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Discussion Starter · #1 ·
I'm using a 4248 cm yagi antenna, but haven't got my tower up to mount it properly. Just as a temporary measure and because I'm extremely impatient, I mounted the antenna on the handle of a floor jack just to see if I could pick anything up.


I have noticed 2 things:

1) My reception of the digital channel improves after sundown. It makes the difference between receiving a digital picture and not.


2) I get better reception with the antenna tilted up in the front about 5-10 degrees.


My question is, will my antenna perform similar when I get it 30-40 ft up in the air? If so, I'll plan on having it tilted when I do install it in the tower. I plan to mount my rotor down and inside of the top tower section and run a mast pole down through the middle of the tower a few feet. It seems that this would take a lot of stress from side loading the rotor. In doing so, the opening in the middle of the tower is somewhat larger than the mast I'll be using. If I need tilt, I thought I may be able to dial it in there by using a set screw or bolt to tilt the mast and antenna one way or the other.


Any suggestions or answers?


Thanks!
 

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bash,


Night-time reception is always better.That's normal.


You probably won't have to worry about tilting it when you get it up higher,unless you have very large hills between you and the transmitters.


Also,I would forego the inside rotor mount,unless you're going to add a 15ft VHF,along with the 4248.


Are you putting the tower next to the house? If so,what's the highest point above ground that it can be fastened?


From reading your other posts it sounds like you have a bracketed type tower.Are the legs 1-1/4"? Are the round horizontal braces 24" apart? One bolt per leg joint? If so,you shouldn't go any higher than two sections,or about 20ft above the attachment(or guyed, point)


Also,if you are burying the first section in the ground,put about a foot of crushed stone in the bottom of the hole so water can drain out,to keep from freezing and splitting the legs.Then backfill with concrete or dirt.


If you're getting some signal that close to the ground,you may not need a preamp.Where are you located in western Ky?


Greg B
 

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Discussion Starter · #3 ·
Greg,


I can attach it to the house at about 9 feet up. All of the high points don't work out for me for various reasons.


To describe the tower, each of the three legs are about 11 or so inches apart with horizontal tubes bracing/connecting the upright legs about every 17 1/2 inches.


It sounds like 30 ft of total tower is all I should use since I don't think guying it will be practical for me. My problem, or at least what I'm worried about is that I'll be aiming directly at or through two trees in my front yard.

My roofline is about 17ft at the top and the trees look to be about 20 ft higher than that. The antenna will be at the back of my house, so the trees will be about 60 ft or so in front of the antenna.


I should clarify that I'm able to get the digital channel at ground level only with the pre-amp installed and I'm actually aiming under the 2 trees that I just described.


Is it likely that I'll be able to continue receiving the uhf broadcast once I get it up around the 35ft mark even if aiming at/through the trees in front of me?


I'm on the western edge of Hopkins Co. just about 8 miles west of Madisonville, 35 miles south of Henderson and 50 miles north of Ft. Campbell.
 

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I doubt your yagi has a vertical capture angle in the forward lobe to make any difference that is consistently measurable. There are some exceptions of phenomena that have been observed and published but not very well explained so if you want to try, here's a suggestion:


Continue to plan to put the rotor down inside the tower with the rotating pipe mast up through the center pipe in the tower ( this is called the thrust bearing pipe). Do not use set screws and keep the fit loose. There is enough lateral sway that will pivot at the base mounting of the rotor but most of the extended sway will be stopped by the tower pipe thrust bearing and this is good and is the way it was designed to work.

You will need to create a special mounting block that will angle the boom of the yagi to the mast, not at right angles but in a way to point the yagi 5-10 degrees into the air as you intended. You do not want the mast to be at an angle, otherwise as you rotate the mast it will point the antenna toward the ground in one diirection and into the air in another. If you build the yagi boom mounting block as I suggested, you will have the yagi pointing into the air in all 360 degrees. The existing mount is probably a right angled bracket that uses a U bolt and aligns at 90 degrees. You can replace this with a rectangle aluminum plate with two U bolts for the boom and two U bolts for the mast. The drill holes for the top U bolt so that it mounts the mast an some small angle other than 90 degrees.


Have fun but don't be fooled into thinking you have done anything here without establishing a long period of benchmark data to compare the angled antenna data with. And then there will be lots of variables that will mess with your data accuracy. Lots of data over a long period of time will be necessary to establish any sort of pattern or advantage to the angled yagi.
 

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bash,


I have found vertical angle to be very important with highly directional antennas, especially when stacking them. 5-12 degrees is about where I run my antennas. My signals are blocked by a mountain ridge, so either I am aiming the antenna toward the signal or I'm aiming it away from unwanted signals. I have done a lot of testing of many popular antennas, you might want to take a look at my site for some suggestions. I am sure you will find the reception greatly improved when you get the antenna up on the tower. You don't need to run a support bearing unless you plan to extend your secondary mast higher than 5 feet or you are using a antenna array.
 

