I don't understand something about the Calls service and have looked around for an answer. Let's say the local scanner is monitoring 50 talkgroups and you have 4 of them set up in Calls. If the scanner is locked on a TG other than the 4 in Calls how can it at the same time provide audio from the 4 TGs set up in Calls?
Confused about Calls
- Thread starter aslc
- Start date
Did you ever see the Movie Mavrick? If so you remember the line about the card game when ask how Mavrick drew the card to win?
MAGIC
MAGIC
Calls typically use an SDR package, such as SDRTrunk or Trunking Recorder. I'll speak for SDRTrunk. I monitor a county simulcast with 8 voice channels. I have set up SDRTrunk to send voice traffic from all 8 voice channels (when/as they are active) up to my BCFY Calls Node. People who monitor larger systems can [and typically will] set their SDRTrunk to allow the capture/uploading of audio from every active voice channel on the site they are monitoring with SDRTrunk.
It isn't like a scanner at all, since a scanner can only capture one voice conversation at a time. Something like SDRTrunk can capture many many different talkgroups active on a particular site at any given time and upload them to BCFY Calls.
To answer your question, if a scanner is locked on a TG, then it isn't going to tune and decode the audio for any of the other 49 or 4 talkgroups. Scanners just aren't capable of that. If the scanner were not locked on a TG, it could still only pick up one conversatoin (talkgroup or private call) at a time, even if there are 3 or 4 or 20 other calls on other talkgroups occurring on the site at the same time.
Thank you for the explanation. I did notice after sending my original msg that there are only a few systems locally here that are in Calls and that made me think that they weren't using regular scanner feeds. SDR explains it. Is there a limit as to home many TG can be monitored simulatenously with SDR? Thanks again.
I think that is limited by
#1 Your Computer you are using
#2 How many SDR Dongles you are using
#3 You outbound Internet connection Speed
#1 Your Computer you are using
#2 How many SDR Dongles you are using
#3 You outbound Internet connection Speed
Remember, all talkgroups aren't active at once on a system. You guy by site. If the site has 10 voice channels, you monitor 10 voice channels with SDRTrunk. If the site has 20 voice channels, you monitor 20 voice channels with SDRTrunk.
No matter if the system has 5000 talkgroups, on a site with 20 voice channels it is only possible for there to be a maximum of 40 or maybe 41 simultaneously active talkgroups (Phase II) or 20 simultaneously active talkgroups on a Phase I only system.
So it isn't a matter of asking how many talkgroups can be monitored. You can monitor them all, on any given site, because the site is only going to allow the voice calls for the number of talkpaths it has.
Thanks for the clarification. When you say channels is that the number of frequencies in the pool/site? So, if our county Phase II has 25 frequencies in the site that means there can be 50 simultaneous active TG and the SDR can monitor all of them?
"The SDR" -- I'm speaking specifically about SDRTrunk. Not just every SDR-based tool can do it.
And yes, if your computer system has enough resources and SDRTrunk is set up properly, including giving Java the additional memory it needs, then if you have a 25-channel county site (one active control channel, 24 voice channels with up to 48 talkpaths) then yeah SDRTrunk can handle it. I don't use anything else so I can't speak of anything else.
It's important to note that many sites that have a lot of frequencies assigned to them often do not use them all for TDMA (Phase II) but have some in use to support Phase I radios. So usually, that system with 25 freqs is unlikely to be carrying 48 simultaneous voice calls under any normal circumstance.
You need to have enough dongles / Airspys / RSPs / etc to cover the whole range of frequencies though. For instance, in Ohio we've got a lot of sites that have both 769-775 and 851-859.xxx frequencies on them. For those, there has to be enough SDR capacity to potentially cover any active frequencies on the site in those ranges -- that's 15 mhz. That's a lot of dongles, or a combination of dongles and higher end devices that allow 6-10 (5-8 mhz) of spectrum to be monitored.
The site I monitor is Phase-I only simulcast, 8 voice channels, with all of the voice channels between 851.1625 and 858.4625. I use a single Airspy R2 to monitor all 8 voice channels of that simultaneously. In addition, that same setup also allows me to monitor the local AEP Phase II P25 site because its frequencies fall within the range that the Airspy can handle. So that's another two voice channels.
With the sites I monitor, rarely are more than 4-5 voice channels active out of those 10, and in fact 4-5 active at once is rare. Of course, I've seen other systems (like the simulcasts up in Northern ohio (Stark / Summit / Cuyahoga) be extremely busy at times.
And of course you can monitor less voice channels, but you'll miss some traffic. For instance, I could set SDRTrunk to monitor only four voice calls instead of 8. When the system isn't busy, I'd still pick up everything. But if the system gets busy and there were more than 4 voice calls, I wouldn't pick them all up.
SDRTrunk seems to work great, even throwing 10 or 20 voice conversations at it simultaneously. I've never monitored a site that had more than 20 simultaneous voice conversations on it. I'm sure they are out there, but I've never monitored them.
