Beverages for Listening, II

Contained is the second half of the article, due to the overall length limitations of wordpress.

Wire-

For my simple BOG antennas, I use 14 gage THHN house wire, which is sturdy and double insulated, and comes in a variety of colors. If you want the antenna to stand out, use bright red or orange; I usually prefer the brown wire which blends in nicely with the ground. If you are piecing wire together, make sure the connections are soldered tight and that they are fully and completely waterproof.

Ground rods-

I take an 5/8 diameter 8‘ ground rod and cut it in half; this gives me two ground rods for about $12. If your soil is not rocky, you can use copper pipe for a ground rod, reinforced with a wooden dowel at the top to reduce mushrooming, and if budget is a particular concern, scrounged 1/2“ galvanized pipe will work too, especially with a couple of bare copper wires looped through the pipe and up the outside. If really stretched, a piece of rebar would probably work, too, although I have not tried it.

Enhancing the conductivity of the ground is a good idea; Epsom salt (magnesium sulfate) solution is the ‘school answer,’ and it works very well although I would not use it with a few feet of any concrete structure, but urine works too, and so does plain water. If you use urine, keep in mind that if you are moving around you’ll be handling the box and the ground rod, so remember the restroom sign- “We aim to please- we hope you aim too, please!”

Impedance transformer-

transformer.pngThe impedance of a BOG antenna runs from about 200 to 300 ohms, depending on soil type, height above ground, and other factors; you’ll need to find an approximate match between the antenna impedance and the transmission line you are using. If you are using 75 ohm RG6 television coax, as many do, then an impedance ratio of about 3 or 4 to 1 is about right. This is what one looks like; I use a 73 mix binocular toroid (Fair-Rite p/n 2873000202) with 24 gage teflon and 26 gage enameled wire. You can buy these from Mouser or Allied very inexpensively; I get a couple dozen at a time and they cost 50 cents apiece in bulk. A group buy will save money over one-at-a-time, or you might find them at a hamfest. For less than a dollar you can make a good BOG transformer.


Some folks directly connect the coax to the antenna and ground, but there are a couple of issues with this approach. One is that doing that couples the outside of your coax to the antenna and enables your coax to become part of the receiving array, eliminating the directional ability of the Beverage and increasing reception of unwanted signals and noise. The other is that the significant mismatch in impedance will reduce the already low signal level still further, and may make your beverage a bit ‘deaf’. It can and has been done, but such shortcuts do significantly impair the perrformance of the BOG. Better to make a transformer, even a field expedient out of a nut or a small piece of pipe.

trans2.pngDon’t get too panicked about making a transformer or impedance matching. If you don’t know what impedance coax you have, then do this: put three turns of insulated wire through both holes of the binocular core and leave 4“to 6“ legs. This is the primary, and hooks to the coax, one side to ground and one side to the center conductor or hot lead. Then run 5 turns of wire through both holes of the binocular core and leave 4-6 inch legs. This is the secondary and one leg goes to the Beverage wire terminal and one goes to the ground clamp. If I had to make a BOG from field expedient materials, I’d use a chunk of Cat 5 or Cat 6 cable for wire, and a steel hex nut for a transformer core. As good as my ferrite binocular toroid? No, but it will work.

It is a good idea to weather proof the transformer assembly and the connections to the antenna and the coax; here is how I do it.

I spent about $6 for the box, $2.50 for the SO-239 connector, about $3.50 for the two zinc ground clamps, and about $2 for the brass nuts and bolts from Home Depot. I put the SO-239 on the bottom of the box (3/4“ hole with 9/64” for the brass attachment bolts) , the ground clamps on the back (1/4“ holes) and I pick a side for the Beverage wire terminal (3/16“ hole) Here is another view –

trans3.png

As a field expedient one could do well with a cottage cheese container or any sort of plastic container sealed with tape or silicone sealant.

One needs transmission line to go from the transformer at the end of the BOG to the receiver; typically this is RG58 or RG6 coax, but you can use twisted pair line or even 16 gage insulated landscape wire which has an impedance of around 125 ohms; if you do this, then adjust the transformation ratio accordingly when winding your transformers. I ran across a 500‘ roll of new old stock RG6 for $20 at a ham-fest recently and this cheap coax works just fine for short term use. Longer term, the flooded quad shielded coax sold by DX Engineering and others is a better bet, as mice and other vermin apparently don’t like the taste of the goo that fills the coax.

RG6 is bigger and heavier than RG58, so if weight is an issue, use RG58. If you scrounge around you can often find perfectly good used coax being pulled out of a remodeled home; if you ask the electrician he may simply give it to you. Home Depot sells a 500‘ roll for $50, or 10 cents a foot. If you are on a typical suburban lot, you probably won’t need more than 100‘ of coax; another opportunity for a group buy.

