Linear Simulcast Mode?

[Kumba]

The pending update for BCD396XT says it improves performance on systems using "Linear Simulcast Mode". What exactly is LSM and how can we tell what sites might be using this mode? Is this only found on P25 FDMA systems, SmartZone, etc?

Gotta love vague changelog entries...

 

[AK9R]

See this article in the RadioReference Wiki:

http://wiki.radioreference.com/index.php/Simulcast_digital_distortion

 

[Kumba]

See this article in the RadioReference Wiki:

Simulcast digital distortion - The RadioReference Wiki

Already looked there. The word "linear" isn't found on the page, thus I am not sure if that article fully covers the topic.

That said, in Charles County, MD, they recently got the MdTA Bridge Police onto the county radio system. I suspect they're using simulcast, because MdTA has their own radio system. Sometimes, after a unit keys off and closes the channel, you'll get a shot of digital motorboating before the scanner squelches the TGID. Might that be an example of LSM?

 

[AK9R]

From that Wiki article:

"This problem is most evident when monitoring true Project 25 simulcast trunking systems (9600 baud control channel) using the LSM CQPSK modulation scheme..."

LSM = Linear Simulcast Mode

See also:

APCO Project 25 - The RadioReference Wiki

 

[Anderegg]

The problem is MOST EVIDENT.....well, does the new firmware update fix reception issues with ALL simulcast systems, or just LSM specifically??????

Paul

 

[troymail]

Symptoms indicating you're dealing with (suffering from) LSM:

- digital voice
- signals/system that was once receivable "across" (outide) the county line no longer received (well)
- scanner has serious difficultly locking onto the control channel
- voice transmission received are choppy and/or fade in and out

The problem for scanners is caused by the digital signals being transmitted from multiple towers simultaneously and arriving at your scanner/receiver at slightly different times -- the scanner is trying to decode the signal(s) and is getting confused over which over to pay attention to.

 

[troymail]

That said, in Charles County, MD, they recently got the MdTA Bridge Police onto the county radio system. I suspect they're using simulcast, because MdTA has their own radio system. Sometimes, after a unit keys off and closes the channel, you'll get a shot of digital motorboating before the scanner squelches the TGID. Might that be an example of LSM?

I don't think the Charles County system changed (yet). MdTA is primarily on the new Maryland FiRST Phase 2 system (First Responders Interoperable Radio System Team (FIRST) Trunking System, Various, Maryland - Scanner Frequencies) that went live the end of 2012. However, since there is limited or no coverage in some areas (Charles, Montomery), MdTA in those areas are relying on the local juridiction's trunked system for now (to my knowledge).

However, it is true that the Maryland FiRST system suffers from the LSM issues -- essentially all new digital systems/upgrades seem to have this problem for scanners

In Maryland, at least these systems have this problem making them all difficult to monitor:

Baltimore City
Baltimore County
Prince George County
Kent County (on Maryland FiRST)
Maryland FiRST
CMARC

Frederick, Washington and other counties may also need to be on this list.

Take a look at the some of the threads in the Maryland section of RR for these systems and you'l find alot of discussion about the problems scanner users have experienced and the efforts some are making to try to overcome it.

 

[fredva]

If I could try paraphrasing what the OP and others are asking - are there any other types of digital simulcast that cause problems with scanner reception, that aren't LSM? Or does digital simulcast always equal LSM?

 

[jmarkey]

Digital simulcast is not all LSM.

You may find the explanation in this doc useful:
http://www.simulcastsolutions.com/userfiles/file/simulcastforums/motorola_simulcast_part4.pdf