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robinst

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About robinst

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    Vacuum
  1. I don’t think any serious person with the knowledge here will help you with this task, as the only possible outcome is that your transmitter will disturb someone else’s radio astronomy Receiver. No one will listen and answer to your transmissions at that frqency band, just leave it alone.
  2. Why do you want to transmit at this frequency? This frequency is usually called the hydrogen line and reserved for listening radio astronomers. https://en.m.wikipedia.org/wiki/Hydrogen_line In the danish frequency plan transmission on this frequency is forbidden. https://www.retsinformation.dk/Forms/R0710.aspx?id=190132#id8290c825-2945-4113-b191-d1301b41e96a Therefore I woluld strongly advise against trying to repurpose a radio transmitter for use on this frequency.
  3. That filter looks corect bur regarding if it will help I don't know, it depends on what kind of noice you need to get rid of. A low pass filter (switching positions of the capacitor and resistor) might help better with getting rid of high frequency switch noice from the laptop charger. A FFT is usually good at extracting signals from noice as long as the noice is not saturating anything, like the ADC. Another way to tackle the EMI noise from the charger. You can try to add some (or lots) of clip on ferrite filters on all cables to and from the charger. https://en.wikipedia.org/wiki/Ferrite_bead That might help a little bit if the noice you see is a high frequency aliased down to a lower frequency instead of an actual low frequency signal. Another thing that might be good to clarify is if the noice is radiated and then picked up by the antenna or if it is coupled to the sound card trough the cable from the charger. How does a spectrum look with the charger connected and the antenna disconnected? A fourth alternative is to use a USB extension and put the sound card directly at the antenna, this might reduce the risk of the analogue cable picking up noice. Regarding the data analysis, maybe looking at writing like a python script to automate it instead of using a spreadsheet? Using a package like pandas might be a good start?
  4. Hello, nice work with the rig and posting all the data, really interesting to read and got myself to try to set up a system too. Regarding the filter, the resistor should be connected to the other lead from the antenna and not your house electrical ground. The filter needs to work against the signals "ground" or reference to be effective, in this case, the other lead from the antenna. The filter circuit is basically a voltage divider with the capacitor as a frequency dependent resistor. A 10 kHz signal will see the 100 nF as 160 ohm, 1 kHz will see it as 1600 ohm and 100 kHz sees it as 16 ohm. Basically the current from the loop antenna has to pass trough your capacitor and resistor and then back to the antenna, and depending on the frequency you will see that more or less of the voltage will be seen over the resistor or the capacitor. At 10.6 kHz equal amount of voltage will be seen over the resistor and the capacitor. The resistor might dampen the total signal thou, as the antenna is a quite weak current source, but if that becomes a problem you can try to scale the filter to use maybe 15 kohm instead, as it will "load" your loop antenna less.
  5. Another thing for easily reduce electrical noise is to add a clamp on ferrite to the cable close to the noise source, see link below. It wont probably make that much of a difference in this application but if belt and braces is wanted it is a common solution for EMI problems. Regarding capacitors, a 100 nF capacitor directly over the output (and input) from the controller might be a good idea to further reduce high frequency noise. As stated above, a big capacitor will only generate current spikes when it is to be charged each cycle but a small one only will take out some of the sharpness of the rising voltage and reduce its high frequency content. http://www.mouser.se/Passive-Components/EMI-Filters-EMI-Suppression/EMI-RFI-Suppressors-Ferrites/Ferrite-Clamp-On-Cores/_/N-bw7t7/
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