Hello and welcome!
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Originally Posted by Rosa
After the transition, several of the Bay Area stations moved the location of their broadcast antenna on Sutro Tower in San Francisco, work that wasn't completed until October. I lost ABC7 KGO-DT for a while after October, but I can get it most of the time now. I regularly have to rescan and sometimes even do the power off thing, which is supposed to clear the converter's memory.
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Yes, KGO was broadcasting with lower power for a while, but things should be better now. They are on a VHF channel, so if you antenna is not good at handling VHF channels (some antennas that say VHF are not actually that good at VHF), that might be part of the problem. KGO is quite strong at your location, so the right antenna should be able to pick it up easily.
Do you know the make/model of your antenna?
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It seems to me that certain weather patterns interfere with the reception. Is that possible with DTV?
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Yes, weather can affect signals. The water in the air can absorb a little of the signal energy. Another common phenomenon is that trees in the path of the signal get wet and become better signal blockers due to the increased water content. This was true even in the days of analog television.
If you can visually observe these weather-related signal dropouts, it usually means that your signals are operating near their minimum levels. If losing a small amount of signal causes a channel to go away, then it means the channel has dropped below its operating threshold (the so-called digital cliff). If you can improve the signal strength and/or quality reaching your receiver, then you'll have more margin for error when dealing with these external influences (seasonal changes, storms, interference, etc.).
A better antenna might fix some of your "borderline" channels.
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I have never been able to get KNTV-DT (NBC). It's transmitted from a different tower down in the South Bay. Yet, I can get KFTL-CA, which seems from your Google Earth map to be transmitted from a tower in nearly the same location.
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KNTV is being broadcast from San Bruno, which is just a little south of San Francisco. It's about the same distance and about 20 degrees further to the south than Sutro tower. It is also broadcasting on VHF (channel 12), which makes me think that maybe your antenna's VHF performance is really not what it should be.
FYI, KFTL-CA is also broadcast from San Bruno.
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How important is the angle at which the signal leaves the transmitter?
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It is very important. Many broadcasters use directional antennas, so their emitted power is not equal in all directions. In some cases, the broadcaster must try to minimize power in certain directions to prevent interference with stations in neighboring markets. So a 1 megawatt transmitter does not mean that it emits 1 megawatt in all directions. You may, in fact, be seeing much less than the "peak" power that a station claims.
The signal analysis tools at tvfool already take this into account. If you are receiving signals from "directional" transmitters, your angle with respect to each transmitter has already been factored into the equations.
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Another question, do TV stations increase/decrease their power at certain times of the day? Could that be a factor in reception?
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That used to be a common practice, but is not so common today.
What you will see more often is that the changes in the atmosphere will cause signal increases and decreases throughout the day. Sunspot activity and meteor showers can also have an effect. There can be some days when you might receive channels from usually great distances (sometimes hundreds of miles away), which is a hobby/sport that is sometimes referred to as DXing.
