OTA Antenna Frustration - Help !!!

[rjs0905]

I live in Atlanta very close (approximately 5 miles) to the OTA transmitters. So close, in fact, that they are in two different directions: UPN, ABC, and NBC (which is VHF, Ch. 10) at 280 deg. and the rest at 300 deg. My backyard is about 20 yards of open space leading to a pretty solid wall of trees about 100' high. There is no way to get any antenna above the treeline or even anywhere even close to it.

I put up my first antenna, an Antennas Direct DB-4, last November. Worked OK, but not good enough (I've got to have OTA reliability at least as good as the satellite, 'cause if that TV starts pixellating during Desperate Housewives, the spouse starts throwin' stuff!!) So I replaced it with a CM-4228 because it seemed to be the universally-endorsed antenna of choice on a lot of these boards. Worked great, except because of the narrower beam I couldn't "split the difference" between the two compass headings like I could with the DB-4, so I got a second 4228 and joined them on a single mast (stacked vertically) mounted on my back deck, about 15 feet off the ground. They are joined with equal lengths of quality RG-6 into a very good HDTV splitter/combiner, which in turn runs about 40 feet inside to the TV.

That worked great - high 80's to low 90's on all channels, very reliable for the most part except for very windy days, where I'd get some dropouts. At one point I tried moving the whole contraption up to the roof, which gave another 10 feet or so of height, but reception actually got worse so I moved it back.

Now it is spring, and the foliage is pretty much fully grown in. I am now experiencing much more multipath than I used to on certain stations (NBC, ABC, and, to some extent, CBS & Fox. UPN, WB, and TBS seem to be bulletproof for some reason). If there is any appreciable wind through the trees, then I get frequent pixellation on all these channels. I say multipath because my signals still peak at the high 80's and low 90's on my HR10-250 (yes, lousy OTA tuner, I know), but will bounce all over from there, whereas the better ATSC tuner in my Samsung TV has no problems at all with the same signal. Unfortunately, the HR10-250 is the only way we watch OTA because we are so addicted to Tivo, and for that same reason the D* HD locals are not an option pending release of the oft-discussed but never-seen HR20-250.

Now I read for the first time that the 4228 is not the best antenna for reducing multipath and that a good Yagi can do a better job in those situations!! Arrgh !!! Is this true? Would two good stacked or spread Yagis pointed at 280 or 300 do a better job with multipath than the two 4228's? If so, I assume at least one of them would need to be a VHF/UHF combo so I could pick up the NBC affiliate on Ch. 10? Would they need to be the really enormous kind, like the Winegard HD7082P, or could they be one of those more compact ones like the Antennas Direct 42XG or the CM 3022 / 3023 ?

I understand the physics and see why the Yagi may perform better, but just wanted to get some feedback on this before I sink any more time and dollars and see whether anyone thinks a Yagi solution would do away with the problem.

Thanks.

 

[bsr2002]

You may want to go here http://www.hometheaterspot.com/
head over to the antenna spot
and talk to a guy named Tigerbangs. This guys been settin'
up antennas for decades just kidding. He is very
knowledgable.:up

 

[Rick0725]

Before you decide on switching antennas try adjusting the 2 screens till they just touch and install 7 nylon ties spaced evenly to deter the screens from flopping about in the wind. That may help alittle during the wind gusts. Also check to see if the antenna is flopping about on the mast during the wind. You may need to strengthen/shorten the mast to reduce this.

but the trees /leaves may scatter about the uhf signal. The only thing you can try is changing location some...up, down, or side to side ...but what change may help one channel may make another channel worse.

Newer version tuners have the improved chip set which helps with the multipath issues (generation #5). This may be a large factor. The new receivers have improved electronics to counteract the multipath.

there are so many variables and unfortunately you do not find out a change is for the better until you try. I was fortunate enough to have a variety of antennas at my disposal to experiment with.

your issue may just be alignment/adjustment ...rotating the antenna just a tadd either way to see if this lessens the effect.

Combining the 2 antennas the way you have can contribute to your problems. Joining 2 antennas pointed in different directions combining like you have can create issues and is not suggested.

There are no electronics in the marketplace that I know of that can improve this...1 or 2 channels maybe, not a cluster of channels. You can experiment with an a-b switch instead of the splitter to determine if that setup could have created your problems.

So to make a very long story shorter...I would experiment with what you have before you go to the expense of another antenna, since the outcome of a different antenna may not show much improvement.

It could be the older generation chip set contributing to your troubles.

There is also the affect of tropospheric ducting that affects signal in the spring and fall and the south gets hit pretty hard.. see maps below.

http://home.cogeco.ca/~dxinfo/tropo.html

let us know how you make out.

 

[NightHawk]

Now I read for the first time that the 4228 is not the best antenna for reducing multipath and that a good Yagi can do a better job in those situations.

This general statement is based on anecdotal internet evidence and there is no technical reason for it.

