AirSpy comparisons?

[Voyager]

I was talking with one of the AirSpy guys asking if he knew of a comparison between the AirSpy and the RTL/R820T2 dongle, and he said to check RR and Google and there were lots of comparisons out there. The only one I've found is comparing a prototype AirSpy to a RTL/R820T (not T2).

Does anyone have a link to one of these "many comparisons" that are supposedly out there?

 

[DK327]

Here are a couple I visit frequently:

Roundup of Software Defined Radios - rtl-sdr.com
Airspy Archives - rtl-sdr.com

As for comparing it to the T2, it'll be basically the same comparison as the T because the difference between the two dongles are not significant enough ($5 difference) to warrant a whole new comparison IMO...

 

[Voyager]

Thanks. I've seen those two sites. Sensitivity seems to be a fairly moot point, as even the cheap dongles have some pretty good sensitivity. The benefit of the T2 was supposed to be a lower noise floor and increased selectivity. While that may be true, the difference is not that great from what I've seen. It's just odd that someone would say there are many AirSpy/R820T2 comparisons when there are none (except for an early AS prototype).

I'm mainly trying to justify spending $200 on an AirSpy. Is it really worth the additional cost? (not rhetorical - I really would like to hear opinions)

 

[Voyager]

Just to see if I have the essential differences... (RTL = RTL/R820T2)

AS sensitivity is a reported -113 dBm. I don't think the RTL is much worse, if any.

RTL 8 bit vs AS 12 bit (a good improvement)

RTL 2.4 MHz BW while AS about 4x that (a big benefit although even 2.4 MHz is hard to click on exact signals - 10 MHz would be worse)

AS has tracking filters. That may be the biggest benefit, and worth 5x RTL cost.

I don't know the RTL's front end specs. I'm sure they aren't that great. This may be the other factor that makes the AS worth the cost.

AS brags about high precision clock. I've never found the RTL to be an issue once it warms up (a minute or so).

I do like the SMA over the MCX, but as either would be using a BNC jumper it's not a big deal.

Am I missing any key differences? I know there are other things the AS does, but I'm trying to focus on core performance as a receiver.

 

[Boatanchor]

Airspy / FuncubeDonglePro+ comparisons

While this doesn't compare Airspy to cheap RTL dongles, you may be interested in the FCDP+ comparisons below..

I have both the Airspy and the FucubeDonglePro+. Both of these SDR's are roughly the same price or ~US$200.

IMHO, these are the Pros & Cons of each:

Airspy pro's

* Up to 10Mhz receive bandwidth/span. Display's a nice 10Mhz slab of the spectrum and should eventually permit ADSB reception etc. (If you have a fast PC/USB) or, 2.5Mhz with a slow PC.

* Fast tuning speed - Great for various SDRsharp scanning pluggins.

* Nice tough little aluminum enclosure.

Cons:

* Requires a fast PC/USB combo for full 10MSPS. My relatively recent Dell laptop with an I5 2.66Ghz processor won't run 10MSPS through the USB port and I am forced to run at the reduced 2.5MSPS sample rate.

* With the RF/IF/LNA gain controls set to 'Auto', the unit produces lots of unwanted spurious signals if there are very strong signals on the band. Reducing the gain of any of the above reduces the spurious, but also degrades weak signal reception & S/N performance.

* Questionable Micro USB reliability. I have already experienced intermittent USB connection problems with the Micr USB socket on the Airspy. I will be trying another USB cable shortly to eliminate this possibility.


FCDP+ Pro's

* 150Khz - 1.9Ghz (minus a gap between 240-400) coverage.
* Excellent HF, VHF & UHF weak signal performance (slightly better than Airspy IMHO).
* Multiple hardware based bandpass filtering.
* Runs fine on a relatively slow/old PC.
* Also contains a TCXO for stable frequency reference.

FCDP+ Cons:

* Only capable of up to 196Khz wide spectrum display/receive bandwidth. Not compatible with ADSB or other very wide band modes. Handles FM broadcast fine but you can only 'see' one station at a time on the Spectrum display.

* Somewhat fragile plastic USB dongle case and USB socket. Have had to re-solder the USB port to the PCB several times as there is no strain relief provided by the enclosure.

* No manual LNA gain adjustment settings - This is not necessarily a bad thing as the FCDP+ seems a little more resilient to strong signal handling and produces less spurious signals than Airspy.

* Tuning speed appears to be a fair bit slower than Airspy. This becomes apparent when using scanning software as you end up having to slow the scan speed down to 150mS per channel. Airspy on the other hand will scan at 60mS per channel.

Anyway, for what it's worth...

B

 

[Voyager]

Had to read your post several times. Lots of great info to digest. I never thought about the increased speed required for the wider display of the AS. I have a modified RTL for HF which seems to work very well (very comparable to my HF rig), so that's not really an advantage of the FCDP+ for me, and I went with the RTL over the FC mainly due to the limited bandwidth of the FC and the coverage gap.

