Home‎ > ‎Pursuits‎ > ‎

HDTV_Antenna

2/21/2009 -- A YouTube or Google search on homemade HDTV bowtie antennae will bring up a number of projects.  Most of these are made out of coat hangers, screws, and washers.  I decided to built one of my own designs out of copper with soldered connections.  I consider the project a success!  The final result worked well, and the only item I needed to buy was a 300-ohm to 75-ohm transformer (less than $2 at Lowe's home center).

Theory -- Reading the theory behind these types of antennae actually took longer than making the antenna.  Fundamentally, the antenna is based on the concept of a dipole antenna, sized to a wavelength in the UHF TV broadcast band.  The purpose of the "bowtie" aspect of the antenna is to "de-tune" the resonance frequency so that its response if more uniform over the TV band.  The number of bowties seems to be optional, with the notion that the more, the better.  I had enough scrap wire for six bowties.  This type of design requires an even number of bowties, with the tap point for the coax in the middle.  The spacing between the bowties also seems to be non-critical.  I decided to vary the distance, on each side of the tap point, while keeping the design symetrical on each side of the tap point. 

From my location I do not have multipath concerns, nor concerns about conflicting signals from behind the antenna.  If I did have these issues, the solution is to mount a wire mesh behind the bowties, at a distance of about four inches.

Thoughts on Construction Technique and Materials -- I decided to use some scrap #12 and #14 solid copper house wiring.  The #12 copper wire is almost as stiff as coat hanger, so I used that for the whiskers.  I used the #14 for the feed wires that connect the bowties.  Since the feed wire needs to criss-cross itself between bowties (except where the center tap is), I decided to run the feed wire from side-to-side through the wood, such that the feed wires would be insulated where they criss-cross.  Since I plan to permanently mount this antenna in the attic, I was not concerned with wind resistence nor wood rot.  Therefore I used a piece of scrap wood that was less than a half-inch thick.  Finally, the copper bowties were soldered to the feed wires.  This gave me the chance to finally use the soldering attachment to my propane torch set!  As you will see in the photo, Some of the wood got charred until I got the hang of it.  With the feedwires strung through holes in the wood, and with the bowties soldered in place, I found no reason to use any screwed in this design.  At the end I did add a plastic tie around the 75-ohm transformer lead, for strain relief.

Testing -- I connected the antenna to the HDTV with a 10-foot coaxial cable, and clamped the antenna to a ladder, raising the antenna as high as possible.  I aimed the antenna toward the Tampa Bay TV antenna farm (about 32 miles away), and ran the TV through it's auto channel finder routine.  The TV found VHF analog channels 3, 8, 10, and 13, and digital channels 3.x and 13.x, but 8.x and 10.x were missing.  I received all the UHF analog and digital channels that I expected.  I experimented with aiming the antenna in other directions, and was eventually able to get digital channels 10.x, but I was never able to get 8.x.  I am hopeful that getting the antenna up in the attic, which would raise it another ten feet or so, will make a big difference. 

In the experimenting I also lowered the antenna (off the ladder).  Several digital channels dropped out completely.  I also tried turning the whole antenna sideways (so the whiskers point to the ceiling and the floor), and that made reception impossible on all channels.

If I were closer to the broadcast towers, I would not need to put the antenna in up higher in the attic.  If that were the case, I would be tempted to paint it the same color as the wall, and maybe hide it somehow behind a painting, drapes, or fake plants or something.

Here are some photos of the construction process and the final results.

ą
Art Stadlin,
Feb 21, 2009, 7:22 AM
ą
Art Stadlin,
Feb 21, 2009, 7:22 AM
ą
Art Stadlin,
Feb 21, 2009, 7:23 AM
ą
Art Stadlin,
Feb 21, 2009, 7:23 AM
ą
Art Stadlin,
Feb 21, 2009, 7:23 AM
Comments