HFU HF Underground
Technical Topics => Equipment => Topic started by: Rafman on December 02, 2012, 0205 UTC
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I noticed that some members are using BOGs or Phased BOGs to listen on. I'd like to try some but need some clues:
- What length would you recommend for 7MHz?
- How do you feed/terminate them [IF terminated at all]???
- What do you employ to phase them together?
- Does anyone have a circuit/scheme for phasing [again around 7MHz]
- If using coax, do you short ends/leave open & how are coaxials fed at RX end if using coax [have a bunch of RG59 foil CATV avail. to me]
Thanks in advance!
Rafman
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I use phased BOGs with great success for medium wave DXing, but it wouldn't be my first choice for 7 MHz. I think there are better antennas choices (horizontal loops come to mind), but since I'm already using them for MW I make the best of it for shortwave and they seem to work well enough up to about 10 MHz considering it's just a wire laying on the ground with absolutely no elevation. With that said...
What length would you recommend for 7MHz?
I use a 500 FT length phased against a 400 FT length. On medium wave, they are highly directional off the ends. On shortwave, they seem omni-directional. For phasing to properly work (medium wave), one needs to be shorter and they should be spaced about a foot or two apart and parallel to one another. On shortwave frequencies I find that the phaser has no effect in nulling signals as its intended purpose on medium-wave. Instead, the phaser is useful for cancelling man-made noise on shortwave frequencies. I've never tried shortening the wires for higher frequencies above 1700 KHz, so I can't comment on the proper length needed. Again, I think there are better solutions for 7 MHz.
How do you feed/terminate them [IF terminated at all]
I use a pair of 60 FT RG-8X cables, from the house to the feedpoint out back. I have 8 FT ground rods just outside the house where the coax enters, and another out back where the transformers are at the feedpoint (to ground the coax shields). Inside the shack, the two coax cables connect to the antenna phaser. Out back, the coax cables are connected to a pair of I.C.E. 182A transformers. The BOG wires connect to these transformers. The BOG wires are not terminated at their far ends. This allows the desired null to be "steerable" on medium wave frequencies. At shortwave frequencies, the effect is lost but still useful for cancelling noise and lowering the noise floor a bit.
What do you employ to phase them together?
There are several different antenna phasers on the market, or you can roll your own. I use this one: http://www.dxtools.com/Phaser.htm
For medium wave DX, I don't think there's a better setup. I've logged some unbelievable stuff including Australia on 702 KHz at 9,000+ miles on more than one occasion.
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Thanks for the write-up, Kilokat7. Do the BOG wires actually need to be on the ground, or can they be a few feet above? I have some woods behind the house I could probably run them through.
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Thanks for the write-up, Kilokat7. Do the BOG wires actually need to be on the ground, or can they be a few feet above? I have some woods behind the house I could probably run them through.
I've never tried raising the wires as I also wanted a stealth antenna. After a year or two of ground growth and falling leaves, the wires are no longer visible for most of their length.
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FWIW an avid contester I've met in my travels with 10+ acres of room to spare has about 5 of these in different directions. He uses them on 160M for receive, and has them rigged so he can reverse them with some sort of relay arrangement. He uses 450 ohm ladder line and has them suspended about 4 feet above ground. I think he said most of them are around 500-800' in length.
+-RH
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FWIW an avid contester I've met in my travels with 10+ acres of room to spare has about 5 of these in different directions. He uses them on 160M for receive, and has them rigged so he can reverse them with some sort of relay arrangement. He uses 450 ohm ladder line and has them suspended about 4 feet above ground. I think he said most of them are around 500-800' in length.
+-RH
That sounds like a standard Beveridge antenna, rather than a Beveridge-On-Ground. Just sayin'.