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Discussion Starter · #1 ·
Hey all, the weather is better and it's time for me to start trying to get OTA HDTV again. Last years experiments lead me to the conclusion that I may have a multipath problem as well as a weak signal problem. Short of putting up an 80ft. tower, I don't know if I'm going to get reception. I am about 40 miles from the Needgam, MA towers as the crow flies.


Some quick questions:

1) To see if you have multipath, is it true that you can tune into an analog signal ans look for ghosting?

2) To check for a weak signal, is it true that you should look for snow?


I am getting both of these and I don't feel that I can do anything about the snow, but I do know that if I could get rid of the ghosting, I should be better off for getting HD reception.


I was planning on horizontally stacking 2 Radio Shack Yagi's with a CM preamp. I would go with CM 4248 yagi, but my local store won't let me return them, whereas with RS, I can. I figure this will allow me to fix any multipath problem I have. If i get intermittent reception with RS yagi's, I'll upgrade to the CM 4248 and try again.


I read I should space them apart by 36", does that sound right? To join the signals, what should I do? I read that making sure the coax cable from each antenna to a splitter(which will work in revers as a joiner) should be the same length. Is it accurate to say I can use a standard 5MHz-2GHz splitter as a joiner?


You responses are greatly appreciated.
 

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Quote:
Originally posted by Beefcake
Hey all, the weather is better and it's time for me to start trying to get OTA HDTV again. Last years experiments lead me to the conclusion that I may have a multipath problem as well as a weak signal problem.
I take it you were involved in a thread on this subject previously. If you furnish a link to it, we can all find out what opinions and advice have already been contributed.


There are lots of threads on stacking in this forum that you may find helpful. You can find those using the SEARCH function.
 

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Beefcake - I too have been battling multipath in my area. I am about 20 miles from the transmitting towers and have had chronic "ghosting" on my analog stations. I've tried a CM 4228, but it did not solve my problem. I have created a horizontal stack of the RS 2160 antennas...about 46 inches apart, and I can say, that I have since watched multipath free reception on two local channels for the past several weeks. I still need to "fine tune" the location of the antenna, but I do believe you would see better results with a horizontal stack. Keep in mind that you have to be very precise with the horizontal and vertical adjusting of them...I believe you want to ensure that they are no more than a couple of degrees in difference from one another - This I found to be the most challenging.


Snow is either a week signal or a lot of interference. A amp may help. I would suggest trying the horizontal stack first, and checking your signal strength with it. If it is in low to mid 70's, introduce the amp. Some say an amp can just introduce more potential multipathing and interference and should only be used in drastic situations.
 

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Quote:
1) To see if you have multipath, is it true that you can tune into an analog signal ans look for ghosting?
YES
Quote:
2) To check for a weak signal, is it true that you should look for snow?
YES

Here's a technical overview of antenna stacking, discussing the benefits of horizontal and vertical stacking, and how far apart to mount.

Stacking TV Antennas
 

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I agree if you see ghosting on analog channels, you have a multipath problem. I would say the opposite is not necessarily true.


Multipath can be very frequency specific, as to what actually hits your antenna location. I have very bad ghosting/multipath on only 4 channels (19, 42, and 56).


I have virtually no multipath problem with other channels, and no ghosting or multipath problems with close by channels like 43, 44, and 20.


Note: 19, 20, 43 and 44 are even broadcast from the same tower!
 

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Quote:
Originally posted by jhe
... Multipath can be very frequency specific, as to what actually hits your antenna location.
Very true. Which also means that good or bad analog channel reception will not necessarily mean the same for the station's digital counterpart.


I have 2 analogs that are unwatchable due to multipath, but the same station's digital channels come in drop-out free. And another analog channel is nearly perfect, but I sometimes can't get reliable reception from that station's digital channel, due to dropouts caused by multipath.


All of these stations transmitters are on the same mountain, and most are on the same tower.
 

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IMO, the best tutorial on stacking is here: http://www.grantronics.com.au/docs/StkYagis.pdf


Extensive threads on fighting multipath and how stacking can help are here:
http://www.avsforum.com/avs-vb/showt...0&pagenumber=1


and
http://www.avsforum.com/avs-vb/showt...hreadid=191672


An excellent source for hardware for tilting and stacking (and results of tests with and without stacking) is here:
http://www.atechfabrication.com/


Also, jhe (posting above) has many very useful posts on the subject.


As for my own experience, I have no line of sight to the xmitters and all analog UHF channels had tremendous ghosting (multipath) and lowish signal amplitudes using a single Blake JBX21WB antenna with preamp. Stacking two of these Blake antennas got me stable reception on all but one of the digital stations here and cleared up the ghosts on analog UHF channels.
 

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quote:
Stacking two of these Blake antennas got me stable reception on all but one of the digital stations here and cleared up the ghosts on analog UHF channels.


Horizontally, or verticallly?
 

