What is simulcast?

[jonwienke]

I've been looking at the Unication models because my 436 is deaf in my rural area (it does fine when I get closer to the city).

I've seen this stated before but what features are lacking in the Unication for scanner users? Could it scan local NOAA for alert tones and a P25 Phase 2 system?

Unications can only be programmed for one p25 system at a time. The ONLY advantage they have over the 436 is better simulcast reception. If your 436 reception problems are due to weak signal rather than simulcast interference, then you would be better off spending your money on a better antenna. The factory antenna on the 436 is nothing to write home about.

 

[belvdr]

Unications can only be programmed for one p25 system at a time. The ONLY advantage they have over the 436 is better simulcast reception. If your 436 reception problems are due to weak signal rather than simulcast interference, then you would be better off spending your money on a better antenna. The factory antenna on the 436 is nothing to write home about.

Thanks for the suggestions. I have no idea if the problem is simulcast or general reception. I get a lot of garbled voice regardless of which antenna I use. As a disclaimer, I don't have an antenna cut to 700-800Mhz. I tried a long wire, 2m mag mount, and a 2m/440 Arrow yagi, all with the same results.

A fire station is about 2-3 miles from me and we're both on the top of a hill (a valley between us). I would assume the area is covered. Even when they had an accident about 1/2 mile up the road, I heard nothing on the 436.

 

[jonwienke]

None of those will work very well for 800MHz. Are your antennas indoors or outdoors? If your house has metal siding or insulation with metal foil backing, no indoor antenna will work well.

The next thing to figure out is whether simulcast is a possible issue. What system are you trying to receive? Are you only having reception issues with one system, or everything in your area?

 

[belvdr]

None of those will work very well for 800MHz. Are your antennas indoors or outdoors? If your house has metal siding or insulation with metal foil backing, no indoor antenna will work well.

The next thing to figure out is whether simulcast is a possible issue. What system are you trying to receive? Are you only having reception issues with one system, or everything in your area?

I knew they weren't the most effective but tried them anyway.

Indoors and outdoors, all are handheld, so to speak, in the terms they aren't attached to anything and can be moved inside/outside.

It is just this particular system. With my RSP2, I can use any of the antennas and receive fine, including ADS-B traffic.

The system is the Ohio MARCS-IP, particularly the Butler County area. With the RSP2, I can definitely hear the digital noise on the frequencies, even from the basement with the mag mount.

That last statement is the reason I was considering the Unication.

 

[KA1RBI]

But you say there is no relation between phase and frequency in simulcast systems? Are you perhaps refering to phase and FM demodulation?

/Ubbe

Respectfully, what I think may be happening here is that "phase" is being used in two wholly different ways.

The "phase" of the signals at the RF carrier frequencies (such as for example 800 MHz) is one thing, but when radio engineers talk about adjusting the Launch Delay of a particular tower they aren't talking about that at all. Instead they're talking about tweaking the phase of the symbol clock, which (for P25 systems today) is at one of two frequencies: 4,800 Hz or 6,000 Hz. This adjustment of Delay Spread is done to minimize Time Delay Interference, TDI).

As you can see there are orders of magnitude separating these two..... I don't know enough about the tower infrastructures to say authoritatively, but it seems to me that expecting the various towers to all be phase-coherent with each other at RF (i.e., 400/800 MHz) frequencies would be ludicrous.

73

Max

 

[jonwienke]

It is just this particular system. With my RSP2, I can use any of the antennas and receive fine, including ADS-B traffic.

The system is the Ohio MARCS-IP, particularly the Butler County area. With the RSP2, I can definitely hear the digital noise on the frequencies, even from the basement with the mag mount.

That last statement is the reason I was considering the Unication.

MARCS uses a lot of simulcast. If you can receive other systems OK, and can hear noise on analog but can't decode the digital into intelligible voice, then the Unication would probably work for you.

 

[belvdr]

MARCS uses a lot of simulcast. If you can receive other systems OK, and can hear noise on analog but can't decode the digital into intelligible voice, then the Unication would probably work for you.

