Odd Reception Problem

GeorgeIoak · 21-Nov-2010, 2:51 AM

First post in this forum and I tried to find some good answers before posting.

I'm trying to help someone install an antenna at this location:

http://www.tvfool.com/?option=com_wr...81a302332c8386

This project started a couple of weeks ago before I looked up the signal strength on this forum. I picked up a new TV and grabbed a Philips amplified indoor antenna thinking that he was close enough to the tower to get the San Francisco channels (202 degrees).

The indoor antenna was this Philips one http://www.frys.com/product/5915404?...H:MAIN_RSLT_PG. After not having much success I walked down to the Radio Shack and picked up what they had left in stock which was this antenna, http://www.radioshack.com/product/in...uctId=3537124#

After some breath holding and pointing just right we picked up enough channels (~14) and more importantly we were able to watch the Giants playoff game. After the game we decided to try and put the antenna up in the false ceiling (this is a restaurant) and when we did the signal strength dropped enough that we only got 1 or 2 channels. The building is made of metal studs so I just wrote it off that there was too much metal to get a signal.

I just went back today and we tried up on the roof however with a commercial building the roof is lower than the building walls by about 4 feet and those walls have metal flashing. I have a signal strength meter and couldn't get it to read much more ~40dBv on any channel which created my first confusion. I ever stood on a ltter and tried to hold the antenna above the walls of the roof and didn't due much better.

Bummed and confused I figured well lets try that Philips indoor antenna up here and sure enough when it was resting on top of the roof wall we picked up the most channels ever (29) and that was after 100' of coax. When I connected my signal strength meter I was seeing most channels at ~60dBv but this is the first time checking an amplified signal so I wasn't sure if that improvement was just the amplification or if it was really the antenna style.

It began to rain pretty good so I couldn't finish testing but bottom line is that the Radio Shack antenna (I know it's a crappy antenna but it shouldn't be worse than the Philips should it?) barely could get any channels. The ONLY time I found it to pick up channels was when it was inside the building 2 feet off the floor.

I didn't take down notes on everything but I don't think the Philips picked up the KGO station which is the only "real" channel in the VHF band but it's "important" because it's ABC.

Sooo

1) Is the Radio Shack Antenna really that bad of a design?
2) possibly the balun is bad on the Radio Shack?
3) Did I get signals on the Philips because it amplified and overcame the 100' of coax or do I need a dedicated UHF antenna and add a preamp even though there is only 1 coax run to 1 TV. We probably could shorten the cable run to 50' but I think that's splitting hairs.

Any comments or suggestions would be greatly appreciated because I went there armed with my signal strength meter and location maps all rpinted and expected to leave with him getting all these great channels in the bar.

Thanks in Advance!!!
George

John Candle · 21-Nov-2010, 3:53 AM

I say the balun matching transformer is bad. The antenna is a very good design , it is designed for the UHF channels and VHF high channels and thats the channels you are receiving to the south east / south west. Also look inside the coax connector on the end of the coax and see if the outer shield and shield wires are pushed in toward the center wire , use a Small flat blade screw driver or Small point of a knife and push the shied and shield wires away from the center wire. Also the center wire of the coax needs to be sticking out a little ways past the end of the coax connector. Sometimes if the wire is to short and is back in side the connector it won't make the connection inside the balun that the connector is connected to. Connect it all up with the 100 feet of coax and see what you can receive with the antenna pointed somewhere in between KGO 7 and KTNC 14. If a preamp is needed then use this preamp Winegard AP8700 . If one or two tv's are connected.

GeorgeIoak · 21-Nov-2010, 4:28 AM

As I was driving home I was thinking more and more that the balun had to be the most suspicious part of the chain. The coax was a purchased 100' length he bought so the terminations "should" be good.

I think you started to recommend a preamp, possible the ChannelMaster 7777?

I am curious about the high readings I was getting with the small amplified antenna. The meter I have is a DigiAir so it's not some cheap meter. The antenna was using it's own power source and not going through the coax although the meter says it can supply power to some preamps (I think up to 50mA).

