Overload is very possible as a factor in the reception problem; the math supports that theory.
Channel Master says this in their description of the 7777:
Quote:
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This antenna amplifier is a high gain, low noise preamplifier used to allow weaker signals at the antenna to be amplified to a viewable strength, and is ideal for installations in which all broadcast towers are located at a distance of more than 80 miles.....The Titan 2 High Gain Preamplifier is recommended for professional installers only. Due to the high gain output of this product, it can result in over amplification if not used in the appropriate scenario. Over amplification can cause issues with the television tuner’s ability to receive and display some or all channels.
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http://www.channelmaster.com/TV_Ante..._p/cm-7777.htm
OTA signals are constantly changing in strength. I have measured changes of over 10 dB in 30 minutes. Atmospheric changes can cause changes in signal strength, which might account for day/night differences if you are close to overload. The direction of the antenna is certainly a factor.
KVCR has a signal power of -29.6 dBm = 19.4 dBmV
Max input of 7777 is 15 dBmV
You are already at preamp overload before adding antenna gain.
19.4 dBmV + 12 dB Ant = 31.4 dBmV; with antenna aimed at KVCR
If you add the preamp gain, the tuner has a problem:
KVCR -29.6 dBm + 12 dB Ant + 30 dB preamp = +12.4 dBm; tuner overload
A tuner is not designed to handle signals stronger than -5 dBm.
THREE TYPES OF OVERLOAD
There are three types of preamp or tuner overload, in order of increasing signal strength:
1. The strong signals almost cause enough intermodulation distortion (IMD) to interfere with the reception of weak desired signals, but the spurious signals are at or below the noise floor of the weak signals. This is the point that holl_ands uses in his preamp charts to obtain max SFDR (Spurious Free Dynamic Range). No damage will happen.
As the strongest signals continue to increase in strength, more of the weaker signals are damaged until you reach:
2. The strong signals cause overload to the preamp or tuner that makes it impossible to receive any signals. No damage will happen. The strongest signals are still there, but they can't be decoded because the IMD products have damaged them so that they contain more errors (high BER....bit error ratio/rate) than can be corrected by the FEC (forward error correction).
3. The signals are so strong that the input transistor is toast. You are not likely to encounter OTA signals that strong, unless you live next door to a high power transmitter and you have your high gain antenna aimed at the transmitter's antenna.
As a general rule, tuners can tolerate stronger signals than preamps before overload. The difference in strength is approx. equal to the preamp gain.
Looking at it from the standpoint of Noise Margin:
KVCR has a NM of 61.2 dB. If you add the antenna gain of 12 dB, that brings you up to 73.2 dB, which is overload territory.
Interpreting Noise Margin in the TV Fool Report
http://www.aa6g.org/DTV/Reception/tvfool_nm.html