Multipath is greatly exacerbated by combining two antennas pointed in two different directions, particularly with the highly reflective situation you are in with the 'solid wall of trees'

 

[Rick0725]

In the above post, I outlined what things can be done to troubleshoot the situation. If all else fails, trying a different approach or antenna is a last resort. But that can be successful or not.

Situations/variables at various sites are different and usually the fix is not always cut and dry.

 

[rjs0905]

Thanks for the feedback. I'll keep tinkering and agree with your statement that it's oftentimes more art than science.

I also know that I'm asking for more issues when I combine 2 antennas into a single downlead, but is there a better solution in this situation? My old DB-4 had enough beamwidth to catch both the 280 signals (NBC, ABC and UPN) as well as all the rest at 300, but the 4228 gave a noticable increase in gain and reliability. Unfortunately, the 4228 is just directional enough that I can't pick up everything on a single antenna, and a bandpass filter (like the CM Jointenna) doesn't seem like a good solution because I need to pick up at least two (ABC/39 and NBC/10) stations off the second antenna.

Is there a comparable antenna to the 4228 that offers slightly less directionality, but still good gain for an urban setting? There is an 8-bay version of the DB-4 called the DB-8, but I've read also that the less directional the antenna the greater your potential for multipath!!!

 

[Rick0725]

rj....

-Why go through the expense of another antenna till you try experimenting a little with the suggestions above. The db-8 will not receive ch 10, is double the money of the cm4228, and you are happy with the results with the cm4228.

-try an a-b switch and see if the 2 antenna setup affects your problems.

-The effects you are seeing may be caused by the movement of the antenna in the wind because the mast is too tall.

-I mentioned that there are not any electronics available to accomodate multichannels on the separate antennas.

Its nice out. Im going to go open the pool.

 

[rjs0905]

So I went out and adjusted the two 4228's, and an interesting thing happened: When I aligned both of them so that they faced precisely the same direction, at a compass heading that appears to be somewhat in the middle of the 280-300 spread between my OTA stations, I was able to get good signal on almost everything I need (low 90's on all stations except for CBS, which is low 80's). Of course, today is not particularly windy or rainy, but it is definitely much better than before.

With only one 4228, the antenna was much more directional and I could only pick up those stations that were within 5 degrees of each other.

I read this article about combining 4228's, one of which is this one:

http://www.hdtvprimer.com/ANTENNAS/16bay.html

Do you think combining the two antennas made the forward "lobe" broader, or perhaps I reversed the polarity, as suggested in the article, and inadvertently created two forward lobes 30 degrees apart, which the article implies is a bad thing but which may not be so bad given my situation?

 

[bhelms]

...Do you think combining the two antennas made the forward "lobe" broader, or perhaps I reversed the polarity, as suggested in the article, and inadvertently created two forward lobes 30 degrees apart, which the article implies is a bad thing but which may not be so bad given my situation?

I suspect the latter, in which case you lucked into a good solution for your specific location/situation. There's enough science to apply to all of this if we could only adequately quantify the results of our trials. Short of that, it's left to "hit or miss" experimentation (albeit, with some seasoned logic applied) and that's what most of us "black artists" are fairly successful with...!

I have yet to solve my OTA situation, but with good weather upon us and the tax refund on its way I hope to make some serious progress in the coming week...!

 

[rjs0905]

One more thing - The original reply mentioned securing the antenna and stiffening the mast against wind.

My antenna is definitely secure, and the mast securely mounted, but it is only a 1" diameter metal pipe that extends about 7" above my deck rail. Given that, it defintely will sway about an inch or so in either direction in high winds, and even will wiggle slightly in a gentle breeze. Is this enough to cause problems, in anyone's opinion?

 

[Rick0725]

radio shack sells a heavier gauge antenna mast, powder coated grey. believe its 1.25" dia.

I purchased a 10' section and cut off about 3' off the top. It is much sturdier then the other mast out there. there should only be about 7' of mast supporting the 2-36" deep cm4228's with about a foot above tripod and a few feet below. anything more is too much.

Deck rail????

Where do you have this antenna and how is it mounted???

sounds shabby!

 

[rjs0905]

Currently, it's mounted through 2 same-diameter holes drilled in the top and bottom 2x6 rails of our back deck, with the bottom of the pole anchored to the deck itself. So the bottom 3 feet is supported by the railing structure (which is plenty sturdy, believe me) and the remaining 6 feet of pole is freestanding above that. But it does sway a little if you give it a push - I think it's just too much weight for a 1" pole.

Following your advice, I've got a 1 5/8" galvanized steel pole that's 7' long. If it doesn't rain tomorrow, I'm going to attach it to the 6x6 post holding up the corner of the deck with some CM antenna mounting brackets I got at Lowe's, ground it, and then mount the 2 4228's to that. Should be almost no movement on that setup - perhaps that will help the situation.