How to build a UHF antenna... - Page 162 - AVS | Home Theater Discussions And Reviews
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post #4831 of 4836 Old 11-30-2014, 03:09 PM
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A Bowtie improves SWR Bandwidth compared to a Dipole....a VERY FAT Dipole is needed to even come CLOSE to what a Bowtie does.
The FATTER Bicone (aka "Caged Dipole") may improve SWR Bandwidth....it does NOT significantly improve Raw Gain.

Expanding the "Fatness" into another Dimension (X-Coordinate) only provides a SMALL improvement in Raw Gain and the already sufficient SWR provided by the Bowtie (esp. when used with a Reflector which further improves SWR)....and chews up a LOT more metal....increasing cost and wind resistance.

Which is why you'll very rarely come across them....except in "Calibrated" EMI/EMC Measurement Antennas. The fol. is fairly "typical", with a fairly narrow bandwidth range where SWR is acceptable:
http://schwarzbeck.de/Datenblatt/k9116.pdf
http://schwarzbeck.de/Datenblatt/s9116.pdf

When specifically designed to minimize SWR, they CAN provide a small improvement in performance....just don't expect much more Raw Gain than an equivalent FAT Dipole:
http://glendash.com/Dash_of_EMC/Mode...g_Antennas.htm

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post #4832 of 4836 Old 01-29-2015, 03:55 PM
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Hello All,

Was hoping someone could recommend an antenna configuration given that I am located right in the middle (or pretty close to middle) between two adjacent city transmission towers. I'd like to get signals from both towers.

I want to either get:

A) one DB4 antenna without a reflector (I'm thinking this may have one tower's signal interfere with the other)

-OR-

B) two back-to-back DB4s separated by a reflector (thinking that the reflector will prevent interference from each tower's signal )

Attached is my TV Fool Radar signature/details and an illustration detailing my two options.

Thanks.
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post #4833 of 4836 Old 01-29-2015, 04:30 PM
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Sorry all, I tried to delete my above post as it was a double post but I don't have permissions to edit my posts:

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post #4834 of 4836 Unread Yesterday, 04:25 PM
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I made a bow-tie antenna like this


It's about 12 or 13 inches wide. I can pick up some channels but not all the channels I know are out there. I live about 50 miles south of Chicago and I'm getting about half of the channels. If I were to build the same thing but larger, maybe 2 feet wings instead of the 1 foot wings, would this increase reception? The antenna works pretty good, but it's hit or miss depending on which side the reflector is on (signal side or opposite). Does a larger antenna guarantee better reception for such a long distance?
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post #4835 of 4836 Unread Yesterday, 05:11 PM
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Quote:
Originally Posted by anikun07 View Post
I made a bow-tie antenna like this

It's about 12 or 13 inches wide. I can pick up some channels but not all the channels I know are out there. I live about 50 miles south of Chicago and I'm getting about half of the channels. If I were to build the same thing but larger, maybe 2 feet wings instead of the 1 foot wings, would this increase reception? The antenna works pretty good, but it's hit or miss depending on which side the reflector is on (signal side or opposite). Does a larger antenna guarantee better reception for such a long distance?
This another antenna thread question, not about building a UHF antenna. Please start a new thread following the sticky at the top including your TV Fool report and then maybe we can help you.
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post #4836 of 4836 Unread Today, 01:29 AM
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MODELING is the only way to know what works and what doesn't.....and those very WIDE Feedlines may also be a problem, since the Transmission Line Impedance is MUCH different than thin wires....

For example, when forming a Bowtie using SOLID FLAT TRIANGLES, it turns out that 17-in Total Width is OPTIMUM for UHF BAND for assumed Tip Vertical Separation = 12-in, whereas when forming a Bowtie using a WIRE OUTLINE INDENTED BOWTIE, Total Width of only 10.5-in Total Width is Optimum for assumed Tine Separation = 5-in.
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