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i did remote control for garage opener with cheap module supply with 3v coin cell battey,i got 30-40 meter range by spiral type antenna setup and got 80 meter range wipe type antenna setup. i purchased antenna for receiver side also. (using USART for data transmission)

but how dose the car key working over 100meter without an antenna? tell me any tips to develop like those wide range remote controls, i have cheap 433mhz rf tx and rx module, and also PIC12LF1840T39A (rf transmitter with mcu) and MRF39A (RF receiver ic)

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Without an antenna RF does not work so you have to assume it does have an antenna.

The attenuation between transmitter and receiver increases as operating frequency rises. This fact is contained in the Friis equations for link loss: -

enter image description here

The important parameter I refer to is the 20log\$_{10}\$f part.

Basically if operating frequency doubles the power received quarters (20log(0.5) = -6dB).

Given that you haven't specified what the chevy key fob runs at I can make the assumption that it transmits at a frequency somewhat lower than 433 MHz. On the other hand, it may emit more power.

Without knowing power output, operating frequency and antenna types you can't really assume anything solid.

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  • \$\begingroup\$ Sounds nice put like that but no, the output power will probably be only a few milliwatts and maybe even less than 1 mW \$\endgroup\$
    – Andy aka
    Commented Sep 12, 2015 at 15:51
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  • most car remotes are using PCB antenna or chip antenna
  • antenna size is minimized when you use 830mhz/above
  • its difficult to design PCB antenna for 433mHZ and below
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  • \$\begingroup\$ I realise that English may not be your first language but please use capital letters and punctuation in the right places. It will make your posts more readable and more intelligent. \$\endgroup\$
    – Transistor
    Commented Jul 27, 2016 at 13:57

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