Thank you to Rodrigo Freire for writing to us and sharing his project called 'SignalSurge'. The SignalSurge project started when Rodrigo discovered that adding an RTL-SDR Blog FM Bandstop filter to his Yaesu FT-991A significantly improved his reception in the 2-meter band.
An FM bandstop filter can improve reception by reducing the power of strong broadcast FM signals, which can overload the front end of radios, causing the desensitization of signals on other bands.
This finding led Rodrigo to design SignalSurge, a bandpass filter for VHF and UHF bands, with a selectable LNA. The design includes selectable 2m and 70cm bandpass filters, a selectable 15dB LNA, automatic LNA shutdown when the radio is transmitting, and ESD protection. A 50W relay gives the ability to select between filters and switch the LNA in or out.
Recently Salil (aka NUCLEARRAMBO) uploaded a blog post on his website detailing how he designed and tested a low noise amplifier (LNA) with a filter for 130 - 160 MHz, which is useful for improving reception for the Meteor M2 LRPT weather satellite. If you were unaware, an LNA can help improve the reception of an SDR by reducing the noise figure of the system, and by overcoming losses from long coax cable runs. The filter helps reduce the strength of out-of-band signals which if too strong, can desensitize and cause imaging on the RTL-SDR.
In his design, Salil used a PGA-103+ LNA chip which has excellent noise figure and OIP3 specifications. His blog post details how he designed the circuit around the PGA-103+, added a bias tee for power, and how he designed the filter.
In part 2 of his post, he details how he tested the LNA+filter combinations frequency response, input voltage range, noise figure, and bias tee with an RTL-SDR Blog v3 and a NanoVNA V2.
Back in 2018 we posted about Igor Yatsevich's Easy-SDR project which consisted of open source designs for a Mini-Whip antenna and upconverter. Igor has now added several new open source designs to the project including a bias tee, LNA, LNA with filtering, attenuator and SPDT antenna switch. On his Reddit post he notes:
The most interesting thing I've added so far:
Most of the devices are now prepared for installation in a metal case measuring 80 x 50 x 20 millimeters.
Completely redesigned LNA design. Now, Bias Tee powered amplifiers are housed in a 50 x 25 x 25mm metal case and have N-type connectors.
Added an amplifier based on the PGA-103 microcircuit.
Added the ability to install filters in final amplifiers (a separate printed circuit board, depending on the filter used).
Added a new device - SPDT antenna switch for receiving antennas.
The UP converter has been redesigned. Added intermediate buffer stage between crystal generator and mixer.
RF lines in all devices were recalculated to correspond to the characteristic wave impedance of 50 Ohm.
Reduced size of PI attenuator PCB.
In this project, I focused on the simplicity of self-assembly devices, which you can make at home. In the repository, you can find detailed assembly instructions, a list of necessary components for assembly, and GERBER files.
SPDT Antenna Switch from the Open Source Easy-SDR Project
Over on his YouTube channel TechMinds has uploaded a new video showing how to use RF amplifiers to extend the transmit range of transmit capable SDRs like the LimeSDR, HackRF and PlutoSDR. Whilst they are transmit capable, most low cost SDRs like those mentioned above can only transmit at very low power levels typically much less than 30 mW. In the video TechMinds tests a wideband SPF5189Z and filtered 2.4 - 2.5 GHZ CN0417 based amplifier, and shows the output power obtained using an inline power meter.
He also notes that these wideband amplifier will also amplify harmonics so filtering is recommended. At the same time we note that you should only transmit if you are licenced to do so (for example with a ham radio licence), especially if you are amplifying the output.
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
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.
We've just released two new products in our store. The first is a low cost general purpose wideband LNA and the second is some spare RTL-SDR V3 aluminum enclosures. The wideband LNA is currently available for shipping from our Chinese warehouse and will be available on Amazon in a few days time. It costs US$17.95 including worldwide free shipping. The spare aluminum enclosure is only available from our Chinese warehouse and costs US$5.95.
