1

In a VHF radio system using TDMA can a time slot be used to carry both voice and data bits together or is it necessary that both be transmitted in two different time slots. Also while reading an article on channel size, I read channel size=12.5Khz and also the channel spacing. Should it be correct? Shouldn't be the channel spacing less than channel size?

sk1
  • 719
  • 6
  • 13
  • 22

1 Answers1

1

For TDMA, voice and data need to be on separate slots.

For FDMA systems, if channel spacing is 12.5kHz, a channel's bandwidth cannot be more than 12.5kHz. Imagine floorboards at 4 inches wide. You could space them at any pitch but you can't pack them any closer than 4 inches.

Andy aka
  • 434,556
  • 28
  • 351
  • 777
  • 1
    That's a bit questionable. Unless you're talking about a specific protocol, there's no reason why you can't multiplex voice and data into a single TDMA timeslot, as long as you're able/willing to share the available bandwidth. – markt Oct 13 '13 at 01:25
  • @markt then that timeslot becomes two timeslots. I don't believe the op is expecting trick answers. – Andy aka Oct 13 '13 at 10:05
  • @Andy aka why should it become two time slots? – sk1 Oct 13 '13 at 18:13
  • 1
    @sk1 Calling it two time slots is probably a little confusing - the time slot would be used for data the fist time and the third time and the fifth etc and in-between the time-slot would be used for voice on the 2nd time and the fourth time etc.. It's perfectly fine to do this but in effect you are manufacturing another time slot albeit interleaving voice and data. You are also reducing the avaialble bandwidth for both the voice and the data. Didn't want my answer to be too complicated. – Andy aka Oct 13 '13 at 18:28
  • @Andyaka ok i think i got it. And how does this happen in FDMA. I have read that there are different modulation techniques. One for digital radios where the same channel is used for voice and data. How does that happen. Does it then in effective becomes FDMA + TDMA? or is it something else? – sk1 Oct 14 '13 at 18:35
  • @sk1 a single FDMA channel can be multiplexed like i described above - as far as the radio transmitter is concerned it is just a signal from a source - it doesn't need to know anything about the signal. FM Modulation - the carrier is shifted up and down in frequency with the amplitude if signal coming in. AM modulation - the amplitude of the carrier is modified to take on the amplitude of the signal coming in. – Andy aka Oct 14 '13 at 18:54