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KFF Homebrew Tips

 
 Weather Resistant Beverage UNUN Construction DE KFF
 
 

 The cast aluminum box is an electrical department item. Made for outdoor lighting junctions etc. This one is called a single gang, three hole. A gasketed blank cover is selected to fit, along with some threaded aluminum plugs. Stamped right on the box and cover, it says "Suitable for Wet Locations". Smear a little SILICONE GEL on the edges to keep the gasket supple:

 
 
 
 

In order to mount the Brass 5 way binding post, one of the hole plugs was punched using a 1/2 D punch. This makes a hole with a flat side, and that mates perfectly with the connector, so that it wont spin. Brass nuts hold the 5 way assembly secure, and the plug is bottomed out in the top hole. A few drops of Locktite Outdoor Fixture Adhesive (Home Depot) keeps the plug in place, and further waterproofs it.

Inside you can see the Toroid, it is wound according to designs in ON4UN's book, Low Band DXing, and this one is a large core. In many applications a similar transformer on a smaller core is used. Fiberglas tape is wrapped around the homemade aluminum bracket, which itself is held down by a stainless steel screw. The TyRap secures the core from moving, and simply passes through two holes punched in the bracket: 

 
 
 

Notice the routing of the wire coming from the antenna wire. It is made to run parallel to the side of the box, with a little space in between. This is merely an effort to control the arc path in case of lightning. Later designs included spark gap devices as well. Notice the conduit fitting on the bottom panel. . I use a 6 foot section of copper water pipe as the ground rod, the top of which slips into the conduit fitting, supporting the BevBox. A separate heavy ground wire is clamped to the rod and attached to the big brass screw on the bottom panel.lightning ground is provided via the big brass screw shown on the bottom panel. (Note, copper pipe makes a good, inexpensive ground rod. To install it, slip a regular ground rod inside then work the pair up and down in a shallow hole filled with water. On each stroke, it will go deeper into the earth, no pounding needed. When it is as far as you want, slip out the rod for use on the next pipe).In this unit the silver/Teflon type M (UHF) connector comes out the bottom also: 

 
 
 
Some versions have the connector coming out the back:
 
 
 
 
Winding the transformer:
 
It seems that every LowBand DX'er prefers his own brand of transformer.
 
Large Core, Small Core, Binocular Core etc.:
 
 
 
Whatever your preference a few standard mechanical techniques apply.
 
 
Wrap round core with Fiberglas Tape to keep the wires from chaffing:
 
Dip the finished transformer in Q-Dope:
 

The third hole is sealed with a plug in this instance.

Just before we seal her up, a packet of dry Silica Gel in wedged in place: 

 
Sealed boxes used outdoors need the breathe a little bit. Screened hole plugs work great but are a bit hard to find today.
In my designs, a small hole is drilled in a brass screw, which is then threaded into the body of the box. Small
enough to block insects but pass water vapor. This weephole can be easily replaced should an insect decide to plug it up!:
 
Final Thoughts:
 
For reference, see my other eHam article "Beverage Hub".
My Beverage's (all single wire) are designed to use 75 Ohm cable, which I picked up for nil surplus.
They are installed all around a 10 acre tract, some far from the shack.
 
Some of my Beverages are fed at both ends. These use a version of this BevBox but with a
Bias Tee and relay inside. The relay will drop the transformer out and insert a load resistor
instead. At the other end, the load resistor is dropped out and the transformer inserted.
At the Bev Hub, the particular coax is selected and sent to the shack. Some of the
Beverage's terminate at the Bev Hub, that is their single wires are fed from there.
These are relay selected and matched by the Bev Hub switching.
 
One is a 500' #10 Ga. copper wire running off the bluff, in a southerly direction. It has worked me
some outstanding DX contacts.
 
Lightning is a real concern when your whole house and property is 150+' above the surrounding ground level.
My station was designed with lightning protections as the primary design element with
feedline loss coming in as priority #2.
 
Later on I will discuss my "single point grounding system", tower grounding, proper installation of TVI, LP filters and lightning arrestors, AC power protection, wind,feedline loss concerns
and other factors that went into the original layout of my 7 tower HF-UHF system on the edge of this bluff:
 
 
 
 
 
See you in the pileups,
Happy Building, Geo>KFF