On September 12th Frederick County switched to a 12-channel Motorola P25 Phase I digital simulcast system, which uses linear simulcast modulation (LSM) using CQPSK/C4FM. The best scanning success has been found by managing how much you are asking the scanner to do, and how much signal gets in to the scanner (how many simulcast sites can be heard). This is somewhat counter-intuitive for many who think adding gain will help get clearer reception. With LSM most people inside the county do not have too little signal strength, their scanner can hear too many sites and the scanner front-end can't deal with it.
craigg:
Since you have your P25 card enabled already, I suggest you remove everything but the primary and alternate control channels (854.9875 is the primary CC) and use control-channel trunking. The data on RR regarding frequencies and talkgroups is right on. You may want to check your firmware version regarding any need to adjust for rebanding. I'm not familiar with your particular scanner.
If the new P25 system Frederick is now using is also using LSM modulation, you may well be SOL. We now have a fair amount of experience with LSM in Maryland - Baltimore city and county as well as PG county - that suggests that the current crop of trunktrackers simply can't deal with LSM very well, particularly where there's more than one tower being received at the same time. In some cases, at least, you need to run some attenuation if this is the case.
I present this only as a possibility - not a real answer. But it does seem like there's at least some possibility of this here, as the symptoms all seem to be the same...Mike
I have to tell you this system stinks! Yeah it's LSM-Simulcast, but I've never seen worse coverage!
I have a Uniden 996 in a mobile w/ an external antenna, and I come up 270 and can only get a decent lock
on the control chnl once I'm over the "scenic overlook", and lose it once I'm past Jefferson on Rt 340.
I don't know how the public service folks are dealing with this system on one poor site, And the Bruswick
site, furgetaboutit...
That's probably why you're not getting them where you are.
What did they tell Moto., give us 1 site for the county @ 25 watts?
No they are just using true P25 radios designed for LSM operation instead of a scanner that is not designed to be able to do LSM.
What benefit, if any, is there to using LSM rather than C4FM (and H-DQPSK for the TDMA) like Loudoun?
Frederick's license shows the emission designator for C4FM.
Is Frederick a case of C4FM for the subscriber units, but LSM for the sites?
There are several explanations of "why use LSM?", but there are a few slides in this presentation that may help illustrate it well for all quickly and clearly.
http://www.simulcastsolutions.com/userfiles/file/simulcastforums/motorola_simulcast_part4.pdf
Frederick's system is a seven-site system that covers 660 square miles. Coverage testing was performed in accordance with TIA TSB-88 by dividing the county into 4,308 0.4 x 0.4 mile square test grids (4,308 grids), 3,684 were accessible for testing (the majority of the inacessible grids are in the mountainous, undeveloped areas in the State and National parks), with 3,491 grids having successful tests. This is a pass rate of 94.7%.
This testing also had in-building and method-of-use signal losses added to the test kits in the following amounts: countywide 17dB; the triangular area between I-70 and I-270 21dB; and City of Frederick 33dB. Obviously, the performance of mobile radios (and scanners) will exceed the 94.7% figure above, if they can process the CQPSK signal. As ka3jjz correctly points out, scanners quite often can't do what the radio does.
ERP ranges from 140 to 380 watts on the FCC ULS site.