Computers generate interference and some swl and hams will tell you that Software Defind Radios, which need a computer connected, are not worth bothering with because of the interference problem. I disagree and I would go as far as to say that my QS1R is very useful for locating the sources of interference. Also, the way the SDRMAXII and QS1R server software can be run on entirely different computers seems to help reduce the QRM. It seems to me that older, less powerful computers generate less QRM than the fast, hot, energy consuming P4s etc. of a few years ago. I only have one fairly modern, quite efficient, dual core PC, so I can't say for sure whether these generate more or less than their predecessors. On this page you can see what interference looks like in a waterfall display, and you can read about its source. I hope to expand this section with tips on how to reduce interference. |
The picture above shows interference generated by a Nokia phone charger. Notice how much worse it gets after a minute or so. Thanks to Cathy for contributing the pictures. |
Not sure what this is. Probably interference, but it moves over quite a range and even a drifting oscillator wouldn't drift around that much. Would it? Do you see, or hear it too? The signal to which the receiver is tuned is quite odd as well. Every few seconds it goes pop. Strangeness at LF... |
The picture above shows the effect of first turning off my main, home built, desktop PC and then switching off its power supply. I was running the QS1R server on an old Packard Bell 500MHz laptop and the SDRMAXII GUI on a slightly more modern (1.6GHz) laptop. It's unfortunate that my main computer generates interference in the amateur 40 meter band, but I only use a loop antenna in the loft, so it is to be expected. |
I don't usually watch TV while I'm listening to the radio, but this picture shows the effect of turning my ancient CRT TV off. I could probably calculate that the frequencies at which the interference is strongest are harmonics of the 625 line horizontal scanning frequency. I will leave that as an exercise for you, if you need to know :) |
The effect of switching on a CCTV camera connected to the computer. Another contribution from Cathy. |
In the picture above you can see where I first switched off the TV and then my CRT monitor. The monitor doesn't seem to interfere further up the band. I hope to replace it with an LCD type soon. |
Cathy was getting really bad interference at the lower end of the RF spectrum. Replacing the computer PSU with an older, less powerful one made a striking difference! |