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Discussion Starter · #6 ·
Thanks guys.


Neither of you mentioned my issue with the trees, so I guess I'm to assume that shooting through the top of them won't be a major concern?


Thanks again for the tips and pointers.
 

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Glenn_L


Very nice site on antennas-

From your reports I gather that the tilt adjustment you have found is better realized with each station at each time and not by using a fixed angle of tilt. I had always suspected this back when I was playing around with it on the UHF ham bands years ago. I never did what you did with a rotor to remotely adjust the tilt. That is sweet!
 

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bash,


The trees 60ft away should not be a problem.One of my UHF antennas is right next to a dense maple tree and has no problem seeing through it.


You may experience some overload when you get your UHF high in the air because of two fairly close transmitters,WAZE-19 and WKMA-35.What preamp did you end up getting?


As far as mounting the rotor inside,or above the tower,it's your choice.If you're working by yourself,the inside mount is a little tougher getting everything lined up just right.


Greg B
 

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Discussion Starter · #9 ·
Max,


Thanks for the reply about the trees. They were starting to worry me.

I ended up with the Channel Master 3041, but had still planned on getting the 7777 or the 7775 since I can choose to only amplify uhf with either of those two.


The specs on the 3041 are: 2.2dB Noise on UHF, and 23dB Gaine on UHF.

I wasn't crazy about it having a 300 ohm in instead of the 75 ohm in coax that the 7777 and 7775 have, but it seems to work fairly decent.


I had originally planned on the 4228, but because of the stations that you mentioned, chose the yagi for it's directional characteristics.


I plan on welding a small bracket on the inside of the tower so I can center the rotor inside the top section. I have a 10' steel round mast made for antenna use. I assume it's from structural steel, so it should be okay with about 3 ft. down inside the antenna and 7 ft. above as long as I don't put anything other than the 4248 on it.


I just did a trial fitting and was able to easily stand 20ft of tower upright after having assembled it. With that in mind, I'm thinking I'll be able to assemble 30 ft. of tower and already have my wire and rotor in place and with the help of one or two other guys, just stand it all into place.


Of course, I'll throw in the "I'm just a newbie" clause as nothing I say may work.
 

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bash,


You remind me of myself,when I started jacking with this stuff.The first tower I put up was two sections on a hinged stub base.I got it up and down ok by myself,but it was a little heavy.Then I decided I needed more height,so I went and got another tower section.With every thing on it I couldn't lift it,so I recruited some help.With three of us and using an extension ladder as a prop,we got it up at about a 45deg angle.Then the wind came up.I decided at this point to let it back down before someone got hurt,or have it fall over sideways and mash the neighbors fence and ruin everything.I found a guy with a bucket truck and finished putting it up-so easy and much safer.


I'm not trying to discourage you,of course,but do be careful.That extra 10 ft of tower,with everything already mounted up top, was much more unwieldy to handle,for me anyway.


If you can put two guys on the roof with ropes to help pull it up,it will make it easier for the people on the ground.Also,have your attachment point ready on the house so you can secure it quickly, when you get it vertical.


If you want a pre-made inside rotor mount,RS usually has them.


Greg B
 

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RF engineers tell me that a vertical tilt up in the front by just a few degrees on the receive antenna can be beneficial if you're right on the edge of the radio horizon from the transmitter.


Also, keep into account that multipath reception which arises from horizontally oriented reflective objects can sometimes be reduced by raising or lowering the receive antenna's overall height by inches or a foot or so. In such a case the interference will just be "moved" up or down in the spectrum away from the frequency of interest to n adjacent channel.
 

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I need to use 0 tilt mostly.


For distant stations at 50 miles to 60 miles:


When the atmosphere is reflective I need typically 10 degrees or 25 degrees for distant stations, and just 1 degree error kills my signal, so it can not be pre-set!


For over the horizon stations, when then are receivable at all, it is typically with 30 degrees tilt.
 

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Don,


Even though all my locals transmit from the same mountain top 15 miles away, the transmitting antennas are on different peaks. I have found that each station does have a optimum setting in regard to vertical and horizontal angle, but what I do is adjust my antennas for the weakest channels. This setting will normally work for most of the other stations, but I usually have tweak it a little from time to time. I have several channels that are right on the border of no reception, so every little bit helps. The optimum angle varies as the seasons change too.


Dave,


I have my rotator mounted on a telescopic mast with 6" increment adjustments. I use this to fine tune the height. There have been times when a channel will come and go with just a 6" change.
 
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