Re: [Flexradio] Silly question / Noise floor
Hello, Thanks for the explanations, now I have another silly question : Why not normalizing the noise floor value to either 1Hz (consistant with the -174dBm/Hz) or 2,5kHz which in general is the 'normalizing filter width for noise measurement'. I would vote for the 1Hz norm , I understand that it will expand the dBm axis of the panadapter/panafall by approx 13dB but , at least comparison could be made on the noise floor in between f1,5k, f3000 and f5000. 2,5kHz would give a noise floor greater than usual one with cw,ssb filters so will be useless on a graphical display. What would you bargain ?. Kind regards Jean-marc Le 29/06/2011 15:53, Robert McGwier a écrit : Forgive the typo, 117 = 10 * 48000/4096 Hz. On Wed, Jun 29, 2011 at 6:48 AM, Robert McGwier rwmcgw...@gmail.com mailto:rwmcgw...@gmail.com wrote: Or put another way, if the filter is 10 bins wide (117 Hz = 10*4096/48000) the noise power in that 117 Hz is the sum of the noise lower in those ten bins and thus should be ten times or 10 dB bigger than the noise floor. This is what the meter reads: all the power, noise + signal, in the ten bins of the main part of the filter. This does not account for the filter edges perfectly but the difference is minuscule because of the tremendous shape factor on the filter. Great discussion! Bob N4HY On Jun 28, 2011 7:55 PM, Graham Haddock gra...@flexradio.com mailto:gra...@flexradio.com wrote: Hello Jean-Marc: Not a silly question at all. In fact, a great question. The panadaptor is fixed at 4096 bins. Each bin is essentially a receiver with bandwidth equal to the sample rate divided by 4096. Example: for a FLEX-1500, which has sample rate of 48,000 samples per second, the bin bandwidth is 48000/4096 = 11.7 Hz The noise level is lower on the panadaptor, because of the lower (bin) bandwidth. The difference in dB relative to the S-Meter window can be calculated as the log of the difference in bandwidths. Example: The difference in noise level seen on the S-Meter, receiving through a CW filter of 500 Hz, and the panadaptor on a FLEX-1500 would be: dB = 10*LOG(Bandwidth-of-Receiver / Bandwidth-of-Panadaptor-Bin) = 10 * LOG (500/11.7) = 16.3 dB So the panadaptor noise floor will appear to be 16 dB lower than the S Meter value with a 500 Hz filter selected. This only applies to noise. The level of a narrow signal (one that will fit entirely inside of your filter) is independent of the filter bandwidth, so the level shown is the true level and no correction difference applies. --- Graham / KE9H FlexRadio Systems == On Tue, Jun 28, 2011 at 11:14 AM, F1HDI f1...@orange.fr mailto:f1...@orange.fr wrote: Hello, In Powersdr, how is computed the values of the noise floor across the spectrum in spectrum, panafall modes ?. To be more specific, those values relate to which bandwitdh ?. Kind regards Jean-marc F1HDI __**_ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz mailto:FlexRadio@flex-radio.biz http://mail.flex-radio.biz/**mailman/listinfo/flexradio_**flex-radio.bizhttp://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/**flexradio%40flex-radio.biz/http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flexradio.com/ Homepage: http://www.flexradio.com/ ___ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz mailto:FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flexradio.com/ Homepage: http://www.flexradio.com/ -- Bob McGwier ARS: N4HY -- 73's from F1HDI *http://www.f1hdi.org* ___ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flexradio.com/ Homepage: http://www.flexradio.com/
Re: [Flexradio] Silly question / Noise floor
