Frequency allocation of Smartnet

[ericcc65]

I'm brand new to this world of trunked mobile so please bear with me. I've been trying to read all I can on Smartnet and trunked radio in general. Smartnet is particularly frustrating as it seems to be reverse engineered but I can't find a single good reference on some of the design, it's scattered in bits and pieces all over.

A little background. I'm an electrical engineer and I work primarily in the DSP field. I just got a USRP and I want to play with detecting and understanding various trunked systems that are out there. Which leads me to my questions:
1. Is there some sort of frequency allocation plan for Smartnet? I know there are the FCC approved bands in the US, but is there an equation or standard for what might be mandatory base frequencies? In looking through the database they seem to at least be multiples of 6.25 kHz. Is that always the case? Is there any equation governing them that incorporates offsets? I can tell it's not difficult once you have the base frequency to get to the channels, it's just a matter of knowing which channels can be used and what the range is. Seems similar to MPT1327 without the documentation.
2. For the lower frequencies is there a standard duplex spacing (I know 45 MHz is standard >=800 MHz)? It's nice in some other technologies because the duplex separation means you know if a given band it is either uplink or downlink. Is it that way for Smartnet or can they be randomly interspersed? For instance, in iDEN it looks like this, so if I detect something on a frequency I know if it's uplink or downlink
806-821 - Uplink
851-866 - Downlink
821-825 - Uplink
866-870 - Downlink
etc.
3. Is there a better sub-forum to be asking these questions?
4. I know iDEN is proprietary but I found a good "Technical Overview" document. Does something like that exist for Motorola Trunking systems (most interested in Type II - Smartnet)?

 

[WA0CBW]

Here goes.....
1. Smartnet is a "feature set" of functions for a Motorola trunk system. It is a proprietary trunk system. It follows a set of features proposed by APCO for analog trunk system. Each manufacturers trunked systems had to be capable of performing those features. Each manufacturer added proprietary features to make their system more desirable to the user. The FCC set aside frequencies for trunking systems in the VHF, UHF, and 700/800 MHz bands. The FCC also determined the frequencies and frequency steps for each band. These analog trunk systems are being replaced by trunk systems using digital protocols such as P25, MotoTrbo, NextEdge, MPT1327, etc.
2. Repeater offsets are generally 45 MHz for 700/800 MHz, 5 MHz for UHF and anything from 600KHz to several MHz for VHF. Repeater input/output can be either high or low depending on the coordinators and other existing frequencies.
3. That would be up to the moderators.
4. Type 1 and 2 trunk Smartnet systems are no longer available and are being replaced by digital Smartnet/Smart Zone systems.

How a trunk system operates and their feature sets are two different things. Trunk systems can be of several different types such as a dedicated control channel (centralized) or distributed (de-centralized) trunking. where each channel acts as a control channel.
BB

 

[ericcc65]

Thanks for the reply.
1. I knew I was missing something in the lingo (is that why there's MPT1327 but for the physical layer stuff I need to look at 1343?). I also didn't know the FCC established the BWs and center frequencies within an allocation of spectrum. I'll see if I can hunt that down.
2. So I guess I'm on my own for the lower bands. I guess my real question is if it can be totally randomly interspersed across systems or do they tend to clump up/down together? I suppose if it's settable by the system admin then it's the former.
4. When you say digital Smartnet/Smartzone do you mean that the voice uses the APCO 25 Air Interface? I understand Smartzone is for linking multiple Smartnet sites.

 

[radioman2001]

I think in some respects your are mixing FCC channel and band allocations with a vendors(Motorola) brand name for as mentioned above feature set. When the 800 MHZ band was first allocated a standard offset and frequency range was created. The standard offset for 800 Mhz is 45 mhz for both 2-way and cellular, with the base transmitting on the higher of the 2 frequencies, which is opposite to the UHF band which has a standard offset of 5mhz 406-470 and 3Mhz for 470-512 mhz.The individual frequencies in the 800Mhz band in most radios is found by channel number, just like the old cellular channels were before they went broadband. There has been some swapping going on across the country due to a vendor(Nextel) interfering with Public Safety users in the 800 band. Nextel was created by the using of what was commercial frequencies interspersed with the Public Safety ones making the need to move them to one end of the 800 band.
If you want to know more about the actual decoding of trunked signals there already is a software package out there call Unitrunker that does exactly that. For a more detailed description as how Smartnet works see the Wiki on it.

