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Step 11Digital signal strength 101
There are tools on the internet to help you determine the stations in your area, their power, distance, and your chances of getting them to show on your TV.
http://www.tvfool.com/?option=com_wrapper&Itemid=90
I suggest you try 'TV Maps' link. Type in your address, height of your antenna and you can determine your chances of reception.
You'll also see a list of stations in your area. If you choose one you'll see a color coded map of signal strength from the station to your location. The list shows the distance in miles and and important number NM or noise margin. The antenna we're making should have a gain of at least 15, hopefully more. Think of the NM as the loss of the signal to your house. It could be hills, leaves, walls or weather. It's also distance and location of you and the signal tower. The goal is to get a net gain of at least 0. At zero you'll get a signal. For a reliable signal a higher number is beneficial. 5-10 means you'll probably get a signal over 0 consistantly.
So, take your antenna gain. Let's use 15 and add the NM For the positive numbers it's no problem. The negative numbers might be another issue. An antenna of 15 db hoping to get a stations that's -11 db leaves a net gain of 4. Marginal but a reliable steady signal is possible at this level. The thing is every splitter, length of cable, branch in front of the antenna, Snow in the air, and many other factors can lower the db of gain bringing that gain of 4 down to 0 or lower meaning loss of signal.
http://www.tvfool.com/?option=com_wrapper&Itemid=90
I suggest you try 'TV Maps' link. Type in your address, height of your antenna and you can determine your chances of reception.
You'll also see a list of stations in your area. If you choose one you'll see a color coded map of signal strength from the station to your location. The list shows the distance in miles and and important number NM or noise margin. The antenna we're making should have a gain of at least 15, hopefully more. Think of the NM as the loss of the signal to your house. It could be hills, leaves, walls or weather. It's also distance and location of you and the signal tower. The goal is to get a net gain of at least 0. At zero you'll get a signal. For a reliable signal a higher number is beneficial. 5-10 means you'll probably get a signal over 0 consistantly.
So, take your antenna gain. Let's use 15 and add the NM For the positive numbers it's no problem. The negative numbers might be another issue. An antenna of 15 db hoping to get a stations that's -11 db leaves a net gain of 4. Marginal but a reliable steady signal is possible at this level. The thing is every splitter, length of cable, branch in front of the antenna, Snow in the air, and many other factors can lower the db of gain bringing that gain of 4 down to 0 or lower meaning loss of signal.
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