Category: Airband

Radio For Everyone: Testing Several ADS-B Antennas Under $50

Over on his blog ‘Radio for Everyone’ Akos has shared results submitted to him by FlightAware forum user ‘Nitr0’ which compares several ADS-B antennas that cost under $50 USD. The antenna that we most recommend for ADS-B is the FlightAware antenna, but for European buyers there are also many lower cost alternatives available on eBay, most of which are made by fellow radio hobbyists or hams. The tests use the six antennas listed below, comparing each one against the ‘reference’ FlightAware antenna.

  1. The FlightAware Antenna – $45 USD
  2. A Bulgarian made antenna by LZ3RR – $31 USD + shipping
  3. A Slovakian made collinear antenna by stanislavpalo130 – $25 USD + shipping
  4. A Slovakian made 5/8 antenna by stanislavpalo130 – $24 USD
  5. RTL-SDR stock antenna – Included with generic RTL-SDRs
  6. A 3.5 dBi loaded whip – $3 to $15 USD

In summary the tests seem to show that nothing beats the FlightAware antenna, with the closest in performance being the Bulgarian made antenna. We should mention however, without knowing the real radiation patterns, SWR and various other factors it is hard to say which one will work best for everyone. Different locations/obstacles/mountings could mean that antennas with different designs and therefore radiation patterns work better than others. But it seems that the FlightAware antenna is the top performer in the common scenario of being able to mount the antenna on a roof with a good view of the horizon.

Two ADS-B antennas being tested by Akos.
Two ADS-B antennas being tested by Nitr0.

dumpvdl2: A Lightweight VDL2 Decoder

The VHF Data Link mode 2 (VDL2) is a relatively new wireless transmission mode used on aircraft for sending short messages, position data (similar to ADS-B) and also for allowing traffic controllers to communicate to pilots via text and data. VDL2 is an evolution of ACARS and is eventually supposed to replace it entirely. The advantage over ACARS is that VDL2 can transmit data 10 times faster, and supports a much wider range of services. The main default channel is at 136.975 MHz, but channels could exist on other air band frequencies too.

Over on GitHub Tomasz Lemiech (szpajder – also the author of RTL-Airband) has uploaded a new VDL2 decoder called dumpvdl2. This is a lightweight command line Linux based VDL2 decoder and protocol analyzer. The features include:

  • Runs under Linux (tested on: x86, x86-64, Raspberry Pi)
  • Supports following SDR hardware:
    • RTLSDR (via rtl-sdr library)
    • Mirics SDR (via libmirisdr-4)
    • reads prerecorded IQ data from file
  • Decodes up to 8 VDL2 channels simultaneously
  • Outputs messages to standard output or to a file (with optional daily or hourly file rotation)
  • Outputs ACARS messages to PlanePlotter over UDP/IP socket
  • Supports message filtering by type or direction (uplink, downlink)
  • Outputs decoding statistics using Etsy StatsD protocol

In a previous post we showed how VDL2 could be decoded with MultiPSK on Windows. But the advantage of dumpvdl2 is that it allows you to set up a lightweight monitoring station on something like a Raspberry Pi. dumpvdl2 can also be interfaced with PlanePlotter, and statistics can be graphed with another program such as Grafana.

dumpvdl2 running.
dumpvdl2 running.

Radioforeveryone New Posts: PiAware Step-By-Step Guide and a Guide to Feeding Other ADS-B Aggregrators

Akos from the radioforeveryone.com blog has recently uploaded some new posts. The first post is a tutorial on setting up a PiAware server with an RTL-SDR. PiAware is the official ADS-B feeder software from FlightAware.com, which is a web service that provides real time tracking of aircraft. Most of the flight data comes from volunteers around the world running a PiAware server with an RTL-SDR, ADS-B antenna and Raspberry Pi. The installation is fairly simple, involves burning an SDcard with the PiAware image, setting up the WiFi and then seeing your receiver online on the PiAware website. From there you can then configure the device further.

In the second post Akos describes how to feed other tracking websites, e.g. not just FlightAware, but also similar sites like Planefinder.net and flightradar24.com. Akos has also mentioned that a single Raspberry Pi can be used to feed all three aggregators simultaneously.

FlightAware vs FlightRadar24 vs Planefinder Plots
FlightAware vs FlightRadar24 vs Planefinder Plots

Radio For Everyone New Posts: Building an ADS-B Station, Easy Homemade Beginner ADS-B Antennas

Akos the author of the radioforeveryone.com blog has recently added two new articles to his blog. The first post is a comprehensive guide to setting up your own ADS-B station. The guide focuses on creating a system that is easy to use, has good performance and is value for money. In the post he shows what type of computing hardware is required, what software can be used and what RTL-SDR dongles work best. He also shows what choices are available when it comes to amplification and filtering to improve signal reception and goes on to talk a bit about adapters and the antennas that work best for him.

BuildingADS-Bstation
Building a ADS-B station

 In the second post Akos shows more on how to build your own beginners antennas for ADS-B reception. The post focuses on showing how to modify the stock magnetic mount antenna that comes with most RTL-SDR dongles, and how to build a half-wave ‘spider’ antenna entirely out of coax cable. The post is full of easy to follow images which make it great for beginners.

EDIT: It’s been pointed out in the comments by antenna experts/enthusiasts that the 1/2 wave ground plane antenna described by Akos in his tutorial may not be technically correct. A 1/2 wave antenna has a huge impedance which requires some sort of matching. Without matching there is going to be about 10 dB of loss due to the mismatch, and so the antenna will perform poorly. We recommend sticking with a 1/4 wave design, which is essentially the same as Akos’ 1/2 wave ground plane antenna, just with the element lengths halved.

