2020-08-15, 13:37:56
I spent a few hours this morning trying out a LoG receive antenna. QRN is very high on the bands today so it has been a good day for testing the noise reduction feature of a LoG. I used 66ft of wire set out on my lawn in a diamond shape. I fed it at one corner, as described in the article Tom posted. The good news is, it did reduce the noise level - a little.
The original article recommends an isolating transformer between the feedline and the antenna. The author used a type 73 ferrite binocular core for his isolation transformer. I don't have any type 73 material or binocular cores so I had to improvise. A binocular core does a great job of containing the magnetic flux close to the windings. I used this clue and wound a tight bifilar coil around two different types of toroid to concentrate the flux as much as possible. The first core was a type 61 ferrite that I had in my junk box. The second was a type 2 powdered iron core. Due to the lower permeability of powdered iron, I increased the number of turns on the type 2 core.
I tried both in my backyard and couldn't hear the difference. I also tried an old 75/300 ohm TV antenna transformer built for VHF/UHF. Then I tried the LoG without any transformer at all. All tests were done on 80m, 40m, 30m and 20m using my old Yaesu FT-817 as a receiver. I could not truly claim any real difference in noise reduction between the different tests. Admittedly, the tests were very subjective. In all tests I reduced my radio's RF gain and increased AF gain correspondingly to reduce the noise. I also turned off my radio's RF pre-amp.
If I were a top band op I would probably consider it worthwhile to install a Loop-on-Ground or Beverage receive antenna. But for temporary use in a RF noisy campground where I will only be staying for a few days it is probably less valuable. My portable rig is a Yaesu FT-891 which has excellent IF filtering options that I can use to reduce noise. It helps a little for SSB but the ability to shrink RF bandwidth for CW is terrific.
Loop antennas are claimed to be less noisy than other types of wire antennas - even when erected fairly high. That's another option for improving reception.
John VA3KOT
The original article recommends an isolating transformer between the feedline and the antenna. The author used a type 73 ferrite binocular core for his isolation transformer. I don't have any type 73 material or binocular cores so I had to improvise. A binocular core does a great job of containing the magnetic flux close to the windings. I used this clue and wound a tight bifilar coil around two different types of toroid to concentrate the flux as much as possible. The first core was a type 61 ferrite that I had in my junk box. The second was a type 2 powdered iron core. Due to the lower permeability of powdered iron, I increased the number of turns on the type 2 core.
I tried both in my backyard and couldn't hear the difference. I also tried an old 75/300 ohm TV antenna transformer built for VHF/UHF. Then I tried the LoG without any transformer at all. All tests were done on 80m, 40m, 30m and 20m using my old Yaesu FT-817 as a receiver. I could not truly claim any real difference in noise reduction between the different tests. Admittedly, the tests were very subjective. In all tests I reduced my radio's RF gain and increased AF gain correspondingly to reduce the noise. I also turned off my radio's RF pre-amp.
If I were a top band op I would probably consider it worthwhile to install a Loop-on-Ground or Beverage receive antenna. But for temporary use in a RF noisy campground where I will only be staying for a few days it is probably less valuable. My portable rig is a Yaesu FT-891 which has excellent IF filtering options that I can use to reduce noise. It helps a little for SSB but the ability to shrink RF bandwidth for CW is terrific.
Loop antennas are claimed to be less noisy than other types of wire antennas - even when erected fairly high. That's another option for improving reception.
John VA3KOT