NOAA Weather on 157.2000 in Des Moines?

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Radioman96p71

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Scrolling thru the band tonight, picking up NOAA weather from the Des Moines site (WXL-57) loud and clear on 157.2000 MHz. Coming in at at 4 on my IC-R7100.

Do the weather sites have relays from the NWS office? I always thought they were computer generated messages originating at the site itself.
 

WyoWabbit

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WXL57 is licensed at 162.55 MHz. If your radio has a 10.7 MHz I.F. stage, then 162.55 - (1/2 of 10.7) = 162.55 - 5.35 = 157.2. In other words, it's an image. - Tom
 

Radioman96p71

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Ahhh makes perfect sense now, used a handheld receiver and i don't hear anything.

Would using a preamp have any effect on that at all?

Thanks!
 

WA1ATA

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Ahhh makes perfect sense now, used a handheld receiver and i don't hear anything.

Would using a preamp have any effect on that at all?

Thanks!
Image rejection is specified as being xx dB down from normal receiver response. If you feed in a stronger signal, then the it will increase the strength of the image frequency. In other words, yes, the preamp will make images more likely. Anything that increases the signal strength of the strong nearby signal will make the image more likely to appear. Even without a preamp, an outside antenna will deliver more signal than will a rubber ducky antenna, and therefore you would be more likely to pickup the image freq.

There is another, distinct, effect common with preamps. That is intermod. Thats when you get spurious frequencies that are the combination of two or more strong signals and their harmonics. The spurious signals will show up on weird combinations, such as 3rd harmonic of one freq - 2nd harmonic of another. This mixing or intermodulation happens when the signals are so strong that they overload the preamp.

Image rejection is greatly improved by triple conversion receivers, which have 3 IF freqs such as 380MHz, 10.7MHz, and 455KHz.
 
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