Jean Marc: I think it would be impossible (or at least difficult) to rescale the noise without also rescaling the signal levels in the same bandwidth. Even though you can tell them apart, the signal processing algorithms can not, so it would introduce errors in the reported levels of the incoming signals. Currently, the panadaptor accurately reports the signal levels, and the noise floor that a receiver would see if it was set to the same bandwidth. We normally use 0.5 kHz (500 Hz) for the 'normalizing filter width for noise measurement. It is the normal choice for reporting amateur radio sensitivity specifications, and has been used on all worldwide noise level charts I have seen from the ITU. Best Regards, --- Graham / KE9H == On Fri, Jul 1, 2011 at 1:28 AM, F1HDI f1...@orange.fr wrote: ** Hello, Thanks for the explanations, now I have another silly question : Why not normalizing the noise floor value to either 1Hz (consistant with the -174dBm/Hz) or 2,5kHz which in general is the 'normalizing filter width for noise measurement'. I would vote for the 1Hz norm , I understand that it will expand the dBm axis of the panadapter/panafall by approx 13dB but , at least comparison could be made on the noise floor in between f1,5k, f3000 and f5000. 2,5kHz would give a noise floor greater than usual one with cw,ssb filters so will be useless on a graphical display. What would you bargain ?. Kind regards Jean-marc Le 29/06/2011 15:53, Robert McGwier a écrit : Forgive the typo, 117 = 10 * 48000/4096 Hz. On Wed, Jun 29, 2011 at 6:48 AM, Robert McGwier rwmcgw...@gmail.comwrote: Or put another way, if the filter is 10 bins wide (117 Hz = 10*4096/48000) the noise power in that 117 Hz is the sum of the noise lower in those ten bins and thus should be ten times or 10 dB bigger than the noise floor. This is what the meter reads: all the power, noise + signal, in the ten bins of the main part of the filter. This does not account for the filter edges perfectly but the difference is minuscule because of the tremendous shape factor on the filter. Great discussion! Bob N4HY On Jun 28, 2011 7:55 PM, Graham Haddock gra...@flexradio.com wrote: Hello Jean-Marc: Not a silly question at all. In fact, a great question. The panadaptor is fixed at 4096 bins. Each bin is essentially a receiver with bandwidth equal to the sample rate divided by 4096. Example: for a FLEX-1500, which has sample rate of 48,000 samples per second, the bin bandwidth is 48000/4096 = 11.7 Hz The noise level is lower on the panadaptor, because of the lower (bin) bandwidth. The difference in dB relative to the S-Meter window can be calculated as the log of the difference in bandwidths. Example: The difference in noise level seen on the S-Meter, receiving through a CW filter of 500 Hz, and the panadaptor on a FLEX-1500 would be: dB = 10*LOG(Bandwidth-of-Receiver / Bandwidth-of-Panadaptor-Bin) = 10 * LOG (500/11.7) = 16.3 dB So the panadaptor noise floor will appear to be 16 dB lower than the S Meter value with a 500 Hz filter selected. This only applies to noise. The level of a narrow signal (one that will fit entirely inside of your filter) is independent of the filter bandwidth, so the level shown is the true level and no correction difference applies. --- Graham / KE9H FlexRadio Systems == On Tue, Jun 28, 2011 at 11:14 AM, F1HDI f1...@orange.fr wrote: Hello, In Powersdr, how is computed the values of the noise floor across the spectrum in spectrum, panafall modes ?. To be more specific, those values relate to which bandwitdh ?. Kind regards Jean-marc F1HDI __**_ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/**mailman/listinfo/flexradio_**flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/**flexradio%40flex-radio.biz/ http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flexradio.com/ Homepage: http://www.flexradio.com/ ___ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flexradio.com/ Homepage: http://www.flexradio.com/ -- Bob McGwier ARS: N4HY -- 73's from F1HDI *http://www.f1hdi.org* ___ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flexradio.com/ Homepage: http://www.flexradio.com/
Re: [Flexradio] Silly question / Noise floor
