Originally posted by Jon JAnalog 17 is still on the WSMV tower on Knob road.
I have the newest Hughes integrated DirecTV receiver. The newest firmware added a signal strength meter and the receiver recognizes a tiny amount of signal (poor on the meter) for 30-1, 17-1, 5-1 and 5-2.
I have both a directional yagi and the 4228 up at present. The yagi sees very little on 58-1, not enough for a lock, and nothing on the other stations from that area.
Virtually every hill in Davidson county is between me and the 3 Sinclair stations (which are on the same antenna tower) and WTVF-DT.
The whole thing is making my head hurt.
Jon, I might have a theory of what's going on. First, all the stations on the north side of town are very weak coming through the hills of West Nashville as we all know. I decided to review http://www.hdtvprimer.com
and specifically reread the section on antenna and measuring gain.
Here's the chart I'm referring to:http://www.hdtvprimer.com/ANTENNAS/types.html
The UHF channels we're trying to receive are 15 (FOX), 21 (UPN), 23 (WB) and 56 (CBS). In addition, VHF channel 10 (NBC) is on the same vector, although far closer in location. The diagrams on hdtvprimer.com show the gain charts for the ChannelMaster 4228 8-bay antenna that you are using and a ChannelMaster 4248 Yagi, which isn't the Yagi you have but close enough for the sake of argument. When properly pointed, you are trying to get the most gain out of a signal and hopefully avoid nulls if the antenna isn't pointed directly at the tower. Since all signals are on or close to the same vector, let's assume you have the antenna properly pointed. Pointing directly at the target is critical since being off by 15 degrees results in a -5 db drop with the Yagi and -16 db drop at 20 degrees. The 4228 is a bit more friendly but at 25 degrees off target, it plunges to -20 db loss heading for a null at 30 degrees.
What the chart shows is interesting. The 4248 yagi is biased for the least amount of gain loss in the higher channels. Channel 60 sees 0 gain loss which would mean that if all things being equal, it would have the greatest chance of bringing in Channel 56 of the available channels. Indeed, your Yagi does see a weak signal on that channel and you might see better if CBS was running at full power, which it isn't. However, the 4248 starts becoming less effective in the lower channels. Channel 50 sees about a -2 db loss and all other channels are seeing a -3 db loss. That may not sound like much, but gain is a logarithmic measurement for decibels. So decibels of gain looks like this:
20 dB = gain factor of 100
10 db - gain factor of 10
3 db = gain factor of 2
0 db = no gain or loss
-1 db = 20% loss of signal
-3 db = 50% loss of signal
-10 db = 90% loss of signal
At the same time, the signal has to overcome whatever noise it encounters (signal/noise ratio) which could be anywhere from atmospheric noise to noise in the antenna cable or other attached devices.
This preceding data comes from the following page on hdtvprimer.com:http://www.hdtvprimer.com/ANTENNAS/basics.html
The 4228 8-bay antenna is a little different but again does not have the same ability to pull in a signal over the entire frequency range. Best is channel 50 and then other channels between 30-50 give up about a -1 db....again, not a lot unless you are dealing with weak signals. But like the 4248 Yagi, the worst performance is in the lowest channels. Channel 20 gives up -3 dbs (50% loss). Again, great performance overall for an antenna, but we're dealing with very weak signals.
So it's possible that your Yagi's ability to at least partially display channel 56 is born out by the data while other lower channels would not. That leaves the next possible problem....signal loss in the cable from the antenna to the receiver. Given that the signals are so weak in the first place, even if the antenna got a servicable signal, it signal strength might drop beneath the noise level by the time it gets to the receiver. According to hdtvprimer.com, RG-6 cable loses 1 db of signal every 15 feet for channel 52. So on their chart, a 100 ft cable run could result in as much as a -6 db loss in the upper channels like 56. This is one case where the lower channels have an advantage of less gain loss over distance, at -5 db of loss for channel 20 at 100 ft of RG-6 cable, you may still be SOL.
An antenna amplifier could improve the signal enough on the route to your receiver to make a critical difference (if you're not using one already). Most of the time you wouldn't need one in the city limits (as someone else in these pages pointed out) but in this case it could be crucial. A Channelmaster 7775 or 7777 can provide up to 26 dbs of gain on the way from the antenna to the receiver depending on the channel, cable used and the distance. These amps are also known for their very low noise (about 2 dbs), hence a great signal to noise ratio.
Anyone who knows more about this than I do, please correct me if anything above is wrong (since I'm clearly not an expert...I'm just reading a web site). But if what I read is true, then there may be more than can be accomplished in order to crack this problem. It's also possible that a highly directional Yagi meant for extreme distances could be helpful in our situation, especially since all the problem child signals are in one direction only. In your case Jon, that would leave the 4228 to pick up whatever's left in other directions.
Lastly, I'm curious as to what antennaweb.org said about the type of antenna you would need from your specific address. Since their database now corrects for terrain, after their web site upgrade in Jan 2004 all of the stations in North nashville disappeared from my list of possible stations. Since I have a hill right in front of me and lots of trees, this isn't surprising. But I wonder if your address even finds the north Nashville stations in their database.