Amplifying weak signals with a Low Noise Amplifier for your RTL-SDR

I wanted to add a Low Noise Amplifier to my RTL-SDR dongle to amplify weak signals received from ARPS, satellite and HF signals for FT8 and other digital mode decoding. I purchased a cheap Low Noise Amplifier off of Amazon for testing. I decided to test the amplifier using the APRS frequency of 144.390 to see how many packets I could decode without the LNA, and how many I could with it. There is a lack of good APRS coverage in my immediate area and I plan on operating a solar powered Raspberry Pi and Direwolf based APRS RX/TX I-Gate in the future, so I wanted to see what I could receive from these relatively distant stations using my RTL-SDR dongle connected to my Diamond x200a antenna mounted outside on a temporary mast, only about 10′ off of the ground.

This comparison is not meant to be extremely thorough or scientific. I am using waterfall displays and decoded APRS packets as evidence of amplification of weak signals. These results are based on the following setup:

The advertised LNA gain is below:

F=0.1MHz, gain=32dB
F=500Mhz, gain=31dB
F=1000MHz, gain=29dB
F=1500Mhz, gain=25dB
F=2000MHz, gain=20dB


Without a Low Noise Amplifier


In five minutes, I was only able to receive one APRS packet successfully.
23:35:41$ fm KI4BGI-0 to SXST7W-0 via WIDE1-1,WIDE2-1 UI PID=F0
'q/1l .o/"=%}


With a Low Noise Amplifier


In the same time span as the above example, I was able to receive 5 APRS packets with much stronger signals. I did not adjust the GQRX settings, I only added the LNA.


23:46:50$ fm N8QF-0 to APK102-0 via W8BLV-0,WIDE1-0,WIDE2-1 UIv PID=F0
=3927.42N/08418.16W_000/000g000t011r p P000h43b10367KU2k

23:46:55$ fm W8BLV-0 to APN383-0 UI PID=F0
!3930.93NS08421.30W#PHG6438/W3 Middletown,OH Dial ARC Wide3-3

23:46:56$ fm WA8VIW-6 to APW251-0 via W8BLV-0,WIDE-0 UIv PID=F0
>262138 Sam in Miamisburg, OH. TAWG OH 81

23:47:07$ fm N8QF-1 to APK102-0 via W8BLV-0,WIDE1-0,WIDE2-1 UIv PID=F0
=3930.02N/08421.85W_000/000g000t016r p P000h96b10375KU2k

23:48:20$ fm KA8HUZ-15 to S9RV3X-0 via WC8EMA-0,WIDE1-0,W8BLV-0,WIDE2-0 UI PID=F0

23:49:32$ fm KC9MWQ-1 to APTT4-0 via N9AMN-3,N9LQP-2,WIDE2-1 UI PID=F0
/000000h4035.82N/08539.34W#Hosted by Grant County ARC TT4

23:50:41$ fm KI4BGI-0 to SXST7W-0 via WIDE1-1,WIDE2-1 UI PID=F0
'q/1l .o/"=%}

Side By Side

Non-amplified on the left, and amplified on the right.

Final Notes

Increasing the voltage from 9V to 12V will also increase the gain of the Low Noise Amplifier. I used only what I had available on hand at the time.

As the battery loses it’s voltage the efficiency of the LNA will drop as well. The resting voltage of the 9V battery displays as 8.47V on the meter.

I suspect some better results could be had by tweaking the settings in GQRX however I wanted to display the results without any adjustment of settings.