Or put another way, if the filter is 10 bins wide (117 Hz = 10*4096/48000) the noise power in that 117 Hz is the sum of the noise lower in those ten bins and thus should be ten times or 10 dB bigger than the noise floor. This is what the meter reads: all the power, noise + signal, in the ten bins of the main part of the filter. This does not account for the filter edges perfectly but the difference is minuscule because of the tremendous shape factor on the filter. Great discussion! Bob N4HY On Jun 28, 2011 7:55 PM, Graham Haddock gra...@flexradio.com wrote: Hello Jean-Marc: Not a silly question at all. In fact, a great question. The panadaptor is fixed at 4096 bins. Each bin is essentially a receiver with bandwidth equal to the sample rate divided by 4096. Example: for a FLEX-1500, which has sample rate of 48,000 samples per second, the bin bandwidth is 48000/4096 = 11.7 Hz The noise level is lower on the panadaptor, because of the lower (bin) bandwidth. The difference in dB relative to the S-Meter window can be calculated as the log of the difference in bandwidths. Example: The difference in noise level seen on the S-Meter, receiving through a CW filter of 500 Hz, and the panadaptor on a FLEX-1500 would be: dB = 10*LOG(Bandwidth-of-Receiver / Bandwidth-of-Panadaptor-Bin) = 10 * LOG (500/11.7) = 16.3 dB So the panadaptor noise floor will appear to be 16 dB lower than the S Meter value with a 500 Hz filter selected. This only applies to noise. The level of a narrow signal (one that will fit entirely inside of your filter) is independent of the filter bandwidth, so the level shown is the true level and no correction difference applies. --- Graham / KE9H FlexRadio Systems == On Tue, Jun 28, 2011 at 11:14 AM, F1HDI f1...@orange.fr wrote: Hello, In Powersdr, how is computed the values of the noise floor across the spectrum in spectrum, panafall modes ?. To be more specific, those values relate to which bandwitdh ?. Kind regards Jean-marc F1HDI __**_ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/**mailman/listinfo/flexradio_**flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/**flexradio%40flex-radio.biz/ http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flexradio.com/ Homepage: http://www.flexradio.com/ ___ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flexradio.com/ Homepage: http://www.flexradio.com/ ___ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flexradio.com/ Homepage: http://www.flexradio.com/
Re: [Flexradio] Silly question / Noise floor
On Wed, Jun 29, 2011 at 5:48 AM, Robert McGwier rwmcgw...@gmail.com wrote: ...Great discussion! It certainly has been a great discussion, very informative. Thanks to Jean-Marc for bringing this up, and to Graham and Bob for their explanations. Tony KT0NY ___ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flexradio.com/ Homepage: http://www.flexradio.com/
Re: [Flexradio] Silly question / Noise floor
Forgive the typo, 117 = 10 * 48000/4096 Hz. On Wed, Jun 29, 2011 at 6:48 AM, Robert McGwier rwmcgw...@gmail.com wrote: Or put another way, if the filter is 10 bins wide (117 Hz = 10*4096/48000) the noise power in that 117 Hz is the sum of the noise lower in those ten bins and thus should be ten times or 10 dB bigger than the noise floor. This is what the meter reads: all the power, noise + signal, in the ten bins of the main part of the filter. This does not account for the filter edges perfectly but the difference is minuscule because of the tremendous shape factor on the filter. Great discussion! Bob N4HY On Jun 28, 2011 7:55 PM, Graham Haddock gra...@flexradio.com wrote: Hello Jean-Marc: Not a silly question at all. In fact, a great question. The panadaptor is fixed at 4096 bins. Each bin is essentially a receiver with bandwidth equal to the sample rate divided by 4096. Example: for a FLEX-1500, which has sample rate of 48,000 samples per second, the bin bandwidth is 48000/4096 = 11.7 Hz The noise level is lower on the panadaptor, because of the lower (bin) bandwidth. The difference in dB relative to the S-Meter window can be calculated as the log of the difference in bandwidths. Example: The difference in noise level seen on the S-Meter, receiving through a CW filter of 500 Hz, and the panadaptor on a FLEX-1500 would be: dB = 10*LOG(Bandwidth-of-Receiver / Bandwidth-of-Panadaptor-Bin) = 10 * LOG (500/11.7) = 16.3 dB So the panadaptor noise floor will appear to be 16 dB lower than the S Meter value with a 500 Hz filter selected. This only applies to noise. The level of a narrow signal (one that will fit entirely inside of your filter) is independent of the filter bandwidth, so the level shown is the true level and no correction difference applies. --- Graham / KE9H FlexRadio Systems == On Tue, Jun 28, 2011 at 11:14 AM, F1HDI f1...