Full Version: Loop on Ground antenna
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(2020-08-11, 22:40:21)VA3TS Tom Wrote: [ -> ]

Before I cancelled my Facebook account I belonged to a FB group that discussed the LoG. Recently, when I was camping up at Grundy Lake (80km south of Sudbury on Highway 69), I checked in to the GBARC 80m net. My receive signals were noisy so I was surprised when I was told my transmit signal was copyable. My antenna was an End Fed Half Wave (coil shortened version - as posted elsewhere on this forum) set up as an inverted-V with the apex up 30ft.

One consideration is that I'll need separate Rx and Tx antennas and manually switching between them is not practical. For me, the simplest solution to that is to use a separate radio for Rx. My very old, steam-powered, Yaesu FT-817 should do the job. I bought it when they first came out in 2001. It is not the -ND version and is not very useful for CW, my favourite mode, so it has been gathering dust in the shack for quite a while. I will use my FT-891 and the EFHW wire for Tx. It will be interesting to compare the noise floor between the two antenna/radio setups.

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.