First I started sampling with my MacBook Pro and had good and clear results.
You can see sharp constant channels
Macbook Pro, 5mhz bandwidth, 2 frequency hops. (image cropped)
However I want to make this more portable, for example with an Raspberry Pi (3 B).
When I am trying to achieve the above with the same settings I see a lot of 'static?'. The frequency range in this image is slightly different, but the result is overal the same.
Raspberry Pi 3B, 2mhz bandwidth, no frequency hops.
And when I use frequency hopping to get a range of 5mhz the result gets a lot worse. This image is cropped. The soft yellow bars in this waterfall are indicating there is activity, but there isn't. This I have tested with another dongle at te same time on my Macbook.
Raspberry Pi 3B, 5mhz bandwidth, 2 frequency hops. (image cropped)
Then I tried to use Raspberry Pi Zero with worse results.
Raspberry Pi Zero, 5mhz bandwidth, 2 frequency hops. (image cropped)
Also with just 1 mhz bandwidth
Raspberry Pi Zero, 1mhz bandwidth, no frequency hops.
Raspberry Pi Zero, 2.8mhz bandwidth, no frequency hops.
In my experience: the less the bandwidth, the better the result.
I have tried the following things to see if it had an influence on the static:
- Different antennas
- Different antenna cables and connectors
- Different rtl-sdr repositories
- Different power supplies (wall adapter, powerbank)
- Different power cables (short usb cable, isolated cables, directly soldered)
- Different usb connections (onboard usb, with extension cable, soldered directly (raspberry pi zero))
- Different RTL2832 dongles
- Different environments
- Disabled wifi and bluetooth
- Tried with overclocking raspberry pi's
I can get a more worse output when I use an usb hub between my raspberry and dongle (also if nothing else is connected). Or when I increase the bandwidth of the dongle.
Does anyone have any suggestion about how to reduce this static or weird signal reflections in my output? Or does anybody know where this is coming from?
Thanks in advance!