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Voice/Control Channel Decoding Software - For discussion of software applications which decode digital voice formats and trunking control channels. Please use the HF Digital Signals forum for anything below 30MHz.

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  #1 (permalink)  
Old 10-21-2018, 3:30 AM
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Default SDRPLay AirSpy vs Cheapies

Who is using a SDRPlay or AirSpy or any other device to decode and how does it compare to the standard RTL-SDR dongle one gets for cheap (the blue or even black dongles).

I am guessing:
1) The increased bandwidth 8/10/12 is better that the 2.5/2.8 on the cheapies?
2) Better antenna connections. MCX vs SMA
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Old 10-21-2018, 12:05 PM
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Higher dynamic range (12 bit vs 8 bit ADCs) and lower noise floor are the main benefits I see/use.
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Old 10-21-2018, 12:13 PM
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I'm currently using RTL-SDR and, while I'm impressed with how well they do work, I definitely can see the limitations of their 8 bit ADC. At some point, I'll start upgrading. I don't see tHe mcx connector as an advantage.
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Old 10-21-2018, 3:51 PM
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Well, he's got that one backwards; the premium dongles use SMA, not MCX. It's only the really trashy dongles that use MCX; all of the decent ones with good reference oscillators use SMA.
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Old 10-21-2018, 4:13 PM
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Sorry, I though I was posting this on one of the tetra decoding threads. And yes I was referring to the better of the 2 having the SMA socket.
So has anyone used an RTL-SDR cheapie and then moved over to the proper dongles and could see a difference in quality reception and decoding? As noted, the lower noise floor should assist decoding.
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Old 10-21-2018, 4:34 PM
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What is "ADC" and what are these "bits" and why is more bits better?
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Old 10-21-2018, 5:16 PM
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Originally Posted by Homeboys-Scanna View Post
What is "ADC" and what are these "bits" and why is more bits better?
Analog Digital Converter - converts the analog RF signal into digital representation that a computer can understand and process in some way.

The number of "bits" that an ADC possesses is a measure of the degree of precision that the original analog signal can be represented by in the digital world. 8 bits can represent 256 different binary values, whereas 12 bits can represent 4096 different values. If you think of an analog signal varying between -1.0mV to +1.0 mV, each bit in an 8-bit ADC will represent 7.8uV, whereas each bit of a 12-bit ADC will represent 0.49uV. The resulting digital signal will be smoother and retain more detail while generating less artifacts when transformed mathematically by the signal processing software.
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Old 10-21-2018, 5:24 PM
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Thanks. I wonder if that would make for better audio performance from DSD+.
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Old 10-22-2018, 3:29 PM
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Quote:
Originally Posted by tsapers View Post
So has anyone used an RTL-SDR cheapie and then moved over to the proper dongles and could see a difference in quality reception and decoding?
I can easily see differences between the good rtlsdr.com dongles and Airspy Minis. The 8 bit dongles overload so easily in urban areas. Due to some internal mixing products, they also produce false signal spikes in the spectrum that the Minis don't.
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Old 10-25-2018, 6:21 PM
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How do we tell what software the more expensive tuners (SDRPlay / AirSpy) are compatible with? Will they all work with DSD+, Unitrunker, etc. the same way as the RTLs?
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Old 11-03-2018, 5:47 AM
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To add to the above, what is the ADC on the cheap plastic RTL-SDR dongles?
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Old 11-08-2018, 8:50 AM
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Quote:
Originally Posted by boatbod View Post
Analog Digital Converter - converts the analog RF signal into digital representation that a computer can understand and process in some way.

The number of "bits" that an ADC possesses is a measure of the degree of precision that the original analog signal can be represented by in the digital world. 8 bits can represent 256 different binary values, whereas 12 bits can represent 4096 different values. If you think of an analog signal varying between -1.0mV to +1.0 mV, each bit in an 8-bit ADC will represent 7.8uV, whereas each bit of a 12-bit ADC will represent 0.49uV. The resulting digital signal will be smoother and retain more detail while generating less artifacts when transformed mathematically by the signal processing software.
I can understand how an ADC would work for an analog signal but how does it work with a digital signal like Apco 25 where the signal is already digital. The only reason I would want to buy a more expensive dongle like Airspy or SDRPlay would be to get better sound quality when listening to a digital broadcast like Apco 25.

