Can anyone explain this spectogram picture?

[wtr]

Hello,

The picture below is a capture of a FPV drone camera. It's a PAL/NTSC signal. This signal is Amplitude modulated.

I've sampled the continuous wave signal and fed it through an FFT, etc to generate this spectogram.

What concerns me is the fact that the carrier frequency seems to fluctuate. So my questions which i need help with are as follows.
1. Why does it not stay fixed on f_c? Why does it move like an FM signal? Is this because of multipath?
2. See second picture. Why does it work perfectly some times?

Thanks in advance,
Wes

 

[kaz1]

Hello,

The picture below is a capture of a FPV drone camera. It's a PAL/NTSC signal. This signal is Amplitude modulated.

I've sampled the continuous wave signal and fed it through an FFT, etc to generate this spectogram.

What concerns me is the fact that the carrier frequency seems to fluctuate. So my questions which i need help with are as follows.
1. Why does it not stay fixed on f_c? Why does it move like an FM signal? Is this because of multipath?
2. See second picture. Why does it work perfectly some times?

View attachment 178402

View attachment 178403

Thanks in advance,
Wes

The highest power band is around 100MHz when it fluctuates. But around 20MHz when stable. Sounds like carrier lock issue.

 

[noori.re]

The PLL can not lock?!
try for different carrier freqs.