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Re: Strength measurements with RTL-SDR dongle

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  • Bookcollector
    Yes the bandwidth is continuously adjustable and is displayed on the left side, but the screen displays up to two megaHertz at a time and signal levels don t
    Message 1 of 16 , Jan 22, 2013
      Yes the bandwidth is continuously adjustable and is displayed on the left side, but the screen displays up to two megaHertz at a time and signal levels don't change when narrowing the bandwidth or narrowing the spectrum displayed. The only thing that will change the signal level is opening configuration and changing the RF Gain. You can change the bandspread to display only about 100 hz and the level of a signal remains the same as when it displayed 2 mHz. You can narrow the filter to 600 Hz or widen it to 250000 and no difference.

      I thought I was ordering a neat toy but it has turned out to be no toy, but a capable SDR and spectrum monitor 24-1700mHz. I was just reading someone's post about SDRs written in 2010 and the guy was saying that it would cost in the thousands to buy an SDR that really worked at VHF and UHF frequencies. How time flies! I listened to the NA QSO Party last weekend on 10 meters and after getting used to the waterfall and figuring out how to use it to tune SSB signals, it was very competitive with my IC-706mkIIg.

      I see that they have similar dongles for ATSC TV that run about $30-40, but no SDR capability yet there.
      Ernie
      W6KAP

      --- In HDTV-in-SFbay@yahoogroups.com, Ron Economos wrote:
      >
      > Isn't the filter bandwidth displayed on the left like this
      > picture of the program (showing 14.110 kHz)?
      >
      > http://sdrsharp.com/downloads/sdrsharp.png
      >
      > Ron
      >
      > On 1/22/2013 2:03 PM, Bookcollector wrote:
      > >
      > > Yes, using SDRSharp with a dongle that has the R820T tuner.
      > > Ernie
      > >
      > > --- In HDTV-in-SFbay@yahoogroups.com
      > > , Ron Economos wrote:
      > > >
      > > > Are you using the SDR# software?
      > > >
      > > > Ron W6RZ
      > > >
      > > > On 1/21/2013 9:56 PM, Bookcollector wrote:
      > > > >
      > > > > I'm not sure exactly what I'm measuring. What I'm comparing is the
      > > > > level of the ATSC carrier in relation to the area of the signal
      > > > > immediately surrounding it. If I spread out from 1kHz to 250kHz
      > > > > bandwidth it makes no difference. If I look at the whole 2mHz that
      > > I'm
      > > > > able to see, the peak is still the same. I believe that the
      > > display is
      > > > > based on the 2 mHz of spectrum the SDR is looking at. If I tune to
      > > the
      > > > > edge of a channel then the noise level where no signal is present is
      > > > > another 10 db down, more or less. So what I'm measuring when I say
      > > > > that the ATSC carrier is 20db above the noise is that the carrier
      > > > > (xx0.31mHz)is 20 db above the surrounding noise (which is signal) and
      > > > > about 30 db above a quiet frequency with no signal. Of course, the
      > > > > entire signal (adjacent noise level) is also reduced with a weak
      > > carrier.
      > > > > Ernie
      > > > > W6KAP
      > > > >
      > > > > --- In HDTV-in-SFbay@yahoogroups.com
      > >
      > > > > , Ron Economos wrote:
      > > > > >
      > > > > > Be aware that your filter bandwidth on the SDR will make a
      > > > > > huge difference in detecting carriers. A 6 kHz filter bandwidth
      > > > > > gives you a 30 dB advantage over a regular ATSC receiver
      > > > > > that must use a 6 MHz bandwidth.
      > > > > >
      > > > > > Ron W6RZ
      > > > > >
      > > > > > On 1/21/2013 12:10 PM, Bookcollector wrote:
      > > > > > >
      > > > > > > Thanks for the info. KOFY is doing an excellent job of keeping
      > > their
      > > > > > > signal in the horizontal plane over a 110 mile path. It sometimes
      > > > > > > fades but is the most consistent of the Sutro transmitters at my
      > > > > > > location (38.489/-120.589).
      > > > > > >
      > > > > > > Channel 7 is stronger today and the rapid fading is less
      > > obvious. It
      > > > > > > almost sounds like the signal is coming through an Altamont
      > > Pass wind
      > > > > > > mill.
      > > > > > >
      > > > > > > I adjusted the contrast on the waterfall and now I see
      > > carriers that
      > > > > > > are just above the noise on 15 and 31. I think 15 is Reno PBS. I
      > > > > > > notice that the channel 47 I am seeing is about 30khz high with
      > > > > > > carrier on 668.313. Or maybe I'm just seeing the offset today
      > > and not
      > > > > > > the carrier. I think that is 68 in Novato and its one of the
      > > > > strongest
      > > > > > > stations I receive on the horizontal antenna.
      > > > > > >
      > > > > > > Do tuners have an AFC that makes a small difference in ATSC
      > > carrier
      > > > > > > frequency immaterial?
      > > > > > >
      > > > > > > I ordered a cable to interface my 91XG antenna to the dongle.
      > > It will
      > > > > > > be interesting to see what level of quieting is needed to
      > > receive a
      > > > > > > signal.
      > > > > > > Ernie
      > > > > > > W6KAP
      > > > > > >
      > > > > >
      > >
      >
    • Ron Economos
      I would expect the noise floor to change when varying the filter bandwidth. The thermal noise floor should be equal to: P = kTB where B is equal to bandwidth
      Message 2 of 16 , Jan 23, 2013
        I would expect the noise floor to change when varying the
        filter bandwidth. The thermal noise floor should be equal to:

