What is Radio Signal Fading?

In the days of analog Radio and TV signals, you may have heard the signal vary in volume and sometimes pitch as the Radio or TV signal bounced off far objects or one of the many layers of our atmosphere. For Radio this effect is observable with an analog receiver in the Low to High Frequency Bands of 100Khz to 30Mhz and is mainly due to the ionosphere layer.

For analog TV and FM radio this effect is observable as picture ghosting or audio flutter. i.e. When an Aircraft flies between the transmitting station and a receiver the signals bounce off the skin of the aircraft and scatter in all directions. Your receiver detects these signals a fraction of a second apart, adding or subtracting from the main signal being received.

These effects still occur with digital signals but the receiver smarts ignore the multiple signals and lock-on to only one and rejects everything else, then waits for a good sequence of decoded signals before allowing the information (Audio / Visual) to flow through to you.

Hence the frozen, pixelated, blocky picture on your screen or "no signal" message or just audio or a still picture with silence. This can be annoying because you don't know what is happening. Is it the sending station or your receiver?

Debugging the problem for the general user has become much harder. As the digital receiver will only allow content to flow to you when the AV streams can be decoded error free.

0. Has the transmitter stop sending?
0. Has your antenna, antenna lead or connector broken?
0. Has your receiver broken, over heated or starting to fail?

To do any user check you'll need a spare or 2nd system with known working leads & equipment. Then swap over one at a time with your suspect leads & equipment.

Check Steps: for DiGiTaL TV reception...
1. Make sure the spare or 2nd system is all working fine.
Then inspect the antenna connector and all leads. (Wall to receiver) [ Replace (swap out) any suspect leads.]

2. Swap out the receiver with another known working unit.
[ Hopefully it should work or at lease repeats the same fault.] [ If it does work, swap back to ensure receiver is the fault. ] [ Conditions may have changed and now your suspect receiver works.]

3. Checking from the wall outlet to the antenna. (Seek professional help)
[ Inspection of coax lines inside walls and that good termination exist at the antenna & wall plate.]

4. Visually inspect the antenna, from the ground or up close if possible, for any thing dangling off or missing.
[ Extra or missing parts, you may need a new antenna. Seek professional help if needed. ]

If after these steps problem still exist there may be local interference from other equipment, e.g. computers, clocks, digital picture frames or even power line noise. Seek professional help, your local TV antenna installer would be a good starting point. They usually have scanning equipment that can fault find cables, signal sources, local knowledge and experience.

Gary, VK3KHB

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