The Wideband LNA is based on the Qorvo SPF5189Z LNA chip (datasheet pdf) which has the following declared specs:
Frequency range of 50 MHz to 4000 MHz
Noise figure = 0.6dB @ 900 MHz
OIP3 = 39.5 dBm @ 900 MHz
P1 Saturation = 22.7 dBm @ 1960 MHz
Gain = 18.7 dB @ 900 MHz
Compared to most of the other SPF5189Z LNAs found on eBay, our wideband LNA comes standard with a full conductive metal case, includes ESD protection on the antenna input, and is by default powered via 3 - 5V bias tee power. Our RTL-SDR Blog V3 dongles have a 4.5V bias tee built in, so they can be used to power this LNA. Direct power can be enabled simply by changing a jumper position, and removing the metal case.
This is a general purpose wideband LNA. It is useful for reducing the noise figure and thus increasing SNR, and for overcoming coax loss on all supported frequencies between 50 - 4000 MHz. However, because it is wideband you may need additional filtering if you have strong overloading signals in your area. If you're mostly interested in improving ADS-B reception, then we instead recommend our Triple Filtered ADS-B LNA which is also available at our store. The specs of the SPF5189Z are similar to that of PGA-103+ or PSA4-5043+ based LNAs. In the image slider below we compare the gain with the LNA4ALL which is a PSA4-5043+ based LNA.
Spare Aluminum Enclosure
The second product is some spare RTL-SDR Blog V3 aluminum enclosure. A few readers of this blog contacted us as they found RTL-SDR V3 enclosures to be a good fit (after being cut down to size) for home made filters, other LNAs and for FlightAware dongles. Our spare enclosures come with two SMA side panels, and one USB side panel. There is only limited stock of this product at the moment. Note that we're not including a thermal pad, since FlightAware dongles do not require additional cooling since they operate at 1.09 GHz. Additional cooling via thermal pad is only needed for stable operation when using RTL-SDRs above ~1.5 GHz.
Thank you to Rodrigo Freire for writing to us and sharing his project called 'SignalSurge'. The SignalSurge project started when Rodrigo discovered that adding an RTL-SDR Blog FM Bandstop filter to his Yaesu FT-991A significantly improved his reception in the 2-meter band.
An FM bandstop filter can improve reception by reducing the power of strong broadcast FM signals, which can overload the front end of radios, causing the desensitization of signals on other bands.
This finding led Rodrigo to design SignalSurge, a bandpass filter for VHF and UHF bands, with a selectable LNA. The design includes selectable 2m and 70cm bandpass filters, a selectable 15dB LNA, automatic LNA shutdown when the radio is transmitting, and ESD protection. A 50W relay gives the ability to select between filters and switch the LNA in or out.
Recently Salil (aka NUCLEARRAMBO) uploaded a blog post on his website detailing how he designed and tested a low noise amplifier (LNA) with a filter for 130 - 160 MHz, which is useful for improving reception for the Meteor M2 LRPT weather satellite. If you were unaware, an LNA can help improve the reception of an SDR by reducing the noise figure of the system, and by overcoming losses from long coax cable runs. The filter helps reduce the strength of out-of-band signals which if too strong, can desensitize and cause imaging on the RTL-SDR.
In his design, Salil used a PGA-103+ LNA chip which has excellent noise figure and OIP3 specifications. His blog post details how he designed the circuit around the PGA-103+, added a bias tee for power, and how he designed the filter.
In part 2 of his post, he details how he tested the LNA+filter combinations frequency response, input voltage range, noise figure, and bias tee with an RTL-SDR Blog v3 and a NanoVNA V2.
Back in 2018 we posted about Igor Yatsevich's Easy-SDR project which consisted of open source designs for a Mini-Whip antenna and upconverter. Igor has now added several new open source designs to the project including a bias tee, LNA, LNA with filtering, attenuator and SPDT antenna switch. On his Reddit post he notes:
The most interesting thing I've added so far:
Most of the devices are now prepared for installation in a metal case measuring 80 x 50 x 20 millimeters.
Completely redesigned LNA design. Now, Bias Tee powered amplifiers are housed in a 50 x 25 x 25mm metal case and have N-type connectors.
Added an amplifier based on the PGA-103 microcircuit.
Added the ability to install filters in final amplifiers (a separate printed circuit board, depending on the filter used).
