Over on his blog Lucas Teske has been comparing the LNA4ALL and an SPF5189 LNA from eBay on HRIT/LRIT reception from GOES satellites. SPF5189 LNA’s can be found on eBay for less than $8 USD, with free shipping from China, whereas the LNA4ALL costs 27 Euros shipped from Croatia. GOES is a geosynchronous orbit weather satellite which requires a satellite dish or other high gain antenna to receive. It downlinks at about 1.7 GHz, which means that a high quality LNA with low noise figure and good PCB design is needed for reception.
In his post Lucas mentions how he saw a review on eBay stating that the SPF5189 did not work at L-band. However, he found that odd as all of his SPF5189 LNA’s seemed to work just fine with L-band reception. So he did a benchmark comparing the SPF5189 to the PSA5043+ based LNA4ALL which is known to work well on L-band.
From his comparisons he found that the SPF5189 does indeed work well on L-band, and is comparable to the LNA4ALL. He concludes that the reviewer must have received a bad unit, or didn’t know what he was doing.
Lucas also makes an important note regarding the PCB design of these LNA’s. Even though the SPF5189 and PSA5043 chips have similar specs, with LNA’s the design of the PCB is crucial, as a poor design can significantly degrade performance. With the LNA4ALL you can be sure that the design is good, although the SPF5189 LNA’s currently on eBay look to be designed okay as well. Though with some eBay sellers there is no guarantee that you will receive a good board. We note that we have seen some really poor designs for PSA5043 LNA’s out there as well.
Back in March of this year we posted about the release of the FlightAware “Pro Stick”. The Pro Stick is FlightAware’s ADS-B optimized RTL-SDR dongle. It uses a low noise figure LNA on the RF front end to reduce the system noise figure, thus improving the SNR at 1090 MHz. Because the added gain of the LNA can easily cause overload problems if there are other strong signals around, FlightAware recommend using one of their 1090 MHz ADS-B filters in front of the dongle to prevent overload.
FlightAware.com is a company that specializes in live air travel tracking. Most of their data comes from volunteers running RTL-SDR ADS-B receivers.
Over on their forums and on Amazon, they announced the device and specs. They wrote:
FlightAware is excited to announce the next evolution of USB SDR sticks for ADS-B reception! The new Pro Stick Plus USB SDR builds on the popular Pro Stick by adding a built-in 1090 MHz bandpass filter. The built-in filter allows for increased performance and range of reception by 10-20% for installations where filtering is beneficial. Areas with moderate RF noise, as is typically experienced in most urban areas, generally benefit from filtering. By integrating the filter into the SDR stick, we are able to reduce the total cost by more than 40% when compared to buying a Pro Stick and an external filter.
Filter: 1,075 MHz to 1,105 MHz pass band with insertion loss of 2.3 dB; 30 dB attenuation on other frequencies
Amp: 19 dB Integrated Amplifier which can increase your ADS-B range 20-100% more compared to dongles from other vendors which can increase range 10-20% over a Pro Stick in environments where filtering is beneficial
Native SMA connector
Supported by PiAware
R820T2 RTL2832U chips
USB powered, 5V @ 300mA
Note that this dongle is only for ADS-B at 1090 MHz, and not for 978 MHz UAT signals, as the filter will cut that frequency out.
Back in April, we did a review of the original Pro Stick. We found its performance on ADS-B reception to be excellent, but only when a filter was used. The low NF LNA theoretically improves the SNR of ADS-B signals by about 7-8 dB, but in reality there is too much gain causing signal overload everywhere, thus making reception impossible without the filter. Rural environments may not need a filter, but in a typical urban or city environment strong FM/TV/GSM/etc signals are abundant and these signals easily overloaded the Pro Stick when no filtering was used. This new Pro Stick Plus dongle completely solves that problem at a low cost with its built in filter.
Remember that if you are using a run of coax cable between the LNA and RTL-SDR, then it is more optimal to use an external LNA, like the LNA4ALL. Only an external LNA mounted near the antenna can help overcome coax, connector, filter and other losses as well as reducing the system noise figure. The FlightAware dongles are the optimal solution when they are mounted as close to the antenna as possible. This is usually the case when running the FlightAware feeder software on a Raspberry Pi.
