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If They Cannot Pick You Up, They Cannot Watch You
If viewers cannot pick you up, they cannot watch you. If advertisers cannot pick
you up, they will not buy from you.
Most homes today could pick up 90+ channels over-the-air with an outside antenna
or one in the attic. Yet cord-cutters mostly rely on rabbit ears for TV reception.
And today’s popular rabbit ears are plastic that suction cup to the window that are tuned for UHF reception.
As a station owner, you need to know the signal level it takes to "light up"
rabbit ears. The process is simple. Get a TV set, attach the rabbit ears to it,
and scan for channels like your viewers would. Do it in different rooms and even different walls. Write down the channels you get,
making sure to note if the picture is solid or breaking up.
Then get the coordinates 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.
Go to www.Rabbitears.info, click Signal Search Map, enter the coordinates,
and click Go.
Next to Units, select dBm. It will give you the estimated signal level at that location.
The formula for signal strength is :
dBmV=48.7505 +dBm for 75 ohm | dBu=(20*Log(Freq.)+26.32) + dBmV
Since the dBm is negative, we will be subtracting it. Below is a conversion chart that simplifies
the above formula.
|
2
7
12
17
22
27
32 |
110.2
120.0
121.4
128.9
129.4
129.9
130.4 |
3
8
13
18
23
28
33
|
111.1
120.3
121.6
129.0
129.5
130.0
130.4 |
4
9
14
19
24
29
34 |
111.9
120.6
128.6
129.1
129.6
130.1
130.5 |
5
10
15
20
25
30
35 |
113.0
120.9
128.7
129.2
129.7
130.2
130.6 |
6
11
16
21
26
31
36 |
113.7
121.1
128.8
129.3
129.8
130.3
130.7 |
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A scan in my office revealed the following channels and dBm levels. |
Ch
17 |
dBm
-37 |
Ch.
20 |
dBm
-24 |
Ch.
21 |
dBm
-19 |
Ch.
27 |
dBm
-25 |
Ch.
30 |
dBm
-29 |
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Rabbitears.info calculates at 13’ above ground, so we will add 3 db as a
height correction factor since most TV's at 6' above ground. Channel 17 had digitizing, so from the chart above, 128.9 – 37 = 91.9.
We then add 3 db for height and 3 db more to get rid of the digitizing to come up with 97.7 dBu.
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,
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 when we compared those plastic rabbit ears against the old dual dipole with a loop antenna,
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 80 dBu level so viewers
can watch and advertisers will buy.
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Applications * Equipment Sales * Training - R & L Media Systems Does It All !
* Hendersonville, TN 37075 Email |
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