[hpsdr] picoPSU Noise Test #2a - Looking good!

[Ahti Aintila]

Chris,

The noise floor is better now, but still I wonder the high level,
about -110 dBm. For comparision here is my SDR-1000 with Waveterminal
192X and the antenna connector terminated at 50 ohm. I also tuned the
frequency to minimal DDS spurious signals:
<http://kotisivu.dnainternet.net/ahti/sdr-1000/Noise_SDR.png> The
noise is about -140 dBm.The measurement was made with the hardware
according to the latest recommendations of FlexRadio. If I adjust the
preamplifier and the opamp following the QSD to the minimum noise
floor, I can go better than -160 dBm. Of course, then the overload
limit of the QSD will be lower.

When disconnecting the I/Q cable from the radio and terminating it
with 600 ohm, I see the sound card noise:
<http://kotisivu.dnainternet.net/ahti/sdr-1000/Noise_WT192X.png>

I believe, the SDR-1000 is calibrated to a better accuracy than +/-1
dB. I have to ask also like you: "Am I fooling myself somehow?"

73, Ahti OH2RZ


On 12/06/06, Christopher T. Day <CTDay at lbl.gov> wrote:
> I've done several things for this test.
>
> 1) I've opened the MP3+ box and verified that it has no internal
> shielding at all.
>
> 2) I've put a 2ohm load on the 5V rail to give the PSU something to do.
>
> 3) I've followed Ahti's suggestions:
>
>        a) Preamp at "High" [I wouldn't have thought that would matter
> much for audio card pickup, but can't hurt, I guess.]
>        b) Moved the MP3+ as far away from all power supplies as cable
> lengths would allow for the reference measurement.
>        c) Placed the open MP3+ on top of the loaded picoPSU for the
> noise measurement.

 1150103749.0