BZZTT! Wrong answer, but thanks for playing....
You can get a packet, or not. Or get a malformed packet. And it takes many, many packets to make up even a second of broadcast TV.
So you really want to make sure you get as many healthy packets as you can. With poor or marginal reception, you may only have a few good packets come through, with some missing, and some malformed.
This can also be affected by the weather. Temperature, humidity, and precipitation will affect signal propogation. Leaves on trees affects just how much radiation your antenna can absorb, so the seasons play a role, too. And even rain on the ground will create signal reflections that can cause multipath interference.
I myself have a Channel Master CM 4228 antenna on a 15 foot pole, fed through an amplifier that leads into an HD tuner for my Mac. It makes a HUGE difference over any amplified or unamplified internal antenna I tried - and I tried most all of the hyped up ones. (I.e. the Zenith Silver Surfer, or the RadioShack one who's model number I forget.)
And after it's all said and done, and you're recieving the signal solidly, there's another item that is totally out of your hands that affects Over the Air (OTA) HD picture quality: how many subchannels the station is broadcasting. Each of these sucks valuable digital bandwidth away from the "primary", HD channel.
For example, KQED (my local PBS station) now looks like utter crap, as they broadcast FOUR subchannels along with the primary, 24/7. It's ridiculous - they used to be smart and run the 4 during the day, with no HD primary, until 8 PM when they would cut back to 1 subchannel with a nice 1080 primary. But then someone got the bright idea that they should run ALL subchannels all the time, so that "PBS Kids" can be running at 3 o'clock in the morning.
TV execs are pinheads. At least CBS out here has NO subchannels, ever, so the occasional worthy show is in stunning, spectactular picture quality. It's a joy to watch, and makes me want to bitchslap the local execs controlling the other stations.
That’s almost exactly my setup. I’m really not all the far from the broadcast antenna district, but I’m behind a ridgeline, and have lots of trees to contend with. In short, my line-of-sight, sucks.