Designing & Building Your Own EH Antenna

EH Web Site

The following documents should be downloaded and read. They demonstrate the principles on how to build and tune an 'STAR' EH antenna on 80M, 40M, and 20M.

Demonstration #4 - STAR configration

Demonstration #5 - 80M, 40M, 20M EH Antenna

www.eh-antenna.com

20M EH - 2" PVC

I build most of antenna out of commonly available parts (PVC pipe and aluminum roofing flashing). These materials are inexpensive and can be purchased at most hardware stores.

The diagram below illustrates a basic for of the STAR EH antenna. It consists of two (2) cylinders and three coils. The spacing is related to the diameter of the cylider.

Depending on the size of the antenna I usually build each section separately and then glue them together to form a complete antenna. In this manner I have smaller pieces to work with and it is easier to run wire down the inside of the cylinders. For smaller antennas just build the antenna in one piece. Below is a picture of an 80M EH antenna illustrating the separate pieces.

PVC pipe comes in different sizes (nominal pipe sizes - same as water pipe). Use PVC and not CPVC (for hot water) also don't use grey conduit as it absorbs RF and will break down under high voltage. PVC pipe comes in different thicknesses, do not use the thin wall except on 3" or larger diameter pipe. Schedule 40 and thin wall pipe is usually what is stocked, use Sch. 40 for 2" and smaller diameter piping.

PVC Pipe Dimensions

Design Considerations

What band is the Antenna designed for: The frequency band will determine the ratio of the cylinder lenght to diameter. For 80M and 40M you will probably want a high angle of radiation, so select a ratio of 10 - 14. On the other bands you will most like be looking for DX so the ratio should be 3 - 5.

What diameter of pipe are you going to use: The larger the pipe, the larger the bandwidth. For a 20M antenna you can go with 1" pipe or larger. For 40M or 80M you should probably go with 2" or larger pipe.

What materials are you going to use to construct your cylinders? Copper foil from the craft supply store is a favorite but, is not too weather resistant. One inch copper pipe can also be used but it is more expensive than other materials. The one inch copper pipe can fit over 3/4" PVC pipe if it is sanded down a slight bit. I use aluminum roofing flashing and secure the end with sheet metal screws every 2 - 3". I overlap the ends by about 1", this makes the width of the flashing 8 1/2" for 2" PVC pipe. Flashing comes in 10", 12", or 18" widths.

What kind of wire are you going to use? I usually use #14 enamel wire. Some of the guys use # 12 insulated house wiring. Both of these are adequate for 100 watts. Some of the guys are using the center conductor of RG-8 for wiring between the top cylinder and the coil (remove the outside shield and just use the center conductor and the insulation - reduces the chances of arcing).

Example

We will design a 20M STAR EH antenna using 2" PVC with aluminum flashing and # 14 enamel wire.

Using the PVC pipe dimension chart above you have a diameter of 2.375". For 20M you would want a ratio of 3, so the cylinders would be 3 X 2.375 = 7.125". So let's use 7 1/4" (makes it easier to measure - it is not to critical).

You will need a piece of 2" X 2' PVC sch. 40 pipe. I always leave myself a little room for mistakes so I would get a piece 3 foot long. ( 2 * 7 1/2 = 15" + 3" [spacing between the cylinders] + 6" for the coils = 24") PVC pipe comes in standard 10' lenghts. Some stores will have 5' pieces already cut for you but check the price as the cut pieces cost about 80% of the cost of the 10' piece. If you intend to make more antennas buy the 10' piece. You will also need two couplings - in 2" PVC they have long one and short ones - get the short ones.

Aluminumflashing (look in the roofing supplies) comes in different widths, 10, 12, & 18". You will have to buy a roll (it comes in different lenghts also - get the shortest roll ~ 10'). You will need a piece about 8 1/2" X 15".

Go to the Coil Design page and enter you data (cylinder diameter [diameter of the PVC pipe], cylinder lenght, frequency, and type of wire). It will then give you the number of turns required for the two coils (Phasing coil and tuning coil - the source coil will be determined after initial tuning. It calculate that you need 10 turns on the tuning coil - make it wit 12 or 13 so you can have some tuning (it is a lot easier to remove turns than add them!).