3 ms·

The useful range of FM is much shorter. The reason why AM transmitters remain so useful in geographically large countries like the USA is that you need far fewe

The useful range of FM is much shorter. The reason why AM transmitters remain so useful in geographically large countries like the USA is that you need far fewer transmitters to reach everyone.

bigfishrunning 2y ago
That has more to do with the frequency band then the modulation scheme. I wonder if long range FM in the ~1000khz broadcast band would make sense in the future. It would get the range of AM broadcast radio with the quality of FM (but it may require too much bandwidth to be practical)
- wakawaka28 2y ago
  I'm no expert but I think lowering the frequency far below the current standard was not feasible due to the frequencies and ranges being transmitted.
- LeoPanthera 2y ago
  You're not wrong, but that's useless nitpicking. We're not going to suddenly introduce a brand new radio standard that no-one has a radio for. There are literally millions of AM radios out there in the US, at the already agreed frequency range. For emergency broadcast uses, the increased quality of FM is meaningless.
  - nahumba 2y ago
    The advantage of am over fm is the simplicity of the electronic circuit. In am its very easy to create a receiver to listen to broadcast. While an fm radio is too complicated for amature electronic. So i dont belive am will ever be dropped for emergency radio
    - Tor3 2y ago
      FM radios aren't complicated at all. And FM transmitters, in particular, are extremely simple. When I was a student we had a tiny one we made in an afternoon (this was decades ago), we connected it to our 8-hour reel tape deck and had our own music station in the car radio when we drove around in the area. The advantage of AM is, as was mentioned already, the lower frequency used by AM which means much better coverage. FM 87MHz-108MHz is almost just line of sight.
      - kmbfjr 2y ago
        No much to a coil, antenna and a germanium diode.
        candiddevmike 2y ago
        The geranium diode is doing most of the heavy lifting. Good luck building that from scratch.
        fmj 2y ago
        https://rimstar.org/science_electronics_projects/razor_blade_diode_for_crystal_foxhole_radio.htm https://rimstar.org/science_electronics_projects/razor_blade...
        bsder 2y ago
        Galena cat whiskers were quite common: https://en.wikipedia.org/wiki/Crystal_detector https://en.wikipedia.org/wiki/Crystal_detector
        Tor3 2y ago
        And how is that relevant to the alleged complexity of building an AM radio vs an FM one? The point was that the latter is easy, not complicated. The FM transmitter is so easy to make that you can make one by accident - if there's a non-linear element in the rf part.
        nahumba 2y ago
        Its about the simplicity of the circuit. The components are available for any electronic Technician. Use an amplifier is not a basic circuit. Resistor diode capacitor cable and power source are the basic of electronics
    - tzs 2y ago
      You can actually receive FM very simply. Here was an amusing post on Reddit [1] a few years ago from someone who was trying to make a simple audio amplifier and found that it was receiving his local NPR station which was broadcasting FM on 88.3 MHz. After some experimenting he got it down to just a cheap op amp, 2 capacitors, 1 potentiometer, a 9 V battery, a speaker, and some wire for an antenna. It is working through slope detection. Basically if you've got FM at frequency X carrying voice and you measure the energy at a frequency a little bit away from X, as the FM signal