DIY Build your own HDTV Antenna

Posted on July 29, 2008. Filed under: Entertainment, Home & Garden, Uncategorized | Tags: , , , , , , |

Please Note:  on July 6, 2009  I posted an updated version of this article which includes the 4 key things every good antenna must have on LivingWellonABudget.com called The Post DTV Transition Explained Part 2:  How to Build Your Own DIY HDTV Antenna and Save Money

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

Stay tuned and subscribe to the www.LivingWellonaBudget.com 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.

This is the original blog post from last July, 2008:

TV stations are now broadcasting both the analog (VHF) signals and the digital (UHF) signals. In February, 2009 analog will go away. Some of the stations will return to the old channel assignment which will be in the higher VHF range. TVfool.com will give you all the info for the stations, channels and signal ranges in your area. There are also some definitions and good explanations about antenna basics for beginners at HDTVPrimer

My very first post was about switching from cable television to free Digital TV and how I did it. In that post, I mention that I am currently using rabbit ears perched on top of my tv set. I also mention that my father, a true geek in the best sense of the word, has committed to building me a better antenna which I have yet to receive. I think he is contemplating design and packaging for shipping from Massachusetts to California, most likely with some assembly required on my part. He also works full-time as a sales executive in the IT industry, so his free time for his hobbies is limited.

Here is a photograph of one of the antennas my father made that he is currently using at home with a flat panel HDTV. He designed it for the UHF HDTV station spread in the Boston market (e.g. 500 to 650 MHz). He says it works like a champ and receives all the stations in the Boston area at signal 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 28 air miles away.

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 by the US government. 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. Unless you’re an engineer or math whiz, it may not be for the novice antenna builder.

By making it longer with more elements, my Dad says it will beat the pants off of anything you can make or buy. It can also be scaled to cover from VHF through UHF. He feels it’s his best effort to date, although he is constantly looking for ways to improve it or “build a better mousetrap.” To that end, my father has been scouring his local area for a discarded or unused Dish TV satellite dish to design an antenna around. This includes checking out the free “swap shed” at his town dump.

If you’re interested in learning how to build your own HD TV 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.

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15 Responses to “DIY Build your own HDTV Antenna”

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Looking from other sources on the Internet, it seems that for the LPDA the load should be on the opposite side (next to the longest dipole.)

According to my father, the LPDA feed point (e.g. where the transmission line is attached) is always at the front (see figure 1 at http://www.physics.adelaide.edu.au/~dmcintos/docs/Log-Periodic.pdf).

Since the antenna is usually attached to a mast, the transmission line is routed back along the boom (see figure 7). Since a LPDA for UHF channels is small, the mast is attached at the rear of the antenna (and it only appears that the transmission line is attached at this point).

Do you have the actual measurements of how far the elements are from each other, and what length each element is? I would like to replicate this, if possible. Thanks.

Hi RS,

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.

From http://www.tvfool.com/ you can enter your zip code and find the available stations and frequencies where you live and watch television.

This link discusses the selection of tao and sigma.

http://www.physics.adelaide.edu.au/~dmcintos/docs/Log-Periodic.pdf

Basically, you can trade off the antenna gain vs. # of elements and boom length.

This site has a Java calculator applet which calculates the dimensions and spacings of the elements needed to build a log periodic antenna, given tao, sigma and the lower and upper cutoff frequencies.

http://www.fortunecity.com/skyscraper/jolt/345/LogCalc.html

What about adding a MAR-8 (dc-1000Mhz) amp
after the balun, before the conv. box input
to boost the signal 25 to 30dB ? Simple chip
transistor, 150 ohm pull up, two .1uf caps
(input and output isolation) 9V battery

Hi FPuccetti,

According to my father, this will not work well for the following reasons.

The key to reception is maximizing signal to noise ratio and minimizing signal distortion(s).

This begins with the antenna design, which needs to provide sufficient gain and reject multi-path signals (a.k.a. ghosting in analog TV). Adding the coax induces loss which degrades the signal to noise ratio.

Therefore an amplifier should never be added on the receiver end (will just amplify a poor signal). If more gain is needed, the amplifier should always be at the antenna/coax end.

Additionally, the MAR-8 is a poor choice because it’s noise figure (i.e. 3.1 dB) is high, which will further degrade the signal seen at the TV’s tuner.

It’s 25 – 31 dB of gain is too high and likely to over load the TV’s tuner (which will cause inter-modulation distortions.

The signal meter on a DTV converter or TV does not measure strength. It measures ‘signal quality’ (e.g. errors in the bit stream) that are caused by insufficient signal to noise ratio, additional noise and / or distortions and multi-path.

Sometimes an amplifier can be beneficial….but only when it is located at the antenna end, has a low noise figure (1 dB or so) and only the required gain to to off-set the losses from a long run of coax.

Your antenna is interesting. I see in the picture that the horizontal pieces alternate sides of the connection buss up the middle.
So, you can pick up VHF with it, or at least the top half of VHF (7-13)? I also wonder if the coat-hanger bow-tie models will? Looks like my PBS station is staying on VHF-9.1. But UHF is easy. At 30 miles, I can get all but one available UHF (it’s the opposite direction) with a single coat hanger bent into a loop, hanging out the window.

I need specific dimensions on parts used on dad (serendipity) 18″, 7 element, longest 15″ antenna…and Squeeto’s cooking rack antennas. I have built and modified 2 “coat hanger” wood, washer and screws using 14ga. romex stripped wire.
Can get all stations in Tampa area except channel 8 which I can get by using the pass thru w. my Digital Stream DXT9950 converters from Radio Shack. Want to experiment with others. Use 14ga copper loops (up North) connected directly to coax stub with small black transformers (

great analysis! how do i determine exact vhf or uhf frequency for my antenna length

Quarter-wave antenna:
Length in feet=234/frequency in megahertz
Half-wave antenna:
length in feet=468/frequency in megahertz

Use graphite paint (EZ-Slide) to paint an antenna on any surface. Use graphite glue (Google wire glue) to secure your leads.

The LPDA he is showing is for UHF signals. All of that is explained on Lumenlabs site. The elements (horizontal pieces) do alternate so that the back element is being fed from each side of the 300ohm > 75ohm balun. then the next element in is fed by opposite sides of the balun. here are the specs of the antenna like the one above.
cuts:
2 x 18″
2 x 7.5″
2 x 6.125″
2 x 5″
2 x 4.125″
2 x 3.5″
2 x 2.75″
2 x 2.25″

spacing from smallest elements (front of antenna) to rear:
.25″
4.5″
8.25″
11.25″
13.75″
15.75″
17.5″

so you have
.25″ space
1st element
4.5″ space
2nd element and so on.
create a login for lumenlabs and then go here to see the measurements then a few more posts up to see his antenna.
http://www.lumenlab.com/forums/index.php?showtopic=9613&st=850&p=259515&#entry259515

Just a minor correction to the second picture. That’s a DB2, not a DB4.

Very nice UHF LPDA, btw.

Do you think your father would share the dimensions for the log periodic antenna he made? 500-650 MHz pretty much covers UHF broadcast TV and would work in many (most?) areas, including Denver where I live. The reason I ask is I used to be involved heavily in communications, and log periodic design can be tricky in it’s implementation … so it’s great to have a proven antenna to work from.

Thanks.

Woops! Please delete previous comment from a few moments ago … didn’t see the recent posts.

Thanks again, this is useful info.


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