Coverage Is Important Updated 1/21/2023
Your main focus should be Coverage. If cord-cutters and advertisers cannot
pick up your station with Rabbit Ears, you probably don't have much of a chance of making a sale.
And do not rely on the FCC's 48 dBu City Grade level. As you will see, that is
not strong enough. To discover what signal level you need, you should use the same equipment your
viewers will use. A set of rabbit ears and a TV. That is just common sense.
Background. Most folks today are trying to save money by cutting their cable TV bills. And a
major portion of the TV they watch is over-the-air networks. If they would put up an outside
antenna or one in the attic, they could pick up 80+ channels. But when was the last time you
saw an outside antenna on a home? (By the way, if you know someone wanting to start a new
business, talk to them about putting up outside antennas. And give them free
advertising. Nothing will boost your viewership like outside antennas.) |
So as a station owner, your reality is the cheap, plastic rabbit ears. You need to know the
signal level it takes to "light" up the viewers TV with a solid signal. You then have to decide
if it is better to move your station from the tall tower 10 miles outside of town to a 200' tower
in the middle of town. It is all in the numbers.
The process to find the rabbit ears signal level is simple. Get a small TV,
attach a set of rabbit ears and scan for channels
just like your viewers would. Do it in different rooms of your house and on
different walls. Go to a friend's house and do the same. (You may want to ask for
their permission so they don't call the police on you.)
Write down the channels you get, making a note if the picture is solid or breaking up.
Next, get the latitude and longitude for the location by
typing the address into Google. On the map, right click the little red location marker.
The coordinates, will be something like 36.32241, -86.59597.
Now go to www.Rabbitears.info, click Signal Search Map, enter the
coordinates, and click Go.
Next to Units, select dBuV/m. In this intance, Rabbitears. info has
done all the heavy lifting for you and the signal strength is in the Field
Strenght column. The actual formula to convert dBm to dBu is:
dBmV = 48.7505 +dBm for 75 ohm |
dBu = (20*Log (Freq.) + 26.32) + dBmV
A scan in my office revealed the following channels and dBuV/m levels.
Ch
17 |
dBuV/m
91.28 |
Ch.
20 |
dBuV/m
104.46 |
Ch.
21 |
dBuV/m
110.03 |
Ch.
27 |
dBuV/m
104.71 |
Ch.
30 |
dBuV/m
101.23 |
Rabbitears.info calculates at 13' above ground, so we will add 3 db as a
height correction factor since most TV's are 6' above ground. Channel 17 had digitizing, so from
the chart above, we have 91.28 + 3db for height + 3 db more to get rid of the digitizing to come
up with 97.28dBu.
Wow, a little more than the FCC's 48 dBu for digital TV City Grade. That's because the FCC value
is based on an outside antenna, clear line-of-sight, 30' in the air. And that is not reality.
This test proves it. But there is additional hope. When we did additional testing in other rooms,
using the loop antenna and dual aerial, we came up with an average of 77 dBu for UHF, 70 dBu for
channels 7-13 and 60 dBu for channels 2-6. But no happy dance. When we compared those plastic
rabbit ears against the old style antenna we used for signal measurements,
we found its gain to be +1.2 for UHF, -12db on channel 7-13 and -20db on channels 2-6
compared to the old style. So we use 80 dBu for all channels. Which happens to be the City Grade
level for UHF analog TV. Guess RF is RF. So make sure you have at least a 80 dBu level so viewers
can watch and advertisers will buy.
For $59 we will do a coverage map for you. If you cannot wait, below are calculations based
on the Longley Rice F(50,90), 80 dBu signal strength. HAAT is Height Above Average Terrain
in meters. Distance in Kilometers. If you want to convert, Meters x 3.281 = Feet. Kilometers /
1.609 = Miles. You may have to guess on that or simply use the tower height if things are
fairly flat around you.
HAAT
Meters
31m
61m
122m
244m |
100
Watts
6.7 Km
6.8 Km
6.9 Km
7.0 Km |
500
Watts
10.0 Km
13.8 Km
15.1 Km
15.4 Km |
1,000
Watts
11.7 Km
16.1 Km
20.6 Km
21.2 Km |
2,500
Watts
14.1 Km
19.2 Km
28.3 Km
31.6 Km |
5,000
Watts
16.2 Km
21.9 Km
31.2 Km
41.7 Km |
10,000
Watts
18.4 Km
24.6 Km
34.3 Km
45.3 Km |
15,000
Watts
19.6 Km
26.2 Km
36.0 Km
48.7 Km |
To summarize, put your transmitter where the people are. Gone are the days
of transmitter antenna farms and outside antennas all aimed in one direction. Today it is
raw POWER. But raw power that makes economic sense. Do not spend on a big transmitter
that not only cost you a lot of money on the front end, but also high electric bill due to
high power consumption and air conditioning and only gain moo cows.
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Get you a map and draw
circles to find the sweet spot. May not be the exact location due to having to protect other
stations, but it will make you more transmitter power aware. |
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Backup 100 Watt Transmitter
100 Watt Outdoor UHF Encoder/Transmitter
Just $5,250. Low Pass Filter: $225. Mask Filter: $725. |
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