Receiver Testing with NOAA Weather Radio Broadcasts

VHF Marine Band radios, protocol, radio communication theory, practical advice; AIS; DSC; MMSI; EPIRB.
jimh
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Receiver Testing with NOAA Weather Radio Broadcasts

Postby jimh » Fri Jun 01, 2018 10:09 am

Note: this article is an updated version of one that appeared in the old forum. I am reposting it to the new forum so that further updates can be appended to it. The tests described below took place in March and April of 2013--jimh

I have written about testing VHF Marine Band radio receivers by using weather radio broadcasts. I thought I would use my own method to test a radio I had on the bench, and also test my antenna installation. The radio is an older ICOM M402. The antenna is a three-element yagi mounted about 20-feet above ground and pointed southeast toward the Detroit River. The antenna is a directional antenna and has some gain, perhaps 5-dBd, but all of the paths to NOAA stations are over mostly urban terrain. On a boat at sea, the paths will be mostly over water, and a good receiver and antenna should be able to obtain similar reception at similar distances. Here are some observations:

On WX-1, 162.550-MHz, I got a tremendous signal from KEC63, the NOAA station that is literally just down the street from me. The distance is about three miles. This is not a good signal to use for testing receiver sensitivity, but it does have value. It is such a strong signal that it helps to test receiver rejection of strong adjacent channel signals. Some receivers might be completely overloaded by the signal level from a local transmitter like KEC63. That other stations can be received in the presence of this very strong signal is a good indication the receiver has good overload and intermodulation performance.

On WX-2, 162.400-MHz, I got a decent signal from KHB97 in Sandusky, Ohio, about 80-miles away from me. Their coverage is shown by

http://www.nws.noaa.gov/nwr/coverage/site2.php?State=OH&Site=KHB97

This signal was heard with some heterodyne artifacts, which are probably from a competing signal from Sarnia, VJV492. This Canadian station is lower power (42-watts) and is not in the main lobe of my directional antenna as shown in

http://www.michiguide.com/weather/nwr/xjv492.html

but I can hear it beating with KHB97.

On WX-3, 162.475-MHz, I got a very strong signal from VAZ533 in Windsor, Ontario, a path of about 27-miles. Their coverage is shown in

http://www.michiguide.com/weather/nwr/vaz533.html

and they are right in the main lobe of my antenna.

On WX-9, 161.775, I heard the continuous marine broadcast from Environment Canada. This is actually on VHF Marine Band Channel 83B. The service is transmitted simultaneously by several stations. I believe I was listening to the transmitter in Leamington, Ontario, call sign VBE-2. These stations do not individually identify themselves. VBE-2 is a path of 42-miles. I could not find any coverage map for VBE-2.

To summarize:

WX-1: 3-miles
WX-2: 80-miles
WX-3: 27-miles
WX-9: 42-miles

I also observed that the radio receiver was able to receive my local NOAA weather radio signal without the antenna being directly connected. While the radio could not receive the local station with no antenna connected, as the transmission line for the antenna was brought near the radio's antenna connector, the receiver began to receive the local station as the two connectors were brought in close proximity. This is a good indication of how a receiver might be able to receive strong signals when there was actually no direct connection to the antenna due to some discontinuity in the transmission line or the connectors. The local NOAA weather station could be copied with the antenna transmission line connector just held close to the radio antenna connector, without any direct contact. It is this sort of good sensitivity in a radio that often fools people into thinking the radio is able to receive but not transmit. A modern VHF Marine Band radio has such excellent sensitivity it can receive very weak signals, like those provided by antennas that are not quite connected.

My test results above also show the antenna was exhibiting the expected directional pattern. The only stations received were all in the main lobe of the antenna pattern, which is oriented to the SE (in order to maximize reception of ships in the Detroit River for the AIS receiver that is usually connected to this directional antenna). I would normally expect to receive other NOAA weather radio stations from other directions, but the excellent pattern of the antenna has suppressed their signals.

