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UHF affect by building

post #1 of 13
Thread Starter 
UHF affect by building

My friend lives about 5 miles from the local TV UHF antennas. She also lives is an area with mostly low homes except a taller office building about 1/2 mile away in LOS of the TV antennas. She presently has an old radio shack double bowtie antenna in the attic.

She is able to get all the local TV stations except the station with rf ch 42 often breaks up. According to antennaweb.org, most of the stations LOS is blocked near the end of the building. However the station with rf 42 is blocked near the center of the building.

Will replacing the antenna with a larger gain antenna, like a quad bowtie antenna help?

I think the singnal will eventually bent over the top of the building. About how far does it take or at what angle does the single bend?

Thanks
Edited by MikeySoft - 8/2/13 at 10:09am
post #2 of 13
Thread Starter 
The station with the problem is WHDH-DT 7.1, rf 42. It is the middle yellow line near the satellite dish on the building. I believe there is no problem with the yellow line to the right which appears to be blocked by two buildings, the second one is taller. I believe thay are the following: rf 32, rf 31, rf 41.
post #3 of 13
How close is your friend to the office building?
post #4 of 13
Thread Starter 
About 1/2 mile

I have notice that the buildings on the map are from a different angle when I zoomed in for the above map. Zooming out gives a more overhead view of the buildings.

When I do that, the left green/yellow line clears the building, the green and yellow lines still go through the building. The right most yellow line goes mostly between the building and the taller building to the right. My friend is only having problems with breakups for the yellow line going through the building.
Edited by MikeySoft - 8/2/13 at 11:18am
post #5 of 13
The broadcast towers must be significantly higher than that office building. Can you see the top of the towers? I would try to aim the antenna upwards to the top of the towers. Try experimenting with different locations in the attic. A couple of inches could mean a difference of receiving the channel or not. Put the antenna to the highest point in the attic.
If you are receiving the other channels fine, I would think its not the building. As a test, try with the antenna outdoors, maybe facing out the window, and see if you can get RF42.
post #6 of 13
I had this happen here, prior to the transition, using a Silver Sensor for the UHF signals from Walnut Grove. Aiming the antenna east, toward the towers, one station would have some A/V drops. The solution was to aim the antenna directly west for reliable reception. Adjusting the antenna was the solution. Two antennas in the attic could achieve the same results if an A-B switch was employed.

If it's multipath, there's doubt whether a "better" antenna will solve the problem.
post #7 of 13
Thread Starter 
Thanks for the suggestion of looking for the towers. I first looked during the day and couldn't see any of them. At night I could not see them or the offending building from the second floor window because of the homes/trees across the street. The attic does not have windows.

I could not see any of the towers at night until I got on the street WGBH, the offending building, is on. I could then see the blinking lights from the towers, they are low in the sky. I verified the WGBH building is between the antenna farm and my friend's home as antennaweb.org indicated.

The small radio shack double bowtie antenna is OK because it can receive rf 43 without any problems. Rf 43 is on a different antenna in the same antenna farm as rf 42 station and is 7 degrees different according to TV fool.

We are going to try a higher gain antenna and hope that works. The smaller antenna is getting some signal from rf 42 but often breaks up as I've said earlier.

The WGBH building has lots of big windows and we hope that is letting some of the signal through.
post #8 of 13
Thread Starter 
We are hoping its not multipath. The area is mostly flat and most of the buildings in the area are lower then 3 floors. The WGBH building and the taller building next to it are exceptions along with a few apartments and a hospital a few miles north and south.

Multipath was easier to tell with analog stations.
post #9 of 13
Quote:
Originally Posted by MikeySoft View Post

We are hoping its not multipath. The area is mostly flat and most of the buildings in the area are lower then 3 floors. The WGBH building and the taller building next to it are exceptions along with a few apartments and a hospital a few miles north and south.

Multipath was easier to tell with analog stations.

Trying to find a sweet spot in the attic with the current antenna is still a good idea. But, if the higher gain antenna does not work, you might want to try a lower gain antenna. The RS double bowtie is better than many indoor antennas being sold today. Today, I have one of the popular flat antennas that does really well with rf 35. This is something that can't be predicted by the antenna design. In one room, everything from Walnut Grove comes in best by aiming to the east. For NBC, the best aim is south. Good Luck.
post #10 of 13
Mike

You mentioned “trees” across the street. How tall are they? And how dense and thick are they? What is the distance of those trees from the front of the antenna in the attic?

If the RF 42 is doing occasional “short burst multi-path”, like a few or several times a minute plus or minus; then it is very likely the trees and possibly the office building might simply increase the occurrence of the multi-path, if it has any affect at all.

If you have any type of signal meter in the TV or DVR or other device; then the short burst multi-path should be visible by watching the meter pop “up” and “down”, like a yo-yo.

If this is short burst multi-path, and if it is caused by the trees, and/or the interaction with the buildings, then often just moving the antenna about 3 feet can make a big difference for RF's 30-45. This includes moving the antenna to a much lower position. Some trees like very large oak and pecan, you may get a solid signal at just 5 foot off the ground, but the signal could be blocked 25 foot above the ground because of the trees.
post #11 of 13
Quote:
Originally Posted by MikeySoft View Post

We are hoping its not multipath. The area is mostly flat and most of the buildings in the area are lower then 3 floors. The WGBH building and the taller building next to it are exceptions along with a few apartments and a hospital a few miles north and south.

Multipath was easier to tell with analog stations.

Multipath reflection can come from any direction, not just from the buildings along the line-of-sight. Your friend lives in an urban area near Boston so there are plenty of opportunity for multipath reflections. Like others have posted, moving the antenna may help. If not you will have to consider a more directional antenna which will be less sensitive to multipath reflections coming from the sides or rear.

Another possibility for the cause of your interference might be from the nearby FM transmitters. The FM signals can created harmonics that interfere with RF42. A FM stop filter from RS may help.
Edited by retiredengineer - 8/4/13 at 9:35am
post #12 of 13
Quote:
Originally Posted by MikeySoft View Post

The station with the problem is WHDH-DT 7.1, rf 42. It is the middle yellow line near the satellite dish on the building. I believe there is no problem with the yellow line to the right which appears to be blocked by two buildings, the second one is taller. I believe thay are the following: rf 32, rf 31, rf 41.
WHDH's antenna is at a height of about 950 feet. Most of the others on the Needham towers are at 1200 - 1250 feet. Normally that would have little effect on the signal at a distance of 5 miles, but it might if there was an intervening obstruction of just the right height. How are WBPX and WMFP? - they are at around 950 feet also, though not on the same tower as WHDH.
post #13 of 13
Thread Starter 
Thanks everyone for their input and good info. WBPX (RF32) and WMFP (RF18) come in fine. From what has been said and my observations, I believe it is more likely the building is causing the problem and not multipath. A quad bowtie similar to this one is on order. http://www.solidsignal.com/pview.asp?mc=03&p=HDB4X

The attic is difficult to more around in as it has a truss construction, has small floor joists, and lots of thick deep insulation. We plan to mount the antenna as high as possible in the attic.

I redid the antennaweb.org satellite map with less zoom. It gives more of an overhead view of the building in the LOS. I'm also posting the satellite map around the antennas so anyone more familiar with the Needham towers can verify my labeling of the signals. It is interesting that WHDH (RF42) and WMFP( RF18) are about the same direction but only WHDH has the problem.

Please note I label WMFP as WFMP on the tower map, sorry.


Edited by MikeySoft - 8/7/13 at 6:24am
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