Batboard

Hypothetical:

Helicopter is airborne and affiliates with a site that is in city "A". It continues on it's treck at 1500 ft AGL and stays with that site for 75 miles or more. Helicopter lands in city "B" and loses the system completely because it's not able to connect to any of the sites that were in the control channel information of the previous site it was affiliated. Turning off and turning on the radio after a while brings it back on the system and everything is fine until once again, the aircraft goes back to city "A".

I've noticed the Non-Adjacent site search feature that is in the advanced tab of a particular trunking system. By clicking this feature and programming it in the radio, I would hope that it would help alleviate this problem. The text of the feature reads as follows:

Enables the radio to search its CPS-programmed list of Control Channels for a site with a stronger signal. This is only true when the current home site and its FNE-defined (Fixed Network Equipment) adjacent sites are all registering at a certain threshold amount below the CPS-defined Acceptable RSSI Threshold level. This allows the radio the ability to roam-to and use a site that is not FNE-defined as being adjacent to the radio’s current home site, but does have an "Acceptable" or stronger signal. This feature applies only for the current Trunking System.

The only way we would truly know is to test it, but if anyone here has experience with this feature, I would appreciate your input.

I'm going to make a note of this, as I could see this being a good test scenario.

I'm not saying it will be implemented in any of our gear at any point, but I'm going to keep this in mind for later.

I will post here once I know the results of the test. We're going to try it in one of our helicopters and see how it goes.

Do you have Full Specturm Control Channel scan enabled as well?

My take (I'll have to reread some of the other stuff) that FNE referenced in there also delt with data services, more than voice, but I could be wrong.

However, this may answer a problem with a Omnilink system where the opposite would happen in a certain configuration:

When entering System ID x from an out of range condition, the radio will stay out of range until entering System ID y.

However, if in System "y", and enter into system "x", the radio is just fine. From left to right, no go...from right to left, no problem.

I'll have to check that off and see what happens.

Pj wrote:Do you have Full Specturm Control Channel scan enabled as well?

We had that conversation today as a matter of fact. We're going to try it without full spectrum scan on first and see how it goes. If it works, we'll leave it. If not, then that is the next thing we'll try. If I remember correctly, full spectrum scan is used (if checked) when the radio cannot find a good control channel in the list it already has. If this is checked, then it goes outside that list and starts scanning the full spectrum for any control channel then checks to see if that control channel is a match to the system that it's supposed to be on. I could be wrong but I think that's how it works.

My take (I'll have to reread some of the other stuff) that FNE referenced in there also delt with data services, more than voice, but I could be wrong.

I don't know either but the way I read it, it's saying that when you're on a site, you're also receiving information on adjacent sites so that if the radio needs to switch, it's going to try those adjacent sites first. If it can't find one, then it's dead UNLESS you have non-adjacent site enabled.

However, this may answer a problem with a Omnilink system where the opposite would happen in a certain configuration:

When entering System ID x from an out of range condition, the radio will stay out of range until entering System ID y.

However, if in System "y", and enter into system "x", the radio is just fine. From left to right, no go...from right to left, no problem.

I'll have to check that off and see what happens.

I'd be interested to see your results as well.

Give me about a week, and I should know!

Jack wrote:..but the way I read it, it's saying that when you're on a site, you're also receiving information on adjacent sites so that if the radio needs to switch, it's going to try those adjacent sites first. If it can't find one, then it's dead UNLESS you have non-adjacent site enabled.

Are we talking about a 7.x Astro25 system or 4.1 Smartzone? 700/800 or OBT (VHF/UHF?)

Either way, it would be a step back from the behavior of older Smartzone subscriber equipment (i.e the MTS2000.) In those, the radio would first go to the last available list of neighbor sites, then to the full CC list programmed for the referenced system, then if you had Full Spectrum Scan enabled it would scan the entire band looking for a matching SysID. I believe AMSS functioned similarly; Wavetar might want to chime in here. Also, if the radio's controls were programmed for Site Search/Lock the user could manually force the radio to switch sites, and with use of Site Lock/Unlock could force it to park on a site with less-than-optimal RSSI.

motorola_otaku wrote:

Jack wrote:..but the way I read it, it's saying that when you're on a site, you're also receiving information on adjacent sites so that if the radio needs to switch, it's going to try those adjacent sites first. If it can't find one, then it's dead UNLESS you have non-adjacent site enabled.

Are we talking about a 7.x Astro25 system or 4.1 Smartzone? 700/800 or OBT (VHF/UHF?)

800Mhz Smartzone 4.1

Either way, it would be a step back from the behavior of older Smartzone subscriber equipment (i.e the MTS2000.) In those, the radio would first go to the last available list of neighbor sites, then to the full CC list programmed for the referenced system, then if you had Full Spectrum Scan enabled it would scan the entire band looking for a matching SysID.

The radios we're talking about here are mobile radios in aircraft. XTL-5000's. With the XTL's and XTS's, AND MTS2000's, they all build knowledge about the current sites and adjacent sites. They continue to monitor the known sites through the messages sent over the control channel. They also sample the signal strength of those known sites. The radio evaluates all of that and then either switches or stays on the current site. Once it's switches, it starts that process all over again by rebuilding knowledge about the current site and the adjacent sites.

I believe AMSS functioned similarly; Wavetar might want to chime in here. Also, if the radio's controls were programmed for Site Search/Lock the user could manually force the radio to switch sites, and with use of Site Lock/Unlock could force it to park on a site with less-than-optimal RSSI.

We don't include the site function in the menu because we don't want our users to inadvertently lock onto a site. They aren't trained in the use of that, so it isn't there for them.

As for the Site Search button, that IS available in the radio and they know how to use that. However, by hitting that button and holding it down, it does not guarantee that the radio will switch to another site. There are a lot of factors that the radio looks at before deciding to switch, even if you do try and force it. For instance, if the RSSI of the current site is 100 and the rest is under the criteria for acceptable communications, the radio will not switch. Capabilities of adjacent sites is another factor. For instance, if the current site is RSSI of 50 and an adjacent site is RSSI of 100, but that adjacent site doesn't support the capabilities of the radio for the particular talk group it's on, it will still not switch. It will stay on the site with the lower RSSI. RSSI smoothing will affect too, so you cannot guarantee that the radio will switch sites at the same location every time. If you have a raw RSSI of 40 and a smoothed RSSI of 80, the radio uses the smoothed RSSI so it's going to consider that site you're moving away from as still acceptable. Smoothed RSSI is used for both the current site and the adjacent sites so this process works both ways. For instance, if you have a RAW RSSI of 80 and a smoothed RSSI of 40, it's going to think that the RSSI of the adjacent site is 40.

Then of course you have the fact that if the radio is programmed with preferred sites, it's going to try and use those first, but that's not a factor here because we don't use that function. Heavy voice traffic will affect the radio because the radio only samples the adjacent sites when it's idle on the control channel. When idle on the control channel, it will do this every two seconds. Having said all this.....

The non-adjacent site search feature would most likely be useful for people who are operating in the mountains, where they might get a good RSSI from a site far away and for aircraft, who may stay locked on a site for a long period of time and be in a completely different area when landing. Without that feature enabled, the radio will be dead because it's trying to find a control channel from it's knowledge base of the last connected site, and it's adjacent sites. It will not lock onto a site in an area that wasn't in that control channel information without this feature. This feature allows the radio to scan the control channel list for a site with a good signal, regardless of whether or not it was in the list of adjacent sites from the last connected control channel.

Man, I hope this makes sense. I feel like I rambled a little bit.