DIY

How to DIY an NVIS Antenna AKA Cloud Burner Antenna Using a Mag Mount

Part of being a ham radio operator is to provide communications in times of emergencies. With the upcoming Ohio NVIS Antenna Day, I decided to look into NVIS antennas. NVIS antennas, also known as Near Incident Vertical Skywave antennas have a high angle of radiation. Something on the order of 60 degrees, to straight up to 90 degrees. Unlike UHF and VHF signals, which typically have a 50 mile range with a yagi antenna up high, a NVIS antenna is designed for communication in the 75 – 500 mile range. Sometimes an NVIS antenna is referred to as a “cloud burner” since is directs most of its radiation more upward than a typical antenna.

The idea with a NVIS antenna is to radiate as much power as possible at a high angle and have it be reflected off the ionosphere. From a practical standpoint, NVIS communications occurs at 10 mHz and below. Another part of the NVIS antenna is the fact that it is quite low to the ground. This helps radiate the signal at a high angle, as well as make it easy to deploy. There ar many opinions as to the best height of an NVIS antenna, but everyone seems to agree on aprox. 1/8 wavelength above ground and sometimes less.

I wanted a NVIS antenna that was portable, easy to set up, and cheap (of course). As it turns out, I had practically everything on hand. For my NVIS antenna, I started out with my 2 meter mag mount for my car. Then it was just a matter of attaching a quarter wave wire to the mag mount, then just string the wire horizontally from the mag mount to a tree, or a pole of some sort.

Pages: 1 2 3

How To Bond Ground Rods With Exothermic Welding

At work, I recently put in a ground system for our new antenna system, which requires a good ground system. A critical part of that is properly bonding the copper ground wires to the ground rod. The best way to do that is exothermic welding.

A lot of people call it CADweld, which is a registered trademark of Erico, which is one source. However their less expensive One Shot has been difficult to acquire. In searching the internet, I found a different company that makes the same thing. They call it a Uni-Shot, made by Harger and can be found at tessco.com.

Using this method of bonding ground wires to your ground rods, prevents corrosion, and high resistance connections to your ground rods. If you use a clamp, or other compression method to bond your ground system, it will require cleaning the connections regularly, and still won’t insure a good ground connection.

In this blog post, I will show you how to use a CADweld uni-shot to exothermically weld your ground rods. The photo below shows all of the components of the CADweld uni-shot.

Cadweld Exothermic Weld Components

bond Ground rods with exothermic welding

From left to right, you have the following items:

Uni-shot mold
Ceramic Disk
Metal Disk
Starting powder
Ceramic Lid

Pages: 1 2 3 4

How To Build A 2 Meter Vertical Antenna

I needed to replace my old 2 Meter vertical antenna for the 146 mHz. amateur radio band. The old one had lost its radials and I wasn’t able to hit the various amateur radio repeaters around. So being one who likes to build antennas, here is what I came up with. The Image below shows the materials you will need to build a 2 meter vertical antenna for the 146 mHz. amateur radio band.

Here is the list of parts needed to build a 2 meter vertical antenna:

3/4″ PVC pipe – Length to suit
3/4″ adapter 8xMPT
3/4″THD Dome Cap
SO-239 connector
6ft. 14 GA Romex wire
qty. 4 4-40 stainless screws
qty 8 4-40 stainless nuts
50 ohm coax Length to suit

An inexpensive and readily available way to get 14 ga. copper wire is to go to the hardware store and buy some Romex wire. The first thing to do is to strip the copper wire out of the Romex wire sheath, then you will see a bare wire, a black and white wire. then strip off the insulation from the black and white wires as well. When you are finished, you should have three bare copper wires 6 ft. in length. 12 GA. wire might have probably been better, as it is bigger and stiffer, but I used what I had on hand. Cut 5 pieces of wire, each 22 in. long.

I then straightened each wire as best I could, but they still weren’t straight. So I laid a piece of wood on the floor a bit longer than the wires, laid one wire on the board, and placed another board on top of the wire. Then I stood on the board and rolled the wire between the boards. This made them pretty straight without any of those annoying little kinks in the wire.

Build a DIY 2 meter 1/4 wave vertical antenna

Next, I took the 3/4″ THD Dome Cap and drilled a 5/8″ hole through it. I started out with a 5/32″ drill as a pilot hole, then finished off with a 5/8″ speedbor spade bit.When you are done, it should look like the photo on the left.

