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RTL-SDR v3 HF Sensitivity Measurements?

Discussion in 'General Technical Questions and Answers' started by KK5JY, Jul 11, 2018.

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  1. KK5JY

    KK5JY Ham Member QRZ Page

    Oh wow, that's not the experience I'm having here. I wonder if there's some kind of setup issue with yours? Or maybe it's just not working?

    I have no trouble pulling in stations at all kinds of distances with mine... here's 24h of FT8 captures on 20m:

    upload_2018-7-11_12-19-35.png

    ...and 24h of FT8 captures on 30m:

    upload_2018-7-11_12-19-57.png

    The antenna has negative gain, but it still sets the noise floor quite nicely.
     
  2. G0GSR

    G0GSR Ham Member QRZ Page

  3. VK4XJB

    VK4XJB Ham Member QRZ Page

    Not actual sensitivity measurements but I have done is a rough wspr comparison on 30m between mine and an ic-7300. A T piece splitting the coax to each radio. Wsjt-x + 7300 and rtlsdr_wsprd + v3 rtl-sdr direct sampling. A better comparison could be done. What I found was signal readings from the sdr were approx 10dB lower than from the 7300. By the time a signal was down to -20 on the 7300 then odds on the rtlsdr would not show it. I do not know how close the 2 programs are in decoding really weak signals so do not know how much of the difference was software. Have wondered how much of that is the resolution of the adc vs internal noise and being a bit deaf.

    Do you have any kind of filtering between it and the antenna? If I connect mine directly to an antenna there is stuff all on the water fall except maybe some really strong signals. At the moment I always leave a high pass filter with a cut off around 2.5MHz to remove the am broadcast band. Last time I did a comparison on 40 there was a hint of a single ssb transmission with out the filter and with the filter a big reduction in noise and I could see lots of cw, digital modes just below 7.080 and plenty of ssb. The only difference was adding the filter.

    Even when I was using mine to watch the 8.2MHz IF out on a ft-102 the interference from the am broadcast band was very bad and the waterfall full of noise. Adding a T piece and a simple shorted 1/4 wave stub for 8MHz cleaned up the waterfall.
     
  4. W5DXP

    W5DXP Ham Member QRZ Page

    My V3 also works very well with an up-converter - not so well without one.
     
  5. KA9JLM

    KA9JLM Ham Member QRZ Page

    That is not the same one we are talking about. That one goes down to 25 MHz without using direct sampling.

    The V3 is different, Made in China.
     
  6. G0GSR

    G0GSR Ham Member QRZ Page

    OK, sorry. This one does have direct sampling mode also which I can select from the software.
    Frank
     
  7. KA9JLM

    KA9JLM Ham Member QRZ Page

    That Chipset has direct sampling capability, But I think you have to do the antenna input mod for it to work properly. Just like on the V2.

    Without the mod, Range is very limited because no antenna is connected to the direct sample chip input.

    The V3 has a antenna switch and Bias for a preamp built in. Controlled by software.

    Have Fun.
     
    Last edited: Jul 12, 2018

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