Aiming, tilt and preamp question - XG-91?

[Probedude]

Hello Tigerbangs,

If you remember, I'm in a 'no signal' area yet I get great reception from Los Angeles, 63 miles away using an XG-91 and a YA10713, no preamp.

Here's my TVFool
http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id%3d27ee97ea5e8d86

Most channels are 98-100% signal strength


One channel, KNBC (Olympics station) has been suffering from pixellation and signal loss now and again. Weather has been cloudy/rainy a bit, signal strength #'s are in the 70 - 85%, sometimes fluctuating a lot, other times rock solid at 85% still with occasional pixellation.

When I originally aimed the antenna I just used a compass. Today I went on the roof and hoped to aim it better for NBC while my daughter called out signal strength #'s. #'s were all over the place - it wasn't clear that I was peaking anything. 0% to 0% signal strength with antenna rotation was nearly 90 degrees. The center of this span was a mountain in the distance.


Questions:
- Given my signal strength is 98% for stations like KCET, and all the stations in LA have their antenna at one location on Mt. Wilson, why would NBC be pixellating
- With signal strength as high as I have, is there any gain from me getting a CM 7777 preamp? Do you think it would help the NBC pixellation problem?
- Should I tilt the XG-91 so it is pointing above or at the top of the mountain that I see in the distance? Why would one tilt the XG-91 at all?
- Does this sound like a multipath problem? I don't get this on other channels. Maybe it's a bit-rate problem? Higher bitrates are more succeptible to pixellation?
- is it odd that my signal drops to zero with such a large turn in the antenna? (like should I get to 0% in only a 45 degree swing instead of 90 degree total?)

This all could just be weather related. It was pretty bad 2 nights ago as a weather system moved in, today not so much but I did aim the antenna in a slightly different direction earlier.

It's a bummer to watch a gorgeous feed from the Olympics only to have the screen break up and halt for a few seconds now and again.

Thanks for your help,
Dave

[tigerbangs]

Rotating the antenna isn't going to help you much: The compass is your best bet when aiming the XG-91. but putting an upward tilt of the front of the antenna by about 20 degrees may help you situation, since you have an obstructed view of the transmitters, and the XG-91 will allow you to aim at the top of the mountain, where you can take advantage of the refracted signals coming from the top of the hill.

[Probedude]

Got my Titan 7777 yesterday, but it was raining so didn't install it until today.

After I originally put up the XG-91 and YA10713, the XG-91 looked like it had a bow to it lengthwise. On the roof today I confirmed it. The lower boom wasn't bent correctly so when it was tightened on the main boom it was making it arc. Took the lower boom to the garage and bent the legs so they were perfectly 90 degrees, reinstalled it and now the XG-91 is straight as an arrow. Tilted it up a tad - not 20 degrees, maybe 5-10, to see if I could get a bit more signal because of a distant mountain.

Installed the Titan 7777 after setting the innards to 'separate UHF and VHF antenna', put the antennas back up and pointed it in the same direction that I had it at before taking it down.

Before touching it today, my signal strength on channel 4.1 was 86-90%, channel 28.1 was 95-98%.
Afterwards my signal strength for channel 4.1 is 86-90%, channel 28.1 is 98 - 100%.

So not much of a change. Was thinking of going back on the roof and taking the tilt out of the XG-91 to see if I made things worse by tilting it and the 7777 is compensating.

Interestingly, NBC on 4.1 (real channel is 36 UHF) has a much higher ERP signal than 28.1. BIG difference yet 28.1 comes in much much better. Per TVFOOL the effective ERP for 4.1 is 10X that of 28.1.

I wonder why I get 28.1 so much better.

Dave

[tigerbangs]

KNBC uses a directional antenna, which concentrates it's signal in different areas than the non-directional KCET antenna does. That might account for the signal difference.

[Probedude]

KNBC uses a directional antenna, which concentrates it's signal in different areas than the non-directional KCET antenna does. That might account for the signal difference.

Wow! Didn't know that. Yep, that would make a difference.
How can one tell that from the TVFool report?

Dave