Checking the weather signals a few days later, I am also copying WNG647 broadcasting on WX-5 or 162.450-MHz. The transmitter is located in Adrian, Michigan. The coverage map and other information is shown at

http://www.michiguide.com/weather/nwr/wng647.html

and indicates the path is about 59-miles. The signal is not in the main lobe of my directional antenna, and the received signal was noisy and on the edge of squelching out. However, it was decent copy.

Here is a link to a Google Maps plot of 1,013 NOAA Weather Radio transmitter sites:

NOAA Weather Radio Transmitter Sites
https://www.google.com/maps/d/viewer?mid=100vLnERm-RPnR6kpEG1EEyfq9ys&usp=sharing

I found that in some cases the location of the transmitter is not quite exactly shown, but it is generally close enough to be useful in estimating the distance to the station from you receiver for the purpose of assessing the path length.

jimh
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Re: Receiver Testing with NOAA Weather Radio Broadcasts

Postby jimh » Fri Jun 01, 2018 10:11 am

Checking the weather signals about a week later, I found I was receiving WNG698 on 162.500-MHz on WX-6, located Grafton, Ohio. The coverage map of this station falls far short of my location:

http://www.nws.noaa.gov/nwr/coverage/site2.php?State=OH&Site=WNG698

but the signal was good copy, although subject to some fading. The path is 105-miles.

Here are two recordings of the signals received. First, a decent signal from KHB97 on the path of 80-miles:

http://continuouswave.com/whaler/movies/KHB97.mp4

At the end of the above recording you can hear the hetrodyne of the other station underneath the main signal.

Next, a noisy signal with some fading from WNG698 on the path of 105-miles:

http://continuouswave.com/whaler/movies/WNG698.mp4

Also this afternoon, I heard KXI-94 from Angola, Indianna on WX-4 or 162.425. This was very spotty copy with some deep fading. The path is 104 miles and is off the side of the main lobe of the antenna. Their coverage map shows little signal coming this way.

The DX Comprehensive Summary

WX-1, 162.550-MHz: 3-miles, KEC63, Southfield Michigan
WX-2, 162.400-MHz: 80-miles, KHB97, Belleview, Ohio
WX-3, 162.475-MHz: 27-miles, VAZ533, Windsor, Ontario
WX-4, 162.425-Mhz: 104-miles, KXI94, Angola, Indiana
WX-5, 162.450-MHz: 59-miles, WNG647, Adrian, Michigan
WX-6, 162.500-MHz: 105-miles, WNG698, Grafton, Ohio
WX-9, 161.775-MHz: 42-miles, VBE2, Leamington, Ontario

jimh
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Re: Receiver Testing with NOAA Weather Radio Broadcasts

Postby jimh » Fri Jun 01, 2018 10:12 am

While tuning the weather band several weeks later, I caught the station identification of KZZ47 from Carey, Ohio, on WX-7 or 162.525-Mhz. Their coverage map

http://www.nws.noaa.gov/nwr/coverage/site2.php?State=OH&Site=KZZ47

shows no signal anticipated at all in my location. Their signal was very weak, and only readable is short increments when the signal rose out of the noise for a few seconds. The path to KZZ47 from my location is about 110-miles, and most of it over land. Perhaps more noteworthy is the receiver was able to detect and demodulate this extremely weak signal while listening only 25-kHz away from the local KEC63 signal, which is extraordinarily strong at my location. This is further evidence of very good receiver design. There was no evidence of cross-modulation of KZZ47's signal by KEC63's signal, and I would anticipate the difference in signal level must be about 70-dB or more.

An excellent source of information about a particular weather radio station is the website

http://radiostationnet.com/weather/

RADIOSTATIONNET.COM have collected the exact transmitter location for NOAA Weather Radio stations and their transmitter power.