 

[ericcc65]

Thanks for the input. I guess I should rephrase what I'm looking for. Let's assume I don't have access to a database and know nothing about the RF environment other than either the FCC or Smartnet hardware in general allow operation in certain bands. I want to detect Smartnet systems that are within the following bands, and determine what each channel's center frequency is. Let's say 136-175 MHz, 403-512 MHz, and 809-815 and 854-860 (I might be wrong for the US or in general, just stick with me for the sake of argument).

Is there anything that we know about Smartnet or frequency allocation plans that would help me in that search? First, can I assume center frequencies of channels will be a multiple of 6.25 kHz? Is someone going to put a base frequency of 855.133333 MHz for instance? What is the greatest common divisor of the channel frequencies...if there is one? Is there an optional frequency offset that can mess that up at all?

Also, if I detect a signal on a certain frequency, is there any way of "a priori" knowing if it's an uplink or downlink? For the 800 MHz band I will know if I detect something at 855.125 MHz that it's a downlink. Is there any way of inferring that if I detect something at 172 MHz or at 405 MHz that it's either uplink or downlink?

I'm certainly interested in learning WHY the frequency plans are the way they are (FCC, system protocol, etc.) but that's less important than just knowing how it is laid out for me to get started.

Do you mean the wiki linked below? That seems to be about the signalling only and doesn't say much about frequencies, modulation, or other physical layer stuff.

Motorola Type II Smartnet - The RadioReference Wiki

 

[mikewazowski]

With the exception of the 800/900Mhz bands, there are no channel plans for trunked systems. They will show up anywhere and everywhere.

To determine the channel plan on these bands, you will need to run a control channel utility that shows the channel numbers as frequencies are used. You will need a second scanner or something similar to correlate the activity you see on the screen with the actual frequencies in use.

Since these other band trunking systems can have multiple bandplans, it can sometimes take a while to figure out all the channels.

The simplest would be a single bandplan system that you're able to identify at least two channels and their corresponding frequencies. Using that information, you can extrapolate and determine what the other frequencies are.

 

[GTR8000]

With the exception of the 800/900Mhz bands, there are no channel plans for trunked systems. They will show up anywhere and everywhere.

700 MHz as well. In fact, the 700 spectrum is the one with the most rigorous plan at this point, here in the US at least. The channel plan is very specific as far as what frequencies can be used for trunking, which are general use vs usage by the states, standard 30 MHz offset with the mobiles on the + side, etc.

Of course you're not likely to find any Motorola Type II systems in the 700 band, so it's probably a moot point as far as this particular thread is concerned.

 

[ericcc65]

Of course you're not likely to find any Motorola Type II systems in the 700 band, so it's probably a moot point as far as this particular thread is concerned.

I'm definitely interested to know that. I mostly just asked about Smartnet because that seemed like the one that was the least structured and/or documented. I'm interested in trunked mobile in general though and learning about how all this works. Thanks.

 

[WayneH]

All Motorola 3600 systems have a common range of hex codes used to identify frequencies. For 800 you have a few variations for Splinter (US-Mexico Border areas) and certain nations outside of the US. 900 is 900 wherever you go. As mentioned, VHF and UHF are system specific and are referred to as other band trunking (OBT). Due to customization (i.e., non-standard input freqs and offsets) the input frequencies are assigned identifiers on the control channel.

900: 000-22F; 935.0125 spaced every 12.5
800: 000-2F7, 32F-33F, 3BE, 3C1-3FE; 851.0125 spaced every 25.0 except above 257 (to support 866-869 which have their own separate calculations)
+ If Splinter then the starting freq becomes 851.0000 spaced every 25.0
+ Rebanding involves taking the identifiers 1B8-22F and reusing them within the 851-854 sub-band to create assignments for a 12.5kHz spacing (as they are normally calculated for 25.0 [see above])
+ For the shuffle bandplan it takes the identifiers and reverses them so the starting frequency decrements (search for it on here for more info)

OBT: TX to mobile: 17C-2F7; RX by system: 000-17B
+ 3600 OBT systems can have up to three base and offset ranges per TX or RX

Also, "SmartNet" was meant to address various features in the APCO 16 standard. It took the old Motorola 3600 format that had been around for a while (and predominantly used by businesses and "SMR's" and made it more Public Safety friendly). There was also SmartWorks which added the same features but was a scaled down infrastructure version.

If you want more info on the 3600 protocol you can contact me via email. I've never had the time nor interest in writing a "bible" on it.

 

[ericcc65]

Thanks so much Wayne, that's very helpful.