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SDRPLay AirSpy vs Cheapies

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#1
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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#3
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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#4
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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#5
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.
 

boatbod

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#7
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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#9
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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#10
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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#12
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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#13
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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#14
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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#15
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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#16
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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#17
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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#18
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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#19
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...


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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