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Discussion Starter #1
Trying to setup an OTA system with the Samsung SIRT150 box and roof mounted OTA antenna. Here's the setup:


Radio Shack mid-gain antenna, about 5' above roof, pointed nose first straight at towers that are line of sight on top of the local mountain, about 15 miles away. In a strong signal area according to the signal strength site.


75 ohm RG6 cable, about 50-55' run to tuner box located in basement. This is the real high quality heavy RG6 like the cable company uses. Antenna is mounted to metal roof.


Problem--no signal strength, can't figure out why. Antenna is new. Check cable for short, absolutely none. When fully connected to antenna through 75 ohm transformer, measuring about 2 ohms resistance.


When I measured resistance through the SIRT150 when turned on, get infinite resistance, like an open circuit.


Questions:


Is cable run too long, do I need an amp?


Possible problem with antenna, how do I diagnose?


Should I be seeing some continuity across the SIRT150 terminals when the box is turned on?


Do I need to insulate the antenna mast from the metal roof, could that be the problem?


Thanks!


Dan
 

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Try running the antenna directly into the TV to see if you get regular analog programming. That should tell you if you have an antenna/cable problem or a receiver problem.
 

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Discussion Starter #3
Making progress, had the antenna 180 degrees out of phase. But signal still pretty weak for my location. Need amp?
 

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I'd go for a larger antenna first. The signal to noise ratio is a lot better.
 

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what model # is your antenna? i'm surprised your signal is so low if you're only 15 mi away from the towers & you're line of sight. is it possible the signal is TOO strong from the antenna you're using? if that's the case, you'd want a smaller antenna or an attenuator rather than an amp.
 

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The metal roof might be a problem, but I think its not highly likely.


If it is a problem, you don't need to insulate the mast. But you might need to get a lot more than 5' above the metal or get a different antenna that is more tolerant of not being in free space.


If all your stations are all UHF, then you could probably just use a simple single bowtie at that distance with line of sight view of the towers. A single bowties should be a lot more tolerant of not being in freespace than the RS antenna you are currently using (I'm assuming its a corner yagi UHF and log periodic VHF combo antenna).


Being so close to the towers, you also might need an FM trap.
 

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Discussion Starter #7
Signal strength is about 40% of full value on all the stations. Sufficient for lock in with little drop out. But I am surprised it isn't higher given I'm in a prime location for reception. Maybe I do need a better antenna.


Dan
 

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Did you tilt your antenna up and point it at the towers?


As close as you are and with as deep as the Albuquerque valley is, you probably need to actually tilt your antenna up so that it points to the top of the mountain.
 

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Since you are in Albuquerque, I expect the TV transmitters are in the Sandia Mtns which would provide superb coverage of the entire metro area. At 15 miles you should be getting sufficient signal from almost any antenna without amplification if the antenna is connected properly.


I expect you either didn't assemble the antenna properly, are using a VHF antenna for UHF, have a bad transformer, or the RG6 connectors are poorly attached. I would try connecting the antenna cable directly to the TV to verify that you can receive analog UHF. If you can your HDTV tuner is probably bad. If you can't check all of the above possibilites.
 

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Did you check your analog reception as Greywolf suggested? Also, note that I haven't heard of anyone getting much over about 65% on the Samsung meters. Trying your antenna at a 10 or 15% angle above horizonal may also be good.
 

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Radio shack makes an in-line amplifier that you install up on the roof near the antenna. It actually amplifies the signal at the antenna end and then sends it through the cable. The power unit that powers it is at ground level and it is powered through the cable itself so there's no power needed at the antenna. I've done several rooftop installations and have always needed one of these for cable runs of 50 feet or more. Check RS part number 15-1170 or 15-1108. I'd try the 1170 first because the 1108 boosts the signal so much that it can cause ghosting if you are too close to the station, even if you turn it down all the way.


Mike
 

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Discussion Starter #13
Thanks, everyone, I'll tilt the antenna tomorrow. Reception seems pretty good now, only have one channel that sometimes takes several tries to lock in on.


Even DTV is a huge improvement over analog cable!
 

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If tilt doesn't help, try a good low noise VHF/UHF preamp like the CM 7777 . You may need one for a long cable run.


Albuquerque, like many cities, has both VHF & UHF digital stations.
 
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