Signals from Same Tower, but Some Good & Some Bad?

[RhinoRunnin]

Hi, I am about 50 miles North of San Francisco. Sutro Tower broadcast almost all of my channels.

My question is why does certain channels like KQED-PBS (very strong), KRON or KPIX-CBS come in pretty strong, but some like KUTV-FOX or KBCW doesn't come in as well when they are all broadcast from the same place? I can get FOX during certain time of the day (mostly during the evening at 50% signal strength, but in the afternoon (11am-5pm) the signal is dead at 10%. When the football games are on FOX has a co-channel warning, but what does that mean?

Lastly, what can I do to get better reception of the weak channels that I sometime get & sometime can't?

From TV Fool my TV analysis : http://www.tvfool.com/?option=com_wr...46aeffe49731a4

And from AntennaPoint : http://www.antennapoint.com/antennas...&commit=Search

I am using an Antenna Direct 91XG with a RCA preamp on a 20' pole outside with 50' of cable.

I just cut the cable, so I'm new to antenna knowledge. Thank you in advance for any information you can offer

[GroundUrMast]

The mountainous terrain between you and San Francisco makes signal propagation very difficult to predict with the accuracy you can expect when there are line of sight conditions. There may or may not be opportunities for signals of a given frequency to reflect off of natural or man made features.

If you are seeing signals that are predicted to arrive at levels of -100 dBm and lower, you are doing extremely well.


A co-channel warning means that two or more stations are transmitting on the same frequency and the levels from the two are close enough that you can expect them to interfere with each other.

Adjacent channel warnings are an indication that the small amount of 'off-channel' power from a station one channel above or below may cause problems with reception of the neighboring channel.

Lastly, what can I do to get better reception of the weak channels that I sometime get & sometime can't?

When blocked by 1000' and higher terrain, that's quite close:
1) Move.
2) Build and extremely tall tower.
3) Go to other extreme measures. Example, http://forum.tvfool.com/showthread.php?t=1286

[ADTech]

Signals from Same Tower, but Some Good & Some Bad?

Because different frequencies diffract at different angles when crossing the boundary at the terrain obstacle. It's further complicated by the variable effects of temperature and weather conditions not only over the whole signal path but very specifically at the location where the diffraction takes place. If that location is tree or snow covered, then those are additional complicating factors. If your signal path is calculated as "2-edge", then you're getting a double dose of diffraction and the difficulty level rises exponentially.

Your best plan of attack in such cases is a telescoping mast that you can adjust in small (6-12") increments to see if you can find an antenna height where the layered signals line up. This will require substantial patience and persistence, especially when you find out that the "best" antenna height changes with the season or the weather up on the mountain.

[RhinoRunnin]

Thank you for the information! Telescoping mast, that's interesting, I'll check into that.

[ADTech]

Well, the telescoping mast would be the luxury. Just raising and lowering the antenna on a pipe would be the economy version.