I have been experimenting with some Receive-antennas for the Low HF bands (80 and 160 meters is “low-band” to me). I discovered these popular antennas from other Hams at the Contesting Club (Potomac Valley Radio Club) I belong to. Nearly all the serious Contesters in PVRC, and all of their Superstations, have Receive-only Antenna options for the lower Bands.
Receive-Antennas typically provide relatively low signal levels, but also very low Noise levels. So once you amplify the small received signals, you can receive signals with very low noise levels compared to common antennas such as dipoles. There are many different types of Receive-Antennas and I would suggest something like the ARRL Antenna Book for details. While most of these antennas have directional characteristics, some (such as this loop) cover a very broad beamwidth.
My Initial Trials with Receive Antennas
My current operating QTH is on ~ 0.9 acres, but it is narrow, so I do not have huge straight runs for long antennas. The natural first choice for Receive-Antennas seemed to be the Beverage antenna. For optimal performance at 160 meters, these ideally need to be over 400′ in length. That was never happening at this location. I discovered something called a Beverage-on-ground or BOG antenna. Putting a Beverage antenna on the ground, theoretically allows the use of a much shorter antenna than the more common Beverage mounted about 7 feet above the ground. I had about 200′ of straight length to work with, and gave that a try on 160 meters. I did not have much luck with my BOG, although I must admit I only tried for a couple weeks to get it tuned and working. So I put one “Beverage” at about 7′ height, but it is only 200′ long. It helps in some situations, more on 80 or 40 meters than on 160, but does not exhibit the desired directivity at 160 meters.
The Loop-on-ground (LOG) Antenna
Doing some reading, I discovered an article about a so-called Loop-on-ground (LOG) antenna. I found this great article by KK5JY about the Loop-on-ground antenna online. I had heard of this antenna before, but with my failed BOG experiences I was skeptical and never tried one. About this time, I saw an email from a friend (Steve, K3KQ) on the Club email reflector of the Fauquier Amatuer Radio Assoc (FARA). He was working with some other local Hams that were interested in the LF/VLF Bands and telling them they really should try a LOG antenna. Time to give it a try.
There was a 160 meter CW contest in a couple days that I wanted to work, but I currently had no antennas for that Band. I threw a crooked dipole (to fit on my lot) in the trees at about 25′, and planned to try a LOG for help with Receiving signals. The LOG can be a loop of any shape, but I was going to use a square. The article says that a square with 15′ of length on each of the 4 sides will work on 160 meters. You do not need ANY Ground system, no rods, no radials, nothing, according to what I have heard. Of course, you still want to provide a safety-ground at the entrance to your Shack. When the antenna is built, you just put it on the ground and attach a feedline. Almost TOO easy.
Construction of the LOG Antenna
Other than wire, other components needed for this antenna are an impedance transformer (~ 5:2 turns ratio), a couple common-mode chokes to reduce noise pickup in the feedline, and some RG-6 or other 75-ohm coax. The transformer can be wound on a toroidal or binocular core. The core needs to use a ferrite material that is suitable for these low frequencies. Since I had tried some Beverages, I had plenty of Type 31 ferrite material around, including a large binocular core. Several other Types are usable, and may be desired if you hope to use this antenna for LF/VLF work. I did not plan to do that in the foreseeable future.
160-meter Loop-on-ground Antenna Results
I connected it all up and hooked the feedline (about 150′ of RG-6) to my rig. I chose to use an outboard low-noise 160-meter preamp (KD9SV design, purchased from DX Engineering) that I have, but most modern radios also can provide the needed amplification. This preamp was made for 160 meter BOG antennas, and there are several other models that should also work. By the way, KD9SV is very helpful if you should run into any trouble with his products. I discovered this when I accidentally reverse-powered my preamp and it needed repair (yeah “stuff” happens..). The preamps in my FTDX-3000 seemed to be suitable, and you may find that the preamps in your Radio are also sufficient.
The initial results were encouraging. The signals on 160 meters were indeed weak, but the noise was relatively low compared to the dipole. Once I enabled the preamp, I had plenty of signal to work with. The FTDX-3000 already has a very low-noise level on receive. Listening to the 160-meter Band with this setup was very enjoyable. My only other 160 meter antenna to compare with was my low-hanging dipole. I must admit that I could hear every signal on both antennas. But the level of noise was much worse on the dipole. This little loop made the difference between listening pleasure and a painful Contest with high noise-levels. Conditions just happened to be so good, that I had a good Contest run (about 215 QSOS in 4.5 hours) and even some EU stations responding to my CQs. I only listened to the dipole for periodic comparisons.
If you are struggling to get a good Receive-antenna for 160 meters, I highly recommend this Loop-onGround design. Your mileage may vary, but I would be surprised if you do not have a favorable result, and you will never build or install a simpler antenna that the LOG.
I may try some enhancements, or even using multiple loops to get some directionality. But for now, this loop will be a standard part of my station for any 160 meter operating. I have heard it may also be useful on 80 and possibly 40 meters. I hope to find out soon.
Follow-up — I used the loop for several hours on 80 meters in the ARRL RTTY Roundup last night. In a RTTY contest, the Band is full of big signals and lots of noise. Again, the loop was the antenna-of-choice for Receive. I again used this loop for 80 and 160 meter work in the recent North American QSO Party (NAQP) SSB Contest. Again the results were great. Noise levels were very high during this contest, so this Loop really helped me.