4 ms·

There's also PiFM[1] which (iirc) modulates one of the GPIO pins fast enough on a Pi to produce an FM radio signal. It's fun to play with, and is a great hack,

There's also PiFM[1] which (iirc) modulates one of the GPIO pins fast enough on a Pi to produce an FM radio signal. It's fun to play with, and is a great hack, but please don't try and use it for anything or any length of time; it puts out a tonne of horrible harmonics all over the radio spectrum. [1] https://github.com/rm-hull/pifm https://github.com/rm-hull/pifm

j_s 9y ago
Or take the rails completely off (5 KHz-500 MHz // FM,AM,SSB,SSTV,FSQ): https://github.com/F5OEO/rpitx https://github.com/F5OEO/rpitx I have a „Hörmann“ garage door opener. For a long time, I want to use my phone instead of the original sender. Therefore, I thought to run a raspberry and send the signal from there. I recorded the signal with HackRF One as .wav, the problem here is that HackRF records with a sampling rate much higher than 48kHz (by default it is 10MHz!). So one has to downsample the recorded file, which I did with Matlab (downsample(signal, „fs_of_record/fs_for_rpitx“)). The resulting .wav signal is now send at 433MHz (either my garage door listens their too, or 2nd harmonic works?!) src: https://github.com/F5OEO/rpitx/issues/50 https://github.com/F5OEO/rpitx/issues/50
- cadr 9y ago
  For a really good time, I suggest https://github.com/JamesP6000/WsprryPi https://github.com/JamesP6000/WsprryPi - it is super fun run a signal into a long wire and see it picked up around the world! (You do need an amateur radio license for this, but in the USA at least the technician one is very easy to get.)
  - j_s 9y ago
    For the semi-serious there is a pre-made filter "temporarily unavailable" (2018-01-15) for purchase: Raspberry Pi QRP TX Shield for WSPR | https://www.tapr.org/kits_20M-wspr-pi.html https://www.tapr.org/kits_20M-wspr-pi.html the harmonics are filtered by a LPF, and the broadband noise is filtered by a BPF [...] a buffer amp is provided for isolation. This also provides a boost to the TX signal And this project ties in an RTL-SDR for receiving: https://github.com/ha7ilm/qtcsdr https://github.com/ha7ilm/qtcsdr mentioning AM/NFM/WFM/LSB/USB [...] although NFM/WFM works as expected, the AM/SSB modes need a much higher level of filtering
    - sgtpepper 9y ago
      Building your own LPF is surprisingly easy and educational!
      - cadr 9y ago
        Specifically, I would recommend searching for "W3NQN CWAZ" filter. Look at http://www.kitsandparts.com/ http://www.kitsandparts.com/ for the toroids.
j_s 9y ago
> it puts out a tonne of horrible harmonics all over the radio spectrum This is typically limited to a 50-100 foot radius without amplification, right?

j_s 9y ago

Or take the rails completely off (5 KHz-500 MHz // FM,AM,SSB,SSTV,FSQ): https://github.com/F5OEO/rpitx https://github.com/F5OEO/rpitx I have a „Hörmann“ garage door opener. For a long time, I want to use my phone instead of the original sender. Therefore, I thought to run a raspberry and send the signal from there. I recorded the signal with HackRF One as .wav, the problem here is that HackRF records with a sampling rate much higher than 48kHz (by default it is 10MHz!). So one has to downsample the recorded file, which I did with Matlab (downsample(signal, „fs_of_record/fs_for_rpitx“)). The resulting .wav signal is now send at 433MHz (either my garage door listens their too, or 2nd harmonic works?!) src: https://github.com/F5OEO/rpitx/issues/50 https://github.com/F5OEO/rpitx/issues/50

cadr 9y ago
For a really good time, I suggest https://github.com/JamesP6000/WsprryPi https://github.com/JamesP6000/WsprryPi - it is super fun run a signal into a long wire and see it picked up around the world! (You do need an amateur radio license for this, but in the USA at least the technician one is very easy to get.)
- j_s 9y ago
  For the semi-serious there is a pre-made filter "temporarily unavailable" (2018-01-15) for purchase: Raspberry Pi QRP TX Shield for WSPR | https://www.tapr.org/kits_20M-wspr-pi.html https://www.tapr.org/kits_20M-wspr-pi.html the harmonics are filtered by a LPF, and the broadband noise is filtered by a BPF [...] a buffer amp is provided for isolation. This also provides a boost to the TX signal And this project ties in an RTL-SDR for receiving: https://github.com/ha7ilm/qtcsdr https://github.com/ha7ilm/qtcsdr mentioning AM/NFM/WFM/LSB/USB [...] although NFM/WFM works as expected, the AM/SSB modes need a much higher level of filtering
  - sgtpepper 9y ago
    Building your own LPF is surprisingly easy and educational!
    - cadr 9y ago
      Specifically, I would recommend searching for "W3NQN CWAZ" filter. Look at http://www.kitsandparts.com/ http://www.kitsandparts.com/ for the toroids.

j_s 9y ago

> it puts out a tonne of horrible harmonics all over the radio spectrum This is typically limited to a 50-100 foot radius without amplification, right?