new here, roof-mount antenna


Hello everyone:
I'm new here.
I'm not sure this sub-forum is the right place for my question, but here goes...

I live in the western burbs of Chicago where there are over 50 channels of local tv available. I'm tired of **paying for tv. I grew up in the 70s when tv was limited but free. I'd like to go back to those days.

So..... I'm thinking about having a roof-mount tv antenna installed.
My question(s) boil down to this...
What are the things I should keep in mind? Brands to consider? How to hook up multiple tv sets? (can existing coax & jacks in the house be used just as they were for cable?), etc. etc. If we get a bad thunder/lightening storm would I have to go around & unplug the antenna from all of the TVs or risk having them damaged?

Some more info...
I'm told that in the Chicago area the epicenter of all TV is the top of the Sears (now Willis) Tower. My 3-bedroom ranch is about 26 miles away as the crow flies..... and it's all basically nice flat terrain.

Ok, THANKS for the help!!



Staff member
Hi TM,

:welcome: to the forum. There is a really cool tool out there these days at TV Fool. If you're willing to make a "radar plot" for your particular location (giving an accurate antenna height for your report will help more) and post the URL for it here that will help us help you. Given what you've told us so far, I don't think you will have any real issues. You are correct about Willis tower being the main transmitter location.

If your antenna system is properly grounded you shouldn't have problems with lightning (static electricity) though I do recommend protecting your equipment with surge protectors. Yes, you can certainly use the existing cable wiring and jacks.

Here is a sample TV Fool to show you about what to expect. Green stations should come in on an indoor antenna. Yellow and pinks will need an attic or roof antenna. Main columns to look at are the "Real" column (that is the radio frequency channel the station broadcasts on) the "NM(dB)" column (that is the signal strength in your area measured in decibles), and the "(Magn)" column which is the direction in degrees from magnetic north (compass heading).

There are three TV bands. VHF-low (real channels 2-6), VHF-high (real 7-13) and UHF (real 14-51) you need to get an antenna that is designed for the channels you want to watch. I know that some of the guys in your area like WOCK on real channel 4 and that takes a considerably larger antenna than the VHF-high channels (WBBM, RF12) and the UHF channels (pretty much everything else, WLS is on real channel 44).

How to size your antenna: For each band find the weakest channel in the "NM(dB)" column. Then figure the amount of loss there will be in your system. Figure 4 dB of loss for a 2 way splitter or 8 dB for a 4 way splitter, then figure 1 dB of loss for each 20 feet of cable and at least 4 dB for an indoor or attic mounted antenna. You want to try and get 10 dB of signal to each TV for reliable reception. To figure how much signal is at the antenna, add the antenna gain (in dBd which is about 2.2 dB less than dBi) for that channel and the Noise Margin (NM(dB)) then subtract the loss of the system. If you have too much loss you can use a preamp, but you have to subtract the noise figure out of the preamp gain to get the effective gain of the amp. (i.e. an amp with 26 dB of gain and 3 dB of noise will give you an effective gain of 23 dB, not 26). Amps can't create signals that aren't there to start with, and you want an amp with less than 3 dB of noise.

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