[hpsdr] Janus Lives!!

[Ahti Aintila]

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
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>
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