Living Well On A Budget

The Post DTV Transition Explained Part 2: How to Build Your Own DIY HDTV Antenna and Save Money

Posted on July 6th, 2009.

This article is Part 2 of 3 in the series The Post Digital TV Transition Explained: Save Money by DIY — How to Build Your Own HDTV Antenna.  As of June 12, 2009, the change to broadcasting only Digital TV in the U.S. is complete.  But you don’t have to pay for cable or satellite TV to be able to watch DTV. You can watch great quality network Digital TV programming for free. What you will need to get the most DTV free programming and the best reception post DTV transition is a good antenna.

Now that the digital transition has happened, if you have an older TV with a digital converter box and antenna, or have a newer television with a built in ATSC digital tuner, or would like to stop paying a monthly charge to a pay service for access to DTV, you will need a good antenna to enhance your reception and reach.  Why pay up to $150 retail for a good antenna when you can build one yourself for very little money. This article will discuss considerations for building your own HDTV antenna, including a LPDA (Log Periodic Dipole Array) antenna my father built for less than $10.

My father is a DIYer, electrical engineer, ham radio buff and a true geek in the best sense of the word.  He has built a variety of TV antennae for use in his home. He does this for fun and is always trying to build a better mouse trap.

Interference, noise, multi-path and, co-channel signals introduced into the channel band can all cause amplitude variations or errors and signal degradation.  Reception of DTV is on an all or none basis — either you will get crystal clear pictures and sound or none at all (there is a brief transition of breakup). Note: The DTV (8 VSB signal) uses eight defined amplitude modulation levels (or steps) of the transmitted RF carrier. The decoder must detect these eight defined level variations to recover the signal in order to provide that crystal clear picture and audio.

To build a good HDTV antenna, my Dad said it needs to be capable of providing the following:

1. Gain – increasing the available signal, by combining multiple signals, based on an unique antenna design.  Note:  This is the preferred way to improving reception vs. external amplifiers that add noise.
2. Directivity – ability to aim the antenna to get the best signal.  There are numerous situations, such as being either near or far from the transmitting site (tower), where you still might not get reception. The problem is usually multi-path (this was seen as ghosting on analog). The signal is received, delayed, bounced off nearby obstacles (far and near) causing errors (Note: your signal meter on your converter box reads errors not strength). Directivity is important in reducing multi-path errors.
3. Broadband Design – Antenna are typically frequency dependent and only work well at one frequency (or narrow range of frequencies).  The requirement to receive channels 2 – 51 (54 – 700 MHz) is huge. Deviation from the design frequency not only renders the gain useless, further losses come into play by higher losses on the connection cable (up to 4X additional loss on 100’ of connecting cable).
4. Coverage of VHF to UHF – With many of the stations returning to their VHF channel assignment, antennas that worked pre-June12th may no longer be adequate and a new antenna required.  The reasons for this are discussed in my post yesterday, The Post Digital TV Transition Explained Part 1.

There are some additional definitions and good explanations about antenna basics for beginners at HDTVPrimer.

Here is a photograph of one of the antennas my father made that he is currently using at home with a flat panel HDTV with the tuner built in. He designed it for the pre June 12^th UHF HDTV station spread in the Boston market (e.g. 470 to 650 MHz). He says it worked like a champ and received all the stations in the Boston/Southern NH area at signal quality levels of between 9 and 10.  His house is at sea level, the antenna is indoors on the second floor, and the stations are 24 to 50 air miles away.

This version of the antenna is 18″ long and has 7 elements, the longest being 15″ and it works as well (perhaps slightly better) than a db4 or the double quad he also made. My Dad made this antenna (elements and boom) from 1/2″ x 1/16″ aluminum stock that he bought at a Lowes home center for about $8.  Construction is pretty straightforward. He used nylon screws and nuts to isolate and attach the 2 booms together.  The elements were fastened to the boom with 4-40 screws and nuts. The piece that looks like a tail at the end of the antenna is called a coupler, which is an impedance transformer to convert from 300 ohms to 75 ohms.

The antenna shown above is based on a rather sophisticated LPDA (Log Periodic Dipole Array) antenna designed for the US government. The break though was no to define the antenna by wave length (i.e., frequency dependent), but instead by angles, The selection of design parameters to arrive at the antenna’s exact physical design specs needs to be customized to the task.

It requires advanced mathematical calculations that my father used an online Java calculator to perform to determine the dimensions and spacing of the elements needed to build a log periodic antenna, given tao, sigma and the lower and upper cutoff frequencies.

This link discusses the selection of tao and sigma http://www.wseas.us/e-library/transactions/communications/2008/27-145.pdf Basically, you can trade off the antenna gain vs. number of elements and boom length.  Unless you’re an engineer or math whiz, this particular design may not be for the novice antenna builder.

Post transition, the design of this antenna will certainly still work, but would have to be recalculated and scaled to cover from VHF through UHF. The exact antenna dimensions and spacing need to be customized based on your own individual location relative to that of the tv transmitters in your local area. Using the exact measurements of my father’s build won’t be optimized for you.

If you’re interested in learning how to build your own HDTV antenna and other DIY techie projects, a great resource is the forum on the LumenLab website. There are much simpler yet very functional designs, posted about in the HDTV antenna thread. For example, the double or quad array bow tie antenna (also known as DB2 or DB4) which can retail for $50+. Many of these design implementations could easily be built by the average person and use common everyday items and tools you probably have lying around the house or garage, such as glue guns, wire coat hangers, cardboard, scrap wood, metal screws, washers, and aluminum foil. There is a good video on how to build an HDTV antenna out of wire coat hangers on YouTube worth watching.

Here is an example of a DB4 posted by Squeeto on the LumenLabs forum made from copper wire, synthetic building wood and cheap cooling racks.

You can find my father’s posts there under the member name Serndipity (spelled as such). Also look for posts by Pitman2, along with various designs, modifications, and lots of good advice.

Now that many DTV stations have returned to their VHF channel assignments, much of what you will find available (both in DIY or commercial antennas), may no longer be well suited for reception. We’re still designing/making antennas like it was 1950, is there a better solution?

Stay tuned… Part 3 of The Post Digital TV Transition Explained, is a work-in-progess that will provide details on how to build an easy, yet very unique,  compact VHF/UHF antenna (i.e.,  low SWR over a very wide band width, high gain, directivity and scalable).  The design is ‘out of the box’ thinking and is very different.

For additional background and information, read the blog posts:

The Post Digital TV Transition Explained Part 1: What’s in it For You? What You Need to Know Now covers why the Digital TV transition happened, how you can benefit, understanding the UHF/VHF channel reassignments, why you might be experiencing reception issues and which DTV option is best for you?

and also How to Recycle An Old Satellite Receiver Set Top Box instead of Buying a Digital Converter Box

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