Best USB stick/device as Spectrum Analyzer for <= US$ 500

[davorin]

Hello

I'm currently using some cheapo RTL DVB-T and a Funcube Dongle Pro as a USB spectrum analyzer and stumbled today upon this device, which can go up to 3.3GHz:

http://www.rfinstruments.com/SA0314.html

Had anyone had some experience with this device, or knows some other USB devices which could cover at least a continous range of 30MHz to 1GHz for EMC measurements?

Is there any documentation on how to build an antenna for EMC testing as well?



thanks in advance
richard

[thewyliestcoyote]

I have not had any experience with that particular device. It seem to be very much like the RTL DVB-T devices in that it is a just a software defined radio. For the price something like the HackRF maybe a better choice as it has 20 MHz of instantaneous bandwidth and a frequency range of about 30 MHz to about 6 GHz.

One thing to note, all of these USB devices are no substitute for a real spectrum analyser as they are un-calibrated for power. For any real quantitative EMC testing this is a must. That said a lot can be learned by just relative energy of emission, ie what you are doing with the RTL DVB-T device. Take away is when needing to measure power versus frequency in an absolute way a traditional spectrum analyser is what is needed, but for some qualitative investigation any of these devices should work. I will say the HackRF can be made to work with any software you are using for the RTL DVB-T devices. Also there is a very good python wrapping of hackRF with GNURadio that could be used to automate some of the measurements.

Is there any documentation on how to build an antenna for EMC testing as well?

This is a big area, it really depends on the type of measurement you are trying to do. A common antenna or test apparatus is the TEM cell.

http://www.atmel.com/Images/Article_AC10_Open-TEM-Cells.pdf

This could easily be constructed with a pair of N-type connectors and copper clad board. Most are constructed to be system impedance of 50 or 75 ohms. There are formulas out there for the impedance of the parallel plate type transmission line. Just follow these to get the width versus the height of the center section of the cell. Then just do a linear taper to the N-type connectors at each end.

Not sure if any of that is what you are looking for, but just know that EMC testing can get complex requiring anechoic chambers and other expensive equipment. Now for some simple qualitative investigation just a small look made of the center conductor of a piece of coax will take you a long ways.

Really look at the standards you are trying to meet and see what they require you to use.

Best,
Wylie

[davorin]

Thanks for the clarifications :-)

Remember the HackRF One....but never saw it in combination with spectrum analyzer software as the RTL DVB-T sticks, where RTLSDR scanner is the preferred software for scanning between 30MHz and up to 1.8GHz with R820T tuner...

I'm not sure if the HackRF one could do a spectrum plot with power levels differences up to 100dB due to its 8 bit ADC or not....but I don't think a cheapo RTL stick has a better ADC inside (o;

My purpose is to use such a device to compare spectrum plots before and after some modifications electrically or mechanically....having a pre EMC plot from an university lab upfront...but it seems the HackRF one seems to be software wise be supported for radio applications only...

Just found this one: http://airspy.com

With better ADC...but lower frequency range....but still enough for EMC between 30MHz and 1GHz.

[davorin]

Okay...seems the Airspy is also just a pimped up DVB-T with R820T2 tuner inside (o;

Maybe I should save some money and go for a Signal Hound @ US$ 919?

[thewyliestcoyote]

I'm not sure if the HackRF one could do a spectrum plot with power levels differences up to 100dB due to its 8 bit ADC or not....but I don't think a cheapo RTL stick has a better ADC inside (o;

Wow, ok that is a big range,
Sounds like what you need is a real standalone spectrum analyser. The ADC in the RTL is 6 bit IQ. This is to meet the USB 2. full speed spec.

My purpose is to use such a device to compare spectrum plots before and after some modifications electrically or mechanically....having a pre EMC plot from an university lab upfront...but it seems the HackRF one seems to be software wise be supported for radio applications only...

Ok that makes more sense,
I dont use it, but SDRsharp maybe can help with that, else you are stuck writing your own scripts. Not a bad why of doing it if you don't mind the little big of programming.

Okay...seems the Airspy is also just a pimped up DVB-T with R820T2 tuner inside (o;

Maybe I should save some money and go for a Signal Hound @ US$ 919?

