I found an old (but not in use) garage door controller. The receiver is still intact but can't be reached from souterrain. The sender transmits a single tone on 27MHz in the citizen band. The signal is very weak, I measured 2Vpp (which equals to 10dBm, 10mW). I wondered if it is possible to boost the signal. I have a few of those "5MHz - 6GHz Broadband amplifiers" lying around, which you can get on ebay: https://www.ebay.com/itm/5M-6GHz-Low-Noise-RF-Amplifier-Ultra-Wideband-20dB-Medium-Power-Amp-Board-sz98-/283714550135 Is it possible to chain those amplifiers to sum up their gain?


I asked the seller and he states, the modules can be connected together to add the gain of both modules. I connected the RF-Out of stage 1 to the RF-In of stage 2 with a 50Ohms cable and added a 50Ohm dummy load to the RF-Out of stage 2. I was quite suprised that the Gains of both stages were not added, on RF-Out I can read 3.7 Vpp so there was basically no "gain addition".


  1. Are those modules generally not suitable for TX power amplification or would I need other modules?
  2. Someone posted that one could use a Wilkinson splitter and combiner by first splitting the signal, guiding it through two amplifier modules and then combing them again. Will this sum up the amplification power of the modules used?
  3. Both modules use the same 5V power supply. I have read somewhere this should be avoided. Also true for this case?
  4. In general, can the Vpp output voltage outrank the supply voltage?


According to the comments and answers, my whole idea points into the wrong direction. That means, leaving the sender where it was the last years or increase gain on the receiver side (better antenna, LNA or upgrade the system with newer technology).

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    \$\begingroup\$ 10 dBm is anything but "very small" in RF terms. I'd call it "screamingly loud for something that only has to bridge short distances". \$\endgroup\$ Aug 7, 2020 at 9:04
  • 1
    \$\begingroup\$ Do you expect to get 100Vpp from an amplifier that is supplied from 5V? \$\endgroup\$ Aug 7, 2020 at 9:05
  • 2
    \$\begingroup\$ so, a) what you're trying to do will end up being illegal. There's limits on how much power you're allowed to emit, depending on the frequency, bandwidth, and type of transmission, and of course on the country you're in. b) What are you trying to achieve? Because amplifying a garage door opener remote without having the matching garage door opener receiver sounds ... senseless? \$\endgroup\$ Aug 7, 2020 at 9:07
  • \$\begingroup\$ You want to open the garage door from ten miles out? \$\endgroup\$
    – user16324
    Aug 7, 2020 at 10:01
  • \$\begingroup\$ Most (but not all) comments are not useful here, but I got the point. \$\endgroup\$
    – Ranunculum
    Aug 7, 2020 at 11:20

1 Answer 1

  • The module you talk about has a supply voltage of 5 volts
  • It has a maximum output power of 100 mW
  • That's 2.24 volts RMS into a 50 ohm load
  • That's 6.32 volts p-p
  • That sounds about right for a class C output driver running on 5 volts

The problem isn't the addition of gains (dB) but the module running out of ability to produce more power on its output terminals due to only having a 5 volt supply.

Of course expectations of performance from goods supplied via ebay should be taken with a large pinch of salt especially if the device isn't "backed" by a decent PDF data sheet and some form of recognition that the manufacturer is bona fide and has adopted a minimum of quality standards during design and build.

Are those modules generally not suitable for TX power amplification or would I need other modules?

I'm sure they are but their provenance is highly debatable

In general, can the Vpp output voltage outrank the supply voltage?

Yes with a class C output driver stage and a tuned collector tank.

  • \$\begingroup\$ Thanks, your answer indeed gave me a lot more insight in the whole topic. Nevertheless, I decided to drop the idea of TX amplification and instead look into an other direction (see Edit). \$\endgroup\$
    – Ranunculum
    Aug 7, 2020 at 11:29
  • \$\begingroup\$ Focusing on the receiver might be the best option. \$\endgroup\$
    – Andy aka
    Aug 7, 2020 at 11:34

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