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Questions tagged [fm]

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

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1 vote
1 answer
112 views

Does an FM Loop Antenna's Loop diameter affect reception?

I live 75 miles from one of my favorite station's broadcast tower (91.1 FM), and I would like to get better reception. Currently, I am using a NAD 4150 Tuner with a T style antenna. I ran it out a ...
0 votes
1 answer
46 views

Natural dipole / monopole filtering

Word has it these antennas are broadband, however my calculations show one may not need FM / AM BCB wave traps if not operating around those frequencies. I have run the script here for: ...
-1 votes
1 answer
98 views

Why can I connect simplex at 146.52 but not at 145.200 and 147.000? [closed]

I am preparing myself to use Winlink. I am preparing myself to use VARA FM. 145.000 is the Simplex frequency used by our local university (Montana State). It can be used for both voice and digital, ...
3 votes
1 answer
642 views

How to use GNU Radio to demonstrate FM demodulation without baseband signals

Using GNU Radio, I'm currently trying to create a flow graph containing a simple demonstration of how FM modulation and demodulation works. Since the target audience is not accustomed with complex ...
3 votes
1 answer
88 views

Can I use a generic FM 2m radio for meteor scatter or other digi modes?

Firstly, I know it’s possible, but is there any actual activity for 2m MS. I want to get into Meteor scatter but i am wondering if i can use my 2m FM transmitter with a TNC and a yagi for meteor ...
0 votes
0 answers
86 views

High SWR at full height

I operate a low power FM radio station. I have always had issues with high SWRs. Recently I have purchased a new transmitter, new antenna, and new 100 ft cable from the same company assuming they ...
2 votes
1 answer
174 views

2m FM: where do I actually QSY to after establishing contact on 145.500?

I am new to amateur VHF, coming from HF and marine. Online advice says after establishing contact on 145.500 then QSY. What is the range of channels/frequencies most folks use? ie that they are ...
14 votes
1 answer
3k views

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. ...
6 votes
7 answers
9k views

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 ...
2 votes
2 answers
628 views

Why does SDR# sound better than SDR console?

This is kind of odd. I just got my first SDR receiver and I noticed that one application (SDR#) sounds a lot better than another (SDR Console) when listening to stereo FM broadcasts through the same ...
5 votes
5 answers
2k views

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 ...
6 votes
3 answers
5k views

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 ...
10 votes
3 answers
3k views

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 ...
1 vote
1 answer
225 views

How does injecting a carrier allow a FM receiver to demodulate SSB?

I just watched VK3YE's video on demodulating SSB using a FM receiver. (https://www.youtube.com/watch?v=kJ-cj-YwflY) In the video, he demonstrates that by transmitting a very weak CW carrier, the FM ...
0 votes
1 answer
123 views

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 ...
1 vote
1 answer
66 views

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 ...
1 vote
1 answer
145 views

Is SSB and FM voice considered TDD or FDD (and what are TDD/FDD)?

We are looking at the Qorvo QPL9547 LNA and the datasheet notes: For TDD Applications: R1 = 0Ω & R2 = 100K For FDD Applications: R2 = 100K ‘OR’ Pin 6 tied to ground. R1 = DNP/Omitted This will ...
0 votes
1 answer
107 views

Frequency division multiplexing FM Radio stations

Can someone help me with this I'm confused on what it is supposed to look like?
2 votes
1 answer
178 views

can i convert an FM coaxial antenna to just speaker wire?

I have a Sony MHC-GX450 compact mini stereo system. The connector for the FM antenna is coaxial, and is labeled 75 Ω. I'm wondering if somehow I can use speaker wire for the FM antenna.
3 votes
5 answers
1k views

How do VHF antennas compensate for change in frequency in Frequency Modulation?

I would like to understand how antennas specifically, compensate for variability in the frequency while receiving FM waves in VHF. The way FM works is that the receiver system - receiver and antenna ...
0 votes
1 answer
121 views

What would cause 3 bursts of FM radio interference every ~3.5 seconds

I’m trying to locate the source of some interference on the FM band — it’s audible as 3 quick staccato bursts of brownish noise approximately every 3.5 seconds. It’s more pronounced at the low end of ...
2 votes
3 answers
439 views

Store and forward system like voicemail for hams

I want to be able to get in touch with hams in my area when we are not both on air at the same time, but are close enough to each other for VHF communication. I want to be able to use my radio to call ...
1 vote
1 answer
289 views

ICOM IC-910h How much bandwidth does it listen when receiving USB and FM?

CD-audio has a bandwidth of 22kHz. CW usually has a bandwidth between 3 to 5 kHz. But I am wondering what is the bandwidth my Icom IC-910H can listen to in both, the SSB and the FM mode? Also, what ...
0 votes
3 answers
84 views

change LC parameter digitally

LC circuit is the main element of every frequency generator, I intend to make an FM transmitter, but many opensource circuit use analog variable L or C part to set and adjust the target frequency My ...
2 votes
1 answer
123 views

Buzzing FM interference

What kind of interference or other receiver issues can cause a constant buzzing noise (picket fence lines in the audio spectrum) in the demodulated audio of a received NFM VHF signal? With AM, it ...
1 vote
2 answers
301 views

How many cars/devices can connect to a transmission from a 7 Watt FM transmitter

I currently own a 7 Watt Frequency Modulation (FM) transmitter that I purchased from eBay some years ago. We are planning a drive-in cinema setup where the transmitter will be placed 5 meters above ...
8 votes
3 answers
12k views

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 ...
4 votes
2 answers
179 views

Can a phase-modulated voice radio transmission be received and heard properly by an "FM" radio?

