Do I really need this many SDRs?

[gregma]

Was almost ready to buy a uniden scanner to replace my old one and stumbled onto the SDR and was excited. However, upon research it seems as if I will need two SDRs for each 2.5MHz bandwith of each trunked system? If that's the case, then the 7 trunked systems I monitor will require 30 sdr's for those, plus one for the non-trunked frequencies for a total of $1085 (31 * $35) just for those, plus several USB hubs, licensing fees for software, etc. ouch! What am I misunderstanding?

-Greg

 

[lwvmobile]

Woah, hang on, before you start building a small server farm of SDR dongles over there, what all systems are you listening to and what frequency ranges to they occupy? Depending on the hardware and software setup you use, you would only need 1 dongle to park on the control channel, and 1 free dongle to tune to voice channels IF those voice channels are more than 2.4Mhz away from the control channel. Some setups on DSD+ FL only require one dongle and can jump from control channel to voice channel and back again. Monitoring 7 trunked systems simultaneously might be a tall order though, depending on your PC specs AND the frequency ranges they occupy, but I'm not quite so sure you would need 30 dongles.

Also, its worth noting that some higher end SDR equipment can monitor 10Mhz or even 20Mhz of spectrum at a time.

 

[gregma]

I border on two counties in Washington State. There are 7 trunked systems that I'm interested in. Here are the min and max frequencies for each of the systems:

WSnoPS 852.9375 / 857.1625
PSE - 217.50625 / 217.99375
911 - 769.30625 / 774.73125
TRBOWest - 454.39375 / 464.150
KCPS - 851.0875 / 857.0875
WSP1 - 770.20625 / 770.96875
WSP2 - 769.21875 / 774.78125

Plus more local that are not trunked.

-Greg

 

[lwvmobile]

Well, to be honest, I don't think any number of SDR dongles would begin to replace a full blown digital scanner, especially if you intend to monitor all of these systems all at once on one computer system. That doesn't even begin to factor things in like connecting antennas to each individual dongle or connecting them all to your main antenna if you have an outdoor setup.

What kind of system are all of those you listed? P25? DMR?

IF it were my decision, I would recommend buying (2) SDR dongles and giving them a trail run first, see if its something that would be viable for you to use, and go ahead and replace that Uniden scanner with something that can monitor all of those systems. I'm sure others here will have other and probably much better suggestions.

 

[boatbod]

If these are P25 systems you only need one SDR device to receive one system.
How you go about monitoring more than one system is something to be discussed because it really depends how many simultaneous systems you want to track.

 

[Kazzaw]

I wouldn't suggest more than two, for logging (or streaming) purposes only. I have 6, which helps me log systems I run into, however I still use a digital scanner configured with the information I have logged as my primary listening device.

 

[rlmurray56]

I use three (3) to monitor Pierce County South Sound 911, Tacoma/Puyallup PSRS, and WSP District 1-Tacoma. I use boatbod's OP25 software on a Pi4 with 4gb. I am using Orange Flight Aware Pro sdr sticks, $18.75 each on Amazon.

 

[AB5ID]

I am using Orange Flight Aware Pro sdr sticks, $18.75 each on Amazon.

Thanks for the info, that is a great price for a SDR with a TCXO!

 

[Unitrunker2]

Beware the 2.4 million (for a Realtek SDR) is the sample rate, not the *usable* bandwidth. The band edges of the spectrum are highly attenuated to avoid aliasing. Your usable bandwidth is about 80% of the sample rate which is, in this case, less than 2 Mhz.

 

[ww7ch]

@gregma my recommendation for covering that many systems would be to try using SDRTrunk on a dedicated PC with adequate horsepower (i7 or ryzen latest generation processor with at least 16GB RAM), two Airspy R2 units, one for 769-775 and one for 850-860, and use the less expensive RTL sticks for the other freq ranges (several others have raved about the Orange FlightAware Pro sticks, the RTL-SDR blog sticks are good too). However using SDRTrunk doesn't address P25 conv and analog systems, I understand trunk recorder covers these but haven't messed with it because SDRTrunk is able to properly handle simultaneous duplicate calls on TGs from multiple sites on the same system.

