The Official AVS Antenna and Related Hardware Topic! - Page 343 - AVS Forum
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post #10261 of 16266 Old 03-22-2009, 05:48 PM
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Take a look at the last link below. Then follow the link to "Erecting A TV Antenna."
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post #10262 of 16266 Old 03-22-2009, 10:05 PM
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Quote:


I did notice that the rotor is stamped with 1 rpm.

Yeah, Ive never seen an ad for a rotor faster than 1 rpm. Speed demons they are not, heh.
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post #10263 of 16266 Old 03-23-2009, 04:48 AM
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Quote:
Originally Posted by 300ohm View Post

Yeah, Ive never seen an ad for a rotor faster than 1 rpm. Speed demons they are not, heh.

Do you really want a rotor whipping an LP antenna around quickly? Maybe a DB, they seem fairly durable. One of my DB2's has proven to be 3-yr old resistant.
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post #10264 of 16266 Old 03-23-2009, 06:52 AM
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Personally I do, because waiting 20 or 30 seconds can seen like an eternity, heh. Thats why I like the two antennas, two downleads into an A-B switch solution so much.
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post #10265 of 16266 Old 03-23-2009, 08:18 AM
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I can understand that rotors designed for the large 2-69 band antennas would need to move the antenna slowly, but the UHF only and 7-51 antennas are significantly smaller and could be moved at higher speeds. A 3 RPM rotor could certainly work well with the small antennas are take only 10 seconds to do an 180 degree turn.
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post #10266 of 16266 Old 03-23-2009, 03:19 PM
 
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Quote:
Originally Posted by Falcon_77 View Post

What do the TV Fool plots look like in each location?

I would avoid high-gain pre-amps, such as the CM7777 in any area that has signals in the green on TV Fool, unless you don't need to point the antenna in the direction of those stations.

TV transmitters at 15-20 miles are rather close, especially if you have LOS.

Do you need Low-VHF? Most areas do not need Low-VHF for DTV and that might save you some headaches. A 7-51 antenna is less cumbersome as well.

Quote:
Originally Posted by systems2000 View Post

Take a look at the last link below. Then follow the link to "Erecting A TV Antenna."

Thanks guys. After studying links provided, I think that the problem in both of the problem cases was due to short delay multi-path. This would be confirmed by the move of my co-workers dad's antenna to another location, thus accomplishing the desired reception of the local and distant signals. We have lots of trees around here, and in both cases, there were trees prosent, and in the Beaumont case, the land next to my friend's house is heavily wooded. I call it the hundred acre woods. So that is what I need to look for before installing antennas.
Thank you so much for pointing me in the right direction.
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post #10267 of 16266 Old 03-24-2009, 05:33 AM
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For grins, I was using one of the many on-line tools for calculating the lengths for a LP/Yagi capable of 20db gain for channel 2.

The boom length came out to 127 feet. I lost count of the number of directors.
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post #10268 of 16266 Old 03-24-2009, 09:22 AM
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I would like to stack two of those...


Quote:
Originally Posted by ngarrang View Post

For grins, I was using one of the many on-line tools for calculating the lengths for a LP/Yagi capable of 20db gain for channel 2.

The boom length came out to 127 feet. I lost count of the number of directors.

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post #10269 of 16266 Old 03-24-2009, 09:37 AM
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Quote:
Originally Posted by PCTools View Post

I would like to stack two of those...

You have a station 150 miles away you want to receive?

My yard is slightly longer than 127 feet. Let's see...I could top my backyard tree and plant this monster antenna on there. Where to set the guide wires, though, to stop it from becoming a twisted spear of God?
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post #10270 of 16266 Old 03-24-2009, 10:50 AM
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Quote:


You have a station 150 miles away you want to receive?

Probably not. He just wants to annoy the neighbors.
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post #10271 of 16266 Old 03-24-2009, 10:52 AM
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Quote:
Originally Posted by ngarrang View Post

You have a station 150 miles away you want to receive?

My yard is slightly longer than 127 feet. Let's see...I could top my backyard tree and plant this monster antenna on there. Where to set the guide wires, though, to stop it from becoming a twisted spear of God?

