AVS Forum banner
Status
Not open for further replies.
1 - 20 of 27 Posts

·
Registered
Joined
·
94 Posts
Discussion Starter · #1 ·
I understand that tilting a UHF antenna can improve it's reception in certain cases.


Can someone please tell me the best way to tilt it assuming that the antenna will be on a rotor? Is there some bracket for tilting? Is it easier to tilt the 4228 or the 4248?


Thanks in advance, Tom


[This message has been edited by Tom Lewis (edited 05-08-2001).]
 

·
Registered
Joined
·
94 Posts
Discussion Starter · #2 ·
Ed,


Good questions, both.


I do not know whether or not I need to tilt the antenna. However, I would rather have the ability to do it and not use it, than not have the ability. This assumes all I need is some simple accessory. Maybe I am jumping the gun... I just thought it would be nice to mess around with the tilt after I get the bearing correct.


For sure I will need a rotor because I intend to go after signals from both Sutro Tower (San Francisco) and Sacramento.


Tom
 

·
Registered
Joined
·
553 Posts
I have my antenna in the attic too and I had to tilt the 4 bow-tie array about 30 degrees to get one channel. I have it on a rotor as well. I created a "T" connection with the pole going from the rotor vertically to the piece which holds the antenna. They are joined with a bolt so the joint can be manually tilted to any angle. For my purposes a single tilt angle works to solve reception problems with one particular station. Here are some pictures:

http://www.toad.net/~tpfarr/images/antenna1.jpg
http://www.toad.net/~tpfarr/images/antenna2.jpg


Tom Pfarr


[This message has been edited by tpfarr (edited 05-09-2001).]


[This message has been edited by tpfarr (edited 05-09-2001).]


[This message has been edited by tpfarr (edited 05-09-2001).]
 

·
Registered
Joined
·
94 Posts
Discussion Starter · #4 ·
tpfarr,


Is there anyway you could post or send a pic? Sounds like you have solved the mystery of 'tilting with rotor in attic'.


Tom
 

·
Registered
Joined
·
553 Posts

·
Registered
Joined
·
1,386 Posts
I was pondering this problem myself a while back and thought of fabricating a set of custom brackets that would allow me to mount a second rotor on the top of the first rotor at a 90 degreee angle and then mount the antenna to that so that the second rotor could be used to "twist" the azimuth of the antenna.


------------------

HiDefDave


STOP HDCP!
 

·
Registered
Joined
·
553 Posts
Just to clarify my "tee" solution does not change the tilt via a rotor. The tilt is manually set and left that way. The rotor rotates the entire tilted antenna panel towards the intended transmitters.


Tom Pfarr
 

·
Registered
Joined
·
219 Posts
A few months ago I tilted my Yagi a max of 2 degrees and the Signal strength went up by 10 points. I was amazed at the time. I could rotate the antenna thru 20 degrees and get the same signal. Why does tilt makes so much difference?


I've been meaning to play with mine some more, but haven't gotten around to it. I think a one time adjustment may be all thats required. Is there a huge elevation difference between the transmitters in your area?


If you don't know, 100000watts.com will have that info.
 

·
Registered
Joined
·
553 Posts
I added pictures for the "tee" assembly in my previous post.
 

·
Registered
Joined
·
801 Posts
I remember Ham Radio guys used to use something called a "U100" rotator to control both azimuth and elevation for their VHF/UHF satellite communications. Not sure who made them, may be Alliance. If they're still available, there is a lot of information in ham radio publications about using them.


Bob Smith
 

·
Registered
Joined
·
94 Posts
Discussion Starter · #11 ·
livetofly...


OK, I checked the link and here is the result:


My Targeted Transmitters:


DTV# Elevation, ft Location

19 1371 Sutro

24 1433 Sutro

29 1315 Sutro

30 1433 Sutro

45 1463 Sutro

56 1417 Sutro

57 1463 Sutro

25 1948 14001 River Rd, Walnut Grove (Sac)

55 1906 14001 River Rd, Walnut Grove (Sac)

61 1952 14001 River Rd, Walnut Grove (Sac)


According to bsexton.com, it is 26 miles to Sutro Tower and 44 miles to the Walnut Grove tower. Rocky Ridge (elev appx 1900 ft) is between me and Sutro. Mt Diablo (elev 3849 ft) is somewhat between me and Walnut Grove. My elevation is about 520 ft.


Tom
 

·
Registered
Joined
·
1,525 Posts
Quote:
Originally posted by Dave McRoy:
I was pondering this problem myself a while back and thought of fabricating a set of custom brackets that would allow me to mount a second rotor on the top of the first rotor at a 90 degreee angle and then mount the antenna to that so that the second rotor could be used to "twist" the azimuth of the antenna.



I am thinking of doing that also, but I was also going to modify the rotor internally so that the range of motion is limited to about +/- 30 deg, otherwise you will burn up the motor if the antenna makes contact with your mast.