frequency varies due to the voice modulation the energy you measure near X will vary in a similar way, so your voice modulation of the frequency X becomes amplitude modulation of your energy measurement. You can play with this on an SDR, such as a cheap RTL-SDR dongle. Find an FM station and tune to its center frequency with your SDR software set for FM demodulation, and verify that you are indeed on an FM station broadcasting voice and/or music. Then switch the SDR software to AM demodulation and start slowly tuning away from the FM center frequency. You should find a point where you can clearly hear the voice and/or music. It won't sound great compared to FM demodulation of the same station, or compared to an AM station, but it should be serviceable for receiving emergency information. [1] https://www.reddit.com/r/HamRadio/comments/oz5rri/i_accidentally_made_an_fm_receiver_please_explain/ https://www.reddit.com/r/HamRadio/comments/oz5rri/i_accident...
  - kmbfjr 2y ago
    It is not useless nitpicking, it is the sole reason of your argument why the 300 meter band covers more area than the 3 meter band.
    - lolinder 2y ago
      It's useless nitpicking because in the US, AM vs FM comes coupled with those frequency ranges. We're as likely to get a brand new radio standard at this point as we are a replacement to the NEMA connector, so the next best thing is to just use the standard we already have that does the job well enough.
- btbuildem 2y ago
  If I recall correctly, FM needs the higher frequency carrier band to actually M the F effectively. You'd also need much longer antennas for this. The amplitude-modulated signal also needs far less bandwidth than a frequency-modulated one, so it would not "fit" at ~1000kHz because there are other reserved bands nearby.
- asdefghyk 2y ago
  The problem is the amount of Bandwidth taken at the lower frequency.
- kstrauser 2y ago
  The bandwidth is the dealbreaker. Commercial FM radio has a necessary bandwidth of 270KHz. That’s not a lot when your carrier frequency is around 100,000KHz. It’s a whole lot when your carrier is around 1000KHz. For comparison, commercial AM mono bandwidth is 10KHz. SSB AM ham radios use 2.4KHz.
  - anticensor 2y ago
    Commercial AM has a 5kHz bandwidth (4.5kHz in Europe), commercial FM 50kHz (29kHz if mono). The remainder of the channel is guardband.
    - kstrauser 2y ago
      Source for 270: https://en.wikipedia.org/wiki/FM_broadcasting https://en.wikipedia.org/wiki/FM_broadcasting. Search there for “necessary bandwidth”. For AM, that’s 5KHz+-, or 10 total.
- ssl-3 2y ago
  The broadcast AM band is 1.6MHz wide. Broadcast FM stations are spaced at 200KHz intervals, of which about 150KHz is used for modulation and the remaining ~50KHz is used for guard bands. Thus, current standards, the entirety of the broadcast AM spectrum can support no more than 8 concurrent FM broadcasts in a region. And maybe that "works," but it certainly doesn't leave much room for competing markets. When multiple stations with wide propagation all use a singular frequency, they have to be geographically spaced quite far apart: The hypothetical Toronto station centered at 1330KHz station would step on the Detroit station at the same frequency, which would step on the Chicago and Cincinnati stations. And, sure: One could give one channel to each market to reduce this co-channel interference, but then there's not enough density for any meaningful competition. (And our band of capitalism requires competition in order to even begin to work.)
- sidewndr46 2y ago
  Long range FM does not work because of the multipath effect. Even on 29.6 MHz it's quite pronounced.

