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My garage door is sending its status to a control device we have in the house. This signal is not always received by the control unit so it wrongly shows the garage door is open when it's closed. The garage door electronics has a wire as antenna soldered directly on the circuit board and uses 868,30 MHz AM to transmit.

I asked about this here (Are the same type of antennas used for receiving and transmitting?) but that discussion was about antennas.

Now I would like to know if I can use an amplifier like this LNA 0.1-4000MHz gain 20dB Noise LNA RF wideband amplifier Module HF VHF / UHF to amplify the transmission.

I would replace the wire antenna with a short shielded wire, attach it to the amplifier and then put the wire antenna after the amplifier. Does this make sense and would the above amplifier?

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  • \$\begingroup\$ That's an LNA, which is a type of small signal amplifier. You need a power amplifier. \$\endgroup\$ Jan 24, 2016 at 20:16
  • \$\begingroup\$ You should also plan on adding a small filter before the amplifier to make sure you're not interfering with anything else. \$\endgroup\$
    – rfdave
    Jan 24, 2016 at 20:21
  • \$\begingroup\$ @PeterK Are power amplifiers available as easily and in the same price range as LNA? \$\endgroup\$ Jan 24, 2016 at 20:33
  • \$\begingroup\$ @Dave Are filters for this kind of function also available? \$\endgroup\$ Jan 24, 2016 at 20:34
  • \$\begingroup\$ Digikey has them digikey.com/product-search/en/filters/saw-filters/… not on a PCB, but that's pretty straightforward to do. You might need to research how much power your garage door electronics are putting out, as you might overpower it. \$\endgroup\$
    – rfdave
    Jan 24, 2016 at 21:14

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Instead of messing around with a RF power amplifier, which may not be legal, I'd spend the effort to make the existing system work better.

Probably the transmitter and receiver are too far apart, or have obstacles between them that interfere with the radio waves. Since the garage door is where it is, maybe you can move the receiver in the house. If not, maybe you can make it pick up the garage door transmitter better by running a wire from it to nearer the transmitter.

The wavelength is 350 mm or 14 inches, so a directional receiving antenna isn't out of the question. You can do whatever you want on the receiving side without violating any RF emissions laws. As soon as you touch the electronics in the transmitter, the unit is no longer certified, and you're on your own. It is quite unlikely that anyone will come after a private person with a single garage door opener, but if you happen to interfere with something important you could get into trouble.

Both installations are fixed, so you should be able to run some wires. Even if you can't add wires to where the receiver is, you could still make a passive antenna extender. Put a 1/2 wavelength dipole on each end of UHF twinlead. Get one end a few feet from the transmitter, and the other a few feet from the receiver. Look at how the antenna on the circuit board is oriented, and adjust the orientation of the dipole accordingly.

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  • \$\begingroup\$ Ok, so I'll replace the current antenna with a UHF twin lead (like this amazon.com/300-Ohm-UHF-Matching-Transformer/dp/B0002ZPIOG) and put the dipole on that? \$\endgroup\$ Jan 24, 2016 at 21:00
  • \$\begingroup\$ The antenna is now very close to the door motor and all electronics in the opener. Could I replace the antenna with some coax cable and put the antenna at the end of the coax and that way move to transmission antenna to a better place? \$\endgroup\$ Jan 24, 2016 at 21:02
  • \$\begingroup\$ @Mat: Again, as I said, it is better to mess with the reception antenna than the transmission antenna. \$\endgroup\$ Jan 25, 2016 at 11:42

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