When using coax, I use coax connectors to join things together, as this makes it easy to disassemble and relocate the antenna system; RG59 adapters for solder connected pl-259 (common VHF connectors) work well for RG6, and RG58 adapters are readily available commercially. These are probably cheaper for lower volume operators to do, but you do need to solder the connections, which may take time and if you haven’t done it, you are likely to ruin some cable and connectors learning how. I messed up my share of connectors learning how, but after over 40 years in radio and electronics I can do a good soldered PL-259. (A quick tutorial- the secret is being able to apply LOTS of heat very quickly and precisely to avoid melting the insulation of the cable and the connector. Silver plating helps, and so does Teflon insulation…)

These days, though, I don’t solder most of my connectors. I make a lot of cables and antennas, so I bought the required commercial crimping tools, and I mostly use crimp-on connectors for my cables as they are much quicker to produce, especially with the commercial coax prep tools available for RG-8, RG-6 and the smaller cables. You may have somebody local to you that has these tools and can make your cable up for you, or you can buy commercially made coax assemblies from dealers. Any PL-259/SO-239 connector/connection is NOT waterproof, so I waterproof these connectors and their connections with a combination of liquid electrical tape, Coax seal (moldable rubber tape) and regular hand wound electrical tape.

So, you have your BOG wire, your transformer box, your ground rod, and your coax with appropriate connectors. Drive the ground rod, attach the Beverage box to the rod with the ground clamps, attach the wire to the box and stretch it in the desired direction, and attach the coax and run it to your receiver input. Waterproof your connections if they are going to be there for more than overnight. Don’t get too hung up on maintaining a perfectly straight antenna; minor zigs and zags make no difference, and some up and down in the wire run doesn’t much matter either.

Compare the signal with what you hear on an elevated dipole or vertical transmitting antenna. Be prepared to be amazed at what you hear, and DON’T hear! You will hear broadcast band stations in your chosen direction that you cannot otherwise hear, day or night; you will hear 150, 80 and 40 meter amateur signals that were otherwise unreadable; and you will be able to pick up shortwave news broadcasts that have information you will never hear on the mainstream media. What you won’t hear is about 6-9 S-units of noise, and that is the best part. Comms UP! Enjoy your Beverage!

73, Keypounder.

Material list Cost

100-150 feet of insulated wire $7 to $15

4“ x 4“ x 2“ insulated PVC electrical box $6

1 ea #10-24 2“ brass bolt

3 ea #10-24 brass nuts

4 ea #10 brass washers

( the #10 hardware makes up the Beverage wire attachment point)

2 ea #6-32 3/4“ brass machine screws

3 each #6-32 brass nuts

4 ea #6-32 brass washers $2 or less net in bulk

(the #6 hardware holds the SO-239 socket to the PVC box)

1 SO-239 socket (recommend silver plated with Teflon insulator)

2 each PL-259 VHF plugs with adaptors $6 net

2 zinc ground clamps $4

50-150‘ of RG6 coax cable $5 to $15

Misc electrical tape and liquid tape, allow $5

Ground rod $0-$12

Tools-

Multimeter (check coax and beverage box for connectivity)

Soldering iron (100 watt plus recommended for PL-259 connectors)

60-40 electronic solder (DO NOT use acid core, get rosin core flux solder)

Drill bits- 9/64 for the #6, 3/16“ for the #10, 1/4“ for the ground clamps.

Reloading reamer to widen the hole to 3/4“ for the SO-239 mount.

Screwdrivers and nut drivers for the screws and nuts (Leatherman tool works)

Pocket knife or coax prep tool.

Bibliography-

Low Band Dxing” 5th Edition by ON4UN, John DeVoldevere.

Chapter 7 is on listening antennas, and section 7.2 is all about Beverage

antennas. The BOG section is 7.2.12, page 7-84.

The ARRL Antenna Book” 13th Edition. If you are interested in antennas, this is a must-have reference. If you are buying a used copy, make SURE that you get the CD-rom that comes with it; EZNEC and much good added information is on there.

Web links of note-

http://www.antennasbyn6lf.com/2015/04/nec-modeling-of-wire-close-to-andor-buried-in-soil.html (Rudy Severns, N6LF, has done some very good work on antenna research and design; his whole site is of interest to any antenna afficianado)

http://www.qsl.net/wb5ude/bog/

http://www.qsl.net/k1fz/bogantennanotes/

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5 thoughts on “Beverages for Listening, II

  1. Pingback: Brushbeater: Beverages | Western Rifle Shooters Association

  2. Good stuff, I always learn something at this site !
    But I’m not sure why you chose two main components
    -The RG-6 a TV system coax. Why not use RG8X? Cost?

    For a balun — why not a 4:1 UNUN ? (I’m thinking a commercially available one ). Also, I’ve seen write-ups on “beverages” that call for a 9:1, ?

    Thanks

    Liked by 1 person

    1. RG6 is cheaper and lower loss, and as NC Scout points out, it makes no difference in performance.

      Listening antennas have different design criteria than transmit antennas, and the goal here is to eliminate common mode signals, and isolate the antenna and feed line from the receiver. You want to keep the noise out of the receiver. Beverages above the ground have a higher impedance than BOGs, hence the lower impedance for the BOG.

      Liked by 1 person

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