VHF reception in rain

rockstar45 · 23-Aug-2010, 3:00 PM

Just want to find out if this is normal. I have two antennas, a XG91 for UHF in the attic and a YA-1713 for VHF outside on the roof. Both run into a wineguard 2870 preamp.

On a good day my signal meter on my TiVo HD reports 60-70 for my VHF channels (NBC, FOX), but when it rains or is very cloudy it drops in and out from 0-30. My Albany UHF stations (ABC, PBS, CW) are completely unaffected with signal strengths around 90-100.

TVFool report here http://www.tvfool.com/?option=com_wr...9fbede4326facb

Is this normal for VHF in the rain? Is there anything I could do to prevent the drop outs? All of my cable runs are with new RG-6 cable.

mtownsend · 23-Aug-2010, 8:17 PM

Quote:

Originally Posted by rockstar45

On a good day my signal meter on my TiVo HD reports 60-70 for my VHF channels (NBC, FOX), but when it rains or is very cloudy it drops in and out from 0-30. My Albany UHF stations (ABC, PBS, CW) are completely unaffected with signal strengths around 90-100.

Actually, NBC and Fox are not broadcasting on VHF channels. They are on channels 46 and and 19, respectively. The get mapped to channels 6.x and 11.x on your TV through the magic of virtual channel numbers (http://en.wikipedia.org/wiki/Virtual_channel), but the signal is really being sent on channels 46 and 19.

WSWP (PBS) and WVNS (CBS) are the only real VHF broadcasts in your area ("real" channels 10 and 8).

It looks like your attic-installed UHF antenna is the one being affected by wet weather. You are probably not having any problems with your VHF antenna.

It's not necessarily the water in the air that is changing your signal readings. It might be caused by water on your roof or on other objects in your signal path (e.g., wet leaves on trees, neighboring buildings, etc.) that are causing the signals to bounce around differently. If the multipath (multiple reflected signals being picked up by your antenna) is getting worse, it can make life difficult for your receiver. Your receiver's signal meter is reporting a "quality" estimate (it's not a "strength" estimate), so the numbers will go down when the multipath gets worse.

If your VHF antenna is on the roof, can you put the UHF antenna up there too? Getting the antenna up on the roof is a great way to reduce multipath and clean up the signal.

kb2fzq · 24-Aug-2010, 10:59 AM

Quote:

Originally Posted by rockstar45

Just want to find out if this is normal. I have two antennas, a XG91 for UHF in the attic and a YA-1713 for VHF outside on the roof. Both run into a wineguard 2870 preamp.

On a good day my signal meter on my TiVo HD reports 60-70 for my VHF channels (NBC, FOX), but when it rains or is very cloudy it drops in and out from 0-30. My Albany UHF stations (ABC, PBS, CW) are completely unaffected with signal strengths around 90-100.

TVFool report here http://www.tvfool.com/?option=com_wr...9fbede4326facb

Is this normal for VHF in the rain? Is there anything I could do to prevent the drop outs? All of my cable runs are with new RG-6 cable.

Hi RockStar...Bill here in Glens Falls area...
I'm not sure what TVF report mtownsend was looking at, but yes, rf 6, 7, 12 and 13 are our VHF stations, and even tho you're only 45 miles out, TVF indicates they are 2edge, which could complicate matters in inclement weather. Are there mountains around your area, or in the path to the towers?
I actually get a better signal during rain, don't ask me why....but back to your issues...
What I would do, make sure you adjust the direction of the VHF antenna for the maximum signal strength on the TV SS meter while watching WXXA, as you didn't indicate you were using a rotor on the roof. I see the wineguard 2870 preamp is dual input, so any wrong connections there are out, and it's giving 17 db gain on VHF, which is pretty good....the 1713 is a 10 element fire-breather, with 9-10 db gain, so that's good too....
Other then the above direction adjustments, getting the antenna higher up would be my only suggestion, you've got a good system going there...you may find a different antenna direction may yield a higher, more stable SS, other then what TVF suggests the direction should be. Example, my DX stations WPTZ and WCAX should be 24° from me, yet the best SS is at 0°. It may be worth some experimenting....and additionally, you've got one antenna in the attic and one on the roof...if there is a long coax run from antenna to pre-amp on the VHF side, some loss may be occurring with the VHF signal before it gets to the pre-amp...getting that pre-amp as close to the VHF antenna with a short coax would be advised, as the VHF stations are running 10 to 12 kilowatts of power, and the UHF's are in the 600 KW range....the idea of the pre-amp is to bump the signal from the amp to the TV...if you have a lower signal going into the amp, it will be lower out, the old "garbage in, garbage out" theory...my cables between antennas and amp are only 2 feet long...just a thought...
Good luck and let us know how you make out...

