[hpsdr] ISD - more work needed

[Ahti Aintila]

On 27/08/06, Johan Maas <johan.maas at hetnet.nl> wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> Athi,
>
> Can you tell me (and the others in the list) how you are measuring the noise
> floor?
>
> Is there a program to determine the noise floor of a sound card?
>
> 73 Johan PAGSB
>
Hi Johan,

Thank you for interest! I'm preparing a short report of my experiments
with one version of the ISD (Integrating Sampling Detector). Anyhow,
before that a quick answer to your question:

I have an accurate RF signal generator, a step attenuator and a couple
of SDR-1000 radios.  After calibrating the radio with a known signal,
I just simply disconnect the cable, terminate the antenna connector
with a 50 ohm load and see the noise floor line at the bottom of the
radio's spectrum (or Panadaptor) display. As the bin width of the
display is 11.7 Hz, the noise density should be expressed in
[dBm/11.7Hz] units. At the same time you may read the Average Signal
on the meter. Usually people want to use 500 Hz bandwidth for this
reading.

As you understand, I must just rely that the software and hardware
wizards behind the SDR-1000 have made good work. Usually they do! Then
I must also think that I don't make any stupid conclusions. Usually I
do!!!

The purists do not accept my measurements, because I am using the
equipment to be measured as the measuring instrument. After all, if I
am careful, at least I have a chance to see relative results that show
the performance changes.

Sound card noise measuments are equally art and science and really
need  very good instrumentation and good understanding of the driver
programs. That understanding I don't have.

I hope, this helps. Somebody may give you a better explanation.

73, Ahti OH2RZ

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