[ExDilbert]

The first looks like some kind of intermittent RF interference. It could be from electrical or electronic equipment, or a nearby transmitter.

Second type of drop is most likely due to atmospheric conditions, AKA tropo. Signals that are 1-2 edge or more often suffer from signal drops, degradation or interference due to tropo, or lack of it.

It would be nice is a RabbitEars report was posted.

 

[ExDilbert]

Interference sources, especially intermittent issues, can be very difficult to find. Common nearby sources can be things like motors, high efficiency lamps or electronics, especially PC computers, or nearby two way radio transmitters. The best way is with a directional signal detector. A portable AM radio tuned to a quiet spot on the dial will sometimes be useful to detect smaller sources in the house or nearby. I agree that UHF is less sensitive to RF interference. To interfere with a 90% signal it's probably fairly powerful or very close.

 

[ExDilbert]

A few years ago, I used a program called SDRSharp with a RTL2832 SDR dongle for a similar issue. The software is still maintained. It worked well enough but not for the issue I was experiencing. Provided some interference is visible, I'd guess that a laptop and a small directional antenna would work to triangulate the source.