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Why RC toys still operate in 27Mhz band?

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Recently I had opened an remote control (RC) toy to see its circuit and found that it operates on 27 Mhz. Not just that toy even many toys operate in that 27 and 49 Mhz band. These days we find even a small circuit utilizing UHF(300-3000Mhz) band then why these toys are still stuck in that frequency?

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2 answers

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Roughly around 27 MHz is the old "CB" (Citizen's Band, 11 meter) frequency block. The advantage of this band is that it is free to use with limited power. This is the band "walkie talkies" used to use.

I remember back in the 1970s a bunch of us neighborhood kids had walkie talkies. You could simply buy such things and use them, no license or training required. Of course the units themselves were limited in power for that purpose. More powerful units, like those used by truckers, at least came with some rules of use.

One drawback of the 11 meter band is that the antenna needs to be rather large by today's standards to be reasonably efficient. The walkie talkies we had back in the 1970s had collapsible whip antennas that were probably about a meter long. Even then, that was a serious compromise between good coupling and portability.

The 11 meter band makes sense for toys where a license would be cumbersome and where the transmitter and receiver will be close, a few 10s of meters max. In that case, the antennas don't been to be very efficient, and a few extra mW of battery power for transmitting is irrelevant compared to the battery power needed by the motors anyway.

433Mhz is also in CB

No, it's not. That is one of the ISM (Industrial, Scientific, and Medical) bands in the US. The ISM bands are much more restricted in terms of radiated power, repetition time, and overall duty cycle than CB. The two are very different from each other.

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@Olin Lathrop: By surfing net I observed that 433Mhz is also in CB.Now please tell me which will be more efficient for a toy a 27 Mhz or 433 Mhz and also how to decide. ‭aditya98‭ 27 days ago

@aditya98 433MHz can be used license free in most of Europe, Middle-East, South America, Australia and Africa. It has lots of restrictions in North America and South-East Asia, where it is typically either used for ISM or for RFID container systems. Frequency allocation world-wide is a complete mess in general, with little or no standardization. ‭Lundin‭ 26 days ago

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I can think of a couple of reasons:

  • Lower frequencies mean superior range at the same output power. Whereas for example 2.4 GHz technologies tend to behave much more "directional" on short ranges, they are basically line of sight and don't handle obstructing objects/terrain between sender and receiver well.

  • For the above reason, you can get away with worse receiver sensitivity, meaning a cheaper product.

  • The bands 26.957-27.283 MHz and 40,660-40,700 MHz are license free (up to 10mW E.R.P) in the whole of EU and likely in many other countries too.

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