Not necessarily an amateur radio question (but perhaps a licensed amateur should know the answer?) - I note that the specifications for marine VHF radio operating in the 156-157 mhz band call for both ...
4 votes
2 answers
2k views

Yaesu FT-991A: FM and C4FM modes don't work on HF bands

I bought a second-hand Yaesu FT-991A. It works pretty well and by the look of it's internals I don't believe it was ever repaired. However I noticed one weird thing. When I try to use FM or C4FM on ...
4 votes
3 answers
2k views

What are the technical reasons that there are no FM transmissions on the long, medium, or shortwave?

Why are there no frequency modulated broadcasts on the long/medium/short wave, but only on VHF? I'm sure there are many historical and political reasons (long/medium/short wave were already in use for ...
1 vote
2 answers
203 views

What are the practical differences between the different voice modes (and why aren't there any SSB Handheld Transceivers (HT's))?

It's my understanding that FM is used for UHF, VHF, and SSB is generally reserved for other bands. From my understanding, FM better audio quality when reception is good SSB: more efficient (can ...
0 votes
3 answers
207 views

Radio Waves propagation (Intuitive Understanding of Wave propagation)

I have few similar questions regarding Radio waves communication particularly FM and AM type of Radio wave communication. Please bear with the naivety of the questions. Questions: Radio waves in FM ...
2 votes
1 answer
245 views

Receiving an Coded Odd Signal at 137.25MHz but don't know what it might be. It can affect my detection on NOAA 19. Need help

I am a newbie trying to detect NOAA 15, 18, and 19 satellites, which have downlink frequencies between 137 MHz and 138 MHz. I am using an SDR dongle and attached a photo of it to this post. Of course,...
3 votes
2 answers
2k views

What's the difference between the normal and S-meter squelch in IC-2730?

I recently obtained an IC-2730E and can't figure out the difference between its squelch options. Unfortunately, the user manual isn't very helpful. The squelch option had 3 types: off, attenuation and ...
3 votes
1 answer
783 views

GNU Radio - Frequency parameter of Signal Source Block

I designed an analog FM transmitter with GNU Radio Companion in order to understand the tool better. The hardware I use is an USRP B200. The carrier was built with a Signal Source block and the ...
1 vote
3 answers
2k views

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. ...
1 vote
3 answers
181 views

Need antenna for mobile mag-mount LPFM broadcast 88.3 MHz

I am doing some temporary FM broadcasting for car events such as COVID-safe car parades and drive-in movies. The terrain is horrible, urban areas with lots of buildings. The cars snake around a city, ...
0 votes
3 answers
679 views

Recommended Books For AM/FM (especially AM) Radio Design

I am trying to gain a better grasp of how to build an AM radio receiver. Can you direct me to some books (or other information) that will help?
0 votes
1 answer
264 views

What determines the bandwidth of an FM signal?

With an FM signal, it takes up more room in the radio spectrum presumedly because the carrier frequency is changed. On average what's the width of the FM sidebands? Does the deviation from the center ...
4 votes
2 answers
2k views

How does FM station have fixed frequency when FM modulation changes the frequency?

I am not sure if this question fits better in physics.stackexchange or ham.stackexchange, feel free to correct me. I am new to studying RF and SDR in general, I was looking up how modulation works and ...
1 vote
0 answers
541 views

LA1185 FM downconverter shows weird behavior

I've built FM CCIR/OIRT downconverter based on Sanyo LA1185 IC. I've used most famous schematics for it with slight modification (added DC blocking capacitor 1 nF rated on the output) Coils L1 and L2 ...
5 votes
1 answer
242 views

FM spectral amplitudes during silence

General setting I'm playing around with an RTL-SDR and recently captured some FM spectrum in Hannover, Germany. I want to undersand what's going on, so I've read a lot about FM and its spectra, but I ...
1 vote
0 answers
41 views

power limit on wireless FM microphone transmitters [duplicate]

I am building a "toy" radio station as a teaching tool for high school students to work with. I intend to use a small (short-range) wireless FM microphone module as the transmitter. What is the legal ...
0 votes
1 answer
1k views

Frequency modulation with gnuradio

I'm trying to understand way which Frequency Mod block works in gnuradio. According to my intuition there should be at least two inputs: signal to encode base frequency / carrier signal Instead ...
4 votes
4 answers
6k views

What are some equivalents of a BF199 transistor?

I'm planning to build an FM radio receiver using the instructions on http://www.instructables.com/id/Build-your-own-Crude-FM-Radio/ The schematic uses a BF199 transistor which is marked "obsolete" by ...
1 vote
1 answer
149 views

Radio antenna for my FM receiver / Android FM

I want to make a radio antenna at home which will be able to receive all FM frequencies for my FM radio or Android FM. How do I make it? Frequency it can catch : 88 - 108 MHz Thanks.
2 votes
2 answers
1k views

Bad squelch on a TYT MD-380: user error or hardware?

I have a new TYT MD-380; it works well for DMR channels, but on analog, the squelch doesn't seem to open when it should. I'm relatively new to ham and my first suspicion is user error, but it's ...
2 votes
2 answers
4k views

Can a FM tuner (receiver) be detected and triangulated?

In movie "6 Below", based on a true history, a lost snowboarder at Mammoth Mountain (California) is located by search and recuse when they detect and triangulate a signal from his MP3 player that also ...
1 vote
3 answers
115 views

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 ...
17 votes
3 answers
7k views

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 ...