5 ms·

Keep in mind that comparing bandwidth between bands that are very far apart isn't super useful. You can easily select down to fractions of 1khz at 1mhz but not

Keep in mind that comparing bandwidth between bands that are very far apart isn't super useful. You can easily select down to fractions of 1khz at 1mhz but not at 2.4ghz so 1.1mhz of bandwidth means something different at UHF vs HF/MF.

muxator 9y ago
My memories about radio are a bit faint, so forgive me if I am wrong, but the fact that you ate able to discern narrower channels does not mean that you can transmit more information, doesn't it? As far as I remember, the upper limit to the quantity of information you can send is solely set by the bandwidth, and is not dependent on the carrying frequency.
- baobrien 9y ago
  That's mostly right, the theoretical limit to the amount of information you can carry over a channel is set by the bandwidth and the channel signal to noise ratio. See the Shannon Limit [1]. I should add, however, the lower frequency you build your radio to operate on, the narrower your channel usually is. Antennas and filters tend to only be well matched over one or a few narrow frequency bands. These bands of good impedance get smaller as you go down in frequency, logarithmically. [1] https://en.wikipedia.org/wiki/Noisy-channel_coding_theorem https://en.wikipedia.org/wiki/Noisy-channel_coding_theorem
  - pdelbarba 9y ago
    There's also the limitation of oscillator precision IIRC. 1ppm deviation is 1hz at 1mhz and 1khz at 1ghz
    - baobrien 9y ago
      Modern frequency synthesizers can easily do a few Hz step size up in the gigahertz range and be within a few ppm. That doesn't really matter that much though, since modern radios (at least these digital ones) are built as SDRs. They can shift the signal around and select whatever band they feel like.
      - pdelbarba 9y ago
        Sure, but that's on the receiver side for carrier recovery. Wouldn't it be problematic if you mashed a bunch of channels/allocations sufficiently close together that they started wandering on top of each other?
        PoachedSausage 9y ago
        Modern DAB/DVB receivers are usually zero-IF, the wanted band of frequencies is mixed down to baseband and filtered with a sharp cutoff Surface Acoustic Wave filter then sampled with a fast ADC. Selectivity is then dependent on DSP. On the transmit side, you have to carefully combine the outputs of your various transmitters with a complex filter network, which at high powers looks something like: http://admin.mb21.co.uk/tx/userimages/8448proc20120403120238.jpg http://admin.mb21.co.uk/tx/userimages/8448proc20120403120238...

muxator 9y ago

My memories about radio are a bit faint, so forgive me if I am wrong, but the fact that you ate able to discern narrower channels does not mean that you can transmit more information, doesn't it? As far as I remember, the upper limit to the quantity of information you can send is solely set by the bandwidth, and is not dependent on the carrying frequency.

baobrien 9y ago
That's mostly right, the theoretical limit to the amount of information you can carry over a channel is set by the bandwidth and the channel signal to noise ratio. See the Shannon Limit [1]. I should add, however, the lower frequency you build your radio to operate on, the narrower your channel usually is. Antennas and filters tend to only be well matched over one or a few narrow frequency bands. These bands of good impedance get smaller as you go down in frequency, logarithmically. [1] https://en.wikipedia.org/wiki/Noisy-channel_coding_theorem https://en.wikipedia.org/wiki/Noisy-channel_coding_theorem
- pdelbarba 9y ago
  There's also the limitation of oscillator precision IIRC. 1ppm deviation is 1hz at 1mhz and 1khz at 1ghz
  - baobrien 9y ago
    Modern frequency synthesizers can easily do a few Hz step size up in the gigahertz range and be within a few ppm. That doesn't really matter that much though, since modern radios (at least these digital ones) are built as SDRs. They can shift the signal around and select whatever band they feel like.
    - pdelbarba 9y ago
      Sure, but that's on the receiver side for carrier recovery. Wouldn't it be problematic if you mashed a bunch of channels/allocations sufficiently close together that they started wandering on top of each other?
      - PoachedSausage 9y ago
        Modern DAB/DVB receivers are usually zero-IF, the wanted band of frequencies is mixed down to baseband and filtered with a sharp cutoff Surface Acoustic Wave filter then sampled with a fast ADC. Selectivity is then dependent on DSP. On the transmit side, you have to carefully combine the outputs of your various transmitters with a complex filter network, which at high powers looks something like: http://admin.mb21.co.uk/tx/userimages/8448proc20120403120238.jpg http://admin.mb21.co.uk/tx/userimages/8448proc20120403120238...