Also interesting about the images of the AS. I thought it was supposed to be immune from those.

One other question on the AS: Can the enclosure sit with the antenna facing upward or did they put ports on the end opposite the antenna? (I think I know the answer to this, but would like confirmation they do have ports on opposite ends which is a bummer)

And thanks for all the great info. About the only other questions I have left relate to the selectivity of the AS vs RTL (or other dongles like the FC).

BTW, did you see they have an upconverter for it now? (Spyverter)

 

[prog]

What about higher dynamic range? What most people fail to grasp is that a good receiver has to be both sensitive AND have the highest dynamic range that can be achieved. This is even worse for those who learned most of what they know about SDR by playing with the cheap TV dongles. They have no idea what a higher dynamic range can put on the table.
Let's put it this way: Your noise floor is around -95dBFS and you are tuning a weak signal that's just 10dB over the noise. Say you have another strong signal of 90dB over the noise nearby (easy to have in HF); In such situation your RTL dongle just can't compete whatever trickery you do since it is limited by its 7bit ADC. Where does the -95dBFS figure come from? Well, when you decimate the input 10MSPS stream by 32, the -80dBFS noise floor you start with gets lower down to -95dBFS.
This reminds me of the discussions about the home-brew NE602 direct conversion receivers being just as sensitive as high end HF rigs...

EDIT:
I found an example from the beta testers illustrating the dynamic range difference:
http://airspy.com/downloads/as-rtl-snaptg.png

 

[SCPD]

Also interesting about the images of the AS. I thought it was supposed to be immune from those.

A high mixer gain seems to bring these out. I leave it at a medium setting.

Can the enclosure sit with the antenna facing upward or did they put ports on the end opposite the antenna?

The antenna SMA connector and micro-USB port are at opposite ends of the case. If you screw the antenna directly onto the SMA connection, you have to find a way to prop it up.

The AS is demanding of CPU. I can run two RTL sticks on a machine (dual core 1.3 Ghz) that barely runs the AS at 2.5 msps. On a faster machine (quad core 1.8 Ghz), I can run the AS at 10 msps but if I turn on decimation, it starts to stutter.

You'll want quad core and 2+ Ghz.

The 10 Mhz bandwidth would be ideal for covering all of 851 Mhz trunking (851 to 861 Mhz) but because of rolloff at the ends, you only get about 9 Mhz. Likewise, dropping the sample rate to 2.5 msps - for slower hardware - falls short of covering the 851-854 Mhz public safety trunking band. At 10 msps, full coverage of 935 Mhz trunking is no problem. Likewise for the 770 Mhz public safety band.

One problem is spikes from clock noise. I have a strong spike at 860 Mhz. They seem to appear every 20 Mhz or so.

 

[prog]

The AS is demanding of CPU.

That's because it replaces all the cheap 8bit processing of the dongles with proper DSP. In case you didn't update airspy.dll for a while, grab the latest version from GitHub. If an Atom tablet can run 10MSPS, I don't see why you PC cannot.

 

[Voyager]

What about higher dynamic range?http://airspy.com/downloads/as-rtl-snaptg.png

Like many other factors, finding specs on the RTL is nearly impossible. But yes, I'm sure the AS is better, and I do understand dynamic range.

 

[prog]

Like many other factors, finding specs on the RTL is nearly impossible. But yes, I'm sure the AS is better, and I do understand dynamic range.

Easy. RTL dongles produce 8bit samples. That's 48dB theoretical SNR, assuming 8 ENOB. The ADC not being perfect, I'd go with 7 ENOB at most which gives 42.1 dB SNR at 2.048MSPS.
Airspy has a 12bit ADC with with 10.4 ENOB which gives 62.6dB of actual SNR at 10MSPS. After the decimation by 4, you get 68.6 dB SNR at 2.5MSPS (to get a comparable bandwidth).
All this gives a noise floor of -60dBFS for RTLSDR and -90dBFS for Airspy. There are many other parameters that enter into the dynamic range equation, but I don't think a post on a forum is sufficient to explain everything. I suggest you to get some reading on the topic.

 

[SCPD]

Just to see if I have the essential differences... (RTL = RTL/R820T2)

AS has tracking filters. That may be the biggest benefit, and worth 5x RTL cost.

Those are integrated in the R820 tuner chip.
An RTL SDR has the same tracking filter on-chip.
Afaics AS uses no filtering prior to the chip front end.

Tracking may be more properly calibrated by firmware though.

73
Paul
PD0PSB

 

[prog]

Tracking may be more properly calibrated by firmware though.

That's it. And it works as expected and experienced by people like scancapecod.

 

[SCPD]

It would be even better if the BPF could be calibrated or manually tuned in "expert mode".
Tuning the BPF slightly higher or lower can give more attenuation on a specific side, avoiding the need to reduce overall gain.

