G5 phase 2 simulcast tower switching

[mdsxfire]

I did not have my g5 before phase 2 so not sure if this has always been the case but..

I was driving around today just testing how the pager holds the system while moving. I have 2 towersnear me, one a few miles to my east and one a little further to the northwest. While driving west away from the one I believe I was connected to I watched it go from full bars and bounce between 2-3. Once I was much closer to the NW tower the pager beeped and said out of range then about 3 seconds later came in range with full bars. I thought I read that u pretty much had to force them to change towers with a power cycle, just wondering if anyone else has noticed this with the phase 2 release?


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[jmontes77029]

I did not have my g5 before phase 2 so not sure if this has always been the case but..

I was driving around today just testing how the pager holds the system while moving. I have 2 towersnear me, one a few miles to my east and one a little further to the northwest. While driving west away from the one I believe I was connected to I watched it go from full bars and bounce between 2-3. Once I was much closer to the NW tower the pager beeped and said out of range then about 3 seconds later came in range with full bars. I thought I read that u pretty much had to force them to change towers with a power cycle, just wondering if anyone else has noticed this with the phase 2 release?


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Usually it will change to the best signal on its own. You can try to force it to your preferred site by turning pager off and on until it locks on your preferred site. Another option is to use a know channel with only the site you want so it will always stay on that site.


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[jmontes77029]

Usually it will change to the best signal on its own. You can try to force it to your preferred site by turning pager off and on until it locks on your preferred site. Another option is to use a know channel with only the site you want so it will always stay on that site.


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*knob position not know channel***


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[JSsignal16]

Another thing that you can do that helps a lot is change the out of range notification from 20 to 35 seconds. This gives the pager more time to search for a better site before telling you it's out of range. Unication David recommended this on one of his latest videos.

 

[troymail]

If your currently monitored system has multiple sites programmed (properly), the radio will (always has) automatically try to find a better site if/when the signal control channel signal drops in quality. This can even happen while stationary depending upon several factors.

This can be both a good and a bad thing as you might not want the radio to switch sites.

If you want that level of control, you must create multiple "systems" in the Unication programming - one "system" for each site you want to control. Then, you also must create additional zone/knobs that use those specific site "systems" that you programmed.

 

[mdsxfire]

This was on a simulcast single site system


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[troymail]

This was on a simulcast single site system


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If it is a single site simulcast system, it isn't going to change at all. You're always receiving from all of the towers/transmitters all of the time.

 

[APX8000]

Sounds like you just had a drop in the signal. If the Site number on the system you are monitoring is not changing on the front screen next to RFSS, then it is not acquiring a new site. It is simply losing the same site and reacquiring it.


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[dcr_inc]

How do you simulcast on a single site?

 

[troymail]

How do you simulcast on a single site?

"site" can mean different things --

Some folks use "site" to speak of a tower/transmitter location - which is accurate.

A "simulcast site" is a "set of tower/transmitter sites" that are all transmitting the same thing on the same frequencies all at the same time.

Listings of "sites" in the RRDB could be reference a "standalone site" (single tower) or a "simulcast site" (2 or more towers as a single "site").

It all depends upon the system.

 

[RFI-EMI-GUY]

This was on a simulcast single site system


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Whenever you are receiving a simulcast signal, there will be areas where there might be signal cancellation due to the phase difference between one site and another. This is similar to multi-path where one signal arrives directly to the receiver and another arrives later because it has been reflected from the ground or an object like a water tower or building. That phase difference causes the amplitude to drop*. I assume the "Bars" on the G5 respond to signal strength as I describe this. If they respond to bit error rate (BER), then the same multipath effect also results in a high bit error rate either by reduced amplitude, a phase difference in the bitstream or both.

Your radio is not "switching towers, it is responding to an aggregate of multiple signals.

To complicate this, in FM systems, there is a phenomenon called FM capture ratio which is a point where the receiver will favor the stronger signal and ignore the rest. In linear simulcast on narrow band channels, FM capture ratio requires a very large differential in signals, meaning you would need to be very close to a tower.

* In analog systems, while in motion, this multipath exhibits as a "picket fence" popping noise pulse at regular intervals. The higher the frequency (shorter wavelength) , the more frequent the noise.

 

[mdsxfire]

Whenever you are receiving a simulcast signal, there will be areas where there might be signal cancellation due to the phase difference between one site and another. This is similar to multi-path where one signal arrives directly to the receiver and another arrives later because it has been reflected from the ground or an object like a water tower or building. That phase difference causes the amplitude to drop*. I assume the "Bars" on the G5 respond to signal strength as I describe this. If they respond to bit error rate (BER), then the same multipath effect also results in a high bit error rate either by reduced amplitude, a phase difference in the bitstream or both.



Your radio is not "switching towers, it is responding to an aggregate of multiple signals.