        P = kTB

        where B is equal to bandwidth (k is Boltzmann's constant
        and T is temperature) . For room temperature, the
        thermal noise floor in dBm can be simplified to:

        P(dBm) = -174 + 10log (B)

        So for a 6 MHz bandwidth, the noise floor is at -106 dBm, but
        at 10 kHz, it's at -134 dBm. Since we're interested in signal to
        noise ratio, the filter bandwidth makes a big difference.

        Your actual noise floor will be degraded by the noise figure of the
        dongle and any man made noise at your location.

        BTW, the pics you posted to the group photo folder are too small
        to be able to see much.

        Ron

        On 1/22/2013 8:46 PM, Bookcollector wrote:
         

        Yes the bandwidth is continuously adjustable and is displayed on the left side, but the screen displays up to two megaHertz at a time and signal levels don't change when narrowing the bandwidth or narrowing the spectrum displayed. The only thing that will change the signal level is opening configuration and changing the RF Gain. You can change the bandspread to display only about 100 hz and the level of a signal remains the same as when it displayed 2 mHz. You can narrow the filter to 600 Hz or widen it to 250000 and no difference.

        I thought I was ordering a neat toy but it has turned out to be no toy, but a capable SDR and spectrum monitor 24-1700mHz. I was just reading someone's post about SDRs written in 2010 and the guy was saying that it would cost in the thousands to buy an SDR that really worked at VHF and UHF frequencies. How time flies! I listened to the NA QSO Party last weekend on 10 meters and after getting used to the waterfall and figuring out how to use it to tune SSB signals, it was very competitive with my IC-706mkIIg.

        I see that they have similar dongles for ATSC TV that run about $30-40, but no SDR capability yet there.
        Ernie
        W6KAP

