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Author Topic:   Using NOAA Weather Broadcasts For Receiver Testing
jimh posted 05-24-2008 10:07 AM ET (US)   Profile for jimh   Send Email to jimh  
The NOAA Weather Radio stations provide a continuous broadcast transmission that can be useful for testing a VHF Marine Band receiver. Most all VHF Marine Band radio sets have receivers which can receive weather broadcast frequencies.

To assess the sensitivity of a receiver, reception of a NOAA transmission in your area should be tested. NOAA has provided coverage maps which show the signal contour anticipated from each station.

NOAA Coverage Maps

Select the coverage map for your area, for example, Michigan:

Use the drop down menu at the bottom to isolate a single station's coverage in your vicinity, for example, Detroit:

Coverage map of station KEC63

This results in a coverage map for a single station. The color coding of the map shows the expected signal levels. The heading of the map shows the station call sign and frequency, for example:

KEC63 on 162.55 MHz

The weather station broadcasts are channelized. Here is the breakdown in the channelization which is typical for a VHF receiver:

CH - MHz
1 - 162.55
2 - 162.400
3 - 162.475
4 - 162.425
5 - 162.450
6 - 162.500
7 - 162.525
8 - 161.650
9 - 161.775
10 163.275

(NOAA stations are generally only on Channels 1 to 7.)

Using the coverage maps you can determine the signal level available for each station in your area. The color coding used on these charts is

White: Signal level of greater than 18dBuV: Reliable coverage
Green: 0dBuV to 18dBuV: picking up a signal is possible but unreliable
Red: Less than 0dBuV: Unlikely to receive a signal

The signal levels are given in terms of their ratio in decibels to one microvolt, thus a level of 0-dBuV is one microvolt. Most VHF Marine Band radio receivers are specified to a sensitivity of a fraction of a microvolt, therefore we can expect that a radio receiver which is working properly and is connected to an antenna that is working properly should be able to receive the NOAA broadcast transmissions from stations whose coverage map is shaded green for the receiver location.

Using the pull down menu on the state coverage area maps, select some alternative stations until you find a coverage map that shows your receiver location in the station's green area. In my case, I can use "Flint" as an alternate:

Coverage map for KIH29

I should be able to receive station KIH29 on 162.475 MHz with a signal level between 0 and +18 dBuV. This will be Channel-3 on my radio. And, indeed, KIH29 comes in loud and clear. Therefore I have verified that my VHF Marine Band radio receiver is working in a normal fashion and has sensitivity in the range expected.

This sort of testing of receiver sensitivity is much more useful than just random listening on marine channels where the power, antenna height, coverage, and distance to another station are generally unknown.

jimh posted 05-24-2008 10:17 AM ET (US)     Profile for jimh  Send Email to jimh     
The NOAA broadcast stations identify themselves at approximately five minute intervals. Listening to the broadcast for a few minutes should allow positive identification of the station being received.

You can also get a listing of stations in your area from

jimh posted 05-24-2008 10:58 AM ET (US)     Profile for jimh  Send Email to jimh     
It goes without saying, although perhaps I should mention it explicitly, but you can't receive a station with a lower signal level which is on the same frequency as a stronger, closer station. To test for receiver sensitivity, the more remote station has to be on a frequency which is not shared with a closer station.

In my case, for example, there is a station in Toledo (WXL51) whose coverage would be a good test, but it is also on 162.55-MHz, the same frequency as the station just a few miles from me. I'll never hear a trace of the Toledo station as long as my local station is transmitting.

Another use for the NOAA broadcast transmissions is to set the volume control of your receiver to a nominal level. The modulation of the NOAA transmitters is expected to be set to a standard level. If you set your VHF Marine Band receiver volume on a NOAA weather broadcast station, you can then compare the audio level that is recovered from other vessels' transmitters. This is a way to inform another vessel if their transmitter modulation level is proper.

In the VHF Marine Band radio service there generally is no way for a user to adjust the modulation level of their transmitter, so most variation in transmitter modulation level comes from grotesque variations in microphone technique and speaking level.

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