Dongle Shootout: Funcube vs RTL SDR


Kanal von MegaOscarVideos from Germany presents a two-part video comparision of the Funcube dongle and a RTL-SDR DVB-T dongle, in this case a Hama Nano version. The two devices are connected to the same antenna and using identical test systems from a geostationary INMARSAT satellite to compare received signal to noise ratios (SNR).


Here in Part II Kanal compares reception of identical test signals from geostationary UHF military satellite downlinks in the 240 – 270 MHz range to compare received signal to noise ratios (SNR). The test was conducted with the two devices connected to the same antenna with no preamp.

Kanal reports: “Most of these satellite downlinks are encrypted data links except for the illegal Pirates from Brazil or occasionally other unintended uplinks or harmonics making it into the uplink.”

“The FCD was used ‘live’ in these videos while the DVB-T IQ stream (1MHz bandwith) was prerecorded a few minutes before the video in order to avoid having to switch the dongles and reconfigure software back and forth and thus save some time in the video.”

This entry was posted in demonstrations, RF, SDR and tagged , .

Comments

  1. jan says:

    i ordered on the other day but i’m not a radio person so i wonder what would be a good antenna to get started with. any suggestions?

  2. Michal says:

    Probably worth notign, that the video is wrong about SNR.
    SNR it NOT “peak of my signal to the baseline of the avg noise”.

    SNR from FFT would be SUM(my signal) / SUM(everything except my signal)

    http://en.wikipedia.org/wiki/Signal-to-noise_ratio

  3. Squonk says:

    Interesting comparison between the 2 devices, thank you!

    However, I would be very interested in a comparison of the amplitude resolution, as the FunCube Dongle is supposed to have a 16/24 bit resolution, whereas the RTL SDR only has a 7-bit resolution (i.e. only 128 pixels in vertical resolution), which is rather low if you are interested in AM signals.

  4. harry says:

    @Squonk, as the radio calculates the radio signals from two real time samples that are 90 degrees phase shifted it is possible to have a very high SN and fidelity in the decoded signal even if the AD is low resolution, in fact it would be perfectly possible to use a one bit AD and still decode high fidelity AM signals.
    What the radio lack in amplitude resolution it makes up for in speed. This speed can be mathematically transformed to narrow band decoded signals with high amplitude resolution that goes beyond the raw sample resolution.

  5. Squonk says:

    @Harry, I don’t understand how come a complex I/Q digital signal can provide a better resolution and a better SNR than a pure real digital signal?

    and having only 7 bit samples provides only a maximum theoretical 44 dB SNR ‘http://en.wikipedia.org/wiki/Signal-to-noise_ratio#Fixed_point), vs. 146 dB SNR for 24 bit samples!

    But I completely agree with you: I forgot that having a higher sample rate (2.8~3.2 MS/s for the RTL2832U vs. 96 kS/s for the TLV320AIC3104 used in the FCD) enables oversampling of the signal and the use of even single-bit ADCs, provided that the oversampling rate is at least 64 times higher than the highest signal bandwidth.

    The RTL2832U is “only” 30~33 times faster, so you can expect a slightly worse SNR, but with a big advantage on cost and flexibility for the RTL-SDR vs. FCD!

  6. Chris says:

    Ive found that the addition of a simple homemade LNA, especially with a pre-selector and or adjustable attenuator pad on the input makes the RTL-sdr a very decent quality receiver that can pick up almost anything that I have wanted to hear in the working frequency range with minimal additional hardware required beyond that.

    That gets the noise level of the RTLSDR down – without it its marginal on very weak signals. (Acceptable on many signals, though with the recent driver improvements.)

    You will want to use an antenna that is appropriate to the signals you are trying to receive in terms of polarization and directionality.

    However, its easy to overload them with spurious signals and they themselves have internal voltage converters that add to the din. Also many of our houses are filled with RFI from e-junk.

    If you build a small RFI detector, its illuminating what turns out to be spewing noise. You can eliminate a lot of it yourself by putting small inductors and bypass capacitors or clamp on ferrites on wiring going into and out of the offending devices. Basically, put them on everything with digital electronics in them.

    I also use them on the outside of coax to keep the RF inside, not outside the coax.

    Using them liberally to cut down on RF interference makes a very noticeable difference..

    You should also use a decent quality powered USB hub with the RTLs.

    One you can open up and modify to add bypass caps and ferrites. Then the USB hub will offer an improvement in stability (the RTLs can draw a fair amount of power at times, causing glitches) as well as noise reduction Use the above technique to make the USB hub as quiet as you can.

Leave a Comment

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>

Notify me of followup comments via e-mail. You can also subscribe without commenting.