Chasing RFI: Introduction

If you've been following along, you'll remember one of the reasons I'm building a portable RF shack is that my house is full of RF interference which is causing me problems. I'm going to try and track down the source of the interference, eliminate it if I can, and hopefully learn a bunch of stuff along the way.

Right now I'm in the very early stages of troubleshooting. Shortly after I got my handheld (a Baofeng GT3 Mk2) I noticed that it would break squelch in certain areas of my house while tuned to the local 2m repeater. When the squelch opens, all I hear is static.

My first thought was that some piece of computer gear was causing the interference, so one morning while everyone else was asleep, I tried to do some rudimentary investigation. I placed my radio in a location where it was picking up the interference, then I shut down my server, and cut power to my network stack. The noise went away. A little further experimenting pointed me to the ethernet switch.

However, changing the switch to a different model resulted in the same interference. Also, it seems that the interference is only present if there's an ethernet device connected to the switch.

A little later on, a friend of mine loaned me his SDR (software defined radio). I plugged it into my computer, installed HDSDR, and took a look at the waterfall display. I could easily see signals present all through the 2m amateur band, spaced at something like 30-50Khz intervals. Reading on the internet doesn't point me to any definite sources.

At this point I'm devising some more rigorous scientific testing so that I can conclusively narrow down the source of the interference. I'll post the results of my experiments here, so stay tuned.

Why a portable shack?

While I would love to have a fixed station in my house, I'm coming up with more and more reasons to forsake the basement radio room for a portable radio shack.

That's not to say that I won't use my radios at home, but I think I'm going to be doing more with the radios while out of the house than in it, and it's easier to accomodate the portable shack at home than it would be to take a permanent station on the road with me.

For starters, I don't have the space in the house to dedicate to a bunch of radio gear. While there are many places where I could set up a radio rig, they all get used for something else at some point. This means having a shack I can set up and take down easily is important, and then I'm halfway to a portable unit already.

Secondly, I don't have the space outside the house for a long antenna. We live on a city lot with neighbours on all sides. Our back yard is completely open; any mast would stick out like a sore thumb.

Thirdly, my house is full of RF trash. I'm going to do some work to narrow down the source and try to filter it out, (stay tuned for more on that,) but the simplest answer is just to get out of the house.

Of course, there are downsides to going portable. I'm going to be limited in power since I'm designing everything to run off a 12V battery. Since I'm not lugging a generator around, I'll be limited in the time I can spend on the air. I'm also going to be limited to portable antennas.

But then again, those limitations present some interesting engineering challenges.

The Router, Revisited

One of my readers asked for more pics of my router table hack, so here they are.

Here's an overall photo of the complete setup. Note the ad-hoc debris collection system. (the router cuts off bits of wood of various sizes, ranging from dust to large chunks.)

Here's what it looks like from below. The table surface is doubled up to bring it to the approximate height of the table saw table, and then a couple rails are added so the router table drops in between the rails of the saw table.

Here's a close-up of the table surface. I used a spade drill bit to provide a place for the bolt heads to drop in so they don't sit proud of the table surface. The hole for the router bit was cut on the drill press with a hole saw. It looks small, but there's no point in making it any larger as the router body stops me from using any larger bits anyway. The grooves in the table surface were accidental; I placed the router on the table surface to change the bit, and because I didn't use hardwood plywood for the table, the force required to break the chuck loose pressed the router body into the table.

A view from the back.