DOS and AM Radio Interference

At work on Tuesday I wanted to listen to the coverage while on my computer.

Our news channel is AM780 I was listening without static and I was working in MS programs like Excel and Word. And going in and out of the internet as usual.

Then I logged on to Fidelio which is our Front Desk Program and it is a DOS program. All of a sudden BOOM radio static and interference.

I noticed when I logged out of Fidelio the static stoppd. So I logged back in and there it was.

Why just this program? Is it because it is a DOS program? If so what causes it?

Is the DOS program run in full screen? This is purely a wild guess, but I’m thinking maybe the monitor resynching might be the problem.

Either in full screen or if I put it to a Window it causes the interference.

I did notice that the program was written in Clipper. Many old Clipper programs used non-default graphics modes to enable a GUI-like interface. Does the program have any such features, such as scroll-bars, radio buttons, etc?

Many things producing RF energy will cause AM interference–flourescent lights, computer moniotors, computers themselves, light dimmer switches, even conventional lightbulbs that are soon to burn out.

Digital signals by their nature cause a lot of RF interference. Digital signals attempt to make very crisp, clean square waves, and these signals by their nature have a lot of high frequency harmonics.

My first guess would have been the monitor frequencies changing due to a different screen resolution, but if it does the same thing in a windows screen then that’s probably not it.

DOS applications access the hardware directly, as opposed to windows applications which access the hardware through windows (example, a dos application reads the keyboard port, where a windows application tells windows that it wants to know what is going on with the keyboard, then the windows keyboard driver actually reads the port). I suspect that something the dos application is accessing is what is causing the noise, and the noise is simply coming from a particular digital line in the computer being toggled at a certain frequency due to the way the software is using it.

FYI - The old Apple II computers were very unfriendly with respect to the amount of RF noise they generated. They would usually swamp any AM radio nearby. Someone figured out that by toggling I/O lines at a particular frequency you could actually play “music” of sorts on an AM radio. I thought it was pretty funny at the time.

For what it’s worth Fidelio, the dos program, is written in dbase.

I have noticed AM interference from some PCs.

Dbase checks the clock frequency, one of the reasons it ‘crashes’ on PCs faster than 450 mHz or whatever. Maybe it is doing something ad an odd frequency.

This is most likely the correct answer if the DOS RF interference is occurring in both real and windowed mode.

I have this problem all the time - try turniong off your monitor and see if it goes away. You can try repositioning the radio or for AM try rotating the radio