I do have a manual adjustment bracket now. I made it by straightening out the 90 deg bend on a swivel base bracket, works great and cost less than $5. I can post a pic if anyone is interested.


Glenn

 

·
Registered
Joined
·
1,525 Posts
Tom,


I thought I could just paste a picture into the message, but you have to link it to web content and I don't have that available right now. The part I used is Radio Shack 15-888 Universal Mast Anchor Mount:
http://www.radioshack.com/product.as...%5Fid=15%2D888


You can alter this part to work with just about any antenna for tilting. I flattened the right angle bend and bolted it in place of the u-bolt on my 4248, then attached the mast to the u-bolt on the swivel. You want the swivel close to the center of gravity of the antenna, not at the lower end of mast.


Glenn
 

·
Registered
Joined
·
219 Posts
Tom, from the #s you give and if you neglect multipath, the tilting should be a one time setup. Both towers are barely off from horizontal. I would suggest starting with a straight forward horizontal setup and see what #s you get. Good Luck!
 

·
Registered
Joined
·
94 Posts
Discussion Starter · #17 ·
Glenn,


OK, thanks for the data. I did not realize Radio Shack sells the specialized brackets; good to know. Thanks for the detail on the fab technique.


livetoflyfish,


I suspect that I will have a multipath issue, considering the number of hills in the area. However, I have decided to start at baseline and then modify as required. I just ordered a 4248, a 7775, and a CM tripod & rotor. I will move the assembly around on the roof to find the best x-y dimension (and naturally use the rotor for bearing.) The z-dimension (mast height) will be fixed at something below 12 feet above roofline (sent advisory to Homeowner's Association today.)


Depending on the results, I may need to tilt using the great suggestions from all of you.


Tom
 

·
Registered
Joined
·
1,897 Posts
Let me take a stab at why tilting might help. With regard to Yagi antennas (this happens to be the one I am most familiar with) The vertical pattern of the antenna does not look like the horizontal pattern. A typical horizontal pattern has a large single lobe in the direction the antenna is aimed and a very small lobe in the reverse direction. This explains the typical front to back ratio that one sees with a Yagi.


In the vertical direction you do not get a single lobe. You typically get 3 lobes, the longest (most gain) is typically about 15 degrees above horizontal. There is no lobe at Zero degrees. The second lobe is at approximately 40 degrees and the last which is small is around 70 degrees. Between these lobes, the gain can be very low. If a signal is coming in predominantly at one angle, then it is possible for that signal to actually be in a null between the vertical lobes and therefore if you tilt the antenna upwards, you actually align one of the vertical lobes with the incoming sky wave signal. If your signal sources are in different directions, then tilting for one may not help for others. The Antenna handbook had a couple pictures of lobes for yagis with a few elements. It did not have any info on what the pattern looked like for longer multielement yagis and no info for the Bow tie type antennas. So, theoretically tilting could help but it would be dependent on how far away someone is from the source. With multi element yagis it is easy to understand that waves coming in from the say 15 degrees would be intercepting the most elements whereas a wave coming in from zero degrees would actually have some of its signal blocked by the elements in front of it. I don't have an explanation for the bow tie antennas. Hope this helps and if anyone understands this please help enlighten as I am taking much of this from the antenna handbook.


..Doyle
 

·
Registered
Joined
·
1,525 Posts
We have covered how to tilt the antenna, but why?


The main problem we have with OTA is multipath, or reflected signals. The main goal in adjusting the antenna is to reduce multipath. Most signals get reflected from objects near the ground. Since most antenna have a somewhat narrow beamwidth vertically, by tilting the antenna upward, you are tuning out some of the reflected signals off the ground. If you have a lot of high rise building around you this probably won't help much, if so, you should try moving the antenna to a different side of the roof, so that maybe the roof itself can block some multipath.


Also, I have a large mountain in my path. It is a 7 degree angle to the top of the mountain from my house. I think in this case, tilting the antenna up is also increasing the gain slightly.


Glenn
 

·
Registered
Joined
·
136 Posts
Hello Tom Pfarr,

That's great how you did the tilting of the CM 4221, up in the attic. I live in a townhome and I just installed my CM 4221 antenna on a mast on the roof. And now I might have to take it off due to HOME ASSOCIATION rules and regs. They don't allow any common antennas to be installed on the roof. I might have to do what you did. I have a small attic and in the attic there's the AC unit and a bunch of wood support. The only free space is right next to the ac unit. Will this create a problem such as multipath? The next question I had is. Are all your RG6 wiring coming from the attic down to the walls? That is my problem I tried fishing and adding more RG6 cable to seperate sat and uhf coax cables but there were to many studs in the wall. If you have an ecliptical dish. Did you combine the uhf & sat together with a multiswitch? Because I think this is the only way to cure my problem. I saw this product called NAS SMS-5/4P. This unit combines 4 sat and a uhf in to 4 outs to the sat boxes. And also are you using any diplexers?

Thanks in advance. Just need some help.


------------------

PeterDz
 
1 - 20 of 27 Posts
Status
Not open for further replies.
Top