Amateur Radio Stack Exchange
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Questions tagged [fm]

Questions about Frequency Modulation, the analog modulation scheme commonly used for voice on VHF and UHF frequencies.

In a radio transmitter, a sine wave at a particular frequency, the carrier signal, is modified by incorporating a second signal, the modulating signal, that contains information to be transmitted. This process is known as modulation. In the radio receiver, the process is reversed to recover the modulating signal; this process is called demodulation.

For analog signals such as voice, frequency modulation (FM) is a modulation method in which the frequency of the carrier signal is varied in accordance with the instantaneous amplitude of the modulating signal. FM was invented by Edwin H. Armstrong in 1935, and has been popular in amateur use on the VHF and UHF bands since the 1950s.

More information about FM is available on Wikipedia.

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FM carrier wave frequency determination

I know the difference between AM and FM, but how does a receiver determine the carrier wave frequency, as the frequency edited during the modulating process?
root
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Pre-emphasis measurement

I am researching a way to build a pre-emphasis circuit, so I looked up the specs for different pre-emphasis standards. An example is the standard for FM broadcast, in the USA it's 75 µs. I am confused on how a filter is measured using time. What…
Skyler 440
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Mini-Din 9600 Deviation Measurement

In an ongoing testing effort to get the highest speeds from VARA-FM, I have been examining the characteristics of the "9600 baud" 6-pin mini-din input on my Icom-7100. Although there is only one input pin, the treatment of the incoming signal can be…
Deepstop
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FM radio demodulator IC usage

An Ebay search for "fm demodulator" results in a whole slew of ICs, but even after reading their datasheets, I have no idea what I should connect where and what input signals the chips will work with. Take an AN7411 for instance. Page 3 of the…
jayded-bee
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How do I build an portable FM transmitter?

I have been bugged with the idea of building a radio in a suitcase, but I have not many clues about where to start. My idea is to make a portable FM station so podcasts can be broadcasted in a small area and later uploaded to the Internet. The…
user648
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Modulation basics

I have a new interest in RF modulation and read the O'Reilly book electronics cookbook. I understand that in FM you start out with a carrier wave and then it is modulated but I don't understand if both waves are sent out or if it combines to make…
user14158
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Can a Harmonics from an Raspberry PI FM Transmitter Interfere with Emergency Bands?

One of my neighbors is an emergency personal and has a police radio at home so he knows when to respond. Anyways, the other day, I saw an article on MAKE on how to make a radio station with a Raspberry PI. This uses GPIO pin 4 to generate a FM…
AntiMalwareFlames
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Looking for an inexpensive FM downconverter for an SDR project

I do a lot of work with DSP and I am looking for an inexpensive down converter so as to down convert from the FM band to some intermediate frequency. Not necessarily to standard FM 10.7MHz but something lower that I can choose. The reason that I…
miner_tom
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