DOES IT HAVE AN "AUX" OR "TAPE" INPUT? Switch it off; If something is plugged in the jack - unplug it. That all will switch of the radio output.

The question is old and apparently has been answered to the satisfaction of the asker. But since I had that same problem when I turned on my brand new Satellit 750 I believe it is worthwhile to supply a more plausible answer. No reflexion is meant on the appropriateness of the answer of esteem experts who tried before me.

This is valid for the Satellit 750 by Eton (current owner of Grundig)
When you use it the first time you go through a system code setting to fix the memory page configuration, the AM gap between stations, the type of batteries and FM frequency range.
If it is used in North Ameraica, you are told not to go through procedure but do it any way.
SYSTEM Code setting
Turn Radio off and press a quick short press on the ENTER Button. -- appears on the upper right corner of the display
1. The first code could be 00, 20,25 or 50, meaning the memory is divided into 10, 20, 25, or 50 pages.
2. The second code fixes the AM frequency gap between stations. Enter 09 for 9kHz or 10 for 10 kHz (in North America)
The 3rd code selects the type of batteries used 29 for D size batteries (1.5V each) or 28 for rechargeable batteries (1.2 V each)

The 4th code concerns the FM frequency range: 76 for a range 76-108 MHz (for Japan) or 87 for a range 87-108 MHz

Read your manual to see how the procedure is performed, or try this one valid for the Satellit 750. It might work. Go through all the procedure and press ENTER to confirm system code.

The grundig satellit 800 antenna has broken, I need to replace it.