I just wanted some place to collect some information about building your own HDTV antennas. The kids and I are going to have a little fun building & testing some antennas. I'll be updating these first several posts later with more information.

Feel free to contribute.

Frequencies and Wavelengths
In my area, the local digital channels are broadcasting from channel 25 to channel 51. The "center" between these two channels is channel 38. The frequencies and wavelengths for these channels are calculated as follows:
Our antenna design should attempt to include this range, and will probably be designed for our "center" channel (38).

Materials
Just about any old metal is good for constructing an antenna. Copper & aluminum are best, but steel works too. We'll probably use aluminum foil and coat hangers for the most part. Maybe I'll try to pick up some cheap solid wire too.

Dipole antennas

A dipole antenna is one of the simplest antennas. It radiates (or receives) in a "donut" pattern around the axis. So, if you keep it vertical, it will receive signals from every direction (which is not necessarily good - multipath can screw up reception). If you keep it horizontal, it will receive best in two directions - in front & behind (assuming there are no satellites beaming straight down, or you would pick those up too).

The entire length of the dipole should be half of a wavelength (9.5" long for channel 38). A half-wave dipole has an impedance of 75 ohms, so it can be connected directly to coax (center conductor to one half of the antenna, shield to the other half).

Note that your good old "rabbit ears" antenna is just a dipole antenna. Ideally, you should have the rabbit ears sticking out straight horizontally, locate the antenna as high as possible, and adjust the length of the ears to match the frequency of the channel you're trying to pull in.

bowtie antennas

I haven't found too much information on the theory of bowtie antennas, but the little I've found seems to simply say that it offers better bandwidth than a simple dipole. It also appears that the length of the bowtie is about 3/4 of the length of a dipole for the same frequency (so about 7" wide for channel 38). The reference seems to suggest that the bowtie should be 1/3 as tall as it is wide (about 2.5" tall?).

Taking measurements from a Channel Master 4221 quad-bowtie antenna, each bowtie is 16" wide and 5.4" tall. That keeps the 1/3 height-to-width ratio, but is a lot larger.

Somebody else has taken measurements of a Terrestrial Digital DB2 antenna. Those bowties were about 13.7" wide and 3" tall. We might have to try some different sizes.

Here's a picture of a double-bowtie antenna that has solid bowties: link

Folded dipole

A folded dipole should be an entire wavelength long overall, so physically it's the same size as a half-wavelength dipole. The impedance of a folded dipole antenna is 300 ohms, so a balun should be used to connect it to coax. Like the bowtie, it's supposed to have better bandwidth than a regular dipole.

Quad antennas

The cubicle quad antenna is a pretty simple design. It is just a loop of wire formed in a square shape. It offers better directivity and more gain than a dipole. Each side is 1/4 wavelength long. I would expect the impedance to be the same as the folded dipole, 300 ohms, so a balun should be used to connect it to coax.


A dual-quad antenna is composed of two square-shaped loops. It apparently has an impedance of about 75 ohms, so no balun should be necessary. Confirmed from this post.

Log Periodic

A fairly complicated antenna to design & build, so I probably won't bother. There are several calculators available online to help you design one for whatever frequencies interest you. These antennas provide very high gain & directivity.

Loop Antennas

A loop antenna is another popular old-time UHF antenna. It is similar to a simple quad antenna. The circumference of the circle should be equal to the wavelength. The impedance should once again be 300 ohms, so a balun is necessary for connection to coax.

Hey garsh, wanna build me a HDTV first?

GO PENS!

Reflectors
Back to the topic, we can place a reflector behind any of these antennas. Reflectors can be anything from a single piece of wire, to a wire grid or mesh, to a solid plate. I'll probably use a piece of cardboard wrapped in aluminum foil. A reflector makes an antenna more directional by doing two things. First, it helps block signals that are arriving behind the antenna. Second, it reflects signals from the front back to the antenna. This reflecting could either enhance the signal, or subtract from it.

