On June 12th of 2009, TV broadcasters shut down their analog broadcasting and anyone receiving their broadcasts the way they been receiving them for decades into a world of snow. Up until then people were warned and told they would need a converter on older sets. People with cable or satellite TV were unaffected and the date meant nothing to them. So many people were in this category that if their situation changed, they would be totally unprepared.
Many do not fully understand the change. Those with some knowledge knew that TV was broadcast on the VHF and UHF bands. You had separate antenna jacks on the back of the set. With the change the entire VHF band was vacated and TV was migrated entirely to the UHF band. But just as large a change is how the picture and audio was transmitted.
The old system used analog transmission which used a lot of bandwidth and had a much lower resolution. When you picked up a weak signal it would be mixed with noise, you knew as snow. The new system sends out a digital signal that is decoded and sent to your screen. If you are receiving a weak signal, it drops off entirely, never snow or noise, just nothing to decode.
If you have a newer TV, it has a digital tuner built in to receive these UHF channels and decode them. An older TV can be fitted with an outboard tuner that does the same thing. If you did not have an antenna connected you pick up nothing, no snow, no noise, nothing. Also if you are trying to use the older VHF antenna jack on an older TV you will pick up nothing. The basic rule of thumb is that if you see snow, you do not have a digital tuner or your TV has not been configured properly if you know it does have a HDTV tuner.
Many people had cable TV and didn’t have to do anything to still be able to watch TV, but in this economy, what if you had to drop your cable service? Or suppose there was an incident that caused your cable to go out, would you know how to get the local news on your TV without cable? Having a backup way to pick up your local TV without cable has its advantages. Also if you have a basic cable package you do not get the HDTV quality picture. All the “off the air” stations are HDTV and high resolution, so it is possible you will get a better picture on your local channels directly off the air with an antenna.
If you have a HDTV ready TV or a HDTV tuner, the only thing you are missing is an antenna to pick up the local channels. You can buy an antenna or you can make one pretty easily that will perform as well and likely even better than a store bought one. Most store bought HDTV antenna use some engineering tricks to make them smaller, but every antenna works on a wavelength and a full size antenna will always outperform a shortened antenna.
There are quite a few DIY HDTV antenna plans on the web but most use metal coat hangers bent in “V” shapes. In my experience I found metal coat hangers to be very scarce and the “V” shape not as effective as a triangle so I designed this antenna to bypass these two factors. The antenna I will be showing you is called a four element bowtie antenna. This is considered a balanced antenna so there are two equal sides to each element, so we will need to create eight bowties.
We are creating these bowties out of sheet metal, not real thick so we can cut the metal with simple aviation snips. I used roof flashing which you can find in home centers in the roofing department. They normally come in 8″ X 12″ sheets. Each triangle we make will be 7″ long and 3″ wide which means we can only get seven of them out of a sheet, so we will need two sheets of flashing. These sheets are very inexpensive and I paid less than $1.50 a sheet. Along with some wood, a few feet of wire, a balum, and some screws and nut, and the total cost of this antenna will be less than $10.00.
Our first step is to make our eight triangle elements. We use triangles because this shape creates a broadband antenna; it covers the entire UHF band and not a select frequency. We need this to pick up all the channels.
If your flashing is the standard 8″ X 12″ sheets, the first thing I did was cut off a 1″ strip off the short side making it 7″ X 12″. I just laid it down on the desk and used a ruler and pen, going over it several times to make it visible. You are free to use whatever form you like and if you have a metal scribe available, I am sure that would work even better.
I measured every three inches on one side and made a mark. On the other side I started at 1 1/2 inches and made a mark every 3″ from that point. Then I just drew diagonal lines across the sheet to make my triangle elements as in this diagram.
Be careful cutting your sheet metal as the point and edges can be sharp. Wear gloves while making the cuts and I used electrical tape on the edges. Cut and prepare all eight of the triangular elements.
The next step is preparing the base which I used a piece of 1×3″ pines board that is 22″ long.
Take careful measurements and mark with a pencil. Start at the end and measure 3″ from the end and draw a line. Then measure 5 1/4″ three times and draw a line each time. Next go to the center of each line and measure and mark 1/2″ so you have 1″ of separation. (You don’t need to draw lines down the entire length). Lastly you need to make a center connection at the center of the antenna as shown.
Drill each hole so you will have a tight connection with a #8 wood screw. Drill 10 holes for the elements and center feed and then drill a hole at the top for hanging the antenna.
Assembly is simple. Stick the pointy end of the triangle into the hole you drilled and then bent it to the side. You will have enough space next to it to run a wood screw in the hole with it. The woodscrew and washer will hold down the element and if you like, you can also drill another hole in the element and use another screw to secure it even better. Also place two wood screws and washers in the center to act as our feedpoint for our balum.
The last part of assembly is to wire each element as show in the example picture. The two end elements on each side have a crisscross wire, do not short that out, and use insulated wire. Almost any form of wire can be used and secure the wire by simply passing it under the screw washers.
Our bowtie antenna will have a natural impedance of 300 ohms and our TV set likely has a coaxial jack which is looking for a coax feed with an impedance of 75 ohms. For this we need a balum at the antenna. This also acts as an adaptor to attach a standard cable.
This is a finished and painted first version. Note that it has a small extra piece that keeps the antenna on a small angle. I found that in my instance this works better for me. It is an area you can experiment with. This Antenna picks up all twenty local channels in the Seattle area.
Some final notes, some items like the balum and cable is much cheaper if you use on-line sources. I paid $2 for the balum on ebay where it would have cost $10 locally.
Been doing some experimentation with a prototype and have found a major improvement. I was origonally using some fairly small copper wire to tie my elements together and it occurred to me that something more substantial could improve performance. At the frequencies we are working with, radio frequency energy behaves in what is called “skin effect”. This refers to the fact that the energy travels entirely on the surface of the conductor and not the interior.
Rather than going out and buy a more suitable conductor, we had quite a bit of metal left over and it made perfect sense to use what we had so I decided to cut thin strips of metal and use them as tiebars as shown in the next photo.
Note that I added tape to the bottom crossbar so that it will not short out my signal but this was just an added factor, they do not touch. Now I am not sure if it is because of skin effect or if the wider bars act as part of the antenna better, but I do find a stronger signal now with these wider bars. You have the extra metal, use it this way. Just be careful as this metal can be very sharp when cut with aviation snips and sometimes there are also micro spars that will hurt!
My friend in the Portland area had one of those flat RCA indoor antennas that used to be annoying in how you position it. I replaced her antenna with one of these in her garage and she now gets all the channels and no longer has to fiddle with her antenna.
In the Seattle area I get all my local channels.