Pages: 1 2 3 4

How To Build A 2 Meter Antenna For Bicycle Mobile

Perhaps the biggest problem with taking your HT bicycling is coming up with a decent antenna on your bicycle. This is because the bike doesn’t provide much of a ground plane. I found an article in the ARRL’s Hints and Kinks written by Charlie Lofgren , W6JJZ, titled “The Bike ‘n Hike Special”. Below are the plans for the antenna for bicycle mobile he described in the article.

This antenna is a 1/2 wave vertical dipole made out of RG-58/U coax. The beauty of this design is that it is cheap, simple, and easy to make with readily available materials. The radiator should be 39 inches long for 2 meter operation. What I use for the radiator, is the center conductor of the RG-58/U coax. I start out with a 12 foot piece of coax. Then there is enough left so it can be run up to the radio. I keep my radio in my handlebar bag.

First measure how long the radiator is to be, then trim off the outer sheath, and shield. Next, on the other end of the coax, I cut off a piece of coax that is going to be the shorting stub. The proper length is dependent on the velocity factor of the coax used (see table below). In all cases, I always make the lengths to the long side. This way the antenna can be trimmed in to the desired frequency with a SWR bridge.

Short the center conductor to the shield of the coax at point C

The dimensions for the matching section are dependent on the velocity factor of the coax used.

Dimension	Vel. Factor 0.66	Vel. Factor 0.80
A to B	11.25 in	13.5 in.
B to C	1.63 in.	2.0 in.

Pages: 1 2

How To Build a HDTV Antenna With These Plans

Since my TV antenna was damaged by an ice storm, I needed to build an HDTV antenna. While searching, I found some HDTV antenna builds that used coat hangers. Being 70 miles away from the HDTV stations, I definitely need my HDTV antenna to be outdoors. Coat hangers rust, and end up with bad connections which makes your HDTV antenna useless over time. In this post, I will show you how to build a HDTV antenna.

Additionally, the HDTV antenna builds I have seen don’t seem to have the long range that I need, such as the DB4. So I have come up with a modified version that works well in HDTV fringe areas. The photo on the left is my HDTV antenna that I built. I have also seen where people will take two HDTV DB4 antennas and gang them and then use a splitter / combiner to feed the HDTV antennas. Although this seems to work, my thinking is that adding a second antenna typically yields 3 db of gain. However a splitter / combiner has a 3 db insertion loss. Which is spelled out on the splitter’s package. It seems to me that you are losing what you have gained in ganging two DB4 antennas. My HDTV antenna build eliminates the need to use a splitter / combiner.

Its surprising the number of people that think that in order to get HDTV stations, you have to have cable. This is not true, as TV stations still transmit their signal in what is called Over the air – OTA. So if you live within say, 70 miles of a TV station, you might be able to receive HDTV over the air too, and eliminate your cable bill.

Pages: 1 2 3 4 5 6 7

Build An Indoor FM Antenna With These Plans

The easiest way to improve your FM reception is to build an indoor FM antenna, instead of using your FM stereo’s internal FM antenna. This indoor FM antenna is easy to build, and cheap. It works every bit as good as other FM antennas that you can buy for as much as $100.

In order to build this indoor FM antenna, all you need is two 3/8” dowel rods 48” long, 10 ft. of 20 ga. wire, and some 75 ohm RG-59 or RG-6 coax (for TV’s). All of this can be picked up at your local hardware store. However sometimes hardware stores don’t have dowel rods 48”. If you can’t find any that long, you can always take two 36” dowel rods and tie them together with cable ties to the correct length.

This FM antenna is what is called a Full Wave Loop antenna. The diagram below shows the design of this indoor FM antenna:

The red is the wire, which is to be 30” on each side. The brown represents the 3/8 inch dowel rods. Also notice that the coax is fed from the side. This is not necessary, as typically full wave loops are fed from the bottom. I was interested in receiving one particular station that transmits a vertically polarized signal. Almost all FM stations transmit circularly polarized, which is both vertical, and horizontal polarization. Also feeding the Fm antenna from the side seemed to be a stronger, more reliable means of connecting the coax to the FM antenna.

Pages: 1 2 3