The question is where your TV is picking off this measurement? It is quite possible that its being picked off downstream of an AGC amplifier, and that will affect the screen reading you see as its trying to adjust the receiver with lots of fancy automatic gain adjustments.
It's also quite possible that you have something close in that is affecting your receiver (local FM, AM station, commercial repeater, or a really close cell site, etc.), changing the gains and you don't even know it. That's why I wanted to do this with an analyzer since I have nothing to influence the measurement, and if there is, I can pretty easily see it on the spectrum display. This is pure what you see is exactly what it is, with no automatic anythings. One measurement I did but did not take a picture of was essentially a full screen display from about 20MHz, all the way to 3000MHz+ to make sure there was nothing out there that might saturate either the Jack or the Batwing amps and contaminate the results. Because I did this where I did, I have nothing within miles that can bother the amplifiers . But I checked anyway..