Unfortunately he's almost a couple hour drive away so this will have to wait. I guess it's good to have a 2nd opinion about the antenna not being a problem. It was on clearance for $25 so I figured I couldn't go wrong and thought I might have had to eat my words!

The roof area is fairly large, I'd guess maybe close to 100' by 50' and think of it as a bathtub shape with the walls of the bathtub covered in metal flashing. Am I correct to think that with such a large opening that if the antenna is about in the middle of the tub that the signal strength should be the same or darn close to being raised another 6' above the wall? I don't think his lease will allow him to have anything visible from the street.

Thanks again,
George

John Candle · 21-Nov-2010, 7:22 AM

The reason the meter is reading high is because the amplifier in the small antenna is increasing the signal level and the electronic noise level. Now this is what is hard to explain. The amplifier does not make more signal out of the signal that is being received at the metal elements of the antenna. However from a 'point of view' the amplifier adds more power to the signal and this added power from the short length of coax from the indoor antenna when connected directly to the tv can overload tv tuners and be the cause of a bad picture. However the added power is useful to over come coax line and splitter losses. . One might think of it this way. Think of a balloon that is not blown up , now think of the balloon after the you blow air in to it. It is bigger and from a 'point of view' it can do more , but really it's still the same balloon. Or think of a tv picture line doubler , a copy of the original lines of picture information are made and put in between the spaces of the original lines of the tv picture. Yes it does look better , but there is really nothing new there. DVD player Up scalers do the same thing. There is more to it then this. This is my current shot at the explanation.

John Candle · 21-Nov-2010, 8:18 AM

Read and understand this , it can make the situation of the height of the antenna a little clearer. This law does not apply directly to commercial buildings , however there are many satellite dishes and all manner of antennas on commercial and business buildings and many are in plain site. Yes I understand the roof structure. The higher the antenna is above the metal flashing the better the reception will be. http://www.fcc.gov/mb/facts/otard.html

John Candle · 21-Nov-2010, 8:26 AM

It's all really insane , your house and your property , every one on the planet wants to tell you what you can and can not do. So there had to be a Federal law made so you can put antennas on you own property. I see plenty of satellite dishes and other antennas on apartment buildings and all manner of other buildings.

GeorgeIoak · 21-Nov-2010, 2:17 PM

I understand about the amplifier not increasing the actual signal level. I tend to think of it as raising the signal above the noise level to compensate for any signal losses introduced into the installation although that may not be a 100% correct statement.

I was a little confused by seeing such a high level on the meter when measuring the small antenna's amplified signal so I wasn't sure if the meter was seeing the true signal or just everything being raised and it sounds like from what you say it just saw everything raised. What I take from this is that when measuring the actual signal level always measure before any amplification. Since the small antenna had the amplifier built into it I wasn't sure if not powering it up would still put the signal out to the RF connector.

Sounds like from the FCC ruling he should be able to install an antenna above the roof line so I might have him look into that.

I wish I had thought to just go buy another balun since it really seems like that was the real problem but I'm thinking still in theory about the height of the antenna and how much difference getting it above the roof line would make. Now that I think of it, when standing up there I couldn't see over the roof line so I'm thinking the walls are more like 6' tall. But since it such a large area up there wouldn't the signal in the middle of the roof area not be impacted so much by the metal flashing? Here's an exact location so you can see what I'm talking about http://goo.gl/maps/Kj7h

John Candle · 21-Nov-2010, 9:14 PM

Read and understand. http://forum.tvfool.com/showthread.php?t=233 http://forum.tvfool.com/showthread.php?t=695

GeorgeIoak · 22-Nov-2010, 4:11 AM

Just to close this out In case someone else runs into a "commercial" installation like this. I found the ONLY way to get reception was to go above the roof line. Even with a new balun and good tight connections the reception was very low anywhere up on the roof. I ended up about 7' above the roof line with a ChannelMaster 7777 and we were able to pull in I believe 44 "channels". Good enough for me to have a beer and consider it job done.

Moral of the story, metal flashing is not your friend if you are an antenna (or rain for that matter too).