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Discussion Starter · #1 ·
I've read exhaustively already, and gather:


- multiple vertical stack bow ties are good for gain, but not multipath because vertical stacking rejects vertical reflections, and most multipath is from horizontal reflections.


- two horizontally mounted yagis are good for multipath rejection, but more difficult to aim precisely (at least more critical where you point them) and best when all stations come from the same point..which is sort of the situation I have.


- positioning and experimentation is everything (my choices are limited, but I'll be high on my chimney)


My 1st question is: Wouldn't the CM 4228, which is basically an 8 bay bow tie arranged in two vertical stacks of 4 each, have more horizontal multipath rejection than a single vertical stack of 4 bow ties?


Granted, it still wouldn't have the directionality of a yagi, let alone a side by side pair...and the stacks on the 4228 are at a fixed distance apart which may not be far enough apart. But would that give additional horizontal rejection, or is the bow tie in general too non-directional for a side-by-side array like this to matter?


I have to buy a new antenna anyway, and they are relatively cheap, so I'd rather buy "too much antenna" to start with rather than keep having to try/buy different ones.


BTW, from what I've learned (and I've read MOST of the posts and referral sites suggested by those who seem most into this) my biggest multipath source is a large body of water 300 yards wide starting about 50 yards from my antenna, between me and all the local towers (which are clustered 30 miles away (over flat land) in the same area.


With regular (non-digital) reception, even though the towers are almost in the same spot, I have one VHF major network channel that's always coming in poorly with snow and some ghosting. I've been told that indicates multipath.


My second question is...would the vertical stacking of the bow ties help eliminate multipath from the water? Or would a yagi still be better?


Yes, I know I shouln't need one this big, but like I said, they are cheap by HT standards.
 

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If your problem is more related to multipath from below the antenna, have you considered a parabolic? It will reject multipath both horizontally as well as vertically, and would be approx the same beamwidth as stacked yagi's without the stacking distance/cable/combiner setup which could actually make your problem worse if its not precisely configured. Stacking can never be accurate for UHF because the distance involved will only cover a couple channels, on the rest, the antennas will either be to close together or to far apart, unless you are lucky enough to have all your channels in a 10 channel spread.
 

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In my humble opinion, Snow is not an indication of multpath. Ghosting is. Snow is a lack of signal strength. Is that one station operating on low power?
 

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I've never dealt with a reflection off water before. Since the distance between a ghost image and the desired image is determined by the additional distance that the reflected signal must travel, I would expect such a ghost to be extremely close to the original image.


According to this chart: http://starkelectronic.com/cmg5.htm , the Channel Master 8-bay bowtie has a slightly tighter horizontal multipath rejection than does their best yagi. I was surprised to learn that.


If the reflection causing the ghost really is coming off the water, you might avoid it by lowering your antenna or relocating it so that your house or other structure acts as a natural shield.
 

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Jeff,


Although the 4228 has horizontally stacked elements, the distance between them is very small. I have found that the wider you space the stacked antennas the better the multipath reduction. Take a look at this test I did here:
http://www.atechfabrication.com/test...x14wb_test.htm

Study the waveform pictures and you will see that the shape of the signal for the 24" spacing is similar to that of a single antenna. When the spacing was increased to 36" and 44" the shape flattens out indicating a cleaner signal with less multipath.


The 8-bay bowtie should have better multipath reduction than the 4-bay, but nowhere near what you can get from two yagi's stacked at wider spacings.
 

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Discussion Starter · #6 ·
Glenn, I've read you stuff before (and again)...wouldn't all the multipath rejection techniques make a rotator (and perhaps adjustable tilt) more necessary if not mandatory? I read about how a few degrees matters with stacking, and even though all of our towers are located in the same area with no hills, many folks here find they have to rotate to get a signal from stations with the same power. One in particular has side by side CM 4248's, set up with professional quidance, and still can't just aim in anywhere near the same direction (he thinks its pine trees) to pull in stations.


I was hoping the 4228 would eliminate the rotator...and the prices I've seen for tilters are in the $300 plus range.
 

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Jeff,


I never used the bow ties, because I started with a Parascope that did not work, and I figured the bow-ties were too similar so went with yagis.


With two yagis side by side I have a lot of beam width control, and can set them as close as possible without getting multipath problems. When very close they become just like one antenna. You don't have this adjustability to customize for what you really need with a single antenna.


As to your water problem, I would think most any antenna would work better with a tilter for you. Some people here have reported in the past that a screen-bow-tie antenna is less ground bounce sensitive though.
 

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Question - when you say stacked yagis are you E stacking or H stacking?
 

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Quote:
Originally posted by jkaiser
Question - when you say stacked yagis are you E stacking or H stacking?
Not sure what you are getting at. I stacked my yagis horizontally, and the antennas are horizontal to line up with the E field. Our locals are transmitting horizontally mostly with some using circular.
 

