondered about this too. I believe they both use the same system but are coded differently so they can't intercommunicate. It would be wicked cool and wicked useful if they could work interoperate/intercommunicate with each other.

The DTR series radios appear to be based on a i325 or i355 design. I notice a lot of commonality in the design, including batteries, chargers, and accessories.

I have an i355 NEXTEL phone and I've used the DT feature with my girlfriend who also has an i355. It worked GREAT! We used it inside Wal*Mart while shopping and it worked EXCELLENT. Normal NEXTEL network service was spotty inside at the front of the store and nonexistent when deeper in the store. The DT feature solved this problem for us.

The i355 and maybe a few others can also use the i325 fixed antenna. I'm using the i325 fixed antenna on my i355. This antenna works way better than the original crappy pull-up antenna on the i355. The i325 antenna cost around $5 and I ordered it through MOL.

--Are they "in the clear"?

They are not encrypted and YES, you CAN listen to other DT users that are in range. The "channel" and "code" have to match for you to hear them and you could also talk to them in this case. You can also set a code on a channel as "receive all" to hear all activity on a channel but transmission isn't allowed in "receive all" mode. Too bad there isn't a DT SCAN feature!

The number (I don't know how many) available frequency-hopping spread-spectrum (FHSS) spreading codes are broken down into "channels" and "codes" to make the user interface appear like channels and codes on an analog radio. The Motorola DTR portables are probably using a different set of FHSS spreading codes and they don't overlap with codes used by NEXTEL phones in DT mode.

I've looked at a DT signal on a spectrum analyzer. It's definitely a FHSS emission and occupies almost the entire 902-928MHz band when transmitting. There's also some handshaking taking place between phones. When you press PTT, your phone briefly transmits a FHSS signal and then waits and listens for a response from one or more phones that are in range. If it hears an acknowledgement from one or more phones, it resumes transmitting and you can go ahead and talk. If the phone doesn't hear any acknowledgement from another phone, you get the "User Not Available" message and all transmissions stop. The DT system is smart enough to know if you're in range of another phone in DT mode using the same channel and code when you press PTT.

They are not encrypted and YES, you CAN listen to other DT users that are in range. The "channel" and "code" have to match for There's also some handshaking taking place between phones. When you press PTT, your phone briefly transmits a FHSS signal and then waits and listens for a response from one or more phones that are in range. If it hears an acknowledgement from one or more phones, it resumes transmitting and you can go ahead and talk. If the phone doesn't hear any acknowledgement from another phone, you get the "User Not Available" message and all transmissions stop. The DT system is smart enough to know if you're in range of another phone in DT mode using the same channel and code when you press PTT.

So it could be another user and not the the intended recipient that gives the acknowledgement. In that case you would not get the "User Not Available" message even though your intended user is actually unavailable. Correct?

billy7834 wrote:

They are not encrypted and YES, you CAN listen to other DT users that are in range. The "channel" and "code" have to match for There's also some handshaking taking place between phones. When you press PTT, your phone briefly transmits a FHSS signal and then waits and listens for a response from one or more phones that are in range. If it hears an acknowledgement from one or more phones, it resumes transmitting and you can go ahead and talk. If the phone doesn't hear any acknowledgement from another phone, you get the "User Not Available" message and all transmissions stop. The DT system is smart enough to know if you're in range of another phone in DT mode using the same channel and code when you press PTT.

So it could be another user and not the the intended recipient that gives the acknowledgement. In that case you would not get the "User Not Available" message even though your intended user is actually unavailable. Correct?

I think that's what will happen. The channel and code has to match on the other user's phone in order for this to happen. I've only heard one other user on DT so far and couldn't hear the guy he was talking to. I heard this when I was visiting Washington DC but didn't try to talk to him.

Actually, the DTR and DT/MT systems use the exact same frequency sets, with the same FSK modulation. The Moto/Direct Talk signal is really simple:

Each time you transmit, the radio begins transmitting on 902.xxx MHz and progressively increases the frequency by 500kHz every 85ms until it reaches 927.xxx MHz, where it starts over again at 902. So its pseudo-quasi-FHSS since the hops are sequential and can be predicted. The only differentiation between channels is the starting frequency - each channel offset by 50 kHz.

Like jim said, the Nextels aren't compatible with the DTRs because the codes are different, but all one would have to do is dig into the phone or DTR and find a way to mod the codes to match those of the DTR.

That's how the really old Symbol FHSS systems worked.

It'd be good if there was a way to get the DTR to start at 915MHz. Our ISM band starts on 915, rather than 902, but 902-915 here is full of GSM BTS input frequencies, so it's a band best not screwed around in.

We just got the ic502 phones here.

I was able to talk from the 2nd story of my house to a co-worker in his house a mile away. There are tons of trees houses and building in between us too. So far we have been really impressed with the range and clarity. It even works great car to car through urban terrain.

Anybody got a list of DT-enabled phones ? Seems to be quite a lot. I might buy some on eBay.

The delay seems to be longer with DT than DC. Anyone notice this?

I tried DirectTalk between my two nextels and the delay seemed to be about the same as DC. For DirectTalk, I measured it to be 0.65 seconds from speaking into one, to coming out the other phone. I don't have another DC phone I can use right now to compare the delays...

You would think the delay would be less since it is actually direct and does not go through the network.

Not sure this is any help but we notice a delay between two XTS2500 on simplex (digital) and there is a delay. We place that to the digital processing.

pr

Nexrad16 wrote:Not sure this is any help but we notice a delay between two XTS2500 on simplex (digital) and there is a delay. We place that to the digital processing.

pr

All digital radios suffer from this problem

MXC911 wrote:Anybody got a list of DT-enabled phones ? Seems to be quite a lot. I might buy some on eBay.

Did you ever get a list of Direct Talk capable Nextels? I know that both the i315 and i325 are capable and probably many (most?) after that are, but I realize that probably isn't as helpful as a laundry list of units that are capable of this. The older i1000s are not and the new i530s are not. My wife and I have an i560 and an i670 and both of them are. I know that there had been some discussion in the past of which Boost Mobile units might be made to work for this, but I do not have first hand knowledge of that. I suspect that the greatest range would be achieved with an i325 due to the fixed antenna, but that might prove to be too cumbersome for many users. Also, the i530s are not Direct Talk capable.

The 580s are DT capable, so are the 760s

Anyone lay their hands on a DTR 710 yet? Still trying to get pricing and availability through big M. FatBoy

Here is a list. The i930 shouldn't be on there though.

Some of the Boost mobile phones have it built in as well but the feature is turned off in the codeplug.

-will

http://en.wikipedia.org/wiki/MOTO_Talk

Medic12 wrote:Here is a list. The i930 shouldn't be on there though.

Some of the Boost mobile phones have it built in as well but the feature is turned off in the codeplug.

-will

http://en.wikipedia.org/wiki/MOTO_Talk

The codeplug is easy to change on the boost phones (with the correct level of RSS). If anyone needs codeplug mods on iden units drop me a note, I'll be glad to do what I can. The change I do the most is disabling the AMBE and 6 to 1 interleave, or allowing the user to do it from the keypad.

Jim

I thought the AMBE was on the newer iDEN phones and considered "better"?

-w