This happened with me also.
At first I thought it is wrong “N-male to F-female” adaptor, may be thin pin 75 ohm version, and ordered 2 more adaptors from 2 different suppliers ensuring there was no mention of 75 ohm in their specs. The other 2 adaptors did not solve the problem.
I then tried gain setting. This also did not solve the problem.
Finally I purchased Flightaware Filter, and bingo! the performance shot up drastically. The reason was very strong Cell/Mobile Phone signals in my area which overloaded the dongle.
The 1/4 wavelength ground-plane antennas (Spider and Cantenna) have hidden advantage of picking much less Cell/Mobile Signals than what is picked by high gain collinear antennas (wire collinear and coaxial collinear). The 1/4wl gp antennas normally work good even without a filter.
I will recommend you run a scan of RF signals to determin their presence and intensity in your area. You can do it very easily with you setup without need to purchase any test equipment or hardware/software:
Do I Need A Filter?
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