Analysis of received signal levels for 25-kHz spaced stations

The received signal level from KEC63 should be -21.3dBM, based on

    Transmitter Power = 1,000-watts = +60dBm
    Transmitter Line Loss = -1dB
    Transmitter Antenna Gain = +6dB
    Receive Antenna Gain = +5dB
    Receive Line Loss = -1dB
    Path Loss = -90.3dB

The received signal from KZZ47 should be around -97.7dBm, based on

    Transmitter Power = 300-watts = +54.7dBm
    Transmitter Line Loss = -1dB
    Transmitter Antena Gain = +6dB
    Receive Antenna Gain = +5dB
    Receive Line Loss = -1dB
    Path Loss = -162.4dB

The difference in signal levels is 76.4dB. That is an extremely large difference in signals for a spacing of only 0.025-Mhz, and indicates good receiver design.

Note: For the path loss of KEC63 I used a free-space model because the path is literally line-of-sight; I can indeed see the antenna. For the path loss of KZZ47 I used a model for loss of 40log(d) because the path is over the radio horizon and mostly an all-terrain path. These are reasonable assumptions.

jimh
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Re: Receiver Testing with NOAA Weather Radio Broadcasts

Postby jimh » Fri Jun 01, 2018 10:16 am

When I decommissioned my boat for the winter, I removed the boat's VHF Marine Band radio, a Standard-Horizon GX1500S. I did this not so much because I was worried about the radio sitting in the boat all winter, but rather to have the radio available on my bench for other uses. A few days ago I connected the GX1500S to my roof-mounted three-element vertically-polarized Yagi antenna, pointed at the Detroit River. This is the same antenna used in reporting to you all the signals I received as noted earlier in this thread of articles.

I tuned around on the Weather Broadcast band with the GX1500S, and the results were very disappointing. Only three channels produced any sort of reception. This came as a surprise, as I had recalled receiving many more stations, as I noted in the previous entries here. Summarizing those results:
WX DX Summary

WX-1, 162.550-MHz: 3-miles, KEC63, Southfield Michigan
WX-2, 162.400-MHz: 80-miles, KHB97, Belleview, Ohio
WX-3, 162.475-MHz: 27-miles, VAZ533, Windsor, Ontario
WX-4, 162.425-Mhz: 104-miles, KXI94, Angola, Indiana
WX-5, 162.450-MHz: 59-miles, WNG647, Adrian, Michigan
WX-6, 162.500-MHz: 105-miles, WNG698, Grafton, Ohio
WX-7, 162.525-Mhz; 110-miles, KZZ47, Cary Ohio
WX-9, 161.775-MHz: 42-miles, VBE2, Leamington, Ontario

With the GX1500S only hearing a few stations, I began to wonder about its sensitivity. To make a test, I connected both the GX1500S and the earlier radio used (ICOM M402) to the same antenna, using a very good quality antenna switch with excellent isolation to switch the antenna between the two radios. With this test set-up I could make instantaneous comparisons between the received signals from the various weather stations.

I was soon relieved to find that the GX1500S was working just fine, that is, it received any station the other receiver could hear, and, judging by ear the signal-to-noise ratio, the GX1500S might have a small advantage.

The limited number of stations I could hear in this recent test is probably due to a general decline in the propagation conditions caused by the weather and other variables in propagation. In checking at various times in the last day or two, I have heard some weaker stations come and go.

I have observed that both radios seem to be limited in their receive on WX-8, 161.650-MHz. Both radios pick up an unmodulated weak carrier on that frequency. It may be some sort of localized interference.

Later, in some random use of my VHF Marine Band radio while connected to my rooftop antenna, I discovered that a considerable variation in received signals was caused by interference from a nearby DVD/CD player. When the DVD/CD player was powered on, it created noise interference in the VHF Marine Band radio receiver, and the sensitivity of the radio was degraded. This is a good example of how local noise sources can affect receiver sensitivity.

In testing a VHF Marine Band radio, it is prudent to begin by powering off all other electronic devices that are close by. Turn on each other electronic device, one at a time, and note if there is any increase in noise or reduced sensitivity in the VHF Marine Band radio receiver. It would not be surprising to find that other modern marine electronic devices, such as color screen chart plotters or high-power SONARs, might be generating some radio frequency noise that could affect radio receivers.