Thanks for the talk through on this. It helps to bounce it off others for sure. Sorry to derail the thread.

 

[troymail]

I've been looking at the Unication models because my 436 is deaf in my rural area (it does fine when I get closer to the city).

I've seen this stated before but what features are lacking in the Unication for scanner users? Could it scan local NOAA for alert tones and a P25 Phase 2 system?

It is true that the Unication G4/G5 pagers are very limited when it comes to scanning features - however, they do an amazing job not only receiving simulcast systems/sites but they also seem to have the ability to receive (in many cases) much more distant simulcast systems than any scanner I have using nothing more than a RS 800 Mhz handheld antenna. Of course, there are lots of factors that come into play.

 

[pinballwiz86]

It is true that the Unication G4/G5 pagers are very limited when it comes to scanning features - however, they do an amazing job not only receiving simulcast systems/sites but they also seem to have the ability to receive (in many cases) much more distant simulcast systems than any scanner I have using nothing more than a RS 800 Mhz handheld antenna. Of course, there are lots of factors that come into play.

I think that short stubby antenna on the G4/G5's is part of the reason for better performance in simulcast systems (attenuation). They sell those bullet antennas on e-bay. Give it a whirl guys.

 

[Forly192]

Cell phone manufactures have figured out a way to prevent a phone from connecting to two towers at the same time, while scanner manufactures are still struggling with that.

I realize that cell phones also transmit which makes the process easier as it sends position data to the tower, but surely, can't they make a scanner that can detect signal strength and lock onto the strongest signal?

It seems so basic. No?

 

[rcool101]

I think that short stubby antenna on the G4/G5's is part of the reason for better performance in simulcast systems (attenuation). They sell those bullet antennas on e-bay. Give it a whirl guys.

Don't bother...they suck....I use a Comet Miracle Baby on my 436....Works great...Good for Simulcast at least here...YMMV as in anything else

 

[Spitfire8520]

I think that short stubby antenna on the G4/G5's is part of the reason for better performance in simulcast systems (attenuation). They sell those bullet antennas on e-bay. Give it a whirl guys.

The G4/G5's performance improves with better antennas. It is rather interesting that scanners need attenuation to get results, which is not guaranteed, while other radios are looking for more gain.

Cell phone manufactures have figured out a way to prevent a phone from connecting to two towers at the same time, while scanner manufactures are still struggling with that.

I realize that cell phones also transmit which makes the process easier as it sends position data to the tower, but surely, can't they make a scanner that can detect signal strength and lock onto the strongest signal?

It seems so basic. No?

You might be thinking of multicast, where different towers might transmit the same radio traffic on different frequencies. This is where reading signal strength and switching to different towers would be relevant. Scanners don't do this, but it is independent of simulcast issues.

Simulcast is specifically designed so that the radio thinks it is a single site that covers a large area because all the towers transmit the same information on the same frequencies. There is no way to differentiate between the towers, and there is no reason to with a properly designed radio.

Scanners need to be redesigned in order to handle simulcast properly. It really should be a basic fix at this point. Simulcast has been around for more than a decade and the solution is well known and proven.

 

[Ubbe]

I have measured co-channel interference rejection on several receivers a few years back and asian made receivers where terrible and the most expensive ones, from Motorola and Swissphone, where very much superior at that parameter.

Maybe it is not only a hardware issues but also a license issue if the most succesful algorithm for the decode process are not used to save costs.

/Ubbe

 

[kayn1n32008]

Cell phone manufactures have figured out a way to prevent a phone from connecting to two towers at the same time, while scanner manufactures are still struggling with that.



It seems so basic. No?

Basic? No. Cell phone networks do not use simulcast, they use multicast. Completely different.


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[Project25_MASTR]

I think that short stubby antenna on the G4/G5's is part of the reason for better performance in simulcast systems (attenuation). They sell those bullet antennas on e-bay. Give it a whirl guys.