The useful range of FM is much shorter. The reason why AM transmitters remain so useful in geographically large countries like the USA is that you need far fewer transmitters to reach everyone.

bigfishrunning 2y ago

That has more to do with the frequency band then the modulation scheme. I wonder if long range FM in the ~1000khz broadcast band would make sense in the future. It would get the range of AM broadcast radio with the quality of FM (but it may require too much bandwidth to be practical)

wakawaka28 2y ago
I'm no expert but I think lowering the frequency far below the current standard was not feasible due to the frequencies and ranges being transmitted.
LeoPanthera 2y ago
You're not wrong, but that's useless nitpicking. We're not going to suddenly introduce a brand new radio standard that no-one has a radio for. There are literally millions of AM radios out there in the US, at the already agreed frequency range. For emergency broadcast uses, the increased quality of FM is meaningless.
- nahumba 2y ago
  The advantage of am over fm is the simplicity of the electronic circuit. In am its very easy to create a receiver to listen to broadcast. While an fm radio is too complicated for amature electronic. So i dont belive am will ever be dropped for emergency radio
  - Tor3 2y ago
    FM radios aren't complicated at all. And FM transmitters, in particular, are extremely simple. When I was a student we had a tiny one we made in an afternoon (this was decades ago), we connected it to our 8-hour reel tape deck and had our own music station in the car radio when we drove around in the area. The advantage of AM is, as was mentioned already, the lower frequency used by AM which means much better coverage. FM 87MHz-108MHz is almost just line of sight.
    - kmbfjr 2y ago
      No much to a coil, antenna and a germanium diode.
      - candiddevmike 2y ago
        The geranium diode is doing most of the heavy lifting. Good luck building that from scratch.
        fmj 2y ago
        https://rimstar.org/science_electronics_projects/razor_blade_diode_for_crystal_foxhole_radio.htm https://rimstar.org/science_electronics_projects/razor_blade...
        bsder 2y ago
        Galena cat whiskers were quite common: https://en.wikipedia.org/wiki/Crystal_detector https://en.wikipedia.org/wiki/Crystal_detector
        Tor3 2y ago
        And how is that relevant to the alleged complexity of building an AM radio vs an FM one? The point was that the latter is easy, not complicated. The FM transmitter is so easy to make that you can make one by accident - if there's a non-linear element in the rf part.
        nahumba 2y ago
        Its about the simplicity of the circuit. The components are available for any electronic Technician. Use an amplifier is not a basic circuit. Resistor diode capacitor cable and power source are the basic of electronics
  - tzs 2y ago
    You can actually receive FM very simply. Here was an amusing post on Reddit [1] a few years ago from someone who was trying to make a simple audio amplifier and found that it was receiving his local NPR station which was broadcasting FM on 88.3 MHz. After some experimenting he got it down to just a cheap op amp, 2 capacitors, 1 potentiometer, a 9 V battery, a speaker, and some wire for an antenna. It is working through slope detection. Basically if you've got FM at frequency X carrying voice and you measure the energy at a frequency a little bit away from X, as the FM signal frequency varies due to the voice modulation the energy you measure near X will vary in a similar way, so your voice modulation of the frequency X becomes amplitude modulation of your energy measurement. You can play with this on an SDR, such as a cheap RTL-SDR dongle. Find an FM station and tune to its center frequency with your SDR software set for FM demodulation, and verify that you are indeed on an FM station broadcasting voice and/or music. Then switch the SDR software to AM demodulation and start slowly tuning away from the FM center frequency. You should find a point where you can clearly hear the voice and/or music. It won't sound great compared to FM demodulation of the same station, or compared to an AM station, but it should be serviceable for receiving emergency information. [1] https://www.reddit.com/r/HamRadio/comments/oz5rri/i_accidentally_made_an_fm_receiver_please_explain/ https://www.reddit.com/r/HamRadio/comments/oz5rri/i_accident...
- kmbfjr 2y ago
  It is not useless nitpicking, it is the sole reason of your argument why the 300 meter band covers more area than the 3 meter band.
  - lolinder 2y ago
    It's useless nitpicking because in the US, AM vs FM comes coupled with those frequency ranges. We're as likely to get a brand new radio standard at this point as we are a replacement to the NEMA connector, so the next best thing is to just use the standard we already have that does the job well enough.
btbuildem 2y ago
If I recall correctly, FM needs the higher frequency carrier band to actually M the F effectively. You'd also need much longer antennas for this. The amplitude-modulated signal also needs far less bandwidth than a frequency-modulated one, so it would not "fit" at ~1000kHz because there are other reserved bands nearby.
asdefghyk 2y ago
The problem is the amount of Bandwidth taken at the lower frequency.
kstrauser 2y ago
The bandwidth is the dealbreaker. Commercial FM radio has a necessary bandwidth of 270KHz. That’s not a lot when your carrier frequency is around 100,000KHz. It’s a whole lot when your carrier is around 1000KHz. For comparison, commercial AM mono bandwidth is 10KHz. SSB AM ham radios use 2.4KHz.
- anticensor 2y ago
  Commercial AM has a 5kHz bandwidth (4.5kHz in Europe), commercial FM 50kHz (29kHz if mono). The remainder of the channel is guardband.
  - kstrauser 2y ago
    Source for 270: https://en.wikipedia.org/wiki/FM_broadcasting https://en.wikipedia.org/wiki/FM_broadcasting. Search there for “necessary bandwidth”. For AM, that’s 5KHz+-, or 10 total.
ssl-3 2y ago
The broadcast AM band is 1.6MHz wide. Broadcast FM stations are spaced at 200KHz intervals, of which about 150KHz is used for modulation and the remaining ~50KHz is used for guard bands. Thus, current standards, the entirety of the broadcast AM spectrum can support no more than 8 concurrent FM broadcasts in a region. And maybe that "works," but it certainly doesn't leave much room for competing markets. When multiple stations with wide propagation all use a singular frequency, they have to be geographically spaced quite far apart: The hypothetical Toronto station centered at 1330KHz station would step on the Detroit station at the same frequency, which would step on the Chicago and Cincinnati stations. And, sure: One could give one channel to each market to reduce this co-channel interference, but then there's not enough density for any meaningful competition. (And our band of capitalism requires competition in order to even begin to work.)
sidewndr46 2y ago
Long range FM does not work because of the multipath effect. Even on 29.6 MHz it's quite pronounced.