What can scan the clmrn?
- Thread starter Matt88ch
- Start date
As stated above, you're either not understanding things or overthinking them here.
CLMRN is H-DQPSK , Linear Simulcast Modulation. Several sites, all GPS locked for carrier reference, operating at the same frequency, at the same time. The SDS uses a SDR chip to deal with the issues of LSM. The Unications can also work it. Nothing else on the scanner radio market handles it well. Older 996P2 models were less sensitive than the newer ones, so they tend to not receive multiple sites, thus having overall better performance on a system like this. But even they don't hold as good as the SDS does. That's all there is to it. In the database, "zones" which have multiple simulcasting transmitters are marked "simulcast" in the name , so the end user knows they're dealing with simulcast.
I assure you that I do not need to read an RR wiki article to understand what simulcast is. 😂
BinaryMode
Active Member
Good video. That makes more sense then. What I'm not understanding though is if say I program a site and its control channel, wouldn't it just receive that one site? I guess the devil is in the details in that there are more than one site using the same frequency for the control channel? Thus my scanner will try to latch onto two of the same control channels?
So from the video, the site with transmitter #1 and transmitter #2 are using the same control channel and voice channel frequencies?
Why doesn't RR list each transmitter location as part of the site?
LOL
I mean, if my scanner locks on to a control channel (one control channel of course) and follows the voice channels, that's just from the one tower. But I can see this being a real PITA if the same frequencies were used from more than one transmitter making up the site. So this must be what the fuss is about about how one would need an SDR type of receiver to receive these sites without data error. What confused me is that the RR database does not list each transmitter location and its frequencies. Thus I saw no frequency duplicates. Then I most certainly would have seen the use of more than one of the same frequency per transmitter for each site.
From the Wiki page: "Simulcast refers to the process of transmitting the same signal from different tower locations over the same frequency at the same time."
wiki.radioreference.com
Maybe that's wrong? I doubt it.
Again. what may be tripping me up is that the table data from the database lists "sites" and not all transmitter locations that belong to a site I assume. I don't think the neighbors entry is a transmitter location relative to the site but rather another site.
This is why I said the following: What can scan the clmrn?
And I said the following:
"So in my non-educated opinion, if anyone is having issues it's the H-DQPSK of Phase II."
From another Wiki entry:
"To begin to understand the problem requires a basic understanding of the way the digital signals are modulated. Simulcast systems use quadrature phase-shift keying (QPSK) in the form of CQPSK (Motorola LSM / Harris WCQPSK) for Phase I systems, and H-DQPSK for Phase II systems. This modulation scheme differs from traditional modulation schemes such as AM and FM. QPSK modulates the phase of the signal rather than the amplitude or frequency. The problem is that traditional scanner hardware was designed to receive the traditional modulation schemes, but not QPSK. The result is that they fall short when attempting to demodulate QPSK signals.
wiki.radioreference.com
Off topic, but one has to wonder why the complex modulation schemes and poor use of bandwidth and whatnot when iDEN and FHSS could have been used over a lousy 2.5 MHz or thereabouts of bandwidth. A portion dedicated to public safety and ONLY public safety in the say, 700 MHz band. Actually, I think I know part of the answer. iDEN is patented...
So from the video, the site with transmitter #1 and transmitter #2 are using the same control channel and voice channel frequencies?
Why doesn't RR list each transmitter location as part of the site?
LOLI mean, if my scanner locks on to a control channel (one control channel of course) and follows the voice channels, that's just from the one tower. But I can see this being a real PITA if the same frequencies were used from more than one transmitter making up the site. So this must be what the fuss is about about how one would need an SDR type of receiver to receive these sites without data error. What confused me is that the RR database does not list each transmitter location and its frequencies. Thus I saw no frequency duplicates. Then I most certainly would have seen the use of more than one of the same frequency per transmitter for each site.
From the Wiki page: "Simulcast refers to the process of transmitting the same signal from different tower locations over the same frequency at the same time."
Simulcast - The RadioReference Wiki
Maybe that's wrong? I doubt it.
Again. what may be tripping me up is that the table data from the database lists "sites" and not all transmitter locations that belong to a site I assume. I don't think the neighbors entry is a transmitter location relative to the site but rather another site.
This is why I said the following: What can scan the clmrn?
And I said the following:
"So in my non-educated opinion, if anyone is having issues it's the H-DQPSK of Phase II."
From another Wiki entry:
"To begin to understand the problem requires a basic understanding of the way the digital signals are modulated. Simulcast systems use quadrature phase-shift keying (QPSK) in the form of CQPSK (Motorola LSM / Harris WCQPSK) for Phase I systems, and H-DQPSK for Phase II systems. This modulation scheme differs from traditional modulation schemes such as AM and FM. QPSK modulates the phase of the signal rather than the amplitude or frequency. The problem is that traditional scanner hardware was designed to receive the traditional modulation schemes, but not QPSK. The result is that they fall short when attempting to demodulate QPSK signals.
Simulcast Distortion - The RadioReference Wiki
Off topic, but one has to wonder why the complex modulation schemes and poor use of bandwidth and whatnot when iDEN and FHSS could have been used over a lousy 2.5 MHz or thereabouts of bandwidth. A portion dedicated to public safety and ONLY public safety in the say, 700 MHz band. Actually, I think I know part of the answer. iDEN is patented...
All the sites are shown. See this example: Connecticut Land Mobile Radio Network (CLMRN) Site: Troop H Simulcast Scroll Down.Why doesn't RR list each transmitter location as part of the site?
I mean, if my scanner locks on to a control channel (one control channel of course) and follows the voice channels, that's just from the one tower. But I can see this being a real PITA if the same frequencies were used from more than one transmitter making up the site. So this must be what the fuss is about about how one would need an SDR type of receiver to receive these sites without data error. What confused me is that the RR database does not list each transmitter location and its frequencies. Thus I saw no frequency duplicates. Then I most certainly would have seen the use of more than one of the same frequency per transmitter for each site.
I think you're overthinking this to a much larger level. There are not multiple sites, there are multiple in-phase and in sync transmitters within a single site.
All of the transmitters in the site broadcast on the same frequency at the same time.Good video. That makes more sense then. What I'm not understanding though is if say I program a site and its control channel, wouldn't it just receive that one site? I guess the devil is in the details in that there are more than one site using the same frequency for the control channel? Thus my scanner will try to latch onto two of the same control channels?
So from the video, the site with transmitter #1 and transmitter #2 are using the same control channel and voice channel frequencies?
Why doesn't RR list each transmitter location as part of the site?
Each location within the site has a stack of GTRs that have the same frequency as every other location within that site. When the system directs a subscriber to "channel X" all of the transmitters for channel x within that whole site all broadcast at the same time. That's what simulcast is.
