OTA Signals OK then... gone now! Help!!

[thewizz]

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.

 

[NightHawk]

You really can't combine antennas that way.

For example look at your CM4228. It's an array of 8 folded dipoles that are carefully placed physically and electrically combined so that the signal from each dipole adds in-phase more or less at the antenna output terminals. Even as carfully as the 4228 is built, it isn't perfect because everything changes with frequency. The outputs from the 8 dipoles could never add perfectly accross the entire UHF band but it's close enough. This is the reason you don't see any 16 bay bowties produced commercially. There is a limit to how many can be combined because the plane wavefront must intercept each antenna at the same time and that becomes more difficult and less efficient as the physical size of the array increases.

With your setup, it's impossible to combine the outputs of several randomly placed antennas anything close to in-phase, regardless of the fact the cables are the same length. At some particular frequency it might come close but your screwed as soon as you change channel.

Place a single 4228 outside and your problem is solved. Remember, antennas are beautiful.

 

[thewizz]

Nighthawk - thanks for the reply. While I understand (sort of) what you're saying... I have been able to combine signals from multiple antennas with no issues, until last weekend of course. I got a reply on another forum from someone with the same receiver and he was able to help me resolve the issues.

The Samsung T451 receiver needs to go through a COMPLETE rescanning of all channels before it will show any signal strength or anything - when you swapout HD inputs, like I did. Once I did this complete rescan, it all started working again. I even get most other channels I didn't get before now that I have the 4228 in the mix. So I have all four antennas combined via the RS splitter/combiner, all being fed by 25' RG6 cables. With a few exceptions (see question below), the picture on most channels is crystal clear and perfect now.

I got the idea for combining the antennas from here:
http://cgi.ebay.com/BEST-HDTV-off-a...ryZ61396QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

I would suggest that anyone who needs better signal strength or point in multiple directions to take a look at this document.

Thanks again!

Quick question: 2-3 channels still looks like a jigsaw puzzle (not a clear signal) compared to the others. Assuming re-aiming the antennas doesn't help, what would be a good pre-amp to get to help bring in those channels and not overload the ones that look good already?

 

[Bulbman2]

cm4228

I have a cm4228 with wingard pre amp 29 db gain. I can pick up all hd stations in a 60 mile radius from channel 7 to 64

the pre amp does the trick


John

 

[thewizz]

Thanks bulbman2 - do you have a model # for the pre-amp?

 

[branchbouncer]

I'm out 90 miles with a DB8 Terresital improved the reception by adding the Channel Master 7777 pre amp. Pulled in stations that I didn't have before I add the pre amp

 

[NightHawk]

Nighthawk - thanks for the reply. While I understand (sort of) what you're saying... I have been able to combine signals from multiple antennas with no issues, until last weekend of course. I got a reply on another forum from someone with the same receiver and he was able to help me resolve the issues.

I'm glad it works for you but they are not really combining to produce a stronger signal. You would do just as well with a single high-gain, properly aimed antenna, no combiner and a good pre-amp. The four way splitter itself is costing you 6 dB of signal.

 

[thewizz]

Thanks again NightHawk. I am going to take your advice and try the various antennas (CM3679 and CM4228) out one at a time without the combiner in the mix to see if the signals actually improve this weekend. I'll let you know what I find out.

 

[Bulbman2]

channel master cm4228 uhf antenna

Thanks bulbman2 - do you have a model # for the pre-amp?

the pre amp is a winegard #8275 with a #9370 power supply. total cost was around 70 us dollars.

I do have a rotor on a tripod on my roof.

this set up does a fantastic job.... this i supposed to be a directional antenna appears to pick up stations for plus or minus 25 degrees of target direction.

good luck

John