NWS All Hazards Modulation/Audio level

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Baylink
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NWS All Hazards Modulation/Audio level

Post by Baylink » Mon Sep 30, 2013 6:29 pm

I have, in my 2000 Land Rover, a factory 1.5-DIN radio, which happens to know how to tune weather-band.

I've actually been using it again lately, and am reminded that when I do, the recovered audio level between *both* local NWS transmitters (Ruskin and Largo) is about the same... and over 20dB lower than all the FM stations I tune (except the NPR affil). Could even be more; blew my damn head clean off.

Should I assume this is just a vagary of the receiver? Or is it possible the NWS modulation levels aren't where they're supposed to me? Anyone in Tampa got an FM meter they can check quieting and deviation on those carriers with? I would assume that NOAA/NWS doesn't do that work themselves, or at the very least, they have a guy who roams around...

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billcroghan
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Re: NWS All Hazards Modulation/Audio level

Post by billcroghan » Mon Sep 30, 2013 6:39 pm

Just a guess, but the NWS radios are probably between 5 and 15 KHz deviation compared to the 75 KHz dev of the FM's. That would account for a great difference if the receivers are nto set up to automatically change.

Baylink
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Re: NWS All Hazards Modulation/Audio level

Post by Baylink » Mon Sep 30, 2013 6:53 pm

I thought there was probably a substantial deviation difference, given the bandplan at 162MHz. I just figured the receiver manufacturers would be smarter than that. Could they really be using the same RF deck, or even IF deck, for both 162 and FMW?

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Re: NWS All Hazards Modulation/Audio level

Post by NECRAT » Mon Sep 30, 2013 7:21 pm

billcroghan wrote:Just a guess, but the NWS radios are probably between 5 and 15 KHz deviation compared to the 75 KHz dev of the FM's. That would account for a great difference if the receivers are nto set up to automatically change.
The NOAA spec is 4.5kHz deviation.
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Deep Thought
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Re: NWS All Hazards Modulation/Audio level

Post by Deep Thought » Mon Sep 30, 2013 7:27 pm

If the recovered audio is that low on your radio...it is a radio design defect. The NOAA transmitters are most probably doing exactly what they are supposed to. I have a Sony AM/FM/VHF-TV/WX radio which handles the various modulation levels swimmingly, as well as a 25 year old RCA 9" TV that sports FM and WX and it also handles the various levels just fine.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

Baylink
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Re: NWS All Hazards Modulation/Audio level

Post by Baylink » Mon Sep 30, 2013 7:29 pm

Ok, Mark; that's what I was looking for; thanks. I'm planning to replace it anyway -- assuming I can find anything 1.5-DIN... :-)

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