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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Why do we not use AM and FM at the same time to transmit more information?

Amplitude modulation uses the modulation of the amplitude of a carrier wave to transmit data while leaving the carrier frequency constant, and in the case of FM it's just the other way round. Why is a modulation of the frequency in an AM signal not…
DK2AX
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Why does the audio on my FM transceiver cut out every 5.5 seconds?

Specifically, my Icom ID-4100a. What's interesting, is that this happens in MR and VFO modes... but NOT when using the built-in WX stations. For example listening to WX-01 (162.550 MHz), no problem. Listening to 162.550 via VFO and I get the…
webmarc
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Resort FM radio station

I stayed at a resort in the U.S. recently that is located in an unpopulated area with virtually no radio reception. To fill the gap, the resort has its own FM station that can be heard only within the resort (about a minute after you drive off the…
JoelFan
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Is FM modulation still more resistant to noise when given the same bandwidth as an AM signal?

FM modulated radio is much more resistant to noise and can deliver better sound quality than AM radio. But FM signals also use more bandwidth than AM signals. In general a wider bandwidth signal is more resistant to noise / can send more data than a…
JanKanis
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Would it be possible for a software-defined FM receiver to demodulate two signals on the same frequency?

When two FM signals are transmitted on the same (or about the same) center frequency, either you hear only one or you hear that noise I'm sure most of you have heard. Would it be possible for a software-defined receiver to track both signals and…
Someone
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How does SDR demodulation differ between wideband and narrowband FM?

What is the difference between software demodulation of an IQ signal between wideband FM and narrowband FM? Both seem to look at the 2nd difference in unwrapped phase angles of IQ samples.
hotpaw2
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Is it legal to transmit with HackRF one?

Is it legal to transmit using HackRF one (in Germany), the purpose is to do some Lab research and Academic experiments. for example i want to broadcast an FM signal using HackRF one and try to receive it using another hardware (RTL-SDR). If no is…
A.SDR
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Is FM appropriate for foxhunting?

I'm thinking about an inexpensive way to create a foxhunt kit for youth groups, and am wondering if the cheap dual band HTs could be used. However, it occurs to me that FM doesn't provide any good audio queues for signal strength, and the SWR meters…
Adam Davis
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How to tune an FM transmitter to a specific frequency?

I am planning to organise a simple fox hunt, a family event. This includes building a transmitter. I am currently considering the following…
Alexander Churanov
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How does FM encode BOTH amplitude and frequencies of full audio signal spectrum?

How does frequency modulation encode both amplitude and frequency of the modulating audio signal only by varying frequency? How do both components get spread across and encoded in the side bands? I generally understand that AM side bands occupy…
Tom Zahner
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Single Side Band AM vs FM

I know the difference between AM and FM, but could anyone explain to me what is the differences between single side band AM and conventional FM? So far as I know the SSB modulation will reduce the transmitting power. But what is the exact function…
hellojoshhhy
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Are there any commonly used digital modes that work with an FM transceiver?

Like many new hams, I have just one radio: an inexpensive 2m/70cm FM transceiver. It doesn't do SSB and it doesn't have a digital input. If I wire up a connection between the radio and my computer's sound card, are there any digital modes that I…
mrog
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What does the term 3 kHz deviation relate to in the FM world?

I am confused when someone says "your audio levels are set right and has good deviation at 3 kHz" when talking about wide-band 25 kHz FM signals. First confusion: Why are audio levels measured in kHz? I find it very misleading when you are…
Skyler 440
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Receiving commercial / public-safety on a general-coverage HAM transceiver

I have an ICOM-7100 that I've installed in my mobile as my primary (nay, only) HAM transceiver; and I'm trying to avoid wasting a ton of space in my vehicle (not to mention money) for a proper scanner, or for a CB¹, to achieve fuller coverage of the…
ELLIOTTCABLE
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Is FM effectively spread spectrum?

My understanding is that FM achieves better audio quality (under the right circumstances) than AM by spreading the narrow audio signal's information into a wider RF signal. Does this mean FM is technically a form of spread spectrum?
Someone
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