Hello:

I have a home that has Techshield (made by LP) in the attic (I know :( ), so I figured I would need a good antenna (or two or three) to pull in the signals from ~35 miles away. I read an article on placing multiple antennas in an attic and combining the signals to get a good reception. I had bought a CM3679 and two Radio Shack (RS) UHF U-75R antennas. I put them in the attic facing south ~172 degrees. I also bought a RS 4-way splitter/combiner and three 8' RG6 cables. I have USTec smartwiring throughout the home, so after I combined the signals, I fed it to the USTec system via an unused RG6 cable in the attic. I then plugged the OTA cable into the USTec system and hooked up my Samsung SIR-T451 and bam! 75-80% signal strength for MOST channels in Houston even with Techshield. All the major towers in Houston are at ~171-174 degrees from my home at same general location (~35 mi. away) according to antennaweb.org. But I wasn't getting any signal for PBS or FOX. So to try and fix this, I bought a CM4228, which could fit into a 2nd floor back of the media room closet, which has large/double-wide bay windows facing south - which should work well given the location of the towers, right?. So I figured I would add the forth antenna and all would be well. WRONG!!! That's when all heck broke loose!

The CM4228 is further away from the combiner in the attic, by about 20', so I bought four new RG6 25' cables to combine all the signals from all four antennas since I was told the cables MUST be the same length from the antenna to the combiner. So I hooked it all up and my signal strength didn't go up... it went away COMPLETELY!!!! I have zero signal now on the Samsung. :(

So I backtracked and reconfigured it the way it was 2 weekends ago when I had 80% strength, and still nothing. I have replaced every cable, connection, combiner - tried a RS amplifier - still no signal at all. I replaced a couple of the 75ohm-300ohm converters as well. I even bought a new Samsung SIR-T451 on the off chance that the receiver went out. Still, no signal. I tried bypassing the smartwiring and running a new/direct cable from the combiner to the receiver with no luck. I even tried running each antenna one at a time to the receiver without the combiner - still with no signal. I am at a TOTAL loss as to (a) what went wrong and (b) how to fix it. I bought a CX200 coax cable line tester, but I doubt that will be the solution since I have switched cables out multiple times. I'd like to have a signal strength meter, but they are way too expensive. It's as if all the HDTV signals in Houston went dark! I worked on this for two solid days over the weekend and am about to pull my hair out with frustration. The signals (it did pick up) two weeks ago were SO GOOD, I just can't imagine how it would change so drastically. If it had never worked, I might believe the Techshield was the root cause, but it did work and quite well for most channels.

What could cause the signal to go from 80% to 0% like this using the same attic antennas, cables, receiver, etc. pointed in the same direction??? Any (cheap) method to test signals coming from the antennas? What (if anything) could cause an OTA antenna to no longer send signals across the 75ohm-300ohm converter to the coax cables? Any ideas or suggestions would be greatly appreciated.

Have you tried going back to ONE antenna? Despite what you may have heard, combining multiple antennas facing in different directions is typically NOT recommended due to the multipath/ghosting nightmare it ends up creating.

Welcome to the world of Attic antennas !!

I have been tweeking my 4228 and my SS2000 for over a year now here in Raleigh,NC.

BTW - What is Tecshield?

You say you hooked up the 451 directly to the antenna - did you actually take the 451 up in the attic along with a monitor? Or you mean you routed down to the 451 with just a direct coax line?

Did you try sticking one antenna outside and connecting it directly to the 451 just as a test?

Maybe the big 18 wheeler that was parked down the street giving you a reflected signal has since moved on .

I say this because maybe you were getting a strong multipath signal and whatever was causing it has changed.

DId you try hooking up a analog NTSC tv to the antenna array to see if you can at least pull in analog? Not a perfect test but it may establish if there is a clean break in one of your wires.

Has Houston been experiencing heavy rain conditions or have you? Are the tree leafing out?

Is your roof covered with water from rain?

Maybe you were getting atmospheric bounce that was giving you a signal and conditions have changed.

I am a distance from the stations also and am down in a valley area. I find I have to tweek the antennas. They are very sensitive to postition.

But... zero signal wow ! You sure you got the 451 programmed correctly ? Maybe it lost the remapping info on you.

Just some thoughts and sorry I can not be more of a help.

Is there some unit in your house that you recently powered up that could be messing with the signal?

Also do you know if these are UHF or VHF stations? I am guessing UHF since you purchased two Radio Shack UHF antennas but I don't know what a CM3679 receives.

-Don B

Techshield (spelled wrong earlier) is a product from LP that is a radiant barrier on your roof - one big piece of aluminum foil.

I ran a line from the attic down the attic stairs which is in my Media Room, so close access to TV and HDTV receiver. I tried against each antenna, to include the 4228 which is inside, but facing a window on the second floor - should get good reception from it.

I did get some analog channels, but they were "ghostly", not clear like HD channels two weeks ago.

It rained one day, and completely clear the next. Still no signals.

What do you mean by programmed correctly? The 451 doesn't really have any programming other than scanning for channels and it can't find any.

The CM3679 is a VHF/UHF blue range antenna from Channel Master. Supposed to me quite good.

Thanks in advance for any further suggestions.

Yes, I discussed that in the original thread (briefly), but I did try them one at a time direct to the receiver. Weird, huh?

BTW- they are all pointed in basically the same direction since all towers are in same general area of Houston.

What do you mean by programmed correctly? The 451 doesn't really have any programming other than scanning for channels and it can't find any.

This applied more to one channel than to all but in Raleigh they occasionly screw up the remapping data and I will find "No Signal" where I use to find signal.

I then have to manually enter the real not remapped channel number before the receiver finds the actual signal.

Had this happen with my 451 and also with my Pioneer Media Box.

