Birds are nice to have in your neighborhood but not in your radio. Computer monitors and network gear are a frequent source of RFI birdies.
For many years, hams have referred to spurious signals on their radio as “birdies”. Typically tones or chirps, birdies are unwanted signals caused by radio or nearby oscillators. You can do without these annoying sources of interference.
Recently, I incorporated the FlexRadio 6300 into my radio room. As part of this build, I added two new computer monitors and an gigabit Ethernet switch into the mix. Monitors and network switches are a frequent source of unwanted RFI birdies. So, I took a few minutes to search the bands for new sources of radio frequency interference from these devices.
Good news first. The gigabit Ethernet switch seems to be silent. I chose the Linksys SE3005 5 port switch to connect the radio and computer to the LAN. It appeared to be well shielded, fast, low power and turns off unused ports automatically. I used my Perseus to scan the HF frequencies but could not detect birdies or hash when I cycled the power on this high speed switch.
Bad news came on the monitor side. One monitor (a low power LED LG model) appears to be silent. But the other, a higher power SyncMaster LCD unit emits lots of birdies above 15 MHz. You can see them in the picture above.
RFI Birdies from my Monitor
It’s easy to spot monitor birdies with a dual display setup and the Flex 6300. Just turn the monitor on and off. You will see the solid lines in both the waterfall and spectrum display. Real radio signals vary in amplitude. Birdies put out a solid signal. The RFI birdies from my Syncmaster monitor range from about 15 to 20 dB above than the noise floor. If you really want to see birdies, disconnect your external antenna. What you are left with are the monitor oscillations in close vicinity.
Now, the SmartSDR software has a feature called “tracking notch filters”. I can use these remove at least some of these birdies. However, the best approach is to try a few other monitors until I find one as RFI silent as the LG.