Just got a few questions for you guys that familiar, and it's purely curiosity, no planned projects or anything.
First off, can a multi-site simulcast support P25 mixed-mode operation? If I key up on repeater 1 in digital, is there enough logic supported that will send the audio and mode to repeater 2 and transmit it in the proper audio or is it limited to one or the other? Can you cross support modes as well? Can repeater 1 transmit digital traffic and pipe that audio to another repeater (different frequency) in analog?
Also, somewhat related, will comparators and voters and what not support mixed mode operation, such as a multiple receive setup feeding back into one transmit site?
Like I said, just trying to get a few curious answers...no plans to implement any of this unless you kind folks want to fund the project ha
A Few General Questions
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trumpetman12
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Re: A Few General Questions
Yes, the system is smart enough to know to select analog or digital mode system-wide in the simulcast. Obviously, to be a simulcast, it has to be multi-site. However, it's analog OR digital network-wide, per call. You can't have one site transmitting digital, and another analog on the same frequency. You'd need a multi-channel simulcast with a console patch in place for that sort of thing. I think you already understand that. Yes, it can be done, multiple frequencies are required, and a console is required to make the patch (or something comparable to a console).
Answer 2: The ASTROTAC 3000 comparator supports mixed mode operation based on the call type. If the incoming call is digital, it votes digital. If the call is analog, it votes analog. It does this on-the-fly, based on the incoming call type.
In a traditional circuit-switched simulcast, the output of said comparator would be dumped into a CSCI for the analog audio, then dumped into channel banks connected to the stations via DSM-IV cards to handle the analog side of the house, and SRU cards to handle the digital side of the house (for simulcast operation).
If it's just a multi-receive, single-transmit, generally the comparator would be directly connected to the Quantar, or the analog audio would be hauled back to the transmitter using 4-Wire analog leased lines/microwave, and the v.24 data hauled by ASTRO modems or microwave subrate units.
From a network standpoint, view the "mixed mode" operation as two entirely separate systems with common receivers and transmitters (and voting comparators). In the early days of digital, before the ASTROTAC 3000, there was the ASTROTAC. That device handled digital voting only, and there was an associated DIGITAC analog comparator next to it that handled the analog audio only.
Motorola is making a concerted effort to sell simulcast systems with digital-only operation based on the ease of engineering and deploying such systems. It's a lot easier to do simulcast in digital than in analog or mixed mode. There's a lot less ancillary hardware required, it can all be done over IP, you don't have PL tone and audio launch times & phasing to worry about, etc.
Catch my drift?
Answer 2: The ASTROTAC 3000 comparator supports mixed mode operation based on the call type. If the incoming call is digital, it votes digital. If the call is analog, it votes analog. It does this on-the-fly, based on the incoming call type.
In a traditional circuit-switched simulcast, the output of said comparator would be dumped into a CSCI for the analog audio, then dumped into channel banks connected to the stations via DSM-IV cards to handle the analog side of the house, and SRU cards to handle the digital side of the house (for simulcast operation).
If it's just a multi-receive, single-transmit, generally the comparator would be directly connected to the Quantar, or the analog audio would be hauled back to the transmitter using 4-Wire analog leased lines/microwave, and the v.24 data hauled by ASTRO modems or microwave subrate units.
From a network standpoint, view the "mixed mode" operation as two entirely separate systems with common receivers and transmitters (and voting comparators). In the early days of digital, before the ASTROTAC 3000, there was the ASTROTAC. That device handled digital voting only, and there was an associated DIGITAC analog comparator next to it that handled the analog audio only.
Motorola is making a concerted effort to sell simulcast systems with digital-only operation based on the ease of engineering and deploying such systems. It's a lot easier to do simulcast in digital than in analog or mixed mode. There's a lot less ancillary hardware required, it can all be done over IP, you don't have PL tone and audio launch times & phasing to worry about, etc.
Catch my drift?
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trumpetman12
- Posts: 71
- Joined: Fri Aug 06, 2010 6:10 pm
Re: A Few General Questions
That is precisely what I was looking for, thank you for taking the time to type all that up. Of course, more often than not, digital is easier to setup now days... I wasn't aware that you didn't need to sync launch times though. I figured with the multi-path issues that CQPSK presents it would require a more stringent effort to setup and critique.
Thanks for the reply.
On another random curious note, I know that some analog repeaters allow use of a RAC which adds some security to who has access to a conventional system. Is this as simple as an MDC pre-transmit squawk, or is there more or less to it than that? And how does P25 address this security feature? I'm not aware of any added security besides the possibility of using a specific ASTRO talkgroup feature or use a different NAC on the input than what is used on the output (both of which can be easily defeated with a scanner. I've browsed through ASTRO 25 CPS and haven't found an equivalent feature for subscribers, but haven't had an opportunity to see the options available on a repeater.
Thanks for the reply.
On another random curious note, I know that some analog repeaters allow use of a RAC which adds some security to who has access to a conventional system. Is this as simple as an MDC pre-transmit squawk, or is there more or less to it than that? And how does P25 address this security feature? I'm not aware of any added security besides the possibility of using a specific ASTRO talkgroup feature or use a different NAC on the input than what is used on the output (both of which can be easily defeated with a scanner. I've browsed through ASTRO 25 CPS and haven't found an equivalent feature for subscribers, but haven't had an opportunity to see the options available on a repeater.
Re: A Few General Questions
Launch times on digital DO need to be synchronized. My point was that there's a lot less stuff required to make it work with digital than analog. Perhaps I used the wrong words to describe it, but you are correct.
As far as RAC is concerned, keep this in mind: More or less, MDC1200 is a Motorola proprietary feature. Sure there are aftermarket option boards for equipment that allow other manufacturers to support it, but as a standard feature, generally speaking, it's a Motorola-only thing. I've never come across a system using RAC.
P25, being an "interoperable" standard, doesn't have any provisions for anything like this because it's not part of the standard. The goal with P25 is "interoperability" and compatibility across manufacturer platforms, so that's likely the reason there's not a similar system (RAC) for P25. It's also possible that it wasn't implemented because of the lack of use of MDC1200 RAC in the field.
While I'm sure there are a few RAC systems out there, I'm sure the percentage is below 1%.
As far as RAC is concerned, keep this in mind: More or less, MDC1200 is a Motorola proprietary feature. Sure there are aftermarket option boards for equipment that allow other manufacturers to support it, but as a standard feature, generally speaking, it's a Motorola-only thing. I've never come across a system using RAC.
P25, being an "interoperable" standard, doesn't have any provisions for anything like this because it's not part of the standard. The goal with P25 is "interoperability" and compatibility across manufacturer platforms, so that's likely the reason there's not a similar system (RAC) for P25. It's also possible that it wasn't implemented because of the lack of use of MDC1200 RAC in the field.
While I'm sure there are a few RAC systems out there, I'm sure the percentage is below 1%.