By the way is an Aluminum sheeth in the attic to an antenna as "Salt" is to a slug?

Boy you have a challenge with that aluminum. Can you open the windows in the attic? Maybe the windows also have some metalic barrier against sun light.

Daniel, Do you think he could ground the aluminum or would that just kill all signal? I am guessing that it would.

I am guessing you are going to have to bite the bullet and roof mount an antenna in some non obvious location.

Don

thewizz,
barlow has listed just about everything you should try, including a couple you might have, if I understood you correctly.

barlow, I don't think grounding the aluminum will make any difference. It is getting in the way of the signal, and connecting it to ground won't change its characteristics in that regard.

thewizz,
I was going to suggest just what you did -- a separate piece of cable run down through the access hole directly to the receiver. Your analog channels are ghosty, so your digital channels will be ghostly, which you don't see as ghosts, but which lowers the quality rating of the signal -- that measurement that we assume is actually signal strength. There could be plenty of signal, so gobbledygooked that the receiver can't make ones or zeros out of it.

About combining antennas: That bit about the cable being exactly the same length is correct if the antennas are all the same distance from the station(s). If they are all in a line like this: | | | then the cables should be the same length. If they are in a line like this, NOT pointed straight but at an angle to one another, like this / / / then the cables should be of different lengths so that the TV signals travel the same distance to the combiner, not to the antennas. Once you add that fourth antenna, at some distance from the others and an unknown same or different distance from the towers, you will have to do some trigonometry to figure out what the wire lengths should be.

The reason you usually don't combine antenna signals has to do mostly with pointing in different directions. If you have a tower to the north and another to the east, and one antenna will always get one of those stations really horribly, you can combine the signals. But what will happen is that the one pointed north will get a good signal from the tower to the north, and the one pointed east will get a horrible or ghosty signal from the tower to the north, and the combiner will combine these, most likely lowering the quality of the better signal. Similarly for the tower to the east.

Since you are aiming them all in the same direction, you shouldn't have much signal difference from one antenna to another.

By the way, you didn't start off telling us why you didn't put an antenna outside, or just put the 4228 in front of the window with an amp. Sorry to suggest these easy things this late in the game.

I think your present problem will turn out to be something terribly dumb that you will be embarrassed to admit. That's usually what it is with me when I get something that makes absolutely no sense and defies all the laws of physics. Remember, when all the laws of physics seem to be being denied, one law is still in play: Murphy's.

barlow - THANK U, THANK U, THANK U!!!!!!!!!!!

Since I swapped out signals, I hadn't done a COMPLETE rescan of ALL channels. I would see "no signal" show-up on 2-X and exit out and stop it - bad move on my part! As soon as I let it do a complete scan, it refound the "real" HDTV signals in the upper UHF range and guess what? It now shows a 80%+ signal meter! :) It even pulls in some of the channels it didn't find before now that I have the 4228 in the mix, which is great!

Now I can take back the "spare" receiver and extra cables I bought over the weekend. ;)

Thanks again!!!

Ernie - thanks for the reply! You were right... the laws of physics were replaced by Murphy's Law, if you read my reply to barlow. Which is why it's good to have a second set of (external) eyes take a look at a problem - can't see the forest for the trees and all that. ;)

Most of the channels now are crystal clear and most of the channels I couldn't see before now show up. There are a couple of channels, namely FOX, which still look like a jigsaw puzzle and reception is spotty. Assuming reaiming the antennas doesn't resolve the problem, I am hoping someone can recommend a good pre-amp to put in that will bring in those jigsaw channels yet not overload the currently good quality channels. Does anyone have any ideas on this?

BTW - here is where I got the ideas for combining multiple antennas:
[Link: cgi.ebay.com]

thewizz, please send me an email, title OTA Madness, so I'll know it's from you.

Thewizz,

The other day I had a light bulb go off in my head that helped me understand this ghosting issue that has been mentioned.

I had to think ATSC and not NTSC.

Ernie can correct me on this if I my theory is wrong but here is what I think.

With conventional old fashion NTSC analog signals you would see on your TV either ghosts or snow when you had a weak or multiple path signals. That is because the analog NTSC tuner was able to transfer the ghost signal thru its circuitry and on to your tv. The analog receivers didn't really care about ghosts they were perfectly happy to amplify them as well as the main signal coming from the stations. Of course you the viewer than had to look at them on the screen which sucked and you would than crawl up on the roof and rotate the antenna in hopes of getting rid of some of the ghosts or you would buy a directional antenna that would help eliminate the ghosts.

BUT... in the digital world of ATSC the tuner can not work with all these simultaneous bit patterns coming from the antenna. It has to decide in advance which one of all those ghosts signals is the one it wants to process into that digital HD signal you see on the tv. It can't do all of them like an Analog tuner does, it can only do one for each channel selected. So... you get 80 percent signal quality but than all of a sudden your signal drops to 30 and picture and sound locks up.

My theory is that the ATSC tuner has temporarily lost the signal it had thought was the strongest one of the ghost signals and has to go back and pick another one.

If you did not have ghosts to deal with, the ATSC digital tuner would be very happy and would just go along happily processing that one good signal it was receiving.

BTY - every one else may already understand what I have said above and I am catching up, or I am totaly wrong which is not unusual.

Dumb Theory - DOn B

You give me great compliments.


I think I do because that is pretty much the theory I have come up with, but I haven't seen it described anywhere. Sometime soon someone will link to an old article that we both missed, I am sure.


The only dumb theory is the one that isn't advanced or has already been disproven.

I heard a great one today -- an AM radio listener was talking to the host, and said pretty much

You're not a loser; there's no way you can be a loser. You are trying, which means you're a FAILURE, not a loser!

No theories advanced = loser. Theories advanced = failure, sometimes.