Their receivers are actually designed to demodulate and decode CQPSK compared to ordinary FM such as what is found with typical scanners. Keep in mind, they are a commercial product designed as pagers for these systems and not scanners. Essentially, equivalent to a subscriber being used for NAS in operation. The other factor with the Unication pagers is that they are extremely sensitive. They tend to operate well beyond the limit of typical subscribers. Great example, I compared a G5 to a XTS5000 and the G5 held the control channel well down to -126 dBm where after -108 dBm the XTS began showing out of range.

Cell phone manufactures have figured out a way to prevent a phone from connecting to two towers at the same time, while scanner manufactures are still struggling with that.

I realize that cell phones also transmit which makes the process easier as it sends position data to the tower, but surely, can't they make a scanner that can detect signal strength and lock onto the strongest signal?

It seems so basic. No?

I believe simulcast versus multicast has been covered as a reply to this comment well enough but also, scanners don't operate according the the P25 protocol like actual subscribers (or even the Unication pagers) do.Scanners will essentially scan the provided control channels (which can be at multiple sites) looking for activity regarding the interested talk groups. If something is found, it will follow the talk group to the assigned repeater. A subscriber on the other hand, will essentially park on an active control channel until it's roaming protocols are met then scan the adjacent sites and roam to the next strongest and repeat the process.

 

[troymail]

I believe simulcast versus multicast has been covered as a reply to this comment well enough but also, scanners don't operate according the the P25 protocol like actual subscribers (or even the Unication pagers) do.Scanners will essentially scan the provided control channels (which can be at multiple sites) looking for activity regarding the interested talk groups. If something is found, it will follow the talk group to the assigned repeater. A subscriber on the other hand, will essentially park on an active control channel until it's roaming protocols are met then scan the adjacent sites and roam to the next strongest and repeat the process.

This is true if scanning more that a single system and/or conventional channels (as most scanner users do). The Unidens will try and scan several sites/control channels for a given system (unless you force it not to). GRE/Whistler scanners (since the PSR-800) will act like a subscriber radio - it will seek and hold on a control channel the meets and remains above a quality requirement and only search for a different CC/site if/when that signal degrades (note that this is more or less the opposite of what Uniden does).

 

[Project25_MASTR]

This is true if scanning more that a single system and/or conventional channels (as most scanner users do). The Unidens will try and scan several sites/control channels for a given system (unless you force it not to). GRE/Whistler scanners (since the PSR-800) will act like a subscriber radio - it will seek and hold on a control channel the meets and remains above a quality requirement and only search for a different CC/site if/when that signal degrades (note that this is more or less the opposite of what Uniden does).

I've not experienced this with my TRX-2...been much scan all the control channels and match the internal database to the site alias for display. I'll have to figure out a way to actually test it in a lab environment now.

 

[troymail]

I've not experienced this with my TRX-2...been much scan all the control channels and match the internal database to the site alias for display. I'll have to figure out a way to actually test it in a lab environment now.

It is because of this reason for some P25 systems, I import the sites of interest and duplicate the system X times (where X is the number of sites I imported) into multiple scanlists to (if desired) force the radio to scan multiple sites.

Some folks struggle with not hearing what they expect because they have imported an entire system and the radio locks onto a site other than what they would expect.... in fact, it is more likely that a Whistler will find and lock onto a non-simulcast site if given the opportunity than a simulcast site... It may try the simulcast site but then "lose it" and then find another. If a good quality non-simulcast site becomes an option, the radio can lock onto it and stay there for quite some time....

 

[a29zuk]

This is true if scanning more that a single system and/or conventional channels (as most scanner users do). The Unidens will try and scan several sites/control channels for a given system (unless you force it not to). GRE/Whistler scanners (since the PSR-800) will act like a subscriber radio - it will seek and hold on a control channel the meets and remains above a quality requirement and only search for a different CC/site if/when that signal degrades (note that this is more or less the opposite of what Uniden does).

Correct me if I'm wrong, but don't the older Unidens (396T,etc) handle the sites as the Whistler scanners do now?



Sent from my standard laptop using a standard keyboard.

Jim