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Would 14 MHz ISM Worldwide band have superior range and penetration (equal tx power)capability than the 433 MHz band? In that case, why aren't any transceivers made for this band?

My application is deployed in a forest for collecting data from animals collars. It is expected to work using the 433MHz transceiver by TI I am wondering why I shouldn't use 14MHz band which in contrast is also Worldwide! offering superior characteristics for my application than the 433MHz band.

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  • \$\begingroup\$ If a data collar transmits in a forest and the receiver is out of range, does it make a noise? \$\endgroup\$
    – Russell McMahon
    Feb 22, 2015 at 10:47
  • \$\begingroup\$ If a man encodes his voice in a digital format and sends it via a data collar in a forest and no woman hears it, is he still wrong? If ... :-) \$\endgroup\$
    – Russell McMahon
    Feb 22, 2015 at 10:48
  • \$\begingroup\$ I think that is out of the scope of my research. However I can make some room for animals to call their mates in my design so that they dont have to keep on screaming and their calls will be parsed digitally. \$\endgroup\$
    – Denis
    Feb 22, 2015 at 11:45

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Lower frequencies generally means that receiving antennas have larger effective apertures. This means they collect more power but, of course they have to be bigger in order to match the wavelength of the transmission.

A dipole at 433 MHz is going to be about 30 times smaller than one at 14 MHz of course. This is usually the first reason to go for a higher frequency despite the effective aperture limitations.

I would also imagine bandwidth is important. The allowable bandwidth at 14 MHz is very tiny compared to other ISM bands and this usually means that a practical system will only work over a short range due to overlapping interference from other users.

So, in short, antenna practicalities and interference are the main reasons for not choosing the lower frequency.

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    \$\begingroup\$ Besides this, there is probably also a regulatory issue. I think that transmitting data is not allowed in 13 MHz, just ISM applications (as an induction heater for example). In contrast 433 MHz can be used for ISM but also for transmitting data at low power. \$\endgroup\$
    – Roger C.
    Feb 22, 2015 at 9:46
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    \$\begingroup\$ 13.56MHz most certainly is used for data - it's the band on which most contactless "swipe cards" are used. See all these "how can I get my RFID reader to work over longer range" questions... So this is a legitimate question and, while long range may be possible with suitable antenna design (and possibly, high transmitter power) it could interfere with any POS terminals in the forest. (If there are any) \$\endgroup\$
    – user16324
    Feb 22, 2015 at 10:15
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    \$\begingroup\$ 13MHz is used a lot for transmitting data such as RFID applications etc. \$\endgroup\$
    – Andy aka
    Feb 22, 2015 at 10:15
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    \$\begingroup\$ Yes, you are right, RFID is indeed allowed at 13.56 MHz and I've checked that also generic short range devices (SRD) are allowed at this frequency (at least in Europe). But the range is very limited. Actually the regulations doesn't talk about a maximum transmitted dBm but a maximum dBuA/m at 10m, as it is expected to be working in the near-field. \$\endgroup\$
    – Roger C.
    Feb 22, 2015 at 10:53
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    \$\begingroup\$ An antenna is like a flexible stick held in the hand. If you move your hand up and down slowly the stick (all along its length) follows your hand. If you move your hand too fast the end of the stick remains stationary. If you move your hand at the right speed you'll find that you hardly need to move your hand at all and the end of the stick is moving massively. This last scenario is an antenna being fed the "correct" frequency signal. Wrapping this around that etc is just really hard to analyse. Try it and see - it won't be perfect but it should be tunable to make it work reasonably effective. \$\endgroup\$
    – Andy aka
    Feb 23, 2015 at 10:53

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