As it is, listening to an Apco 25 signal can be a tough go at times. So I would imagine an 8 bit vs a 12 ADC wouldn't make much difference. I am by far no expert on this subject, I am just trying to understand.

MB
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Old 11-08-2018, 9:25 AM
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I can understand how an ADC would work for an analog signal but how does it work with a digital signal like Apco 25 where the signal is already digital.
Modulating an RF carrier is essentially an analog function, even on digital formats like P25. You're either changing the frequency, the amplitude, or the phase of the carrier. Some methods use amplitude and phase.

The difference is, for analog, the variations of the carrier follow the baseband signal, for digital, the variations are at fixed discrete values that correspond to ones and zeros.

The sampling process in the SDR receiver doesn't care.

More bits means you get better resolution to see the small variations in phase and amplitude.
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Old 11-08-2018, 9:53 AM
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Originally Posted by zz0468 View Post
Modulating an RF carrier is essentially an analog function, even on digital formats like P25. You're either changing the frequency, the amplitude, or the phase of the carrier. Some methods use amplitude and phase.

The difference is, for analog, the variations of the carrier follow the baseband signal, for digital, the variations are at fixed discrete values that correspond to ones and zeros.

The sampling process in the SDR receiver doesn't care.

More bits means you get better resolution to see the small variations in phase and amplitude.
Like I said, I am just trying to understand lol, so does that mean SDRPlay or Airspy would decode a signal like Apco 25 better than say an RTL-SDR v3? If it wouldn't decode better then I guess a scanner would be a better option for me.

Thanks
MB
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Old 11-08-2018, 10:00 AM
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I have SDRPLAY V1 and airspy V1 and airspy mini . I prefer sdrplay but I'm using Airspy because only airspy can be used with DSD + and fmpa , only aispy can be use with TETRA decoder (windows) .

Only because SDRsharp is airspy mind restricted ...
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Old 11-08-2018, 10:11 AM
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Quote:
Originally Posted by moonbounce View Post
Like I said, I am just trying to understand lol, so does that mean SDRPlay or Airspy would decode a signal like Apco 25 better than say an RTL-SDR v3? If it wouldn't decode better then I guess a scanner would be a better option for me.
Yes, it does. An SDR receiver is sampling a chunk of spectrum and digitizing it. More bits means it gets a bigger sample, and builds a more accurate representation of what's in that piece of spectrum. There's less aliasing, which is an artifact of the AD-DA process, and better dynamic range, the difference between the noise floor and overloading.

Within the individual P25 signal itself, it probably doesn't make much difference, except that it's a higher quality interface between the software and the outside world.
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Old 11-08-2018, 10:55 AM
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Thanks for that explanation. So I wonder what the ADC bits of some digital scanners would be, more than 12 bits? Just curious.

MB
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Old 11-09-2018, 12:24 AM
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Um, doesn't DSD+ use an alternative (read, free) version of AMBE vocoder, which is not as good quality sounding as AMBE? I might be wrong.
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Old 11-09-2018, 12:44 AM
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Quote:
Originally Posted by moonbounce View Post
Like I said, I am just trying to understand lol, so does that mean SDRPlay or Airspy would decode a signal like Apco 25 better than say an RTL-SDR v3? If it wouldn't decode better then I guess a scanner would be a better option for me.
Yes. Higher dynamic range and lower noise floor means better decoding of marginal signals. But I repeat myself...


Quote:
Originally Posted by moonbounce View Post
Thanks for that explanation. So I wonder what the ADC bits of some digital scanners would be, more than 12 bits? Just curious.
No, they would not.
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