mtownsend · 24-Aug-2010, 3:40 PM

Quote:

Originally Posted by kb2fzq

I'm not sure what TVF report mtownsend was looking at, but yes, rf 6, 7, 12 and 13 are our VHF stations, and even tho you're only 45 miles out

Oops. Sorry, my mix-up. Please ignore my earlier post.

rockstar45 · 24-Aug-2010, 6:36 PM

Quote:

Originally Posted by mtownsend

Actually, NBC and Fox are not broadcasting on VHF channels. They are on channels 46 and and 19, respectively. The get mapped to channels 6.x and 11.x on your TV through the magic of virtual channel numbers (http://en.wikipedia.org/wiki/Virtual_channel), but the signal is really being sent on channels 46 and 19.

WSWP (PBS) and WVNS (CBS) are the only real VHF broadcasts in your area ("real" channels 10 and 8).

It looks like your attic-installed UHF antenna is the one being affected by wet weather. You are probably not having any problems with your VHF antenna.

It's not necessarily the water in the air that is changing your signal readings. It might be caused by water on your roof or on other objects in your signal path (e.g., wet leaves on trees, neighboring buildings, etc.) that are causing the signals to bounce around differently. If the multipath (multiple reflected signals being picked up by your antenna) is getting worse, it can make life difficult for your receiver. Your receiver's signal meter is reporting a "quality" estimate (it's not a "strength" estimate), so the numbers will go down when the multipath gets worse.

If your VHF antenna is on the roof, can you put the UHF antenna up there too? Getting the antenna up on the roof is a great way to reduce multipath and clean up the signal.

Hi Bill.

Thanks for the advice. I'll try rotating it when I get the courage to get on the ladder again. No rotor.

I have a 10 foot mast with about 10 feet of coax between the VHF antenna and the amp. I'll see what I can do to reduce the cable length. The total cable I have in the system is about 90 feet from the antenna to the TV. I may be able to reduce this to about 60 by being creative.

If it doesn’t help with my drop outs at least I’ll have a stronger signal. I’ll be sure to report back.

mtownsend · 25-Aug-2010, 10:10 PM

Since you have a pre-amp, the cable losses don't really matter any more. Your pre-amp has enough gain so that it should more than make up for the losses I'd expect to see with about 80 feet of cable.

At worst, I'd expect 80 feet of RG6 cable to drop the signal by around 6 dB on upper UHF channels. Your pre-amp's 19 dB of gain is more than adequate to deal with that.

Tower Guy · 25-Aug-2010, 10:42 PM

Quote:

Originally Posted by rockstar45

I have two antennas, a XG91 for UHF in the attic and a YA-1713 for VHF outside on the roof. Both run into a wineguard 2870 preamp.

On a good day my signal meter on my TiVo HD reports 60-70 for my VHF channels (NBC, FOX), but when it rains or is very cloudy it drops in and out from 0-30. My Albany UHF stations (ABC, PBS, CW) are completely unaffected with signal strengths around 90-100.

In most cases VHF reception is less bothered by rain than UHF. I believe your observation, but question your conclusion.

It looks like you are in North Adams, MA. You have two choices for ABC and NBC. Where is your 91XG aimed, at the Helderbergs, or Mt. Greylock?

Neither of your antennas are designed to pick up channel 6 and you do not show a CBS. It there a reason that you don't have a low band antenna?