Radio Frequency Interference In The Ham Shack

     I am sure many of us have had RFI in the ham shack at some point. There have been problems with RFI getting into speakers and headsets, RF bites when we touch metal microphones, etc. These can all be quite annoying.
     However, these things can be easily fixed. One general rule of thumb that I use is that if any connector is loose, it can vibrate and act like a crystal in the presence of strong RF and emit RFI. So the first thing you should make sure of is that all audio and coaxial cable connectors are absolutely tight.
     Using a good shielded audio cable is essential to making your speaker system and other audio routing RF proof. Never use simple audio coax with center conductor and shield. Use two conductor (red and black wires) cable with a good copper braid shield and foil shield under the braid. You need both the "hot" wire and ground wire to be shielded.
     When soldering PL-259 coax cable connectors on, here are some tips. When using coax that has a stranded center conductor such as RG-2013, always coat the center conductor with a bit of solder to keep the strands together. One little stray whisker in contact with the connector barrel can cause a coax connector to be shorted. When soldering the connector, always file the nickel plating off the area around the 4 little holes in the barrel. This will make the solder flow on much better. I use a 200 watt soldering gun. I have a set of Swedish files to do this with and they work great. They come in a set of 5 or 6 in a plastic pouch and are available in any hardware store. When soldering the holes shut, get your tip down on the top edge of the hole, feed some solder on to the tip and pull the tip toward you in a downward sweeping motion. This works well. Do not try to clamp the connector into a vise before soldering because this will just act like a heat sink. Gently clamp the coax cable itself into the vise instead, leaving about 1 1/2" of cable sticking out past the connector. The advantage of soldering the 4 holes shut is that it somewhat keeps moisture out and it keeps small amounts of RF from leaking out. I used to get RFI in my headphones and speakers a lot until I started soldering the 4 holes shut on all my coax connectors.
     Using a good quality solder is essential for making good RF connections. Kester "44" solder has been a "gold standard" of the industry for many years. Another good brand is Multicore 500G which is a 60/40 blend of tin and lead. Alphametals also makes some good solder.
     Some hams use ferrite chokes for RFI suppression. This is a good "band-aid" approach for a quick fix. I have never had much luck with them. The drawback is that you need to wrap as much wire around the choke as possible in order to get the full effect. Then you have a big old wad of wire and choke laying on your ham desk or shelf, sticking out like a sore thumb. Of course, if it is hidden behind equipment, nobody will see it, but really you need to find the source of the problem.
     RFI can be passed on through the house electrical system by your station power supply! I had a regulated 35 amp power supply that I used for several years until I bought a Tokyo Hy-Power HL-450B amplifier which required a 60 amp switching power supply. Prior to this, my HF radio transmissions would always blank out my Davis Instruments weather station display unit. After installing the switching power supply(HP-460), the problem went away. Figure that one out!
     Update 9-2-18: Since writing this, I have installed an MFJ-2990 vertical antenna and my RFI problems have gone away.  I used LMR-400 coax and greatly improved my grounding system.  Now, I can use my amplifier at full output without causing QRM to anything inside or outside the house.

I hope this blog helps in some way. I appreciate any comments you might have.

73,

John Gercken, AA9UF