Low Noise Amplifier Question


I’m interested in building my own ground station, focusing on the 1.7GHz frequency. I already have an RTL-SDR V3 dongle, an appropriate antenna, and an LNA with 40dB gain. I tested the LNA at my university laboratory, and it showed excellent results at 1.7GHz. However, I’m hesitant to connect the LNA directly to the SDR because I’m concerned that the 40dB gain might damage some of the SDR’s components. Does anyone know if this could be a problem?

Hello fioruci,

Interesting question…The following article by VK6FLAB is probably going to give your some good answers… It is mainly dealing with the RTL-SDR used near a transmitter but there is some info that I think will help you. The bottom line seems to be that you will overload the front end causing spurs and birdies before you blow it up. Have a read.

Hope this helps.
John - VK4JBE

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Hi, I am not going to talk about exact numbers here but rough ones.
Measure the maximum power out from the LNA as well, you will see it will probably not produce 40dB (10W) if you feed it with 0dB signal. Somewhere long before this level it will start to compress (P1dB) and flatten out. The total gain stops making sense there.
As we’re talking L-band here, losses in the coaxes can be quite high, and this is what the LNA compensates. Assuming it is at it’s correct location, that is at the antenna feedpoint. Then you will loose some of the gained signal over the coax down to the SDR.

The SDR itself has it’s absolute maximum ratings, should be in the datasheets of the tuner or whatever chip is at the front end. IIRC somewhere in the region of 10-20dBm, but do look it up.

Talking from experience, I have yet to fry a rtl-sdr or similar device with a antenna+lna+coax into the SDR. If you have a very expensive SDR you should probably have some sort of limiter at the input that keeps the signals safe.

In this case, with a cheap rtl-sdr, just go for it.

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Thank you so much for both responses, they helped me a lot. I read the article and decided to plug it before my SDR. Nothing exploded, haha. It worked perfectly. Thanks again.