Yeah for the kind of dynamic range you are talking about something more like a traditional spectrum analyser is a good choice. There is a lot of automatic gain and attenuation in a traditional spectrum analyser to handle this kind of thing. Else they would all be the size of  a small USB device. There are other options like the Ettus B200 or the Nxxx. They are more expensive and are still SDR's and have higher resolution ADC's.

These do not sounds like what you need. A traditional sweep spectrum analyser is going to far outperform any SDR topology device.

I sounds like you know this but I will say it anyways. There are 2 figures of merit here. First is the instantaneous dynamic range, this is a function of the ADC and the front end. Second is the total dynamic range, or the range largest signal to the smallest signal that can be measured. This factor is all about the gain, linearity, and out of band rejection of the system. This is why you can feed a signal at 10 dBm at 3 GHz into a spectrum analyser and still see a signal at 2 GHz at -80dBm. They don't need an ADC that is 16 or 20 bits.

[thewyliestcoyote]

What about this Android application?
http://tech.mantz-it.com/2014/10/rf-analyzer-explore-frequency-spectrum.html

Thanks for the link to the app. I have application to link a hackrf to a smartphone, and this is a big help.

BTW: Where to buy the HackRF? How much does it cost? Do they have different versions?

Here is the list official list:
http://greatscottgadgets.com/hackrf/

The cost is about $300 to $330ish. Sparkfun I know has a couple right now. I am not sure if this helps you where you live.

https://www.sparkfun.com/products/13001

[davorin]

Okay...a regular DVB-T stick based on RTL is absolutely a no-go (o;

Just did a frequency scan between 100Mhz and 200MHz and it shows harmonics from the internal 28.8MHz clock....

If anyone has another USB device.....a frequency plot with no input signal, or better, ground with 50 Ohm, would be nice (o;

[kripton2035]

rf explorer ?
http://rfexplorer.com/

[pascal_sweden]

Why is the HackRF One not a good spectrum analyzer?

Is it not sensitive enough for measuring the power strength of a signal peek?

Isn't everything controllable from software, given that it is Software Defined Radio? =)

[davorin]

I don't own a HackRF one....nor have I've seen that anyone uses it as a spectrum analyzer...
Also not sure if it is really supported by the Python RTLSDR Scanner software for frequency scans/plots...

Just to spend US$ 330 just to find out it is of no use either hardware or software support wise...dunno (o;

Would love to have some feedback from people having one :-)

[Mr Simpleton]

There are a *few*  problems with the simple "thumb-drive" SA's...

Sweeptime... the receiver is not optimized for fast frequency change, and this means s-l-o-w sweeps (i.e. steps). Trying to capture a dynamic signal is no fun at all!
Dynamic range. Most SA's do have a proper switchable attenuator, to improve dynamic range. The sticks only adjust internal gain and tries to survive.
Most are not calibrated and will only show the rough amplitud...
Spurs....


There are other shortcomings too, but I agree that for a *very* tight budget these little devices can, and will, allow the user to get a simple overview over RF spectrum. Maybe better than nothing if you really need an RF-indicator rather than a full blown SA.

I would go cracy using one for my RF needs though!

[slurry]

I have a HackRF, not been using it as a spectrum analyzer in that sense but it sure is impressive with its 20MHz bandwidth 
with HackRF and a noisesource i adjusted a UHF bandpassfilter without any problems.

[davorin]

Ah...finally someone using it :-)

Can it be really used with almost any software which also support the regular RTL DVB-T sticks?

[KD0CAC John]

I've been looking at most of these , with no need to transmit .
Just for field testing for possible sources of RF that may affect other equipment and then may check transmitters with out the need for the accuracy of a bench Spec analyzer [ ham radio gear ] .
As an example , lower frequency at least down to 40 mhz [ I would prefer down to 2 mhz ] 40 and up for broadcast TV getting too much local RF into tuner [ right now I helping someone with the TV blanking as cars drive by , reflecting the source ] and then the same place is having issues with WiFi getting interfered with by possible RF in area , lots of drop outs , freeze ups etc. , so 2 gig & 5 gig .   

[pascal_sweden]

What about this solution?
http://www.saankhyalabs.com/sites/default/files/avtar_1.pdf

[davorin]

Got some feedback on the hackrf dev mailing list....seems this device is noise wise even worse than regular USB sticks (o;

So leaves only the signal hound as a solution.....

The pocket device seems nice...but I would like to have a device that is also open in terms of open source software support...