To increase it, the reflector should be 1/4 wavelength behind the antenna. For channel 38, this means the reflector should be 4.8" behind the antenna. However, this post suggests that the reflector should be 0.148 wave length from the antenna, at least for a dual-quad antenna. I'm not sure where this number comes from though. I suppose I could just hold a reflector behind the antenna, move it back & forth, and see how it affects reception.

There is also a corner reflector antenna which we may also want to try.

I currently have a 30 year old VHF/FM/UHF combination antenna in my attic, roughly aimed towards the Pittsburgh transmission towers. It looks something like this:

It's basically a V-shaped log-periodic antenna (the larger part, for VHF & FM) combined with a yagi antenna with corner reflector (the smaller part in front, for UHF).

I will be comparing our homemade antennas to this one. If any of them look promising, I'll run them up to the attic and see if it can outperform this beasty. It's unlikely, but you never know.

Multiple Antennas
Many of these simple antenna designs can be improved simply by connecting several antennas together. You need to be careful about aligning the antennas together, and how you connect them, to make sure that they add their signals together instead of canceling each other's signals out.
Here are pictures of 2, 4, and 8-bay bowtie antennas:

I have the one in the middle ($25 shipped). Works great

Well, the kids and I have run through some preliminary testing. We created three simple antennas:

• Dipole
• Loop
• Bowtie (form bowtie)

We used channel 42 as our test channel, because our current attic antenna can only pull in a 40% signal for it. The testing was done in the bedroom, with a roughly 5' long coax, while the attic antenna has roughly 17' of coax.

Surprisingly, the bowtie antenna did the worst. The loop was slightly better than the dipole. Both the loop and dipole got close to 40% signal.

But then, I took an old cookie sheet and held it behind each of these antennas. The dipole shot up to about 70%, and the loop antenna went up to about 77%!

So, I think we're going to try a double-loop next.

I built both a double-loop and a quad-loop. They seemed to work better than the single loop.

Next, I took a large piece of cardboard, covered it with aluminum foil, and used this as a reflector behind the antennas. It seemed to help.

But then the moment of truth. I took the quad-loop antenna with reflector up into the attic, and used it in place of the current antenna. Once I did this, the two strongest stations were still strong, one strong station was completely lost (I have no idea why, very strange), and the one weak station that we were using during our testing was no better than with the attic antenna. So my guess is that the ~18' of coax between the antenna and the TV must be attenuating the signal a good bit.

So, next I'm going to look for a deal on some type of antenna amplifier.

Just a small update.

I've switched from the VHF/FM/UHF combo antenna to the homemade quad-loop antenna with no reflector. Since Pittsburgh PA & Youngstown OH are almost in exactly opposite directions from my house, I can pick up stations in both cities with a single bidirectional antenna. A loop antenna is a bidirectional antenna, as long as you don't have a reflector behind it.

So basically, I doubled the number of digital stations I receive by switching to the homemade antenna.


P.S. - the one strong station that I mentioned "losing" with the loop antenna is coming in again with the loop antenna. I'm not sure what was wrong before.

After installing an Insignia Digital-to-Analog Converter Box on one of the tvs @ home, I picked up a few additional channels that weren't present before. However, when the reception/signal is low, the screen either freezes/audio garbles or just blanks out with a "no signal" message.

I currently do not subscribe to cable tv, so I only get local channels on my network. I was considering a DIY antenna. Since I live in an apartment and my current "rabbit ears" antenna is set up indoors and not on the rooftop, would a DIY option work out for me? TIA.

I was looking at various websites and on Youtube to see what I need for this project.

How to Build a UHF Antenna

It might. Unfortunately, you probably have a few things working against you:

• You have other buildings - and the walls of your building - blocking the signal from reaching your antenna.
• You have other buildings around you reflecting the signal back towards you from other directions (multipath).
• If you're close to the transmitters, some signals might be too strong and drown out other ones.

