RFI Cures

This page has solutions for many real world RFI problems.  It is a compilation of emails we receive and recommendations to reduce or eliminate specific RFI problems.  You may find your solution in the Q & A text below.  In most cases we refer to specific Palomar Engineers products, but you may also want to consider one or more of our standard RFI kits that have been designed for a specific devive (like computer, telephone, stereo systems, etc).

If you can’t find your answer – email us at sales@Palomar-Engineers.com and we will recommend a specific product and add your problem/cure to this page.  We don’t guarantee you will become famous from your listing, but we hope to cure your RFI problem!

CB Interference

Do you sell or can you direct me to where I can get something that will eliminate rfi from cb radio? I’m trying to use a uniden pc68xl but it keeps making interference for people close to me. I am in a apartment on the 11th floor using a 9ft wire antenna. I tried building my own balun, but i can still hear the cb through my computer speakers.

Can you help?

Ed

Hi Ed,

I had the same problem with one of my transmitters getting into my computer and the speakers on 10 meters.  The problem is quite common if the antenna is close to the computer or other devices like cable modems which have wires on them that act as receiving antennas for your transmitted signal.  You have to “clean up” your signal on both the transmitting end and also protect the other devices from receiving your signal.

A couple of suggestions for your radio.  If you are just using a 9 foot wire for the antenna, make sure you have a counterpoise wire at least 9 feet long connected to ground of your radio.  This wire acts as the other side of the antenna (like two sides of a dipole).  If you don’t have this wire consider using a dipole antenna across the ceiling (9 feet on each side) fed with a good balun/line isolator available from www.Palomar-Engineers.com.  This choke will keep the radio waves from using your coax as the other half of the dipole (the other 0 feet that is missing).  When you dont have the other half of the antenna, your coax becomes the other half and radiates to the other devices like your computer and neighbors stuff.
Ok so get that choke/balun and that will clean up your transmitting signal radiation from the coax.

NOW for the computer, you need to suppress the radio waves that are being received and picked up by the computer speaker wires.  First try twisting each speaker wire pair in a spiral so the wires are wound around each other – this helps a lot to cancel any radio waves received.  The second thing to do is put a RF choke on the speaker wires.  This is a snap-on ferrite bead, made specially for radio frequencies.  The speaker wires is wrapped through the bead several times and chokes off the interfering RF.  Each speaker wire pair needs 1 choke.  Your computer may also have other “antennas” like the mouse cable, printer cable, or their AC power cords.
To eliminate the RF interference to the other parts of your computer you need to isolate their antennas by using similar ferrite chokes on these antennas until the interference problem is negligible.  It may just be the speakers acting as antennas into a powered speaker, but I have found that small powered speakers have 3 antennas – each speaker lead AND the speaker power supply – you need a ferrite choke on each one.  I suggest the snap on chokes with the wires wound through 3 times. If that does not eliminate the problem, the other antennas on the computer are probably picking up the signal and your are hearing it in the speakers so these other antennas will also have to be choked off from RFI – more ferrites are needed.

We sell  RFI-4 kit with multiple ferrites in it  or you can get a computer specific kit at on our RFI Kits page.  There is a kit for laptops and a kit for desktops.

Hope that helps.  Keeping your antenna isolated from your computer will also help.  If your neighbors have a similar problem with your signal, clean up your side first with the dipole or counterpoise first to reduce the RF interference transmitting source and then attack the receiving antenna problems.

Sprinkler System RFI

Problem: Automatic Sprinklers turned on when transmitting on 10 meters.

Solution: Added CB-1-1500 common mode choke to vertical antenna to suppress feed line radiation and ferrite split beads at sprinkler system control box.

Testimonial:

I added 10 of these split ferrites to my sprinkler system power cable, directly at the sprinkler valves. It solved my sprinkler RFI problem, finally, once & for all!! I can now run full power 600W on 10 meters.

10 beads may be overkill, but it was a persistent problem, so I’ll leave it like it is.

73,

Roger

AC6BW