        --- In HDTV-in-SFbay@yahoogroups.com, Ron Economos wrote:
        >
        > Isn't the filter bandwidth displayed on the left like this
        > picture of the program (showing 14.110 kHz)?
        >
        > http://sdrsharp.com/downloads/sdrsharp.png
        >
        > Ron
        >
        > On 1/22/2013 2:03 PM, Bookcollector wrote:
        > >
        > > Yes, using SDRSharp with a dongle that has the R820T tuner.
        > > Ernie
        > >
        > > --- In HDTV-in-SFbay@yahoogroups.com
        > > , Ron Economos wrote:
        > > >
        > > > Are you using the SDR# software?
        > > >
        > > > Ron W6RZ
        > > >
        > > > On 1/21/2013 9:56 PM, Bookcollector wrote:
        > > > >
        > > > > I'm not sure exactly what I'm measuring. What I'm comparing is the
        > > > > level of the ATSC carrier in relation to the area of the signal
        > > > > immediately surrounding it. If I spread out from 1kHz to 250kHz
        > > > > bandwidth it makes no difference. If I look at the whole 2mHz that
        > > I'm
        > > > > able to see, the peak is still the same. I believe that the
        > > display is
        > > > > based on the 2 mHz of spectrum the SDR is looking at. If I tune to
        > > the
        > > > > edge of a channel then the noise level where no signal is present is
        > > > > another 10 db down, more or less. So what I'm measuring when I say
        > > > > that the ATSC carrier is 20db above the noise is that the carrier
        > > > > (xx0.31mHz)is 20 db above the surrounding noise (which is signal) and
        > > > > about 30 db above a quiet frequency with no signal. Of course, the
        > > > > entire signal (adjacent noise level) is also reduced with a weak
        > > carrier.
        > > > > Ernie
        > > > > W6KAP
        > > > >
        > > > > --- In HDTV-in-SFbay@yahoogroups.com
        > >
        > > > > , Ron Economos wrote:
        > > > > >
        > > > > > Be aware that your filter bandwidth on the SDR will make a
        > > > > > huge difference in detecting carriers. A 6 kHz filter bandwidth
        > > > > > gives you a 30 dB advantage over a regular ATSC receiver
        > > > > > that must use a 6 MHz bandwidth.
        > > > > >
        > > > > > Ron W6RZ
        > > > > >
        > > > > > On 1/21/2013 12:10 PM, Bookcollector wrote:
        > > > > > >
        > > > > > > Thanks for the info. KOFY is doing an excellent job of keeping
        > > their
        > > > > > > signal in the horizontal plane over a 110 mile path. It sometimes
        > > > > > > fades but is the most consistent of the Sutro transmitters at my
        > > > > > > location (38.489/-120.589).
        > > > > > >
        > > > > > > Channel 7 is stronger today and the rapid fading is less
        > > obvious. It
        > > > > > > almost sounds like the signal is coming through an Altamont
        > > Pass wind
        > > > > > > mill.
        > > > > > >
        > > > > > > I adjusted the contrast on the waterfall and now I see
        > > carriers that
        > > > > > > are just above the noise on 15 and 31. I think 15 is Reno PBS. I
        > > > > > > notice that the channel 47 I am seeing is about 30khz high with
        > > > > > > carrier on 668.313. Or maybe I'm just seeing the offset today
        > > and not
        > > > > > > the carrier. I think that is 68 in Novato and its one of the
        > > > > strongest
        > > > > > > stations I receive on the horizontal antenna.
        > > > > > >
        > > > > > > Do tuners have an AFC that makes a small difference in ATSC
        > > carrier
        > > > > > > frequency immaterial?
        > > > > > >
        > > > > > > I ordered a cable to interface my 91XG antenna to the dongle.
        > > It will
        > > > > > > be interesting to see what level of quieting is needed to
        > > receive a
        > > > > > > signal.
        > > > > > > Ernie
        > > > > > > W6KAP
        > > > > > >
        > > > > >


      • Ernest L. Kapphahn
        Select original to view the full screen. Ernie
        Message 3 of 16 , Jan 23, 2013
          Select "original" to view the full screen.
          Ernie

          On 1/23/2013 4:51 PM, Ron Economos wrote:
           

          I would expect the noise floor to change when varying the
          filter bandwidth. The thermal noise floor should be equal to:

          P = kTB

          where B is equal to bandwidth (k is Boltzmann's constant
          and T is temperature) . For room temperature, the
          thermal noise floor in dBm can be simplified to:

          P(dBm) = -174 + 10log (B)

          So for a 6 MHz bandwidth, the noise floor is at -106 dBm, but
          at 10 kHz, it's at -134 dBm. Since we're interested in signal to
          noise ratio, the filter bandwidth makes a big difference.

          Your actual noise floor will be degraded by the noise figure of the
          dongle and any man made noise at your location.

          BTW, the pics you posted to the group photo folder are too small
          to be able to see much.

          Ron

          On 1/22/2013 8:46 PM, Bookcollector wrote:

           

          Yes the bandwidth is continuously adjustable and is displayed on the left side, but the screen displays up to two megaHertz at a time and signal levels don't change when narrowing the bandwidth or narrowing the spectrum displayed. The only thing that will change the signal level is opening configuration and changing the RF Gain. You can change the bandspread to display only about 100 hz and the level of a signal remains the same as when it displayed 2 mHz. You can narrow the filter to 600 Hz or widen it to 250000 and no difference.

          I thought I was ordering a neat toy but it has turned out to be no toy, but a capable SDR and spectrum monitor 24-1700mHz. I was just reading someone's post about SDRs written in 2010 and the guy was saying that it would cost in the thousands to buy an SDR that really worked at VHF and UHF frequencies. How time flies! I listened to the NA QSO Party last weekend on 10 meters and after getting used to the waterfall and figuring out how to use it to tune SSB signals, it was very competitive with my IC-706mkIIg.

