Over on YouTube Adam 9A4QV has been testing out his HackRF and Portapack with his LNA4ALL. The LNA4ALL is able to be powered inline via the bias tee on the HackRF. In the first video Adam shows that the HackRF and LNA4ALL is capable of receiving L-band satellites easily. The antenna he uses is a homemade circularly polarized antenna with a cooking pot being used as the reflector.
In the second video Adam shows the HackRF, Portapack and LNA4ALL receiving a telemetry signal on 442 MHz.
Finally in the last video Adam shows himself making a full QSO contact using the HackRF, Portapack and LNA4ALL. The software he uses on the Portapack is Furtek’s ‘Havoc’ firmware which has microphone to TX functionality. The LNA4ALL is able to work in transmit mode without trouble. Adam has written instructions for modifying the LNA4ALL so that it can transmit and use the HackRF’s bias tee power at the same time over on his website lna4all.blogspot.com.
On his post Tony tests the LNA4ALL and compares his measured gain specs against the claimed gain specs on the LNA4ALL website. At 5V power supply he found that the real vs claimed gains matched quite nicely.
Although the LNA4ALL is only specified to run down to 3.3V, Tony found that he could still get usable performance out of it with only a 1.2V supply. However, the gain was reduced by a few dB’s, and we also assume that the IP3 characteristics would also be sufficiently degraded at the low voltage.
Testing the LNA4ALL with his NASA Engine AIS receiver, he found that the LNA4ALL boosted his reception range from 15nm without the LNA, to 22nm with the LNA, and also tripled his received messages.
Over on YouTube Adam 9A4QV has uploaded a video showing how good L-band reception can be with only a cheap home made patch antenna, RTL-SDR dongle and LNA4ALL. The video is in response to a question on our previous post, which discussed the prototype Outernet downconverter. The question asked what difference can we expect with the downconverter compared to just using an LNA, like the LNA4ALL.
In the video Adam shows that L-Band reception with the LNA4ALL can be as good as with the downconverter. The main problem with L-band reception on the RTL-SDR is that some units tend to fail to receive properly at around 1.5 GHz. The downconverter bypasses this problem by receiving L-band at around 200 MHz instead. Though we believe that this problem is solved on the units we sell as we heatsink to a metal enclosure, and if that is not enough, it can be solved further by using this modified driver. The other advantages of the downconverter is that it includes filtering, an LNA, and allows you to use much longer runs of lossy cable, which is useful if for instance you want to put a permanent L-band antenna on the roof.
Akos reminds us that the LNA4ALL can actually be bought from Adam with the bias tee enabled already which saves you from the difficulty of needing to source the required inductor and perform surface mount soldering. The post also explains why you might want to use an LNA in the first place and how to enable the bias tee on our RTL-SDR.com dongles.
The bias tee allows you to inject DC power into the coaxial cable in order to easily power an LNA (like the LNA4ALL) or other device that is placed near the antenna. The antenna could be far away from a power source, such as on your roof or up a mast. It ensures DC power reaches the LNA, but at the same time does not enter the RTL-SDR dongle, as DC current on the antenna input could destroy the RTL-SDR. For best performance it is recommended to use an LNA near the antenna, especially if you have a long run of coaxial cable between the antenna and RTL-SDR.
The filter uses Low Temperature Co-fired Ceramics (LTCC) type components as opposed to the seemingly more commonly used SAW and microstrip filters. Adam writes that each type of filter has its tradeoffs, but he believes the LTCC filter is the best for this application.
The insertion loss of the filter in the pass band is about 2.4 dB and the filter will significantly attenuate broadcast band FM, TV stations, WiFi and 1.8 GHz+ cell phones. However, it does not do so well with 950 MHz cell towers and possible radar on 1.2-1.3 GHz as the LTCC filter is not as sharp as a SAW filter. In Adams own tests he shows that the addition of the filter improves ADS-B decoding performance by about 20%, but the improvement you see will vary greatly with your RF environment.
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.
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.