Need to get a stronger signal - use an antenna pre-amp?

[Mr. Burn]

I live in Round Rock TX (just north of Austin) and use OTA signals with the digital tuner on my HDTV. According to AntennaWeb the major stations are about 15 miles away and all between 195-199 degrees. A year or so ago I put up a directional 40" UHF antenna in the attic. (All but 1 station in central TX is UHF.) I get the main station fine but I also want to get the PBS station in Belton. It's 45 miles away in the opposite direction at 3 degrees. So, I put a second 40" directional antenna pointing at 3 degrees. I used a Radio Shack splitter/combiner to combine the two antennas at their 75 ohm connections from the mask before the RG-6 starts it's 75 foot run to the TV. The Belton signal is not very good with this set up. There's not enough signal for the digital station but we get the analog signal which is very fuzzy. The antennas are in the attic of a 2-story house and there's no big structures blocking the way. Texas is flat so I know there's no mountains in the way either.

My problem is how to get the digital signal from Belton. Perhaps there's a better way to combine the signals but I was thinking an mask amp would be the way to go. I could put the antenna outside the get more signal but that's a last resort since it doesn't look too good and the chimney I'd strap it to comes out of the peak of the house so it's waaaay up there. (Yes, I'm chicken. Especially after falling out of a tree a few years ago.) I was thinking of putting an amplifier at the second antenna before it goes into the combined signal. But, how do I know what dB amp I should buy? If I get one that has too much of a boost, will it interfere with the good signals from the other antenna? I don't know of any good way to figure it out than to buy something and return it if it doesn't work then buy something else. I'm looking at starting with a Winegard AP 8275 (28 dB gain with 2.8 dB noise). Solid Signal has it for $43. Is 28 dB too much? If the signal is low from being inside, it may not matter how much of a boost I give it.

Thanks

[JohnnyMalaria]

Combining the two attenna signals is probably doing you a lot more harm than good. What happens if you take the splitter/combiner out of the equation and try to view the PBS station with your second attenna? Does that improve things? If so, that will indicate that combining the two is not a good idea.

Here's a description of the issues affecting the merging of feedlines:

http://www.hdtvprimer.com/ANTENNAS/merging.html

[edDV]

Which antenna are you using? 45 miles would need a more powerful directional antenna. 15 miles is easy.

You will get better results with a larger directional antenna than trying to amplify a smaller wider focus model. You just amplify noise. Also attic installation requires a larger antenna than mast mount.

Transmmiting power of the target station is also a consideration. They may be trying to avoid overlap with KLRN-DT.

Good antennas for 45miles (red zone?). You may need a blue zone model for attic mounting.

http://www.summitsource.com/antennacraft-mxu37-uhf-tv-antenna-maxus-37-electronic-elem...37-p-6234.html

http://www.summitsource.com/8-bay-uhf-digital-antenna-hdtv-terrestrial-34-electronic-e...le-p-8208.html

PS: You are inside the 41dBu contour so I'd expect a red zone attic mount would be enough. Plus they are 500KW which is good.
http://www.fcc.gov/fcc-bin/FMTV-service-area?x=DT1251496.html

[MOVIEGEEK]

This amp has a variable gain:
http://www.beachaudio.com/Ce-Labs/6001-p-54071.html#Description
More reviews:
http://www.amazon.com/LABS-6001-Prograde-Bi-Directional-Amplifier/dp/B000BLEMHU

[JohnnyMalaria]

As I understand it, an amp for the second attenna before the combiner is a bad idea. You'll compound the problems that combining will have on the other signal.

I think you really need to use one of the options in the link I provided. Or, space the two antennas such that they are in phase for the weaker signal (i.e., an exact multiple of the wavelength which you can calculate from the transmission frequency). This will minimize cancellation. To minimize ghosting, the length of the cables should also be chosen so as to ensure the reflected signal is in phase with the original signal at the combiner. But if that means the other channels are out-of-phase, you are back to square one. I've had to deal with this while designing RF-based scientific instrumentation and it can be a real pain.

[edDV]

Here are the user's targets. They may be reachable with a pole monted omni but with attic install, two directionals would be optimal. Idea is equal signal stregth and S/R ratio at the combiner or one antenna will overwhelm the other with noise or signal strength.

RF follows the square law (like light) where signal strength drops as a square of distance (ignoring blockage). Assuming equal transmitter power, KNCT being 3x the distance will need ~9x the antenna gain to match levels and signal to noise at the combiner.

The active combiner shown by MOVIEGEEK allows gain adjustment to match levels but shouldn't be used to boost a weak antenna since noise would be amplified equal to desired signal. The KNCT pointed antenna needs to be ~9x the gain of the Austin pointed antenna to get a balance at the combiner.



JohnnyMalaria, hopefully the Cable Labs certified active combiner manages impedance within reason.

[JohnnyMalaria]

I was curious to look at the coverage of some of my local stations and came across a helpful section on the FCC's site:

http://www.fcc.gov/dtv/markets/

(Sorry if this has been mentioned before.)

Click on your market and you'll get a PDF file with a page per station. It shows the location of the existing analog and new digital transmitters plus the coverages for each including (what I assume are) empirical measurements to indicate where reception will be gained or lost. In my area, it is interesting to see that at least one station has moved its transmitter a considerable distance shifting the coverage along with it. Most stations are increasing their reception area (radius). But there again the stations that we should be receiving right now are very poor (with rabbit ears). But we get our local channels via DirecTV (at a cost, thought).

