Testing a $2 USB Powered LNA with RTL-SDR

Over on his blog '19max63' has posted about his tests with a $2 Aliexpress low noise amplifier (LNA) and his RTL-SDR. The LNA is advertised as for boosting HDTV signals, but 19max63 has found that it does a decent job on other frequencies too. It can be found on Aliexpress for less than $2 including free shipping, by searching for "TV Antenna signal amplifier". One example listing is this one.

An LNA is useful to help lower the noise figure of a radio system which results in higher SNR values (especially at the UHF and higher bands), and can be used to overcome losses in the signal chain from components like coax cables and connectors. However, an LNA will not always help and when combined with strong in or out of band signals will make reception worse by causing overload and intermodulation products. Better quality LNAs have a low noise figure, and are able to handle stronger signals and not overload so easily.

Ultra Cheap $2 LNA
Ultra Cheap $2 LNA

Upon opening the cover, 19max63 found that the cheap LNA consists of a BFG425W transistor which should cover 40 MHz to 3 GHz, but may be band limited by the passive components. The BFG425W also has a max gain of 20dB at 2GHz and a noise figure of 0.8 dB at 900 MHz. 

In 19max63's tests, the LNA was able to improve his DAB radio (174 to 240 MHz) reception significantly, allowing him to receive several extra stations. His further tests also seem to show that it does a decent job at other frequencies from 137 MHz NOAA satellites to 1090 MHz ADS-B. Many of the comparison images do seem to show signs of overloading and intermodulation, but ADS-B in particular looks to be boosted quite nicely. So this looks like it might be a very cheap way to try and improve ADS-B reception.

Check out the his post for multiple SNR comparison images.

Cheap LNA PCB
Cheap $2 LNA PCB

8 comments

  1. phil

    I thinks it’s a case of “you get what you pay for”.Specs for a tv amp are far from what we need for our SDR programs. Looking at the images on his site, ADS-B has improved but the images showing the actual waterfall show a significant increase in noise (the opposite of what an LNA does). Save your $ and invest on proper LNA.

        • zac

          Poor dynamic range of the RTL and overloading are causing the problem you mention and your suggestion to buy a professional LNA is just a waste of money that will not resolve this problem. You cannot put a Ferrari engine in a Camaro
          and make it run like a Ferrari.
          Your “tv amp” is something that exist only for consumers; engineers, the serious ones, only see a circuit, a transistor and a datasheet. If you are not in the condition to read a datasheet and talk us about the transistor and a circuit stop trolling with trite statements.
          Commonplaces are the paradise of the unskilled tech.

          • snn47

            Zan and Phil without knowing how bad the Extraneous Signal Environment (ESE) is you cannot draw any conclusions from the increase in noise and spikes from a screen shot, and bench meassurements are the only way to prove who is correct with his assumptions.

            If I place a 1/4 antenna outside our lab, our state of the art spectrum analyzer is overloaded by several cell phone base stations a few hundred meter away (average peak -27 dBm). Despite a high dynamic range I cannot use the internal LNA, and have to add 20 dB of internal attenuation to enable RFI free measurement with a FSW (R&S) at 1090 MHz. Without adding very good filter to minimize the impact of the base stations that leaves only ~40 dB of dynamic range.

    • Mike

      ADS-B has improved. Period. The device provides value for the (very little) money. The actual measured parameters are irrelevant after this goal has been achieved.

      • snn47

        Even with Radio Line Of Sight to ground transmitter changes in propagation can significantly in-/decrease signal strength within a few minutes time. Therefore basing improvements on changes in signal strength measured at different times is not conclusive.
        Aircraft in movement are even more difficult as source. Aircraft antenna pattern and gain variation have been measured by FAA before instruction of Mode S to vary by more than 40 dB between lobes and notches. The pattern varies even for the same aircraft type with antenna placement on the aircraft fuselage, protruding objects and moveable gear like aircraft like rudder, flaps and landing gear. Aircraft are not always in level flight, but change flight orientation (~±30°) and flight direction (between 0 to 360 °).
        Therefore it is difficult to conclude that the LNA improved reception, without measuring at the same time in parallel. It is the same like wanting to believing any esoteric antenna gain for a cobbled together wire antenna construction.
        HAM radio operator have proven in the last century that you do it yourself a lot for nearly no money at all, but you have to understand the basics of physical and abide by them.

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