2 of these at 150ft AGL, would be FANTASTIC!

KD0MOF

All opinions expressed (unless otherwise noted) are the poster's only and NOT that of the poster's employers.
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post #10272 of 16266 Old 03-24-2009, 12:43 PM
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You could string a net between the two antennas, and catch bats at night.
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post #10273 of 16266 Old 03-24-2009, 03:53 PM
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Quote:
Originally Posted by ngarrang View Post

For grins, I was using one of the many on-line tools for calculating the lengths for a LP/Yagi capable of 20db gain for channel 2.

The boom length came out to 127 feet. I lost count of the number of directors.

4 antennas with 15 db each would do the same thing and be more manageable.
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post #10274 of 16266 Old 03-24-2009, 04:26 PM
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Quote:
Originally Posted by Tower Guy View Post

4 antennas with 15 db each would do the same thing and be more manageable.

Even at 15 dB, that would still be a big antenna. However, such things exist. Here's a 50 MHz antenna with 14 dBd gain on a 69 foot boom.

http://www.m2inc.com/products/6m/6m11jkv.html

Ron

HD MPEG-2 Test Patterns http://www.w6rz.net
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post #10275 of 16266 Old 03-24-2009, 05:16 PM
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Code:
SPECIFICATIONS
Model
 6M11JKV
 
Frequency range 49.9-50.5 MHz 
Usuable Frequency Range 49.6 TO 50.75 MHz
 
Gain over a Dipole 14 dBd 
Front to back, Typical >21 dB 
Beamwidth degrees E=28° / H=39° 
FIRST SIDELOBE -18 dB 
STACKING (HORIZ POL) 38' W, 36' H
 
Feed impedance
 50 OHM
 
VSWR
 1.2:1
 
Input Connector
 'N' Female 
Balun Half Wave 4:1, supplied 
Power Handling
 1500 WATTS 
Element Type 3/4" Tube W 7/8" Center Sleeve 
Boom length and diameter 69' / 2" / 2", 2-1/2" & 3" X 36" CNTR 
Wind Area / Survival 10.7 SQ. FT. / 100 MPH 
Weight / ShipWt.
 83 LBS. / 95 LBS, Truck or air
Heh, heh. And thats only 1 of 4, heh. And thats 14dbd, 16.15 dbi for each one. Figure another 2.5 dbi stacking two, then 5 dbi stacking all four for about 21.15 dbi.
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post #10276 of 16266 Old 03-24-2009, 09:07 PM
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69' long damn!
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post #10277 of 16266 Old 03-25-2009, 07:33 AM
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Quote:


69' long damn!

Also at 50mhz, the stacking distance is large too. So maybe figure it needs to be 69 ft high for all four. Then of course it wont work well close to the ground, so youll need a good 100 ft tower to mount it on too, heh.

If youre going to go that insane, you might as well have a 60 meter in diameter parabola dish built, heh.
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post #10278 of 16266 Old 03-25-2009, 09:17 AM
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Quote:
Originally Posted by 300ohm View Post

Also at 50mhz, the stacking distance is large too. So maybe figure it needs to be 69 ft high for all four.

There is an aspect of the problem that is easily overlooked when comparing antenna gains and heights. Antennas on channel 2 interact with the ground to steer the main beam upwards. Tvfool doesn't include that factor in their data. Tvfool does assume that there is more signal when the antenna is raised, but that is based on statistics and not the specifics of a particular antenna's interaction with the ground.

If the ground in front of the antenna is flat and you would like to get the main beam aimed exactly at the transmitter antenna, extra tower height adds significantly. At reasonable antenna heights it's 1 db per each 5' of tower height. If the ground in front of the antenna slopes downward, there is an optimum height where the ground interaction adds approximately 6 db to the gain of the antenna.

Therefore, a single 14 db gain antenna at the optimum height with downward sloping ground in front of the antenna would actually have 20 db gain.
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post #10279 of 16266 Old 03-25-2009, 12:40 PM
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If the ground in front of the antenna slopes downward, there is an optimum height where the ground interaction adds approximately 6 db to the gain of the antenna.

