Just like light pollution to an astronomy hobbyist; Living in the city means a ton of electrical noise pollution for us radio nerds. I have managed a pretty decent transmitting setup, a HyGain AV-640 vertical works great on the higher bands, and my 130′ end-fed for the lower bands. People seem to hear me just fine. But, on 40 and 80, I’m plagued with a pretty high noise level and often voices on side-band are right there with the noise.
I’m a listener first, a transmitting HAM second. My enjoyment from the hobby has always come with monitoring the shortwave bands as a whole. I look for utility stations, AM Broadcasters worldwide, shortwave pirates, world news, interesting music from other cultures, and clandestine stuff like ‘numbers stations’. I want to be able to hear everything!
I was turned onto the MLA-30 magnetic loop antenna from a short-wave radio YouTube channel I watch. It’s available for about $50 on Amazon so I thought “what the heck! at $50 it’s worth a shot”. This simple 30″ magnetic loop has been a game changer for me allowing me to null out the electrical noise in my area and get weak signals to pop! This antenna shines below 10 MHz and loses a lot above but it has become my receive antenna for the lower HF bands and it works great.
This made me start looking for other options in low-noise receive antennas. The one that caught my attention is known as a ‘Beverage Antenna’. These can be put together on the cheap using 75 ohm RG6 (CATV cable) which is cheap and very low loss. A simple DC isolator (transformer) can be wound using a type 73 binocular core with two windings on the primary to match about 75 Ohms and as many windings needed on the secondary to match the antennas impedance. There is a commercial Beverage transformer available but it’s $95 and tuned for a ‘conventional’ long Beverage like described in the ARRL Antenna books, etc.
The design I chose to play with is known as the ‘Beverage on the Ground’ or ‘BOG’ as described by KK5JY. He is using 60′ of wire in a square formation of 15′ sides landscape-stapled to the ground and fed with a 2:6 transformer. Again, 2-windings on the primary to match the 75 ohm output (feed line) and 6-turns on the secondary to match the antenna wire. Wire used is insulated 14g stranded electrical wire. I’m told you will get a gain-lobe off the corners perpendicular to the transformer so I oriented mine north/south with the transformer on the southeast corner. This should position my lobe to Europe and the South Pacific (I hope).
Here are some pictures of the 2:6 transformer. I see this method referred to as a DC isolator (?) or Inductive Coupler (?) but someone much smarter than me will have to chime in on that.
The next picture is how I ‘vaulted’ the transformer underground using a Home Depot purchased sprinkler system vault. The transformer in this picture is a DX Engineering transformer that I had for testing prior to installing the homemade 2:6 transformer pictured above.
The next two pictures are marked with a white line so you can see the path of the antenna.
This is where I am at so far. So What do I think?
Well, initial testing is somewhat positive. Being on the ground definitely reduces the noise by 4-5 S-units at 5-Mhz. But it also reduces the signal by 3-4 S-Units. I need to do a lot more testing to dial this in and speak about it intelligently…. but it does appear to have a good signal to noise ratio compared to my antennas in the air. Problem seems to be that I will lose the very weak signals I want to receive.
Next, I will be trying a pre-amp. I hope it will lift the signal and either help reject the noise, or bring it up in perfect proportion keeping the improved signal-to-noise ratio.
I ordered a pre-amp off eBay that is on its way…. I’ll update once I have a chance to experiment with it. I will install the pre-amp at the underground vault and will burry a run of CAT-6 with the feed line to the vault. That way I can power the pre-amp and have a few more conductors available if I want to get ‘fancy’.
More to come…….