To complicate this, in FM systems, there is a phenomenon called FM capture ratio which is a point where the receiver will favor the stronger signal and ignore the rest. In linear simulcast on narrow band channels, FM capture ratio requires a very large differential in signals, meaning you would need to be very close to a tower.



* In analog systems, while in motion, this multipath exhibits as a "picket fence" popping noise pulse at regular intervals. The higher the frequency (shorter wavelength) , the more frequent the noise.

And that dear RR followers is why I love this site, I have a pretty good working knowledge of radios/programming TRS etc but the actual technical how’s and whys I don’t know until someone comes along and explains, and then peaks my interest so I spend the next few days searching for all of this on the internet.
Thank you RFI-EMI-GUY, that was an awesome explanation!!! I think it explains why the bars bounce so much on these simulcast systems.


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[dakota91]

loss of signal

It could also be that because system radios affiliate with the tower with the strongest signal, the listener may be in an area in which the trunk group he's monitoring doesn't have any authorized users of that trunk group operating in his area. In that case, the towers closest to him won't be broadcasting that trunk group, so he'll be receiving signals from more distant towers.

 

[RFI-EMI-GUY]

It could also be that because system radios affiliate with the tower with the strongest signal, the listener may be in an area in which the trunk group he's monitoring doesn't have any authorized users of that trunk group operating in his area. In that case, the towers closest to him won't be broadcasting that trunk group, so he'll be receiving signals from more distant towers.

What you described, does not apply to "towers" within simulcast systems, only with multi site systems. You can have a mix of simulcast and multisite in a system, in which case the subscriber will affiliate with ALL of the towers within a simulcast "subsystem" or to another standalone site. But that is not the case here the OP is operating within pure simulcast. The radio affiliate's only once, no hand-off.

 

[mdsxfire]

So even with affiliating radios, when the request a channel grant its sent out to every tower in the simulcast? They don’t really “know” or care that their are multiple towers because each one is transmitting/receiving the same signals?

 

[troymail]

You need to forget about individual "towers" --- only thing of "sites" (simulcast or non-simulcast).

A "site" could be a single tower (non-simulcast) or a group of 1 or more towers functioning as one (simulcast).

For a simulcast "site", affiliation isn't with a "tower" - it is with a "site" (a set of towers functioning as one).

 

[dcr_inc]

"For a simulcast "site", affiliation isn't with a "tower" - it is with a "site" (a set of towers functioning as one)."
You are affiliating with a "talkgroup" in a simulcast system not a site.. "Site" affiliation is for non simulcast systems, as the system controller sees ALL simulcast sites as one site.

 

[RFI-EMI-GUY]

So even with affiliating radios, when the request a channel grant its sent out to every tower in the simulcast? They don’t really “know” or care that their are multiple towers because each one is transmitting/receiving the same signals?

Yes.
For example a four site simulcast system, a subscriber will initially lock onto control channel (RF frequency, example 855.0125 MHz) whose outbound signalling word (OSW) data is being simultaneously transmitted from all towers.

To affiliate, the subscriber sends a request via inbound signalling word (ISW) on the paired RF frequency (810.0125 MHz, in this case). The ISW may reach 1, 2, 3 or all 4 towers depending on location and propagation.

This inbound data request is voted by central equipment and processed to correspond with the "site" or more appropriately the simulcast subsystem the 4 towers operate within.

A channel grant via the control channel and subsequent voice communications on traffic channels operate in same way.

So a subscriber radio really has no idea which tower(s) in a simulcast sytem it is communicating with. The central equipment, site controllers, voters know which site(s) are receiving the inbound data FROM the subscriber, but this information is primarily to select best inbound signal path instantaneously.

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[KevinC]

Yes.
For example a four site simulcast system, a subscriber will initially lock onto control channel (RF frequency, example 855.0125 MHz) whose outbound signalling word (OSW) data is being simultaneously transmitted from all towers.

To affiliate, the subscriber sends a request via inbound signalling word (ISW) on the paired RF frequency (810.0125 MHz, in this case). The ISW may reach 1, 2, 3 or all 4 towers depending on location and propagation.

This inbound data request is voted by central equipment and processed to correspond with the "site" or more appropriately the simulcast subsystem the 4 towers operate within.

A channel grant via the control channel and subsequent voice communications on traffic channels operate in same way.

So a subscriber radio really has no idea which tower(s) in a simulcast sytem it is communicating with. The central equipment, site controllers, voters know which site(s) are receiving the inbound data FROM the subscriber, but this information is primarily to select best inbound signal path instantaneously.

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And, of course, since we're talking P25 here it's ISP and OSP. :wink:

 

[RFI-EMI-GUY]

And, of course, since we're talking P25 here it's ISP and OSP. :wink:

Hard to lose old terminology when it took nearly two decades for P25 trunking to surface.

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