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Here is the official site which says the frequency which weather radio broadcasts at (around 162 Mhz). The site doesn't say anything about modulation though. What modulation is used in this radio transmission? Also, how could I build a circuit to pick up this transmission?

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  • \$\begingroup\$ This question appears to be off-topic because it is not about electronic design. \$\endgroup\$ – Leon Heller Jul 3 '13 at 19:25
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    \$\begingroup\$ Typically one would do this with a narrowband FM IF/decoder IC which implements at least the 2nd mixer and FM detector. Depending on the IC chosen, it may be up to you to mix the input frequency to a 10.7 MHz first IF and pass it through a filter, or the IC may help you with that. \$\endgroup\$ – Chris Stratton Jul 3 '13 at 19:44
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    \$\begingroup\$ @LeonHeller It is about electronic design if he wants to design his own receiver, which he alludes to in his last sentence of the question. \$\endgroup\$ – tcrosley Jul 3 '13 at 20:16
  • \$\begingroup\$ @skyler This really isn't a good hobbyist project. It takes knowledge of transmission lines to get the trace impedances correct, a PCB with mostly surface mount components, and some more expensive test equipment to validate and trouble shoot it. There is no way you can build it on a breadboard. The parasitic capacitance between the channels will be a dead short at RF frequencies. \$\endgroup\$ – Matt Young Jul 3 '13 at 22:09
  • \$\begingroup\$ @MattYoung oh come on, they used to build those things with discrete transistors in TO-92 sized cases on single layer PCBs in the 1970s. It wouldn't require surface mount and optimized trace impedances. But that said, I'd agree you wouldn't want to bother with a breadboard, and the O-scope you'd want for the job would not come cheap, so probably not the best choice for a casual project. \$\endgroup\$ – JustJeff Jul 4 '13 at 1:48
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If I remember right, narrow band FM is used. "Narrow" refers to the small maximum frequency deviation from the carrier center frequency. In FM, more deviation means more signal to noise ratio. Less fidelity is required to send simple digitally encoded signals and voice weather reports than good quality music as commercial FM does. In this case, the deviation is 5 kHz (again, if I remember right).

As for how to build a receiver, that's no different than any other FM receiver. There are various topologies for that. At 160 MHz or so, you have to wake up and design such things carefully. It's not like 1 MHz AM where simple hacks can get reasonable results.

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The 162 MHz weather broadcasts use narrow-band FM, same as Marine VHF and other services in that frequency range.

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