Im out of luck on that, its flat as a pancake around here, heh. I wonder if that guy with the four stacked 69 ft yagis lives in the Texas hill country ?
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post #10280 of 16266 Old 03-25-2009, 04:03 PM
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Ken Nist updated the 8-Bay Modification webpage, testing an alternative feedline
for the CM-4228HD, as well as a 1/4-wavelength balun:
http://www.hdtvprimer.com/ANTENNAS/TemporaryPage.html
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post #10281 of 16266 Old 03-25-2009, 04:05 PM
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Here's some pics (including some rope yagis):

http://www.bigskyspaces.com/w7gj/6mEMEstns.htm

Ron

HD MPEG-2 Test Patterns http://www.w6rz.net
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post #10282 of 16266 Old 03-25-2009, 04:55 PM
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Quote:
Originally Posted by 300ohm View Post

Im out of luck on that, its flat as a pancake around here, heh. I wonder if that guy with the four stacked 69 ft yagis lives in the Texas hill country ?

This is in Hempstead, TX

http://www.50mhz.org/6m/album02/IMG_0255
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post #10283 of 16266 Old 03-25-2009, 08:03 PM
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Quote:


Here's some pics (including some rope yagis):

I hate to be under some of those when the wind is blowing strong, jeez. Also I noticed some are mounted near power lines. Nothing like living dangerously, heh.

Quote:


This is in Hempstead, TX

Hmm, I believe the hill country may start a little to the west of there. I remember driving from New Braunfels ( a little north of San Antonio) to north of Austin at night and I ran into some pretty darn decent hills, heh. I also remember running over an armadillo. (from what Ive been told, I didnt hurt the little critter, heh)
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post #10284 of 16266 Old 03-26-2009, 03:16 PM
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After reading this thread, I'm almost too ashamed to post this, but after finding rabbit ears are insufficient to pick up my one DTV channel (KWWL NBC 7) I am going to attempt to make a folded dipole for this one channel.

Problem is, nobody in town carries 300 ohm twin lead wire, even the local independent radio supply store and Radio Shack.

This will be for indoor use, and I don't have the ability to access the attic antennas (sep. VHF/UHF Yagi) from the room I want to use this in.

Where do you recommend ordering twin lead from? I'll probably also get a new balun and combiner for it also.

It's depressing nobody manufactures a descent indoor VHF-HI antenna considering the demand for one.

Thanks,
Jay

PS - According to my calculations, I'll be cutting it to 31.68 inches long.
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post #10285 of 16266 Old 03-26-2009, 05:57 PM
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Problem is, nobody in town carries 300 ohm twin lead wire, even the local independent radio supply store and Radio Shack.

Make your own from copper wire. Enter your info here at K7MEMs site for the design measurements : http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=15313
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post #10286 of 16266 Old 03-26-2009, 07:47 PM
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Lowe's carried twin lead the last I checked.
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post #10287 of 16266 Old 03-26-2009, 09:44 PM
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Quote:
Originally Posted by oldsyd View Post

Problem is, nobody in town carries 300 ohm twin lead wire, even the local independent radio supply store and Radio Shack.

There are Menards stores in Iowa, I think. They carry the super-cheapo super-thin indoor Magnavox-branded stuff for like $2 for 50 feet (so you're not exactly getting grade-A stuff, but for $2....)
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post #10288 of 16266 Old 03-26-2009, 09:49 PM
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For the perfectionists out there, here's a link to some transmit quality 300 ohm twin-lead:

http://www.dxengineering.com/products.asp?ID=170

Ron

HD MPEG-2 Test Patterns http://www.w6rz.net
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post #10289 of 16266 Old 03-26-2009, 10:55 PM
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Thanks everyone for the wide array of options!
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post #10290 of 16266 Old 03-27-2009, 06:10 AM
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Quote:


here's a link to some transmit quality 300 ohm twin-lead:

Whew, about 30 cents a ft, but it is strong 18 gauge stuff.

Quote:


Lowe's carried twin lead the last I checked.

Not my Lowes anymore. What it seems they do when their stock gets low, is put it on clearance for a weekend, and then dont stock it anymore.
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