DD4WH
Well-known member
Hi Brian,
sorry for being silent for so long, my professional work has been taking a lot of my time recently! Seems you made a lot of progress with your SDR! Very impressive screenshots and a nice analog S-meter emulation ;-). BTW, didn´t know how to make screenshots back in 1972 ;-).
@twinpeaks: yes, you are absolutely right, that is a bug in the code I will have to fix. Also, the determination of the phase difference for twinpeaks detection does not seem to be as accurate as I want it to be. Thats odd, because the automatic IQ correction works very well with mirror rejection > 50dB . . . will have to investigate that.
And I will think about the sgtl5000.cpp mod and will describe it in the github wiki, so people interested in building the Teensy Convolution SDR will know about it.
@transformer: good that you tested the frequency response.
@QSD and caps etc.: Yes, you are right, the sampling caps have to be smaller in order to allow for a 96kHz/192kHz bandwidth and additionally the lowpass filtering of the OPAMP has to be altered too. Have a look here, where I calculated that for the OLD version of the Teensy phasing SDR (have a look at page 9 of the pdf): https://github.com/DD4WH/Teensy-SDR-Rx/blob/master/Teensy.SDR.Documentation.DD4WH.pdf
OR HERE: https://github.com/df8oe/mchf-github/wiki/How-does-your-mcHF-software-DSP-work
@antenna: your signal levels seem quite reasonable. For investigating internal noise, consider putting 50 Ohms to the input before measurements, not a short circuit or an open circuit. Your wire antenna does not require some particular type of wire, every wire type is fine for a longwire antenna. However, the QSD expects 50 ohms and a longwire will typically have a higher impedance, so a preamp for impedance matching or a passive antenna tuner would be perfect and could improve your reception a lot. When it comes to magnetic loop antennas with a single loop of 70cm or 1m, the skin effect calls for thick loop elements like copper tube or a thick coax cable or just a thicker copper wire. Then you need a special very low impedance amp for that and you can have exceptional performance for receive with that setup. As you mentioned, that active loop is a wideband loop antenna, which is not selectively tuned. You can also build a narrowband selective loop antenna, just parallel a single turn loop with a variable capacitor and you have the bandfilter effect already with the antenna.
Would you mind sharing your source code? I would be very interested in potentially adding some waterfall code to the Teensy Convolution SDR ;-).
All the best, have fun with the Teensy Convolution SDR,
Frank
sorry for being silent for so long, my professional work has been taking a lot of my time recently! Seems you made a lot of progress with your SDR! Very impressive screenshots and a nice analog S-meter emulation ;-). BTW, didn´t know how to make screenshots back in 1972 ;-).
@twinpeaks: yes, you are absolutely right, that is a bug in the code I will have to fix. Also, the determination of the phase difference for twinpeaks detection does not seem to be as accurate as I want it to be. Thats odd, because the automatic IQ correction works very well with mirror rejection > 50dB . . . will have to investigate that.
And I will think about the sgtl5000.cpp mod and will describe it in the github wiki, so people interested in building the Teensy Convolution SDR will know about it.
@transformer: good that you tested the frequency response.
@QSD and caps etc.: Yes, you are right, the sampling caps have to be smaller in order to allow for a 96kHz/192kHz bandwidth and additionally the lowpass filtering of the OPAMP has to be altered too. Have a look here, where I calculated that for the OLD version of the Teensy phasing SDR (have a look at page 9 of the pdf): https://github.com/DD4WH/Teensy-SDR-Rx/blob/master/Teensy.SDR.Documentation.DD4WH.pdf
OR HERE: https://github.com/df8oe/mchf-github/wiki/How-does-your-mcHF-software-DSP-work
@antenna: your signal levels seem quite reasonable. For investigating internal noise, consider putting 50 Ohms to the input before measurements, not a short circuit or an open circuit. Your wire antenna does not require some particular type of wire, every wire type is fine for a longwire antenna. However, the QSD expects 50 ohms and a longwire will typically have a higher impedance, so a preamp for impedance matching or a passive antenna tuner would be perfect and could improve your reception a lot. When it comes to magnetic loop antennas with a single loop of 70cm or 1m, the skin effect calls for thick loop elements like copper tube or a thick coax cable or just a thicker copper wire. Then you need a special very low impedance amp for that and you can have exceptional performance for receive with that setup. As you mentioned, that active loop is a wideband loop antenna, which is not selectively tuned. You can also build a narrowband selective loop antenna, just parallel a single turn loop with a variable capacitor and you have the bandfilter effect already with the antenna.
Would you mind sharing your source code? I would be very interested in potentially adding some waterfall code to the Teensy Convolution SDR ;-).
All the best, have fun with the Teensy Convolution SDR,
Frank