e4000 r820t signal output

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Leif Asbrink leif at sm5bsz.com
Wed Jun 12 17:45:14 UTC 2013


Hi Francesco and all,

If you do it the simple way, that is use the signal as is
like is done in the Funcube you can not use a balun transformer.
Going from DC to 48 or 96 kHz is not possible.
Audio transformers can not provide that bandwidth.
It is possible to go from perhaps 5 to 96 kHz
in a transformer, but highly impractical because
of the heavy magnetic shielding that would be required.

A differential amplifier is cheap and efficient and can
repalce an ideal transformer. Something like the output
amplifier in fig 1. here:
http://www.sm5bsz.com/linuxdsp/rxiq/antiali.htm
R124 and R125 would go to the two outputs of
one audio channel.

A typical soundcard samples at HF. Maybe 5 MHz or higher.
The soundcard uses digital filters for anti-aliasing
and there is no need to add a good filter. Aliasing
may be caused by signals near the Nyquist frequency
and multiples of it, but very simple filters are needed 
to suppress those signals since the Nyquist frequency
is typically several MHz.

Regards

Leif



> If the tuner output impedance is known, you could use a balun transformer
> of the right type to convert the signal, and get total galvanic isolation
> as an extra.
> Also, you need a good lowpass filter because the audio cards sample at
> 44100 or 48000 Hz and the lowest tuner output bandwidth is surely > 1 MHz.
> 
> 
> 2013/6/12 Leif Asbrink <leif at sm5bsz.com>
> 
> > Hello Zilvinas,
> >
> > This should work very well:-)
> >
> > The IQ signals are balanced and the proper
> > procedure would be to use a differential
> > amplifier to convert the voltage difference
> > between I+ and I- to a voltage difference between
> > the ground reference and the input of the soundcard.
> >
> > You can try just putting a wire from I+ to
> > the soundcard input. A capacitor in series
> > might be needed. The simple solution might
> > add hum and noise near the center frequency.
> > Such problems are cured with the differential
> > amplifier.
> >
> > Then, do the same for Q:-)
> >
> > Regards
> >
> > Leif / SM5BSZ
> >
> >
> > > Hi all !
> > >
> > > Please excuse me if this is a bit off topic.
> > >
> > > Is there any sense to tap the IQ signals from e4k or r820t to the
> > > internal or external soundcards.
> > > Is it possible at all (with r820t particularly) ?
> > >
> > > (It could seem like reinventing funcube dongle, bet the
> > > performance/price would be still right)
> > >
> > > Best regards,
> > >
> > > Zilvinas
> > >
> >
> >
> 
> 
> -- 
> Francesco Gugliuzza
> B.Sc. in Computer Engineering
> HackLabProject.org Administrator
> Linux user #374630
> Tel (VoIP geographic number): +39 0921440446
> Tel (Libera il VoIP number): 5125320
> E-mail: f.gugliuzza at hacklabproject.org




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