We hope to soon review the Pro Stick Plus, however we assume it will operate nearly identically to the Pro Stick + FlightAware ADS-B filter combination.
Recently FlightAware released a new RTL-SDR dongle sold at zero profit at $16.95 USD. It’s main feature is that it comes with an ADS-B optimized low noise amplifier (LNA) built directly into the dongle. FlightAware.com is a flight tracking service that aims to track aircraft via many volunteer ADS-B contributors around the world who use low cost receivers such as the RTL-SDR. In this post we will review their new dongle and hopefully at the same time provide some basic insights to LNA positioning theory to show in what situations this dongle will work well.
A good LNA has a low noise figure and a high IIP3 value. Here is what these things mean.
Using the free AppCAD RF design assistant software, Anthony explains how the noise figure of a system increases with longer coax cable runs, and how it can be reduced by placing an LNA right next to the antenna. He also explains why the sensitivity of the radio won’t increase if the LNA is placed close to the radio instead.
In addition to this, he also explains why adding more LNA’s to a system decreases the linearity (IP3) of the system and that if the receiver has a built in LNA that the system linearity can be severely degraded by adding extra LNA’s, causing easy overloading and intermodulation. In conclusion Anthony writes the following:
In summary, a setup with a good antenna system connected to a receiver with a built in LNA:
May not benefit from having a preamp at the antenna.
The presence of a built in LNA is detrimental to the linearity and may degrade the signals.
So in conclusion:
Put the preamp as close to the antenna as possible.
Receivers with a built in LNA may not get the most out of an antenna system or preamp.
Proper gain distribution guarantees better performance than one-size-fits-all solutions, both in terms of sensitivity and strong signals handling.
Over on YouTube Adam Alicajic the designer of the LNA4ALL low noise amplifier has uploaded a video showing the effect of an LNA on reception of a weak signal. He shows an example of how a very weak signal cannot be received by the RTL-SDR even when the gain is set to maximum unless an LNA is connected.
Adam has posted this video in regards to some statements saying that an LNA will only increase the noise floor and cannot bring signals out of the noise floor. There is a discussion about this on this Reddit thread.
Recently a reader named Fabio wrote in to let us know about his new Low Noise Amplifier (LNA) design for the RTL-SDR. Fabio writes that his design is similar to the LNA4ALL, but is small enough to fit inline with an antenna. An LNA can help improve reception especially if you have long runs of coax cable between the antenna and RTL-SDR.
Fabio’s design requires that the LNA be powered inline with a bias-tee power injector circuit which can be easily built from an inductor and capacitor. But instead of building an external bias-tee he modified the RTL-SDR dongle itself to provide the required 5V output power from the USB bus. He writes that with this modification the RTL-SDR could also be used to power an active antenna.
Over on Reddit user soooooil has posted about his work in building an LNA, including etching the PCB. On his imgur page he shows the design and construction process through images, before showing the final result in SDR#. For the LNA he used a ERA-3SM+ MMIC which has 17-23 dB of gain and a NF of 2.6-2.8 dB. While the noise figure is fairly high for an LNA, it is still likely lower than the RTL-SDRs internal amplifier noise figure which is around <4.5 dB.
Back in November last year we posted about the possibility of an “LNA4HF” low noise amplifier (LNA) for the HF bands being made available for sale. The LNA4HF is now available for purchase.
The LNA4HF is a low noise amplifier with built in low pass filter that runs on a 6-12 V power supply and covers a frequency range of 150khz to 30MHz, with a 18-20 dB gain and 1-2 dB noise figure. It costs 20 Euros. The low pass filter can also be disabled with a small board modification which will allow the amplifier to be useful at up to 2 GHz.
Akos from the SDR for Mariners blog has reviewed the LNA4HF on his latest post. His results show that the low pass filter significantly reduces broadcast FM interference and that the amplifier also increases signal strength by around 20 dB as advertised.