[pascal_sweden]

Why can't any company get the noise level right, and make sure that power measurements are accurate?
I want a USB stick that can be used as a decent spectrum analyzer.
Believe that this is very feasible, but it just is not there today, because of the wrong people working on it, and the big companies that already launch their overpriced spectrum analyzers doing lobbying against something that can revolutionize the way people do frequency measurements

I know about the Signal Hound, but believe that it is overpriced, if you compare what you get for that money in the Rigol DSA800 series.

[davorin]

I've ordered now some newer DVB-T sticks with the newer R820T2 tuner....few dB better than the original....

Airspy doesn't seem to be a good device for spectrum analyzer...though it should be better than a regular RTL stick....but apparently RBW can't be set....whatever RBW is (o;

I'm really considering going this way:

http://www.scottyspectrumanalyzer.com
http://lea.hamradio.si/~s53mv/spectana/sa.html

[davorin]

Okay...asking in the airspy forum if this device is suitable as spectrum analyzer I got the reply that I should ask this question somewhere else...seems their forum os only for users who bought the airspy already (o;

Let's see what the guys/girls from RF explorer will send a reply....

First I'm gonna try their software on an existing RTL stick...which supposedly it supports as well....

But the export capabilities are very limited...and I have no clue why all software never have the options to display a logarithmic frequency scale as it is used in EMC testing...making comparison a manual task...

[Fraser]

I own two RF Explorers for quick checks of various frequencies etc. The unit was originally designed as an affordable spectrum monitor for radio remote control interference investigations etc. The Radio Control toy fraternity like it for this reason. From memory the amplitude measurement is based only on the receiver modules RSSI output and so is not the most accurate of of measurement systems. Relative levels are clearly visible however. It is also well supported and most of the the schematics are published. I even obtained the 'commercial sensitive' schematics after signing a simple NDA with Ariel.

The RF Explorer is, IMHO, a very useful spectrum monitor and is quite powerful fro such when connected to a PC and one of the available software packages run. I certainly like mine and I own full size professional Spectrum Analysers so it isn't junk.

The designer is both very friendly and approachable. Ariel has come up with a very neat, polished and affordable RF spectrum monitoring product for the masses. 

http://www.techrepublic.com/article/rf-explorer-a-good-inexpensive-rf-spectrum-analyzer/

BUT, and it is a big BUT....... the RF Explorer is not, IMHO, a serious contender against, or alternative to, a lab type spectrum analyser. It has neither the accuracy not the scan speed of such.

A close friend tested the Signal Hound and was impressed with its capabilities. It is apparently well thought of in the EMC fraternity. It does have its issues though so you are advised to do your research. Its frequency coverage is apparently good value for money when compared to the equivalent conventional bench spectrum analyser. I believe it is quite a slow sweep rate though. The optional software is also good but no idea about its cost. I would have a signal hound as well as my bench SA's if I could justify it. The RF explorer meets my 'quick and dirty' carrier and interference check need though.

Aurora 

[fake-name]

I can't speak to the USB-SA44B, but I did a fair bit of software work with the BB60C from signalhound. It's quite the nice instrument.

I also wrote a pretty comprehensive python wrapper for it's API: https://github.com/fake-name/pySignalHound

It hasn't been tested with anything other then the BB60C, but IIRC they have one API for all their products, so it should be pretty straight forward to patch to support other models.

[davorin]

Maybe someone can tell more about the "slow sweep" rate of the Signal Hound?

Are we talking here several tens of senconds or few minutes for doing a 30MHz - 1000MHz scan?

[Gribo]

I have several SA44B at work, 30M to 1G takes about a second, at the default RBW (30KHz if I am not mistaken). I will measure it when I get back to the office.
I wrote a Labview driver for it, and their new API (3.x) is much better than the old one.

[davorin]

Hi Gribo

That's quick in my opinion ;-)

So you would definitively recommend this model for pre-EMC/after-EMC measurements to see what influence a change in electronics/mechanic can have?

Can their software do a spectrum plot with logarhitmic frequency scale any maybe even define an overlay boundary region?

[davorin]

Playing around with RF explorers Touchstone software, as it support regular RTL dongles as well....

Spectrum scan stops around 90% and hangs forever, when an antenna is connected....

And I can't do a spectrum scan wider than 300MHz.....dunno if that's a limit of the RTL driver or the software itself...