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Jeff,


If the 4228 works to pull in all your signals, you may not need a rotator, but I feel they are mandatory. I have never heard of anyone that removed a rotator because they did not really need it. I think it gives you a little bit of peace of mind when you get drop outs, since you can adjust the antenna from your couch and not second guess if your antenna is pointing the right way.


Narrow beamwidth = multipath rejection. The more narrow the beamwidth is, the more precisely it needs to be aimed. This applies to horizontal and vertical beamwidth.


The farther away your transmitters, the wider the opening of the beamwidth. So, aiming will not be as critical for far away stations.
 

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Discussion Starter · #11 ·
Glenn,


Interestinlgy enough, I spoke with Channel Master's technical dept yesterday, and they agreed with Mike that the 4228 should have a narrower beam width (both horizontally and vertically) than a 4248...I had it backwards.


Too bad there's no way to just try one and return it until you get the right one. I've narrowed it down to one of these two, they're economical and seem well thought of, I just need to flip a coin.


I was also told the wind loading was about equal on the two. I thought the square would be worse.


BTW, why is it there are two widely different shapes when they are both UHF? Is there a general rule of thumb as to why someone would choose one shape or style over the other? Does the square 4228 limit the tilt?


Also, would mounting inside the attic have any advantage other than wind and rain protection? Would being inside lessen multipath?


I know someone locally who has double 4248's who has to adjust his rotator daily...even on the same channel (but gets them all very well), and someone else who has a 4228 in his attic with no rotor that has all but 1 station coming in well. They aren't in the same neighborhood, but both have similar topography, trees, water, distance, and direction to the towers. It made me wonder if the attic was actually a better place.


As usual, I'm enjoying the shopping and learning process here, and appreciate everyones time and input.
 

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Jeff,


Forget about the attic being a better or even a good place.

I have both.


The only advantage of the attic is protection from the wind, which can help with locals on very windy days.


I lose about 5 db of signal picking them up in the attic, and it gets worse in winter with lots of snow on the roof.


Position is everything and my attic antenna can work better on a particular channel under some rain conditions than my outdoor antennna. I also have 2 outdoor antennas just about 15 feet apart, and they also get very different signals.


Multipath varies at every location around my yard.
 

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Jeff,


The main problem with a attic install is that the antenna is not up high enough. If your antenna works well when it is below the roof peak, it might work ok in the attic and if your house is higher than the ones around you. For me, I have to have my antenna at least 10' above my roof to get a good signal.


Adjusting the rotator daily with stacked antennas is common. This is because of the narrow beamwidth you get from horizontal stacking, this is a good thing. It is this narrow beamwidth that gives the antenna its improved multipath rejection. You can increase beamwidth by moving the antennas closer together, but then you also increase multipath.
 

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Quote:
Originally posted by Jeff Smith
Too bad there's no way to just try one and return it until you get the right one. I've narrowed it down to one of these two, they're economical and seem well thought of, I just need to flip a coin.
If you have a local antenna distributor, they may accept a return if it doesn't work for you (mine did). Call the engineering department of a local TV station and ask where to obtain an antenna. The station may even have a loaner for testing.
 

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I'm new to this forum, but am trying to decide on an antenna as well. How good is the terk hdtv 60? Will I need to rotate it for every channel?

I also live only 50 feet from a 150 acre lake. Will this antenna give me good reception for HDTV?


Thanks,

Ray
 

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Ray,


You would need to provide more information for anyone to suggest a antenna, like distance, terrain, immediate surroundings, channel numbers.


Most people are disappointed with the performance of Terk antennas.
 

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Thanks for you response Glenn,


I live in Florida, perfectly flat for me with a 150 acre lake in back. I believe the towers are app 20-30 miles in a couple different directions. The top of my rooftop is about 45ft (three story house). My line of site should be good to just about anything, I am pretty much above the trees.


Thanks,

Ray
 

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Jeff,


I might as well add my two cents worth. First I have not found out how far you are from the antenna towers. Second, water close to you is NOT a multipath problem. Third if you are within 30 miles, over flat terrain, it is highly unlikely you have ANY multipath problem. As reported earlier snow on VHF in not multipath - only a weak signal.


Before you drive yourself nuts chasing non-problems, try a simple antenna and see what your problems - if any - really are. You can get a simple UHF Yagi from Radio Shack for $20 and return it if you need more gain. The CM 8 bay bowtie is a good antenna, but may be overkill unless your are more than 50 miles from the towers.


Multipath results from large terrain variations or lots of tall buildings in the area of the towers. Glenn has the terrain problem in SPADES! A rotator is always good insurance from the odd reflection.


Don Cone
 
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