You can compare the filter to a window you are looking out thru. If you stand right in front of the window you can see equally much at the left and to the right. That's the frequency spectrum your scanner sees thru its filter and the monitored frequency are straight ahead out the window.
If the scanner sees other strong signals at adjacent frequencies, it could be the sun you see if you look to the right out the window, then it could impact the performance of the receiver, it gets "blinded" the same way that you have a hard time seeing anything else thru the window besides the sun.
If you then position yourself to the right of the window you'll see more to the left outside of the window and the wall will block the sun to the right. Now you see clearly again, and the scanner receivevs perfect again when that strong adjacent signal cannot be seen by the receiver.
If you move too far to the right you will no longer see what's right in front of the window, the wall partly blocks the view, and the scanner will more or less loose it's reception of the signal you would like to listen to. It we where a planet that had a double sun, then that sun could be hiding far to the left and now becomes visiable to you and will instead blind you from that direction.
So the Normal and Invert are just the position to the furthest left or right of the window. Wide are when you move half way to the left or right so that you still have a perfect view of whats in front of you but that might not block the sun enough, depending of where it is positioned.
There could be many "suns" in the radio spectrum that makes it hard to use your scanner. The window are always of the same size. It's a cheap one that Uniden uses and there are more narrower windows out there but are much more expensive. If you are lucky your window will not face any suns and you always have a great view but others might have dozens of suns right outside on their own drive way.
You can drop the windows blinds, the scanners attenuator, but you'll then see much less thru the window but the suns no longer blinds you. You can set the scanners IFX function to a frequency, you go to another window at the other side of the house. Sometimes there's no suns there and other times it might be more suns there than in the first window, or all suns are positions at just one side and you block their sunlight by moving to either side of the window.
You can say that other scanner models besides the SDS series wear shades and the sun doesn't bother them as much but SDS scanners has no eye protection and are more sensitive to interfering sunlight.
AGC are a change to the audio level to slightly increase low sounds and attenuate strong sounds. It can be heard, if it is enabled, more easily with weak analog signal that have background noise due to low signal strenght. When someone talks the background noise should be lower and when they stop talking, but the system are still transmitting a carrier, you should hear the backgound noise rise in strenght when the AGC automaticly increase the volume. Uniden uses a very light AGC action and Whistler a very strong and noticable action that sometimes can be a bit annoying. All scanners should have that level of action user adjustable, like it is in Unidens BCT15 scanners.
/Ubbe
