Limitations?

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Ensnared

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I am going to order the necessary equipment to monitor a local PV system and also analyze a DMR system. When, I am done with the analysis, I am going to be using these dongles to monitor the PV.

My questions: 1) Can you monitor more than one radio system with these dongles; 2) can you combine conventional frequencies with another radio system? In other words, can this function as a scanner?
 
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br0adband

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1) The "cheap USB TV tuner" is just that, a tuner and it's controlled by whatever SDR software you're happening to use so, yes, you can monitor basically anything you want given the bandwidth available from the SDR hardware you're using aka the bandwidth. The low cost RTL-based devices (the RTL2832 chip is the USB controller which allows for connection to a PC or whatever to control the tuner - the actual tuner chip in the low cost devices are typically the Rafael Micro R820T or R820T2 tuner chips) have a bandwidth of about 2.4 MHz max (theoretically they can offer more bandwidth but at the max range of about 3.2 MHz you'll end up losing samples from the tuner because it just can't keep up so 2.4 MHz is the maximum workable bandwidth for most every situation).

What that means is when you "look" at the spectrum on an SDR application of most any kind and see the content the tuner is pulling in, the width of what you're able to see is going to be just 2.4 MHz (or lower depending on your settings) wide meaning if you tuned the center frequency of the spectrum to say 150 MHz, you'll see 1.2 MHz on either side of that so you're receiving 148.8 to 151.2 MHz (151.2 - 148.8 = 2.4). Some of the more expensive SDR devices like Airspy and SDRplay offer increased bandwidth - Airspy can max out at a full 10 MHz (so you'd be seeing 145 to 155 MHz with 150 MHz CF) and SDRplay iirc is 8 MHz max (so 146 to 154) and when I say it's receiving that window that's what I mean:

These types of tuners aren't really "tuned" to anything but the center frequency you've chosen or manually selected on the spectrum with a click but the tuner itself is actually listening and receiving everything inside that window in real-time. If you record the raw bandwidth for a period of time you can then go back and "play" that recording and you'll be able to manually "tune" in any frequency that was captured which is one of the things that makes this whole "SDR thing" so cool: we're no longer confined to monitoring just one frequency at a time, or even having to use multiple scanners or receiving devices - with an SDR device and proper software we capture the entire swath of the tuner's available bandwidth at any given time.

2) As just stated, your only limitation is the software and unfortunately nobody has really produced a "software scanner" that works exactly like a traditional scanner does. Probably the most popular option available at this time is using SDR# for your SDR application and then the Frequency Manager and Scanner plugin which provides rudimentary scanning capability aka you program in or add frequencies into a database that's part of the plugin package and then it'll scan them depending on the parameters you specify. It's not the greatest thing in the world, and it certainly isn't the same as having a physical scanner to do the job but even so you still even up with more options than any physical scanner is capable of even today.

Yes we're now getting scanners that are capable of handling DMR and even NXDN at some point (if they don't already, I'm not completely up to date on what Uniden and Whistler are offering by way of firmware updates at the moment) but a "cheap USB TV tuner" + SDR software + a virtual audio cable (if needed) + Unitrunker (if needed) + DSD+ (for decoding the most popular digital formats except P25 Phase II, maybe someday) and a laptop or desktop PC and you can listen to practically anything that's being transmitted short of encrypted content.

So, technically yes you can get this kind of setup to work like a scanner, but for the moment it's vastly more complicated to set up and it still isn't nearly as convenient as having a physical scanner around but it sure can be a lot of fun getting everything working just right. It can be incredibly frustrating working on things, following info and guides and steps and nothing works, so you scrap everything and start over and fail again, and maybe a few more times but eventually everything falls into place and when you actually get some audio from a system - especially a digital one - it all becomes worth the hassles. ;)

Hope this helps...
 

Ensnared

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No Choice

I revisited this post to learn what I need to get SDR going. I am interested in buying one now that my Uniden 436HP and GRE PSR 500 have antenna issues. I am going to send both of these in for repair. At present, the PSR 500 still receives well, but it is a matter of time before it goes south. So, in order to monitor PV in Temple, Texas, I will be buying a SDR setup while my radio visits Uniden repair. Hopefully, I can get it to work. I have some familiarity with Pro96Com. I've never used Unitrunker.
 
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