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tubelab.com 17th April 2011 03:44 PM

DIY TV Antenna 2.0
 
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I made a simple TV antenna from wire several years ago. It was simply hose clamped to a vent pipe on the roof and connected to the TV with coax cable. It served me well for years receiving 30 or so "channels". It was not physically strong enough to handle birds sitting on it, thus it became deformed and reception degraded.

I came home from work Thursday and a storm had mangled it leaving me with two channels. Time for a new antenna. Since this is a DIY forum, this isn't about a trip to Best Buy. It is DIY TV Antenna 2.0.

Criteria:

Total cost ---- under $5. Preferably $0. The old coax cable will be reused. Parts to come from my junk collection.

Mounting------ Clamp to vent stack is OK, but I also have a small mast for my ham radio antenna.

Reception---- There are several Miami stations 14 miles south southeast (azimuth 155 degrees) and several Palm Beach stations 30 miles north (azimuth 5 degrees). I would like to receive as many as possible. There are more stations further north but they are 75 to 100 miles out.

A good place to find out what signals are available and how far away they are is here. Just plug in your particular city:

Choosing the Best TV Antenna for Sunrise, Florida

It is interesting to note that they recommend a $81 antenna with a rotor AND a preamplifier.

The remains of the old antenna is shown.

tubelab.com 17th April 2011 04:06 PM

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Since the signals in my area are from two directions a simple dipole would work fine, and eliminate the need for a rotor. There are no stations listed in the VHF low range (54 to 88 MHz). I need to receive from channel 7 (174 MHz) to channel 49 (686 MHz). A simple wire dipole will not cover this bandwidth.

I came up with an antenna that can be built by anyone. It uses common parts available almost anywhere. The only unique item is a 300 ohm to 75 ohm matching transformer from Radio Shack. I bet the antenna will work without it.

The raw materials.....

Two metal coat hangers, a strip of wood or PVC pipe for rigidity. A small barrier strip to make connection to the coat hangers (they won't solder). Some hardware, a clamp for mounting and the 300 ohm transformer.


Step 1......

Strip back 1/2 inch or so of the coating on the sharp end of the coat hangers. Wire strippers work on the plastic sleeved hangers, sand paper works on the painted ones.

Step 2.......

Bend a small hook in the end if you are using a conventional screw type barrier strip. Teave the ends straight for a "euro strip".

Step 3 ......

Attach the hangers to the barrier strip, and bend to a 90 degree angle.

tubelab.com 17th April 2011 04:12 PM

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Step 4.....

Stretch the ends of the hangers out to form a diamond.

Step 5......

Attach the 300 ohm transformer to the terminal block.

Step 6......

Mount the assembly to a small piece of wood or PVC pipe.

tubelab.com 17th April 2011 04:20 PM

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Step 7........

Attach the coax cable to the 300 ohm transformer.

Step 8........

Mount the completed antenna in a manner such that it is stable. The ends of the wood support should be horizontal and perpendicular to the desired signal. I used a clamp from an old antenna. The installation in the photo shows mounting with the desired Miami signals coming from in front of the camera, through the tall palm trees in the center of the picture. The Palm Beach signals come from behind me and slightly off axis.

tubelab.com 17th April 2011 04:35 PM

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Does it work??????

Well I wouldn't expect this type of antenna to receive distant signals, so don't make one if the transmitters are 50+ miles away, or operating at low power.

My antenna is mounted about 5 feet above the roof, at about 20 feet above the ground. I connected it to an LG 32 inch TV with about 35 feet of coax cable. I ran a scan which resulted in 53 "DTV channels" and 1 analog channel.

All of the full power DTV signals from Miami show 6 signal bars. The West Palm Beach stations show 4, 5 or 6 signal bars. A few of the low power TV stations in both markets show 3 bars but the picture quality is good (no pixelation).

I get signal from two of the Ft. Pierce channels which are 75 miles away and off axis. Both show only 1 bar and the picture is unwatchable.

Dissapointment.....

I can't get Miami channel 9, which is a low power TV station only 14 miles away (actual TX channel is 44). I could not get this one with Antenna 1.0 either, even with a preamp.

Next step.....

I built a preamp for Antenna 1.0. Unfortunately water got inside. Water + electricity + copper = the Green Growth. Time to make a new one. Total cost is $10 to $20.

nic6paul 17th April 2011 05:36 PM

This could be perfect for our break room at work. I think we get one channel...this is cheap enough that I might as well give it a try.

I made one like this when I first moved into my house and it worked real well but got destroyed after we finally got cable.

Richard Ellis 17th April 2011 05:43 PM

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Hi ya George! I'm assuming you did the math.each side of the 'diamond is quarter wavelength? If I recall the terminus of the diamond should come right to the terminal. I don't recall the lobes of this type antenna, front & back?
I "mathed up" log-periodic and a collinear array in school.....never built of course...the collinear was for car mounted cell-phone F ...with a lobing pattern that would reach several factors farther.

__________________________________________________ _Rick........

tubelab.com 17th April 2011 06:21 PM

Quote:

Hi ya George! I'm assuming you did the math
Nope, no math, just a stupid idea to prove a point. This isn't a true diamond antenna since the diamonds are seperated and not even the same size. I couldn't find two hangers that were exactly the same.

This started as a discussion at work. I am an RF engineer designing transceiver equipment for the 100 MHz to 1 GHz range plus a few higher frequency bands. I keep getting dragged into antenna discussions, where I still state that my responsibility covers the DC power connection to the antenna jack (the radio equipment). I don't know much about antennas and don't want to get involved.

There was a design for a broadband antenna which measured bad and worked worse. I joked that a coat hanger would work better. The new guys laugh at some of my statements but the old timers know better. I told people that I could make an antenna out of coat hangers but I never got to it. Yesterday I made it. Today I documented it.

I haven't decided whether I will discuss it at work yet since I may get dragged into antenna work. I may connect it to a spectrum analyzer later today if I get time. I am guessing the response drops off a bit at the high end.

Richard Ellis 17th April 2011 06:29 PM

C'mon!...Antennas are fun stuff! If you got the time & inclination.it is fascinating stuff imagining E & I fields flying around!...trying to "capture" them.
I'll look up the math for this one...........& yeah, theory often doesn't match "real world" results.WAY too many variables.

__________________________________________________ __Rick.........

DF96 17th April 2011 08:22 PM

Assuming that there is no electrical connection where the wire is wrapped at the junction, this is roughly a fat open folded dipole, but with some capacitance loading at the open end. If there is an electrical connection then it is almost a fat dipole, but being thin in the middle and fat at the ends will tend to narrow its bandwidth and lower its resonance.

Given enough signal, anything will receive, and digital will either work or not. Did you mean spectrum analyzer, or network analyzer? My guess is that this would look rather lumpy on a network analyser.


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