Metal Roof and multi-path

[shoman94]

Attached is a screenshot of my location and tower placement. My problem is I have been fighting a reception issue with one station and is my strongest UHF tower (real channel 44 WCSH) and I've had to lower the antenna to 2 feet above the roof peak to stop the glitches/pixels. It is also aimed at about 25 degrees magnetic. If I rotate it from this location is each direction I have issues with this station and only this station. Last night I watched that station for a few hours and saw it glitch a couple times so I have it pretty good. I'm watching it this morning and haven't seen an issue yet. I'm wondering if I should leave it alone or should I move the antenna to the other end of the peak in hopes I could raise the antenna and strength all my weaker station even though they are currently coming in good. Is what I'm seeing due to it reflecting off the roof? It just seems messed up that channel 8 and channel 13 are also coming off that side of the roof and give me no issues.
Yesterday I tried and DB4e in place of my C4V and has the same issue.

Here is my TVFOOL for UHF@20ft
20ft TVFOOL

Here is my TVFOOL for VHF@26ft
26ft TVFOOL

[rabbit73]

What happens to WCSH if you aim the antenna directly at its transmitter 347 degrees magnetic?

I'm seeing due to it reflecting off the roof?

Maybe, but it is more likely because the antenna is not aimed at the transmitter.

It just seems messed up that channel 8 and channel 13 are also coming off that side of the roof and give me no issues.

Even if channels are in the same general direction, they can react differently because of the difference in frequency and terrain path.

Why, if your antenna is aimed at 25 degrees magnetic, do you expect good reception of WCSH which is at 347 magnetic? Multipath reflections are more likely when the antenna isn't aimed at the transmitter.

I'm wondering if I should leave it alone or should I move the antenna to the other end of the peak in hopes I could raise the antenna and strength all my weaker station even though they are currently coming in good.

It is difficult to predict the results of moving the antenna; you just have to try it.

[shoman94]

Originally Posted by rabbit73

What happens to WCSH if you aim the antenna directly at its transmitter 347 degrees magnetic?
Maybe, but it is more likely because the antenna is not aimed at the transmitter.

Yes but any higher than 2ft above the roof gives me problems. But it's only that channel.

Originally Posted by rabbit73

Why, if your antenna is aimed at 25 degrees magnetic, do you expect good reception of WCSH which is at 347 magnetic? Multipath reflections are more likely when the antenna isn't aimed at the transmitter.
It is difficult to predict the results of moving the antenna; you just have to try it.

That channel is very strong and it falls within the side lobe off the main beam for my C4V. It also falls within the beam of the DB4e and also happens when pointed directly at it. The problem is when I raise it above 2 ft above the peak it happens even pointed directly at it.

[rabbit73]

If you did aim the antenna at 347 and you see a difference with a small change in height, then it is probably due to a roof reflection which can help or hinder the direct signal.

The path for the reflected signal is longer than the path for the direct signal. When you change the height, you change the path length of the reflected signal so that it arrives at the antenna at a different time, which changes the phase relationship of the two signals.

[shoman94]

Originally Posted by rabbit73

If you did aim the antenna at 347 and you see a difference with a small change in height, then it is probably due to a roof reflection which can help or hinder the direct signal.

In my case it hinders so that's why I asked about moving to the other end of my roof so then it should not reflect off the roof.

[ADTech]

Move the antenna and try again. Repeat as needed.

[shoman94]

Originally Posted by ADTech

Move the antenna and try again. Repeat as needed.

It's a lot of work lol. I was hoping for some experience that maybe someone experienced. It will also add 40 feet of RG6 and require me to install a new ground rod on that end of the house.

[shoman94]

So I ended up moving my mast to the other end of the house. I had to run an extra 50ft of RG6. So I started with my C4V and being that WCSH was coming from the side lobe even at 95-100% signal I was still having issues. It was mainly audio (DD5.1 cutting out every 15 to 30 seconds). Once I got it with the main lobe WCSH6 was perfect but I started having issues with WPFO. Even though I was able to raise the antenna higher on this end I ended up 34 feet closer to a large tree which made WPFO/WCSH not work at the same time. I then replaced the C4 with the DB4e and all is well thanks to wider horizontal beam.I ended up aiming it at 10-12 degrees magnetic for the UHF and about 25 degrees magnetic for VHF. I lost VHF-hi channel 10 (lost around 15db SNR) for some reason as the Dipole has not changed! Thankfully there is a sister PBS re-broadcasting WCBB UHF channel 45 WMEA.
To anyone who reads this.... try not to place the antenna in a way it had to travel across your roof in any direction or you'll likely end up with multi-path issues no matter how strong your signal is.