After my success using a ground plane, I discovered two other things which have further reduced my noise floor by 2 S-units. Firstly, I connected a 1:1 balun at the transceiver side. Secondly, I oriented the antenna for minimum noise. I will discuss both points.
When I got back into the hobby and began my battle against RFI, I ordered a 1:1 balun from Balun Designs. The description refers to connecting the balun outside of the shack, which to me sounds closer to the antenna. In an apartment none of that means anything. When I went on my Alpha Antenna Adventure, I disconnected the balun to eliminate any extra variables, and never got around to reconnecting it. A discussion about baluns led me to email the owner, and we had a short dialog.
I wondered if I had purchased the correct balun, and I had. He also suggested connecting it as close to the transceiver as possible. Did I connect it to the wrong end this whole time? Excitedly I grabbed the shortest length of coax I had and connected it. I instantly noticed the difference.
My noise floor dropped by another S-unit. Not only that, but my SWR improved on the higher bands. Previously I could get to an acceptable reading on 15 meters, but 12 meters and 10 meters would never tune below around a 2.6:1 SWR. For non-hams, SWR means Standing Wave Ratio, the amount of reflected energy coming back at you. You want it as low as possible, below 2:1. Now with the balun connected I could get down to a 2.1:1 SWR or sometimes a little better. Good enough.
A ground plane blocks signals below the antenna. A balun decouples the feed line so it can’t act like an antenna picking up noise. If you have a magnetic loop, you can make one more adjustment. A magnetic loop has a slightly directional property. You can take advantage of this in two different ways. You can either orient it for maximum signal or for minimum noise.
Instinctively we think about tuning for the maximum signal, but if you live in the gritty city, you may want to consider doing the opposite. Tuning for minimum noise will lower your noise floor. Don’t worry, you won’t miss out on signals.
The two things mentioned in this article, along with using a ground plane, have reduced my noise floor by at least 2 S-units on all bands. I have the reception I imagined that I would have. I don’t hear a horrible electrical hum if I tune to AM. I have a better SWR on the higher bands. I don’t feel a wave of depression when a wall of HF noise hits me. I hope these suggestions will improve your station as well.