@orange.fr wrote: Hello, In Powersdr, how is computed the values of the noise floor across the spectrum in spectrum, panafall modes ?. To be more specific, those values relate to which bandwitdh ?. Kind regards Jean-marc F1HDI __**_ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/**mailman/listinfo/flexradio_**flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/**flexradio%40flex-radio.biz/ http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flexradio.com/ Homepage: http://www.flexradio.com/ ___ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flexradio.com/ Homepage: http://www.flexradio.com/ -- Bob McGwier ARS: N4HY ___ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flexradio.com/ Homepage: http://www.flexradio.com/
[Flexradio] Silly question / Noise floor
Hello, In Powersdr, how is computed the values of the noise floor across the spectrum in spectrum, panafall modes ?. To be more specific, those values relate to which bandwitdh ?. Kind regards Jean-marc F1HDI ___ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flexradio.com/ Homepage: http://www.flexradio.com/
Re: [Flexradio] Silly question / Noise floor
On 6/28/2011 9:14 AM, F1HDI wrote: Hello, In Powersdr, how is computed the values of the noise floor across the spectrum in spectrum, panafall modes ?. To be more specific, those values relate to which bandwitdh ?. It's not a silly question at all, and I would also like to see the answer. It depends, of course, on the bin size from the FFT, which is dependent on the sample rate. It is not as simple as 1/96k, however. I suspect there is some normalization done, maybe scaling it to a 1Hz bin, but that is pure speculation on my part. For reference, on 20m with Pre2 selected on my F3K, my noise floor is a little over -140dBm with a good 50ohm terminator. It goes up by at least 15dB when switching to a real antenna, so the preamp is not needed. Just to clarify, we are NOT talking about the S meter reading, which depends on the Rx bandwidth. The baseline noise level for the panadaptor and waterfall are independent of the chosen bandwidth. So, can anyone tell us what effective bin size is being used? 73 Alf NU8I Scottsdale AZ DM43an ___ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flexradio.com/ Homepage: http://www.flexradio.com/
Re: [Flexradio] Silly question / Noise floor
Hello Jean-Marc: Not a silly question at all. In fact, a great question. The panadaptor is fixed at 4096 bins. Each bin is essentially a receiver with bandwidth equal to the sample rate divided by 4096. Example: for a FLEX-1500, which has sample rate of 48,000 samples per second, the bin bandwidth is 48000/4096 = 11.7 Hz The noise level is lower on the panadaptor, because of the lower (bin) bandwidth. The difference in dB relative to the S-Meter window can be calculated as the log of the difference in bandwidths. Example: The difference in noise level seen on the S-Meter, receiving through a CW filter of 500 Hz, and the panadaptor on a FLEX-1500 would be: dB = 10*LOG(Bandwidth-of-Receiver / Bandwidth-of-Panadaptor-Bin) = 10 * LOG (500/11.7) = 16.3 dB So the panadaptor noise floor will appear to be 16 dB lower than the S Meter value with a 500 Hz filter selected. This only applies to noise. The level of a narrow signal (one that will fit entirely inside of your filter) is independent of the filter bandwidth, so the level shown is the true level and no correction difference applies. --- Graham / KE9H FlexRadio Systems == On Tue, Jun 28, 2011 at 11:14 AM, F1HDI f1...@orange.fr wrote: Hello, In Powersdr, how is computed the values of the noise floor across the spectrum in spectrum, panafall modes ?. To be more specific, those values relate to which bandwitdh ?. Kind regards Jean-marc F1HDI __**_ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/**mailman/listinfo/flexradio_**flex-radio.bizhttp://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/**flexradio%40flex-radio.biz/http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flexradio.com/ Homepage: http://www.flexradio.com/ ___ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flexradio.com/ Homepage: http://www.flexradio.com/