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Thanks for the link to the stacking article. I remember reading it last year when I first got into stacking issues. Another good source of info is member GlennL's site at www.atechfabrication.com . I learned a lot from reading and re-reading Glenn's tests.


I live 60 miles south of the LA transmitters on top of Mt Wilson (5600 feet...), on the east side of a north-south running valley about 4 miles long. The direction to the transmitters is about 350 degrees (true) so I have a pretty clear shot up the valley to the NNW. Even so, the combination of being so far away and having lots of "hills" between here and Mt Wilson means that I still get significant amounts of multipath. Analog reception on a handheld yields very snowy pictures (some where the color is gone...) on most UHF channels and with at least some ghosting on most as well. Moving around helps with some of the weaker stations so antenna location can be as important as any other factor.


I started out with a single 2160 and a DTC-100, soon switching the DTC-100 out for a Hughes E-86. I was able to get a few channels and decided I needed an amp. After trying everything in Radio Shack's catalog and what was available at my local Lowe's, I found that none of these added anything to the SS numbers I was getting on the E-86. After more research here, I found that the CM 7775 worked where the others didn't because of its low noise factor (2.0 dB). I got one and bingo! It mad a very big difference and I was able to get reception on all the channels (12 when they're all working...). Some channels were "borderline", however, and would break up or not work at all on some nights. Again after more research here, I ordered a CM 4228 8-bay BT antenna and mounted it and the 7775 to a 15-foot mast which was attached to an upstairs deck post. That put the 4228 about 3-4 feet above the roofline. This was my main setup until January this year. I still would experience 1-2 dropouts a day on some channels but for the most part it worked quite well.


In January we had some 75 MPH Santa Ana winds that ended up breaking my 15 foot mast in half. The 4228 ended up half mangled, up against the fence on the other end of our yard. As it was, I had been reading up on stacking, thinking it might be the answer to my occasional dropout problem. I ended up using about $10 worth of PVC parts and two 2160s and stuck the combo in a wind-protected corner of the same upstairs deck. Here's a photo:

http://www.ceoanalytix.com/AVSForum/...%202160s-1.jpg


By that time I had found that a RS cable amp (15-1171) worked as well as the CM 7775 if the cable runs from the antenna were about 30 feet or less. I ran the output of the dual 2160s in through a hole in the wall into the bedroom so the cable length was only about 12 feet. From there it is about 50 feet to the receiver. Anyway, this new setup has worked perfectly since setting it up (just before the Super Bowl...) and I haven't had a single dropout since then. Here's a graph based on "numbers" from my HD200:

http://www.ceoanalytix.com/AVSForum/...160x2+1171.JPG


Here's the data from an earlier E-86 test:

http://www.ceoanalytix.com/AVSForum/...est%20Data.JPG


And for "completeness", here's the results of my earlier tests of some other antennas:

http://www.ceoanalytix.com/AVSForum/...t%20Data-1.JPG


There are some other threads here with more of the same but I'm too lazy tosearch for the threads. I think one was titled "New Antenna Tests...".


-- Gary
 

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Discussion Starter · #13 ·
Thanks for all this great info, but there is still one question I don't have the answer to.


What to do use to join the two antennas together? Thanks
 

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Don't use a resistive combiner/splitter such as is commonly available at Radio Shack. They are lossy (about 4db) and therefore worsen your signal to noise ratio.


Instead, use a so-called ferrite "hybrid" coupler from Channel Master. When used to combine two similar signals, the loss of this coupler is only about 0.5db. the part number is: 0538.


As stated above, the cables should be the same type (RG 6) and the same length within a fraction of an inch.
 

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Discussion Starter · #16 ·
sorry if I'm being stupid, but here's a specific question about the combiner/splitter.


I have a Regal 5-1000MHz 2 way splitter that says 'DS2DGH10' and '120dB EMI Isolation' on it. The cable company installed it when I got c able modem service and I don't need it for the house. Can I use this device in reverse? Thanks....
 

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It's almost certainly a resistive splitter. If so, if you use it in reverse as a combiner it will have a loss of about 4db. It might work, but you'll get about 3db better signal to noise ratio with the Ch. Mstr 0538.


It all depends on how strong your signal is to begin with.
 

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I think it's the best.


Remember to keep the cables from the antenna to the combiner a short as possible.


If you have weak signals you may benefit by using a preamp near the antenna connected to the output of the combiner.


A good low noise preamp is the Channel Master model 7775 (UHF only).
 

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A splitter may have a loss when it is splitting a signal but I'm not so sure that is true if you turn it around and ar combining signals. In any case, I've been using a "higher end" (i.e. gold plated so they can charge more...:)) RS unit that does show a 3.5 dB loss per output when using it as a splitter. Turned around for use as a combiner, it seems to work just fine, although I do use it with an amplifier. I'll have to order one of these 0538 and see if it does work better.


-- Gary
 
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