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Leif Asbrink leif at sm5bsz.comHi Zilvinas, There are many OP-amps that you can choose from. The dynamic range of the E4000 is good, but not super-high so you do not need something expensive. (The WSE system is ultra-high performance, but today old.) Have a look at what they use in Softrock and other soundcard based hardware. You should be able to find something very cheap for a single 5V supply. I am not up-dated on what is available, but first I suggest you have a look in your junk-box:-) A poor OP-amp could cause an increased noise floor. That can easily be checked by connecting the two resistors to the same output pin of the E4000. If the noise does not go down significantly, OP-amp noise is too high. A poor OP-amp could also cause distortion. Typically a signal twice as far from the center as a strong signal. There could also be intermodulation. Dynamic range performance will be much better than for the Funcube because there is not a LNA in front of the E4000. With appropriate isolation from USB and computer noise you should get the same NF as possible with the Funcube. Regards Leif / SM5BSZ > Hi and thanks all for the remarks guys! > > On 2013.06.12 20:45, Leif Asbrink wrote: > > 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. > > AD797 - (ouch) this one is quite expensive over here: ~26EUR for both > I&Q channels. I mean not that expensive one couldn't buy but maybe one > could find cheaper solution without degrading overall unit characteristics? > I am not specialist in operational amplifiers (just an amateur) and > don't know what are criteria for choosing right device in this place. > > What about kind of instrumentational opamp f.e. INA333 ? > (This would cost half of that . Besides they are single power supply) > > (or even dual ne5532? less than 1EUR but not sure how to avoid dual > power supply) > > Best regards, > > Zilvinas > > > > > 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 > >