          I see that they have similar dongles for ATSC TV that run about $30-40, but no SDR capability yet there.
          Ernie
          W6KAP

          --- In HDTV-in-SFbay@yahoogroups.com, Ron Economos wrote:
          >
          > Isn't the filter bandwidth displayed on the left like this
          > picture of the program (showing 14.110 kHz)?
          >
          > http://sdrsharp.com/downloads/sdrsharp.png
          >
          > Ron
          >
          > On 1/22/2013 2:03 PM, Bookcollector wrote:
          > >
          > > Yes, using SDRSharp with a dongle that has the R820T tuner.
          > > Ernie
          > >
          > > --- In HDTV-in-SFbay@yahoogroups.com
          > > , Ron Economos wrote:
          > > >
          > > > Are you using the SDR# software?
          > > >
          > > > Ron W6RZ
          > > >
          > > > On 1/21/2013 9:56 PM, Bookcollector wrote:
          > > > >
          > > > > I'm not sure exactly what I'm measuring. What I'm comparing is the
          > > > > level of the ATSC carrier in relation to the area of the signal
          > > > > immediately surrounding it. If I spread out from 1kHz to 250kHz
          > > > > bandwidth it makes no difference. If I look at the whole 2mHz that
          > > I'm
          > > > > able to see, the peak is still the same. I believe that the
          > > display is
          > > > > based on the 2 mHz of spectrum the SDR is looking at. If I tune to
          > > the
          > > > > edge of a channel then the noise level where no signal is present is
          > > > > another 10 db down, more or less. So what I'm measuring when I say
          > > > > that the ATSC carrier is 20db above the noise is that the carrier
          > > > > (xx0.31mHz)is 20 db above the surrounding noise (which is signal) and
          > > > > about 30 db above a quiet frequency with no signal. Of course, the
          > > > > entire signal (adjacent noise level) is also reduced with a weak
          > > carrier.
          > > > > Ernie
          > > > > W6KAP
          > > > >
          > > > > --- In HDTV-in-SFbay@yahoogroups.com
          > >
          > > > > , Ron Economos wrote:
          > > > > >
          > > > > > Be aware that your filter bandwidth on the SDR will make a
          > > > > > huge difference in detecting carriers. A 6 kHz filter bandwidth
          > > > > > gives you a 30 dB advantage over a regular ATSC receiver
          > > > > > that must use a 6 MHz bandwidth.
          > > > > >
          > > > > > Ron W6RZ
          > > > > >
          > > > > > On 1/21/2013 12:10 PM, Bookcollector wrote:
          > > > > > >
          > > > > > > Thanks for the info. KOFY is doing an excellent job of keeping
          > > their
          > > > > > > signal in the horizontal plane over a 110 mile path. It sometimes
          > > > > > > fades but is the most consistent of the Sutro transmitters at my
          > > > > > > location (38.489/-120.589).
          > > > > > >
          > > > > > > Channel 7 is stronger today and the rapid fading is less
          > > obvious. It
          > > > > > > almost sounds like the signal is coming through an Altamont
          > > Pass wind
          > > > > > > mill.
          > > > > > >
          > > > > > > I adjusted the contrast on the waterfall and now I see
          > > carriers that
          > > > > > > are just above the noise on 15 and 31. I think 15 is Reno PBS. I
          > > > > > > notice that the channel 47 I am seeing is about 30khz high with
          > > > > > > carrier on 668.313. Or maybe I'm just seeing the offset today
          > > and not
          > > > > > > the carrier. I think that is 68 in Novato and its one of the
          > > > > strongest
          > > > > > > stations I receive on the horizontal antenna.
          > > > > > >
          > > > > > > Do tuners have an AFC that makes a small difference in ATSC
          > > carrier
          > > > > > > frequency immaterial?
          > > > > > >
          > > > > > > I ordered a cable to interface my 91XG antenna to the dongle.
          > > It will
          > > > > > > be interesting to see what level of quieting is needed to
          > > receive a
          > > > > > > signal.
          > > > > > > Ernie
          > > > > > > W6KAP
          > > > > > >
          > > > > >



        • Ron Economos
          Thanks. Ron
          Message 4 of 16 , Jan 23, 2013
            Thanks.

            Ron

            On 1/23/2013 5:25 PM, Ernest L. Kapphahn wrote:
             

            Select "original" to view the full screen.
            Ernie


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