DIY HD Antenna

9/29/14

 

Three months ago I said goodbye DIRECTV and hello free OTA HD channels. I tell you, TV is like a drug habit that is hard to kick. It was initially hard not able to watch premium channels like Discovery and HBO everyday but three months later I am a recovering addict. Plus, I am no longer spending over a hundred dollars a month for DIRECTV.

Being a do-it-yourself kind of guy with limited budget I set about making the best antenna that rivals commercial antennas costing four times as much. As it turned out there isn't much to it. Some people have even managed to make antennas out of coat hangers based on the very popular m4 design of a guy, known only by his forum name, mclapp. The m4 concept may not be new but mclapp certainly has resurrected the interest of hobbyist around the globe by refining and doing actual field testing of the antennas he has built and shared.

After weeks of perusing through the avsforums.com on the topic, I felt comfortable enough to make my own rendition of the m4 antenna. I will admit I still don't fully grasp all the math and science involved that makes this antenna work so well for so many. The materials I used are PVC pipes, 9 guage galvanized utility wire, 14 guage copper wire, acrylic blocks, screws, washers and 300-75Ω balun. All the materials you can get at HomeDepot. While I won't detail every step it took to put mine together, you can get all the info you'll need from the links at the end of this article. Everything I have learned came from reading materials at those links.

The m4 is a four bay antenna, which is four halfwave dipoles interconnected. Back in the day most TVs came with simple rabbit ears which are dipoles. The m4 essentially has four sets of them.

I constructed the antenna frame out of PVC pipes and welded the pieces together as opposed to gluing pipe fittings. I used my soldering iron to melt the PVC where they came together. The result is a very secure bond. PVC is a great material to use since it acts like an electrical insulator and it's cheap. Some people have used wood but depeding on your region the wood may contain moisture that may impact the antenna's performance. Wood never truly dries and is affected by humidity. So it's best to avoid using wood as a frame.

antenna frame

I elected to go with 9.5" elements. I used galvanized wire and bent them into v-shapes. The 9 gauge is thick enough to give some rigidity and soft enough to be bent by hand.

I cut four acrylic blocks and glued them to the PVC stand-offs. The blocks provide a flat surface for the elements to lay flat on. Screws and washers are used to secure the elements. I used 14 gauge copper wire for the phase lines which are 1.25" apart. Also, I soldered all the elements to the phase lines.

blocks

Mclapp mentioned using either the long or short crossover for the phase lines. The difference between which way is better is negligible, however the short crossover has a minuscule edge so that's what I used. The purpose of the crossover is to keep the two outer bays in phase with the inner bays. For instance the top-most bay is a quarter wave out of phase with the adjacent bay and so is the bottom bay with its adjacent bay. The crossover remedies all that.

crossover

I had a push-on F-connector balun so that's what I used. I hope to replace it someday with a screw-on type. It will be an indoor antenna so it's not a big issue for me. If you are making an antenna for the outdoors be sure to make it as robust as possible including the use of a weather-proof balun.

balun

Here is my complete m4 antenna. Installed in the attic one story above ground I got phenomenal results. Four TVs are connected to the antenna without the aid of an amplifier. Signals are strong even when raining. It does help that all the stations serving my area are at one mountain top and I have line of sight to them thirty miles away. I am surprised how strong channels 8 and 10 are coming in considering the antenna is optimized for UHF. Perhaps those stations are broadcasting with more power. The peak appears to be on channels 15 and 17. I also get strong signal on channel 51.

m4 antennam4 antenna

Overall, I am happy with the mclapp m4 antenna. I heard the rumors, I read the stories, and I am now a witness to it. The m4 is one nice antenna. Notice I did not even use a reflector. I can only imagine the improvement it will add. For the time being I am content with what I am getting. Every now and then I would even pick up redundant channels from 90 miles away. Perhaps a reflector could lock-in those signals. I am even thinking of doing perhaps an m6 in the near future. Most of the supplies I had on hand bar the utility wire. I figured the antenna cost $20 to make, but with materials I have left over I can probably make another two.

 

 

 

 

Sources:

http://www.hdtvprimer.com/antennas/types.html

http://www.hdtvprimer.com/ANTENNAS/basics.html

http://m4antenna.eastmasonvilleweather.com/Drawings/PDF%20Drawings.html

http://www.frontiernet.net/~mclapp/Antennas/

http://www.avsforum.com/forum/25-hdtv-technical/798265-how-build-uhf-antenna.html

http://www.dtvusaforum.com/dtv-hdtv-reception-antenna-discussion/25057-antenna-test-data-4-bay.html

http://www.tvfool.com/?option=com_wrapper&Itemid=90

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