Temperature and Reception

[freedy]

When I set my antenna up last fall it was nice and warm and the reception was superb. I got every channel I could hope for with a medium to strong signal. As the whether changed and it started cooling down I noticed I would start losing quite a few channels in the evening. As winter came and we had some cold spells (by Coastal Southern California standards) where temps got down into the 40s and 50s I would lose everything. I've had it setup now for four months or so and I can say the temperature reception correlation is near 100%. Before I mounted it outside I had it in the house for about a year and that didn't seem to be affected by the weather, but I think the reception relied on signals bouncing off the walls as I had to readjust the dual antennas from time to time.

I have a Antenna's direct DB8e which is classified as a UHF antenna but I can say that it seems to pick up VHF just as well and there doesn't seem to be any obvious correlation regarding what frequency ranges start dropping first.

Below is my heat map and as you can see nearly everything I get comes from Mt. Wilson 57 miles to my east. After the heat map link I am including a picture of my installation which I'm sure has something to do with the problems. I don't have a lot of choice where I put the antenna so I'm hoping I'm able to gain some insight on why reception is so temperature sensitive.

http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id%3df1f019387c457f

In the picture Mt. Wilson is to the left of that chimney more or less behind and/or above that olive tree in the center of the picture, also more or less to the left of the chimney. I also wonder about the plane of the roof as the antenna is just above the roof. So again, I'm cognizant of these issues I'm just hoping to gain some more intelligent perspective of what is likely to be causing the temperature sensitivity.

[ADTech]

The swings in temperature are also likely responsible for the formation of inversion layers which will affect the propagation of signals from almost 60 miles away. Given your proximity to the coast, there also many be a different pattern of marine boundary layers that move in from off-shore and affect the radio path. The winter months are well known for the anomalous propagation conditions in Southern and Central California.

Your best countermeasure is to get some extra height on the receiving antenna since you cannot change the weather. In addition to getting the antenna into what would be expected to be a stronger signal zone, that extra height will also get the antenna further away from the roof which may be causing a destructive "ground bounce". You will likely have to experiment with the exact height (over time) to find what's the best compromise for your specific location.

[freedy]

Thanks for that information. It's more or less what I expected to hear but now I'm not just guessing or assuming. My guess is that it is the signal bouncing along the roof because I wasn't having these kinds of fluctuations when it was in the house the prior winter.

Regarding raising the antenna, how much higher are you thinking? I have it on a j-mount installed on the facia at the apex of the roof. Is there a way to add an extension of the type required? From what I've found, taller j-mounts will only get me another 6" or so.

[Stereocraig]

Thanks for that information. It's more or less what I expected to hear but now I'm not just guessing or assuming. My guess is that it is the signal bouncing along the roof because I wasn't having these kinds of fluctuations when it was in the house the prior winter.

Regarding raising the antenna, how much higher are you thinking? I have it on a j-mount installed on the facia at the apex of the roof. Is there a way to add an extension of the type required? From what I've found, taller j-mounts will only get me another 6" or so.

I'm not sure I'd want to go too high w/ one of those, unless you mounted it to some sort of spreader plate.
Directly hitting a rafter, or tie beam w/ at least two of the lag bolts, would be a plus.