Added a new device - SPDT antenna switch for receiving antennas.
The UP converter has been redesigned. Added intermediate buffer stage between crystal generator and mixer.
RF lines in all devices were recalculated to correspond to the characteristic wave impedance of 50 Ohm.
Reduced size of PI attenuator PCB.
In this project, I focused on the simplicity of self-assembly devices, which you can make at home. In the repository, you can find detailed assembly instructions, a list of necessary components for assembly, and GERBER files.
SPDT Antenna Switch from the Open Source Easy-SDR Project
Over on his YouTube channel TechMinds has uploaded a new video showing how to use RF amplifiers to extend the transmit range of transmit capable SDRs like the LimeSDR, HackRF and PlutoSDR. Whilst they are transmit capable, most low cost SDRs like those mentioned above can only transmit at very low power levels typically much less than 30 mW. In the video TechMinds tests a wideband SPF5189Z and filtered 2.4 - 2.5 GHZ CN0417 based amplifier, and shows the output power obtained using an inline power meter.
He also notes that these wideband amplifier will also amplify harmonics so filtering is recommended. At the same time we note that you should only transmit if you are licenced to do so (for example with a ham radio licence), especially if you are amplifying the output.
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
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.
We've just released two new products in our store. The first is a low cost general purpose wideband LNA and the second is some spare RTL-SDR V3 aluminum enclosures. The wideband LNA is currently available for shipping from our Chinese warehouse and will be available on Amazon in a few days time. It costs US$17.95 including worldwide free shipping. The spare aluminum enclosure is only available from our Chinese warehouse and costs US$5.95.
The Wideband LNA is based on the Qorvo SPF5189Z LNA chip (datasheet pdf) which has the following declared specs:
Frequency range of 50 MHz to 4000 MHz
Noise figure = 0.6dB @ 900 MHz
OIP3 = 39.5 dBm @ 900 MHz
P1 Saturation = 22.7 dBm @ 1960 MHz
Gain = 18.7 dB @ 900 MHz
Compared to most of the other SPF5189Z LNAs found on eBay, our wideband LNA comes standard with a full conductive metal case, includes ESD protection on the antenna input, and is by default powered via 3 - 5V bias tee power. Our RTL-SDR Blog V3 dongles have a 4.5V bias tee built in, so they can be used to power this LNA. Direct power can be enabled simply by changing a jumper position, and removing the metal case.
This is a general purpose wideband LNA. It is useful for reducing the noise figure and thus increasing SNR, and for overcoming coax loss on all supported frequencies between 50 - 4000 MHz. However, because it is wideband you may need additional filtering if you have strong overloading signals in your area. If you're mostly interested in improving ADS-B reception, then we instead recommend our Triple Filtered ADS-B LNA which is also available at our store. The specs of the SPF5189Z are similar to that of PGA-103+ or PSA4-5043+ based LNAs. In the image slider below we compare the gain with the LNA4ALL which is a PSA4-5043+ based LNA.
Spare Aluminum Enclosure
The second product is some spare RTL-SDR Blog V3 aluminum enclosure. A few readers of this blog contacted us as they found RTL-SDR V3 enclosures to be a good fit (after being cut down to size) for home made filters, other LNAs and for FlightAware dongles. Our spare enclosures come with two SMA side panels, and one USB side panel. There is only limited stock of this product at the moment. Note that we're not including a thermal pad, since FlightAware dongles do not require additional cooling since they operate at 1.09 GHz. Additional cooling via thermal pad is only needed for stable operation when using RTL-SDRs above ~1.5 GHz.
We're happy to announce the release of our new high performance low noise amplifier (LNA) for improving 1090 MHz ADS-B reception. The LNA uses a low noise figure high linearity two stage MGA-13116 amplifier chip and three stages of filtering to ensure that strong signals or interference will not overload either the amplifier or SDR dongle.
The LNA is currently only available from our Chinese warehouse, and costs US$24.95 including shipping. Please note that the price may increase slightly in the future, and that Amazon USA may not be stocked until March.
An LNA can help improve ADS-B reception by reducing the noise figure of the system and by helping to overcome losses in the coax cable and/or any other components such as switches and connector in the signal path. To get the best performance from an LNA, the LNA needs to be positioned close to the antenna, before the coax to the radio.
