How to build a UHF antenna... - Page 162 - AVS | Home Theater Discussions And Reviews
Forum Jump: 
 1Likes
Reply
Thread Tools
post #4831 of 4839 Old 11-30-2014, 03:09 PM
AVS Special Member
 
holl_ands's Avatar
 
Join Date: Jun 2004
Location: San Diego, CA
Posts: 3,971
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 125 Post(s)
Liked: 85
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

Last edited by holl_ands; 11-30-2014 at 04:47 PM.
holl_ands is offline  
Sponsored Links
Advertisement
 
post #4832 of 4839 Old 01-29-2015, 03:55 PM
Newbie
 
Join Date: Jan 2015
Posts: 10
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Liked: 0
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.
Attached Thumbnails
Click image for larger version

Name:	94404.png
Views:	33
Size:	73.9 KB
ID:	510721   Click image for larger version

Name:	DB4-Configs.png
Views:	36
Size:	15.5 KB
ID:	510817  
Nik Kershaw is offline  
post #4833 of 4839 Old 01-29-2015, 04:30 PM
Newbie
 
Join Date: Jan 2015
Posts: 10
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Liked: 0
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:

Quote:
Originally Posted by AvsForm View Post
You may post new threads
You may post replies
You may post attachments
You may not edit your posts
Nik Kershaw is offline  
post #4834 of 4839 Old 01-30-2015, 04:25 PM
AVS Special Member
 
anikun07's Avatar
 
Join Date: Jul 2011
Location: Northwest Illinois USA
Posts: 1,213
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 13 Post(s)
Liked: 46
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?
anikun07 is offline  
post #4835 of 4839 Old 01-30-2015, 05:11 PM
AVS Special Member
 
Calaveras's Avatar
 
Join Date: Jan 2007
Location: Mountain Ranch
Posts: 3,529
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 364 Post(s)
Liked: 123
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.
Calaveras is offline  
post #4836 of 4839 Old 01-31-2015, 01:29 AM
AVS Special Member
 
holl_ands's Avatar
 
Join Date: Jun 2004
Location: San Diego, CA
Posts: 3,971
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 125 Post(s)
Liked: 85
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. Unless you actually MODEL a proposed design and then OPTIMIZE the Dimensions, you should pick a design that is KNOWN to work.....

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.

BTW: Simply increasing the Total Width will usually improve Gain on the Lowest Channels.....at the expense of the Higher Channels. But without modeling it, I have NO CLUE whether it is already TOO LARGE or TOO SMALL...or whether the SWR is even in the right ballpark...

Last edited by holl_ands; 01-31-2015 at 01:34 AM.
holl_ands is offline  
post #4837 of 4839 Old Today, 10:49 AM
Newbie
 
Join Date: Mar 2015
Location: 50263
Posts: 4
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 5 Post(s)
Liked: 0
Greeting all, another newbie here.

I have only moderate success with my store-bought attic mounted antenna, so I'm looking at the various DIY ideas.

I'm considering something different than the preassembled antennas I see in this forum. What if I were to string copper from stud to stud, creating the horizontal Vs employed in most designs? In my attic (upper crawlspace actually, not intended to be used for storage and filled with blown cellulose) I could create something that is ridiculously large. The more wire there is to capture the signal, the better...right? I'm sure it's never that simple, which is why I'm asking. I understand that the orientation would be fixed, but maybe that's not an issue if it's big enough.

Is uniformity and ratio important in the sizes of the various components? For instance, should the Vs all be a multiple of a particular length with a particular spacing?


Thanks for your thoughts,
Chris
TheIowan is online now  
post #4838 of 4839 Unread Today, 12:59 PM
AVS Special Member
 
Calaveras's Avatar
 
Join Date: Jan 2007
Location: Mountain Ranch
Posts: 3,529
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 364 Post(s)
Liked: 123
Quote:
Originally Posted by TheIowan View Post
I have only moderate success with my store-bought attic mounted antenna, so I'm looking at the various DIY ideas.

This is another antenna thread. Please read the sticky at the top of this forum and put your location in the title and supply a link to your TV Fool report and start a new thread. You should include exactly what you've done so far; i.e. make/model of your purchased antenna so we know your starting point.
Calaveras is offline  
post #4839 of 4839 Unread Today, 03:34 PM
AVS Special Member
 
fbov's Avatar
 
Join Date: Nov 2006
Location: Bushnell's Basin, NY
Posts: 1,219
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 109 Post(s)
Liked: 61
Quote:
Originally Posted by TheIowan View Post
...I have only moderate success with my store-bought attic mounted antenna, so I'm looking at the various DIY ideas.

I'm considering something different than the preassembled antennas I see in this forum. ...
Pre-assembled antennas on a DIY forum??? Where?

Read some of the early pages where we were just starting to figure this all out for answers to your question. As soon as you proposed that you "string copper from stud to stud" it was clear you need a primer on antenna design.

Antenna elements are each designed for a specific function. In a Yagi, some are directors, some are reflectors and one is usually a dipole that's benefitting from the directors and reflectors.

In a bowtie dipole, size determines frequency of maximum gain. Double the size, you halve that frequency. Also, element spacing and polarity are carefully controlled so multiple elements work together to increase antenna gain. Same with reflectors. Element size (wire gauge) is also a factor.

The better approach is as Calaveras suggests; get us some signal strength data (TVFool) and tell us about the antenna you have, where it's mounted, etc. There may be an easy solution.

HAve fun,
Frank
fbov is online now  
Sponsored Links
Advertisement
 
Reply HDTV Technical

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page


Forum Jump: 

Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off