That said, there's nothing really special about antennas. They're just specially-shaped conductors.

To start with, I suggest optimizing your rabbit ear antenna. First of all, they should be completely horizontal. Second, place them as high as you can. Third, the optimal length is determined by the frequency of the broadcast that you're trying to receive. See the first two posts of this thread for more information (rabbit ears are just a dipole antenna). Finally, you want the broad-side of your antenna to face the transmitter that you are trying to watch. You can use TV Fool to determine the location of the transmitters in relation to your position.

Good luck, and have fun! My DIY antenna is doing an excellent job for me.

So, I got myself a new HDTV and moved the old one into my master bedroom.

Due to circumstances I don't feel like getting into, I have a need to connect an antenna to receive HDTV broadcasts in the bedroom. I connected an antenna and have been experimenting a little. I find that I get some HDTV channels with the antenna in one position and others if I place it in another position. I also found that placing the antenna by the window resulted in stronger signals, however walking around the room can result in some signals dropping out.

Anyway, I finally got the antenna in a position where I get the channels I want without having to get up and move it. I don't get all available channels, but that's OK. I felt a sense of accomplishment until my wife saw the antenna on the window sill and said "do you think that's staying there?".

Well, at first I thought it was my antenna that was old and rusty since we've been using the same rabbit ears for ~25 years.

I found another set of rabbit ears in my room and hooked it up to the converter box and the reception was much better. But garsh may be right, there's buildings surrounding me, so that may be the reason why some channels are more sensitive than are others. Other thing I found interesting was that when I walked towards where the antenna was pointing at, the reception weakened.

So pretty much, I was hoping the DIY version would solve my problem. Well Alan, my antenna is pretty close to the window already, but I guess it's those darn buildings across my street that's causing this.

Somehow I missed this post earlier. This is great. I plan to try this out with my kids this summer.

Awesome!
It's pretty easy to do. And most HDTV's have some sort of "signal strength meter" built-in, making it easy to compare the difference between antennas objectively.

normalicy posted a link in another thread to this PDF file which shows how to build a quad-bowtie antenna from a bunch of wire coat hangers. It looks pretty good. There's also a video available (HD, non-HD)

This site describes some basics of antennas.

I like this site which gives a step-by-step on how to build the equivalent of a ChannelMaster CM4221 for next to nothing.

This design works pretty good for me:

Pringles Can!! :-P

Nice thread Garsh

I tried a single loop and that was OK.
Want to try a double next.
So with a double it would be a figure 8 with two 19" loops and then connect a balun to the end?

I see the balun talked about in one of the other posts?

Also I saw a picture of your quad loop garsh in a post some where but don't see it today.

Thanks

I think I still have the double-loop antenna at home. I'll have to take a look. This page says that the double-loop should be connected at the bottom of the bottom loop! That's not what I did, but perhaps it would work better?
Baluns are used for impedance matching. Your TV is expecting an antenna with 75 ohm impedance. If your antenna naturally has 75 ohm impedance (I believe the quad antenna does), then you do not need a balun. If you do not match the impedance, then you'll get signal reflections within your antenna, causing the performance to be less than it could be.
That was from this thread.
Here's the picture:

Could you give some more details on the antenna you made for the 4 loops.

I get the figure 8 part BUT how do I connect the feed wire?
Is a Balun needed? What size are the loops. 7" 8" 9"?

Thanks

I used a coax splice like this:

On one side, I connect the coax going to the TV. On the other side, I wrapped one side of the antenna around the body of the splice (the ground connection), and I inserted the other conductor into the middle of the splice (the signal connection). Here's a diagram of how the connections were made in the middle of the antenna:
Click to view attachment
No. I did not use one.
Mine are 19.1" circumference (about 6" diameter).

Thanks for the info.
My next step is to get this stuff outside to get some more gain.