[hpsdr] Janus Lives!!

[Gerald Youngblood]

The bin bandwidth is 48000/4096, which is about 11.7 Hz.  10 * log10(11.7)
is equal to 10.7 dB.  That means that a noise floor of -160 dBm would give
you -170.7 dBm/rt Hz for the sound card -- highly unlikely at room
temperature.  This equates to ~3dB NF for the sound card.  The absolute best
audio A/D converters have an equivalent noise figure of 30-33dB.  High speed
A/D converters will have a higher NF than that.

Hope that helps.

73,
Gerald

Gerald Youngblood, K5SDR
FlexRadio Systems
Ph: 512-535-5266
Fax: 512-233-5143
Email: gerald at flex-radio.com
Web: www.flex-radio.com
 

> -----Original Message-----
> From: hpsdr-bounces at hpsdr.org 
> [mailto:hpsdr-bounces at hpsdr.org] On Behalf Of Ahti Aintila
> Sent: Monday, July 03, 2006 2:00 PM
> To: Robert McGwier
> Cc: hpsdr at hpsdr.org
> Subject: Re: [hpsdr] Janus Lives!!
> 
> ***** High Performance Software Defined Radio Discussion List *****
> 
> Hi All,
> 
> I wanted to repeat my earlier measurements with WaveTerminal 
> 192X using obviously the same method as Phil_H with Janus. 
> See the picture:
> <http://kotisivu.dnainternet.net/ahti/sdr-1000/OH2RZ_noise.png>
> The test was made with carefully calibrated SDR-1000, PowerSDR 1.6.2.
> The signal was fed directly to the sound card at IF-frequency 
> at calibrated level of -120 dBm. I put on PEAK and collected 
> data about 10 seconds.
> 
> Please, understand that is a sound card test only, but 
> PowerSDR is used as a spectrum analyzer, because I have no 
> better instrument. If the radio is connected to the sound 
> card the noise floor rises up to -150 dBm/10Hz (or would 11.7 
> Hz be more accurate bin width value?).
> This tells me that in order to reach the best sensitivity, I 
> should reduce the nois figure of the SDR-1000 by about 10 dB.
> 
> 73, Ahti OH2RZ
> 
> 
> For the Signal meter reading I cannot give any explanation, 
> but the readings of the "spectrum analyzer" I trust. Perhaps 
> Phil_H will give us some comment about my an his measurements.
> 
> 
> 
> 
> On 03/07/06, Robert McGwier <rwmcgwier at comcast.net> wrote:
> > ***** High Performance Software Defined Radio Discussion List *****
> >
> > A typical receiver measurement in the ARRL labs consists of 
> donig the 
> > MDS in 500 Hz.  This is the correct measurement to ask for 
> if we are 
> > to compare the results to others.
> >
> > If this were calibrated and we saw -159 dBm in 500 Hz ( the 
> meter is the
> > integrated noise power in the 500 Hz bandwidth in 
> PowerSDR),   then at 1
> > Hz,   if we could do such a filter,  we would get 
> approximately 26.9 dB
> > less power in the 1 Hz bandwidth  (  10* log_10(1/500)).   
> This is below
> > the theoretical noise floor since 1 Hz cannot be less than that for 
> > room temperature since this is not in a system, it is the 
> naked A/D.  
> > It cannot be calibrated.  Gerald is right.
> >
> > Bob
> >
> >
> >
> > Alberto I2PHD wrote:
> > > ***** High Performance Software Defined Radio Discussion 
> List *****
> > >
> > > Gerald Youngblood wrote:
> > >
> > >> There appears to be one problem with the measurements 
> though.  The 
> > >> noise floor in the screen shots cannot be accurately calibrated 
> > >> since the 500 Hz RMS noise measures -159 dBm.  If you 
> subtract 26 
> > >> dB for the 500 Hz bandwidth, you get a noise floor of 
> -185 dBm/rt 
> > >> Hz.  This is below kTB of
> > >> -174 dBm/rt Hz.  That would equate to a negative NF (-11dB).  I 
> > >> would be interested in seeing the 500 Hz bandwidth shot after 
> > >> calibration with the radio attached.
> > >>
> > >> 73,
> > >> Gerald
> > >>
> > >
> > > Hmmm, IMHO those are not -159 dBm at a bandwidth of 500 
> Hz.... the 
> > > bandwidth that must be considered is that corresponding 
> to the bin width of the FFT that has been used to compute the 
> spectrum.
> > > The 500 Hz are the bandwidth of the audio filter, which 
> has nothing to do with the FFT bin size.
> > >
> > > 73  Alberto  I2PHD
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> > --
> > AMSAT VP Engineering. Member: ARRL, AMSAT-DL, TAPR, Packrats, 
> > NJQRP/AMQRP, QRP ARCI, QCWA, FRC. ARRL SDR Wrk Grp Chairman 
> Time for a 
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