I’ve noticed a strange issue when monitoring the two SIRN sites in Hampshire County. I’m wondering if anyone has any theories about the cause…
With my external antenna, I can monitor both Hampshire County SIRN sites: Romney and Ridge—almost equally well. The Ridge site does come in slightly stronger. I routinely monitor both sites, since the traffic on each isn’t 100% identical—no surprise there. I have both sites programmed into all of my scanners as separate systems, and they share the same talkgroup scan lists.
Every now and again, when a mobile unit is in a “bad spot,” the transmission on one site might come in a bit digital-sounding. When that happens, I usually just hit the scan button, and go to the other site to hear that transmission. That solution works about 95% of the time, since the traffic on both sites is almost identical. So, with two scanners, you can usually hear identical transmissions on both the Romney and Ridge sites at the same time. Lately though, I’ve noticed that—100% of the time—when the transmission hits the Romney 460.6125 Mhz voice channel and the Ridge 460.6000 Mhz voice channel at the same time, the Romney 460.6125 Mhz voice channel seems to have some type of impairment and no voice is heard—even though the signal is strong. The Ridge 460.6000 Mhz voice channel comes across just fine.
I’ve been able to replicate the issue on all my scanners, and it’s strange that I never noticed it before—wondering if it’s something that’s just happened lately. I’ve also noticed that the voice channels aren’t exactly on frequency: the listed 460.6125 Mhz freq actually measures at 460.611875 Mhz, and the 460.6000 Mhz freq actually measures at 460.599375 Mhz. Whatever the actually freqs are, they’re both exactly 12.5 Khz apart—so I’m guessing that has to have something to do with the issue. Still, the voice channels are designated as 8K10F1E—so in theory, the max bandwidth of 8.1 Khz should not interfere with a freq that’s 12.5 Khz away. Or is my thinking incorrect? I’m just not technically savvy enough to know.
I’ve done quite a bit of research on the issue—as you can probably tell—but I’m hoping someone more knowledgeable with trunking systems and their programming may have a theory. What bothers me the most about this issue is that when it happens, I’ll often hear the first responder mention that they couldn’t copy anything. This is a small place, and I actually know some of those folks—it makes me worry for them.
For now, my work-around is simply to monitor both sites on one scanner—as I always have—but I take another digital scanner and just park it on 460.6125 Mhz, programmed as a standalone freq—not a trunked system. Whenever the trunked 460.6125 Mhz voice channel “chokes,” the standalone scanner, sitting on the identical, non-trunked freq, receives the transmission just fine.
It is a puzzlement… and you're a real trooper for reading this far.
With my external antenna, I can monitor both Hampshire County SIRN sites: Romney and Ridge—almost equally well. The Ridge site does come in slightly stronger. I routinely monitor both sites, since the traffic on each isn’t 100% identical—no surprise there. I have both sites programmed into all of my scanners as separate systems, and they share the same talkgroup scan lists.
Every now and again, when a mobile unit is in a “bad spot,” the transmission on one site might come in a bit digital-sounding. When that happens, I usually just hit the scan button, and go to the other site to hear that transmission. That solution works about 95% of the time, since the traffic on both sites is almost identical. So, with two scanners, you can usually hear identical transmissions on both the Romney and Ridge sites at the same time. Lately though, I’ve noticed that—100% of the time—when the transmission hits the Romney 460.6125 Mhz voice channel and the Ridge 460.6000 Mhz voice channel at the same time, the Romney 460.6125 Mhz voice channel seems to have some type of impairment and no voice is heard—even though the signal is strong. The Ridge 460.6000 Mhz voice channel comes across just fine.
I’ve been able to replicate the issue on all my scanners, and it’s strange that I never noticed it before—wondering if it’s something that’s just happened lately. I’ve also noticed that the voice channels aren’t exactly on frequency: the listed 460.6125 Mhz freq actually measures at 460.611875 Mhz, and the 460.6000 Mhz freq actually measures at 460.599375 Mhz. Whatever the actually freqs are, they’re both exactly 12.5 Khz apart—so I’m guessing that has to have something to do with the issue. Still, the voice channels are designated as 8K10F1E—so in theory, the max bandwidth of 8.1 Khz should not interfere with a freq that’s 12.5 Khz away. Or is my thinking incorrect? I’m just not technically savvy enough to know.
I’ve done quite a bit of research on the issue—as you can probably tell—but I’m hoping someone more knowledgeable with trunking systems and their programming may have a theory. What bothers me the most about this issue is that when it happens, I’ll often hear the first responder mention that they couldn’t copy anything. This is a small place, and I actually know some of those folks—it makes me worry for them.
For now, my work-around is simply to monitor both sites on one scanner—as I always have—but I take another digital scanner and just park it on 460.6125 Mhz, programmed as a standalone freq—not a trunked system. Whenever the trunked 460.6125 Mhz voice channel “chokes,” the standalone scanner, sitting on the identical, non-trunked freq, receives the transmission just fine.
It is a puzzlement… and you're a real trooper for reading this far.
