am a little confused about this plot i got this frequency spectrum figure from t
ID: 2085453 • Letter: A
Question
am a little confused about this plot
i got this frequency spectrum figure from the scanning function of a RTL-SDR hardware.
my questions are:
1. what is that relative power means?
2. how am suppose to find any broadcaster nearby?by the relative power amount?
Frequency (MHz) X: 96.97 Y: 48.29 X: 106.6 Y: 70.39 X: 93.78 Y: 30.27 X: 97.78 Y: 24.69 X: 105 Y: 25.61 X: 105.8 Y: 32.14 X: 107 Y: 25. X: 99.38 Y: 15.97 x: 96.5 Y: 10.54 X: 102.6 X: 88.4 Y: 6.838 20 x: 98.581002 Y: 13.32 X: 104.2 Y: 18.6 X: 92.95 Y: 11.23 Y: 7.199 100 102 104 106 108 Frequency (MHz)Explanation / Answer
1
Rtl relative power is not constrained by bandwidth or time. It is a survey that basically a summary of an entire band. If anything happens, it will appear in the survey.
Let's use airband-voice as an example. This band occupies the range between 118MHz and 137MHz. I built an antenna just for airband, and then started looking for signals with a traditional waterfall. I found nothing, and came to the conclusion that either my antenna was bad or I was in a dead zone. In fact, it was the waterfall's fault.
It is always desirable that how to minimize noise during communication. Rtl relative power gives a moderately qualitative way of measuring NOISE.
2
You're basically asking about signal hunting / direction finding. Most RTLSDR antennas are more or less omnidirectional. A single omni antenna won't be able to determine without some other information where the signal is, either in terms of bearing or distance. More powerful distant transmissions can appear much stronger than weak, nearby ones. There are lots of factors -- power, distance, atmospheric conditions, buildings and other obstructions in between etc.
You might research directional antennas a bit. Rotating a highly directional antenna around until you find the strongest direction for a given signal will give you an estimate of the direction to that signal.
You would then need a second antenna placed as far away from the first as you can (and not towards or away from the signal.) You can then use parallax to estimate the distance to the signal, as long as it's not too far away compared to your baseline. If you have a few dozen meters to work with, that should do.
It's also possible to use phase difference information to tell direction (but not distance, without a second site).
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