The freq database shows Sullivan County fire & EMS as 161.xxx with "simulcast" in the description. What other system are they being simulcast from? I've always known the term simulcast to mean it's rebroadcasting from another system. The quality of the audio on the Broadcastify feed can be poor at times so I was wondering if this has to do with being rebroadcast from another system.
Sullivan County "Simulcast"
- Thread starter aslc
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The term simulcast means simultaneous broadcast, commonly meant to indicate that there are multiple transmitters broadcasting on the same frequency at the same time. That's the case with Sullivan's 161 MHz channels. There are multiple repeaters throughout the county for each frequency, and they all key up simultaneously, not unlike how a simulcast trunked system works.
Simulcast is also often used to describe the same carrier being broadcast over different resources, although the term multicast would probably be a better description for that.
Simulcast is also often used to describe the same carrier being broadcast over different resources, although the term multicast would probably be a better description for that.
Thanks for the explanation. So, if they broadcast on the same output freq from multiple sites simultaneously how do they not have the simulcast distortion problem that you hear about on trunked systems? It would seem that a non-trunked system would have the same problem.
Analog simulcast does have some issues which is why the feed may sound distorted at times. It is a minor problem in a properly synchronized system within the designed serive area. Reception can be bad at times and locations outside of the home county. But it is an analog signal that any scanner can receive.
The digital simulcast problem is that most scanners can not properly receive LSM digital signals from multiple sources. Digital simulcast is not a problem on a properly designed receiver assuming the sytem is properly designed and synchronized.
The digital simulcast problem is that most scanners can not properly receive LSM digital signals from multiple sources. Digital simulcast is not a problem on a properly designed receiver assuming the sytem is properly designed and synchronized.
Analog simulcast is pretty straightforward and not nearly as complicated as P25 simulcast. Sullivan's network is modern, using GTR8000 repeaters which are time-synced using a GPS reference, so in areas of overlapping RF the timing is extremely tight and therefore not a whole lot of distortion to be heard. Even in areas outside of the primary coverage area (i.e. the county itself) where this is some distortion, it's still analog FM so it's easy to still understand the audio.
P25 simulcast, in particular LSM (Linear Simulcast Modulation) and PSK variants (CQPSK, H-DQPSK) contain a prominent AM component to the signal. The signal itself fluctuates in amplitude, which is not the case with FM analog simulcast or C4FM for FDMA P25 signals. It's this AM component that cause issues with most scanners and receivers that are not designed to properly demodulate the AM component of the signal.
tl;dr Not all simulcast is created equal
P25 simulcast, in particular LSM (Linear Simulcast Modulation) and PSK variants (CQPSK, H-DQPSK) contain a prominent AM component to the signal. The signal itself fluctuates in amplitude, which is not the case with FM analog simulcast or C4FM for FDMA P25 signals. It's this AM component that cause issues with most scanners and receivers that are not designed to properly demodulate the AM component of the signal.
tl;dr Not all simulcast is created equal
Nice to see Sullivan County invest in the infrastructure like that.
Related tl;dr is that not all receivers are created equal.
k2hz mentioned it, but commercial public safety radios handle simulcast much better than scanners. That’s why a system that a scanner listener may experience issues receiving sounds just fine to the user base.
I have not listened, but the issue of quality of the Broadcastify feed you mentioned might be due to the receiver in use for the feed, not the system.
As pertains to P25 simulcast using LSM/QPSK, sure. But we're discussing a network of analog simulcast repeaters here, not P25 modulation, and so the receiver itself is not much of a factor (unless it's a total piece of junk, of course).
The biggest factor here would almost certainly be the location of the receiver. If you're too far outside the envelope of intended coverage, the timing of RF being received from multiple transmitters might slightly degrade the quality of the analog audio. It will still be intelligible, just not pristine. This is a much different issue than the P25 "simulcast distortion" issue that can prevent a scanner/receiver from reliable decoding. Being too far from an analog receiver can also result in poor signal and a lot of background noise, which is what I hear on the Sullivan County Fire/EMS Paging feed. That feed seems to have a lot of issues with some of the audio (in addition to the fact that it's scanning more than the title/description indicates). To my ear it sounds like the feed provider is either outside the county or not receiving some of the frequencies well. I don't hear audio distortion as much as I hear a weak signal a lot of the time.
Or, he could be experiencing multipath and in fact, it's not simulcast distortion or a timing issue at all.
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