The gain of the RTL-SDR Blog ADS-B LNA is 27 dB's at 1090 MHz, and out of band signals are reduced by at least 60 - 80 dB's. Attenuation in the broadcast FM band and below 800 MHz is actually closer to over 100 dB's. In the LNA signal path there is first a low insertion loss high pass filter that reduces the strength of any broadcast FM, TV, pager or other similar signals that are usually extremely strong. Then in between the first and second stage of the LNA is a SAW filter tuned for 1090 MHz. A second SAW filter sits on the output of the LNA. The result is that strong out of band signals are significantly blocked, yet the LNA remains effective at 1090 MHz with a low ~1 dB noise figure.
The LNA is also protected against ESD damage with a gas discharge tube and low capacitance ESD diode. But please always remember that your antenna must also be properly grounded to prevent ESD damage.
Please note that this LNA requires bias tee power to work. Bias tee power is when the DC power comes through the coax cable. The RTL-SDR V3 has bias tee power built into it and this can be activated in software. See the V3 users guide for information on how to activate it. Alternatively if you don't own a dongle with bias tee built in, then an external bias tee can be used and those can be found fairly cheaply on eBay. Finally, if you are confident with soldering SMT components, then there are also pads and a 0 Ohm resistor slot on the PCB to install an LDO and power the LNA directly.
In addition please remember that this is a high gain LNA. It is expected to be used at the antenna side, with some 3+ db loss expected on the coax. However, if desired, it can still be used on the receiver side. If used on the receiver side or with a low loss run of coax, you will need to tune the RF gain on the RTL-SDR dongle. By default most software sets the RF gain to maximum. We recommend turning the RTL-SDR RF gain down to about 32 dB if connecting it directly to the dongle, otherwise the high input power may overload the dongle causing poor performance.
Specification Summary:
Frequency: 1090 MHz
Gain: 27 dB @ 1090 MHz
Return Loss: -16 dB @ 1090 MHz (SWR = 1.377)
Noise Figure: ~1 dB
Out of band attenuation: More than 60 dB
ESD Protection: Dual with GDT and ESD Diode
Power: 3.3 - 5V via bias tee only, 150 mA current draw
Enclosure: Aluminum enclosure
Connectors: Two SMA Female (Male to Male adapter included)
Dimensions:
46.5 x 32 x 15.6 mm (not including the SMA).
Including the SMA the length is 69.8 mm.
Testing
We tested our new LNA against another ADS-B LNA with filter built in that is sold by another company and the FlightAware Prostick+ dongle in an environment with strong out of band signals such as pagers, broadcast FM, DVB-T and GSM signals. The results showed that the RTL-SDR Blog ADS-B LNA gathered the most ADS-B packets. In the tests both LNA's were connected on the receiver side to be fair to the FA dongle. Improved performance could be achieved by moving the LNA to the antenna side.
Other ADS-B LNA vs RTL-SDR Blog ADS-B LNA Received MessagesFlightAware Prostick+ vs RTL-SDR Blog ADS-B LNA Received Messages
Checking in SDR# for out of band signals also showed that the RTL-SDR Blog ADS-B LNA significantly reduces those strong out of band signals, whereas the others have trouble blocking them out. Below we show the results as well as some measurements.
This RTL-SDR Blog ADS-B LNA can significantly improve ADS-B reception, especially if you are in an environment with strong out of band signals. Even if you are not, the low noise figure design will improve reception regardless.
Over on his YouTube channel Adam 9A4QV has uploaded a video showing how an LNA work to improve signal SNR on VHF, as long as the LNA is placed close to the antenna. Adam is the manufacturer and seller of the popular LNA4ALL low noise amplifiers.
On UHF and high frequencies an LNA can help by reducing the system noise figure, but on VHF this effect is small. But if the LNA is placed near the antenna then the LNA can still help significantly by overcoming any losses in the coax cable, filters, switches or any other lossy components in the signal path. It might also help create a better SWR match for the dongle and antenna. The video has some sound issues in during the demonstration part, but on his Reddit thread Adam writes:
