Carrier frequency for transmission of signals

[s.k. sundar]

why do we choose 38Khz as a carrier frequency for transmission:roll:?
i have done a project in infrared remote controlled car , where i have used a t.v. remote and a tsop receiver which also used 38Khz as a carrier frequency.can anyone explain me?

 

[sab123456]

I guess it is a Standard for remote controllers
Consumer IR

 

[betwixt]

Higher frequency is less efficient to produce, lower frequency can't carry as much data per second.
It is a compromise between the two but it has become a standard over time so that interchangeable detector modules can be used. The standardization also defined a band of frequencies in the 38KHz region that other emitting devices, such a CFL should avoid to minimize interference. Please remember that the frequency was first used in the 1970s when LED and IC technology was in it's infancy. You can of course choose any frequency you like if you want to design your own but you will need an unfiltered IR detector to recover the data.

Brian.

 

[FvM]

The standardization also defined a band of frequencies in the 38KHz region that other emitting devices, such a CFL should avoid to minimize interference.

Do you know a standard, that specifies an avoidance band for high frequency lighting power supplies? In my opinion, it's more imperative than ever with the spreading of switch mode LED lighting.

 

[incomplete_jerin]

I think this link might help you.
Audacity Forum • View topic - How to add a carrier frequency.
Regards,
Jerin.

 

[betwixt]

FvM, I've never seen a written standard but I have spoken to engineers from one of Europes biggest CFL 'manufacturers' (I'm sure they really source from China) and avoiding 38KHz is a design consideration.
Brian.

 

[FvM]

avoiding 38KHz is a design consideration

It would be reasonable of course, but I wonder, if you can rely on it. Some years ago, I had a project related to optimal modulation and detection principles for optical sensors. The customer had his own empirical standard describing spectral density of interfering AC light sources, but it didn't explicitely show a gap at 38 kHz. But if I remember right, most CFL lamps have a fundamental above 40 kHz. Because the fundamental is low compared to second harmonic in the optical output, you can actually hope for limited interference at 38 kHz.

As another point, CFL have a moderate modulation index due to the finite decay time of the fluorescent material compared to pwm dimmed LEDs.