[Linrad] Re: Linrad 03.05b and SDR-IQ

[Leif Asbrink <sm5bsz.com; leif@xxxxxxxxxxxxxxxx>]

Hello Thomas,

> The SDR-IQ is stated as useable down to 100Hz.  I know about the low
> freq rolloff.
OK.
 
> > > I want to view signals from the noise
> > > floor to say -50db.
> 
> 
> > -50 dB what? You must specify relative to something. 
> > 
> 
> I think the signal level from NLK in my area is about -50dbm.
OK. You want to see from the noise floor up to -50 dBm.

I do not know what noise level your antenna might give,
but assuming you use a preamplifier that gives you a system 
noise figure of 3dB your noise floor would be at -171 dBm/Hz
or -144 dBm in 500 Hz bandwidth. With a maximum signal level at
-50 dBm you would need a dynamic range of 94 dB (with the 
conventional reference bandwidth of 500 Hz) Your SDR-IQ will
be perfectly adequate.

> I am unsure of the measurement, this is the value from the SV calibrated screen.
> 
> > You will have to connect an analog signal source to the soundcard
> 
> I am not using a sound card, only the SDR-IQ.
OK. I do not know how the front end is designed, but to me it 
seems a little unusual to make the low cutoff 100 Hz in a receiver 
like this.

> > > I want to have the waterfall advance at some slow
> > > rate that I do not know how to specify.
> > You will easily find out once you have your soundcard running
> > with an input signal. (There is an F1 help)
> 
> Is it possible to get a waterfall display with the SDR-IQ?
Yes. Sure.

> I have connected the SDR-IQ to my 12x12x36", 21 turn loop.  I can see
> several VLF stations in the FFT (is spectrum right word?) display.  I
> cannot see the waterfall display, it seems blank.
Presumably you have set the rcf output shift too small. The SDR-IQ
would probably need a preamplifier for a small loop. Or you would
have to tune it and add some impedance matching to make it fit to
a 50 ohm input.

The SDR-IQ uses the AD6620 chip and it might be a good idea to download
the datasheet. It will explain everything about how the SDR-IQ works.

The boxes in the lower right corner of the waterfall graph will set 
the colour scale. Use F1 (but do not click the mouse while you have
the help text on the screen.)

Regards

Leif / SM5BSZ

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