Rule of thumb (at least with SDRTrunk and I believe trunk recorder also) is that the amount of SDRs needed depends on the bands and freq ranges to be monitored. If most of your activity is on 700 and 800, the airspy units will cover those no problem assuming the PC has the processing horespower to handle it. My current non-production test setup is an i5-3550 processor, 16GB RAM running SDRTrunk on ubuntu 20.04.1. Been monitoring 10 CCs on several systems and have seen at least 16 simultaneous calls on the traffic screen. CPU usage is high but that's ok, I'm paying attention to temp. Doing what I can to keep the cores under 70c. Has been running solid for over a month now with no fatal crashes.

 

[gregma]

These are all great suggestions! Thank you! One thing, I do not need simultaneous reception. One at a time is more than adequate. Is this possible?

-Greg

 

[JimD56]

If you use SDR Trunk as your SDR Scanning program you will need 2 SDRs for a P25 Phase 1 or 2 system using simulcast or not.
SDR 1 - Control Channel SDR 2 - Talkgroups. SDR 1 can handle muliple control channels of multiple systems and SDR 2 can handle multiple talkgroups on those systems, but you will miss some stuff. I use an SDS200 spplemented by the 2 SDR's for my simulcast systems with optimal results. I know you dont wnat to hear about the SDS200 ref cost, but for optimal scanning it is the optimal result.
I also use a 3rd SDR on SDR# Sharp with the scanner plugin for all analog VHF/UHF.

 

[gregma]

Thank you @JimD56. That is workable, I really don't mind missing stuff. I can stop scanning on a channel if there is something important. I'm basically trying to replicate a regular scanner. I do have an SDS100 in mind when I can hopefully afford it though!

-Greg

 

[danlewis]

You may need way less thank you think. It depends upon what software you use. For example, trunk-recorder (in part an op25 derivative) can monitor all traffic simultaneously as long as the channels are within a bit less than the 2.4 MHz bandwidth of the typical RTL-SDR stick.

 

[rlmurray56]

If you choose to use the SDRTrunk application be forewarned that there is no talk group "hold" function, you won't be able to stop scanning. However, OP25 does have this feature, as does DSDPlus Fastlane.

 

[PDXh0b0]

That is allot to listen too 😉 The more systems you add, the more you miss even with one of those bells n whistle systems. There is rarely dead air on my local simulcast system, so much traffic that I split Law enforcement & Fire/EMS on two different computers. Still an audio overload to the human ear. Eventually I had to choose what talk groups were a priority to me, I have VB audio cables a,b,c,d & the free one. So 5 voice vfo's I can record on one PC with Trunking Recorder. 4 of my most preferred talk groups and the rest of the systems ranked according what talk groups hold priority over others. The the same setup on another PC for Fire/EMS. Still allot of audio to listen to and keep up, Law enforcement is my preferred listening please so I mute the Fire/EMS. A third PC I listen too Local public transit agency & what isn't yet encrypted in Portland. Main PC I listen to all the other stuff, airband, HF, etc..

Sdr dongles or an all in one like the sds200, you will still be making sacrifices and choices according to what you want to listen to.

 

[gregma]

If you choose to use the SDRTrunk application be forewarned that there is no talk group "hold" function, you won't be able to stop scanning. However, OP25 does have this feature, as does DSDPlus Fastlane.

Excellent. Just ordered two dongles and will see what happens.

-Greg

 

[bdp278]

Once you get setup & running, I suggest checking out Broadcastify's new Calls platform. SDRtrunk will stream all your calls to this platform, and you can access each & every call on a web browser from anywhere, playback specific calls, and also create playlist for specific agencies you wish to monitor at a given time. Also all calls are archived for 30 days. It's not a free service, but if you setup a scanner feed for anyone of the agencies you monitor, which can also be done thru the SDRtrunk program, they will then give you access t the Calls platform for free. However, SDRtrunk is a massive CPU power hungry program, you will need at least i5 processor, and at minimum 8 GB RAM. Make sure you have a good fan in your PC, as your processor will run hot most of the time, and this program will consume about 70% of your processor.

 

[gregma]

@bdp278, unfortunately, I will not be able to use SDRtrunk, it will not do what I need. I just want to duplicate what a hardware scanner does scanning multiple systems with multiple talkgroups associated with each with no more than 2 dongles.