 

[prog]

It would be even better if the BPF could be calibrated or manually tuned in "expert mode".
Tuning the BPF slightly higher or lower can give more attenuation on a specific side if needed, without the need to reduce overall gain.

I can eventually expose these settings. It can be done by firmware. The same applies to the IF filter.

 

[BlueIce]

According to AirSpy's forums someone asked about ADS-B their was a response dated November 25, 2014 at 7:37 pm that stated "I will certainly adapt ADSB# to run with Airspy, but that will need some rework of the detector. Time. All I need is time." Has anyone tried to decode ADS-B with the AirSpy?

 

[jonohudson]

Pros and cons of the SDRplay RSP

While this doesn't compare Airspy to cheap RTL dongles, you may be interested in the FCDP+ comparisons below..

I have both the Airspy and the FucubeDonglePro+. Both of these SDR's are roughly the same price or ~US$200.

IMHO, these are the Pros & Cons of each:

Airspy pro's

* Up to 10Mhz receive bandwidth/span. Display's a nice 10Mhz slab of the spectrum and should eventually permit ADSB reception etc. (If you have a fast PC/USB) or, 2.5Mhz with a slow PC.

* Fast tuning speed - Great for various SDRsharp scanning pluggins.

* Nice tough little aluminum enclosure.

Cons:

* Requires a fast PC/USB combo for full 10MSPS. My relatively recent Dell laptop with an I5 2.66Ghz processor won't run 10MSPS through the USB port and I am forced to run at the reduced 2.5MSPS sample rate.

* With the RF/IF/LNA gain controls set to 'Auto', the unit produces lots of unwanted spurious signals if there are very strong signals on the band. Reducing the gain of any of the above reduces the spurious, but also degrades weak signal reception & S/N performance.

* Questionable Micro USB reliability. I have already experienced intermittent USB connection problems with the Micr USB socket on the Airspy. I will be trying another USB cable shortly to eliminate this possibility.


FCDP+ Pro's

* 150Khz - 1.9Ghz (minus a gap between 240-400) coverage.
* Excellent HF, VHF & UHF weak signal performance (slightly better than Airspy IMHO).
* Multiple hardware based bandpass filtering.
* Runs fine on a relatively slow/old PC.
* Also contains a TCXO for stable frequency reference.

FCDP+ Cons:

* Only capable of up to 196Khz wide spectrum display/receive bandwidth. Not compatible with ADSB or other very wide band modes. Handles FM broadcast fine but you can only 'see' one station at a time on the Spectrum display.

* Somewhat fragile plastic USB dongle case and USB socket. Have had to re-solder the USB port to the PCB several times as there is no strain relief provided by the enclosure.

* No manual LNA gain adjustment settings - This is not necessarily a bad thing as the FCDP+ seems a little more resilient to strong signal handling and produces less spurious signals than Airspy.

* Tuning speed appears to be a fair bit slower than Airspy. This becomes apparent when using scanning software as you end up having to slow the scan speed down to 150mS per channel. Airspy on the other hand will scan at 60mS per channel.

Anyway, for what it's worth...

B

Interesting comparison. I'd like to encourage people to also consider the new RSP from SDRplay which builds on the Mirics technology used in the FCDP+. It addresses some of the cons mentioned above, particularly with 8MHz bandwidth - you can see half the FM broadcast band in one go for example. There are some links to new reviews and video demos on SDRplay

 

[prog]

Not a single word about noise figure and dynamic range Here's a nice note from THE expert about the tuner used in the SDRPlay and FCDP+:

The MSi001 is significantly less good than average amateur transceivers in dynamic range. A radio like the IC706MKIIG is 15 to 20 dB better when it comes to problems caused by inband strong stations.

Source The Mirics MSi001 with Linrad. He's got two airspy units and should confirm what others have already found about the actual performance.
I just wonder how one can give technical "advice" without mastering the subject.

 

[jonohudson]

SDRplay noice figure and dynamic range

You are right that Leif, SM5BSZ, is indeed an expert but his Linrad software needs to know how to use the GPIO to set the RF switches for the different bands. This is something we are working on supporting him with - this will allow Linrad to have proper control of the AGC which hitherto was not possible with any product using the MSi001. So we are aware until we provide that, his comparisons will not look good for us! Watch this space. Regarding noise figures, you can find information in the Detailed Technical Information link on the SDRplay Downloads page SDRplay

 

[prog]

Of course... He also spoke about the sideband noise, where airspy also excels: http://usa-satcom.com/airspy-working-with-inmarsat-decoder/ Take it from another expert ;-) I don't believe any cheap ASIC like the RSP can ever replace properly written DSP code running in a powerful processor or an FPGA, otherwise I would have done an SDR with the mirics years ago.
Airspy was designed and optimized for high performance software defined radio operation. It's not as a cheap substitute to CAN TV or broadcast tuners.