[Mr. Burn]

Thanks everyone for such great advice.

It looks like the first thing I need to do is check one antenna at a time and see if I can get the digital signal from Belton. Depending on that signal strength, I'll either get the 60" antenna (weak signal) or a jointenna for the one channel if there's a strong enough signal from the existing 40" antenna. I'll keep you posted.

[Russ1]

You may want to check this site out. There is a lot of good info.
http://www.dennysantennaservice.com/1485506.html

[lacywest]

Also ... how close are the two antennas to each other ... if too close together that can become a problem. For my outside antenna ... I made sure my antenna ... simple bow tie type with reflector ... was weather proofed.

I added extra insulation material to all the areas that had flimsy thin plastic for preventing the frame from touching each other. I attached the coax cable securely to the antenna and then attached it to the terminals on the antenna. I then used alot of electrical black tape to wrap around everything. I have it mounted on a 15 foot pole on my chimney and I do not want to take it down soon.

I use a Motorola Pre-Amp to increase the signal ... once it enters my attic and then splitters are used to feed the different areas in my house.

I have good results. For your setup ... any chance of mounting a Pole on a structure on your roof ... or attach a pole to the side of your home ... have it located on opposite side of the roof and maybe that TV signal will come in. But for that signal that is 45 miles away ... yep ... try using a Directional antenna [Yagi type] ... and if possible keep it separate from the one you are already using ... their presense next to each other will not help at all.

[Mr. Burn]

Whoo Hoo, I'm making progress!

This morning I was able to try some more things and I think I have a good path forward. First, let me tell you a little more about how my system is set up. There are two 40" antennas on the same PVC-pipe mask facing opposite directions (at about 184 degrees apart). The two feeds go into a splitter/joiner and then out the attic, down the side of the house and into the family room. It's then split to go to both the TV (with an HD tuner) and the DVD/hard drive recorder which has it's own HD tuner. This morning I disconnected both the splitter/joiners so that the antenna pointing toward Belton went directly into the TV downstairs. I found that if I moved the antenna to the other side of the attic, the Belton analog station came in clearly and I can tune in the DTV station. Not only that, but there are THREE digital stations that come from that station and I get them all. However, the signal is still weak since there is a lot of pixelization going on. When I split the signal to go to both tuners, I lose the Belton digital stations which makes sense because of the weak signal to start with. I also noticed that although the antenna is pointing away from the Austin stations (which are only 15 miles away) I get them in clearly, even when I split the signal for both tuners. This tells me that I probably just need to get a larger antenna so that I can get a larger signal from Belton. And, because the Austin stations come in fine, I don't need to add signals from two antennas. I plan to order the AntennaCraft MXU47 (similar to what edDV suggested above but it's the next size up since the MXU37 has been discontinued). I would think that with an 80" boom I should get plenty of signal and be able to split it for both tuners.

Do this sound like the correct course of action?

[edDV]

Whoo Hoo, I'm making progress!

This morning I was able to try some more things and I think I have a good path forward. First, let me tell you a little more about how my system is set up. There are two 40" antennas on the same PVC-pipe mask facing opposite directions (at about 184 degrees apart). The two feeds go into a splitter/joiner and then out the attic, down the side of the house and into the family room. It's then split to go to both the TV (with an HD tuner) and the DVD/hard drive recorder which has it's own HD tuner. This morning I disconnected both the splitter/joiners so that the antenna pointing toward Belton went directly into the TV downstairs. I found that if I moved the antenna to the other side of the attic, the Belton analog station came in clearly and I can tune in the DTV station. Not only that, but there are THREE digital stations that come from that station and I get them all. However, the signal is still weak since there is a lot of pixelization going on. When I split the signal to go to both tuners, I lose the Belton digital stations which makes sense because of the weak signal to start with. I also noticed that although the antenna is pointing away from the Austin stations (which are only 15 miles away) I get them in clearly, even when I split the signal for both tuners. This tells me that I probably just need to get a larger antenna so that I can get a larger signal from Belton. And, because the Austin stations come in fine, I don't need to add signals from two antennas. I plan to order the AntennaCraft MXU47 (similar to what edDV suggested above but it's the next size up since the MXU37 has been discontinued). I would think that with an 80" boom I should get plenty of signal and be able to split it for both tuners.

Do this sound like the correct course of action?

One caution, the longer the antenna the more directive it is, hence less signal will be accepted from the side or back. I'm looking for a polar plot for the AntennaCraft MXU47 but no luck so far.

If this becomes a problem for the Austin staions, a smaller combined antenna pointed at Austin may fill the gap.

40" for Austin at 15 miles seems excessive (too strong).

[Mr. Burn]

Thanks for you help edDV. I'm open to other models as well. Summit source also had a Channel Master 3023 that might work. The MXU47 might be a bit of overkill since I'd be going from a 40' boom to 80"boom.

[edDV]

Thanks for you help edDV. I'm open to other models as well. Summit source also had a Channel Master 3023 that might work. The MXU47 might be a bit of overkill since I'd be going from a 40' boom to 80"boom.

Yes Channel Master and Wineguard are top tier. They are changing models to optimize the new TV bands

Old VHF: 2-13
New VHF mostly 7-13

Old UHF: 14-83
New UHF: 14-51

New combo antennas opitimize VHF-Hi/UHF-Low 7-51
By redesigning these antennas to the narrower bands, higher gain can be achieved in smaller size.