FlightAware Prostick vs FlightAware Prostick Plus: Review

Recently the FlightAware Prostick Plus was released. The Prostick is a modified RTL-SDR with a LNA built into the dongle. It is optimized for ADS-B reception and works very well due to the low noise figure of the SKY7150 LNA which is used as the first stage LNA. However, due to the increased gain from the LNA it can easily overload from strong out of band signals, such as broadcast FM, DAB, DVB-T and GSM. To eliminate this problem FlightAware recommend using their 1090 MHz filter in front of the dongle. 

The FlightAware Prostick Plus is the same as the Prostick, but the Plus also incorporates a 1090 MHz SAW filter into the dongle itself. The overall cost is about $15.95 USD cheaper than buying the Prostick + Filter combination. See below for a tabulated comparison between the two units.

  FlightAware Prostick + Filter FlightAware Prostick Plus
Price

USA: $16.95 + $19.95 = $36.9 (Buy Prostick) (Buy Filter)

Worldwide: $48.99 + $18 Shipping = $66.99
(Buy Prostick + Filter)

USA: $20.95
(Buy Prostick Plus)

Worldwide: $29.99 + $12 Shipping = $41.99
(Buy Prostick Plus)

LNA + Filter Arrangement Filter -> SKY7150 LNA SKY7150 LNA -> Filter
Filter Specs Type: LC
Passband:
980 – 1150 MHz
Insertion Loss: 1.65 dB
Attenuation: 40 – 50 dB
Type: SAW
Passband:
1,075 MHz – 1,105 MHz
Insertion loss: 2.3 dB
Attenuation: 30 dB 
TCXO Old batches NO.
New batches YES.
YES
Current Draw 330 mA 300 mA
The new Pro Stick Plus RTL-SDR based ADS-B Receiver from FlightAware.
The new Pro Stick Plus RTL-SDR based ADS-B Receiver from FlightAware.

The first thing we notice is that the filter arrangement between the two units is reversed. On the Prostick the filter is external and must be placed before the LNA. This has the advantage of excellent rejection of out of band signals, but increases the noise figure (NF) of the system slightly. A higher noise figure means the ADS-B signal will end up being weaker, resulting in less range and reports. However, the FlightAware 1090 MHz filter has low insertion losses and should only increase the NF by 1-2 dB.

The Prostick Plus on the other hand uses a SAW filter positioned after the LNA. SAW filters at 1090 MHz typically have an insertion loss of anywhere between 2-3 dB’s. But since it is placed after the LNA the losses are almost completely eliminated by the gain from the LNA and thus the total NF remains low. The attenuation of the SAW filter is less, but it has a smaller pass band. The small pass band may be useful for people who live near an airport and suffer issues with interference from the 1030 MHz interrogation pulses or from GSM at 950 MHz.

In theory, the Prostick + Filter should operate better in environments with very strong out of band signals (any signal outside of 1090 MHz). And the Prostick Plus should operate better in environments with weaker out of band signals. The theory is that since the LNA is placed first in the signal chain on the Prostick Plus, it is more susceptible to overloading from the strong signals as it has no protection from a filter. The LNA used in both Prosticks is a SKY7150, which has a very high OIP3 rating. High OIP3 means that its performance in the presence of strong signals is excellent, and it will not overload so easily. However, even a very high OIP3 rated LNA cannot withstand the strong broadcast signals in some locations.

The Prostick Plus also has some other enhancements like a TCXO. ADS-B is very tolerant to frequency drift, so a TCXO won’t really improve decoding performance, but the cost of a 28.8 MHz TCXO purchased in bulk is under $1 USD, so they may have decided to add it anyway. They appear to also be using TCXO’s on the new production batches of the Prostick as well. The Plus also only draws 300 mA of current compared to the Prostick which draws 330mA. This may be due to the removal of the LED (Although the new batches of the Prostick might also have the LED removed as they advertise a power draw of 300 mA.) On the image of the PCBs below you can see the difference. The SAW filter is just underneath where the LED used to be.

Again, as we mentioned in our previous review of the Prostick it is a bit odd that the 39 dB OIP3 SKY7150 only appears to be drawing 60 mA, when it should be drawing 100 mA. The lower current usage is probably because they run it from 3.3V instead of 5V. The lower current use probably means that the OIP3 rating is reduced slightly by ~5 dBs.

The Prostick Plus and Prostick PCBs
The Prostick Plus and Prostick PCBs

Real World Testing

Here we test the Prostick and Prostick Plus in a signal environment with lots of strong interfering BCFM, DVB-T and GSM signals around. We’ve seen reports on the FlightAware forums that some users have seen improved performance with the Prostick Plus, whilst others have seen dismal or reduced performance. In these tests and review we are able to show when each stick will perform at its best. We do not test the Prostick without the filter, as without the filter we are unable to receive any ADS-B messages at all due to overloading.

Test 1: Flight Aware ADS-B Antenna

First we set up a test using the FlightAware ADS-B antenna, a 2-way signal splitter and the Prostick Plus and Prostick + Filter. We used Modesdeco2 as the ADS-B software, and ran the test for 45 minutes.

The results show that the Prostick Plus edges ahead of the Prostick + Filter by a small amount. It seems that the 1-2 dB loss in the external filter does not contribute to a huge reduction in ADS-B messaging, but the results do show that the Prostick Plus will give you better results in an environment with favorable reception conditions.

In this test we used the excellent FlightAware ADS-B antenna. This antenna is tuned specifically to 1090 MHz, and performs some rejection of the out of band signals. This rejection is enough to allow the Prostick Plus to work well in our test area without overloading.

In the image slider below we first checked ADS-B reception in SDR#, to see if there was any noticeable visual difference. The reception seemed identical. In the remaining images we checked to see how the reception was on out of band signals with the two units. In these tests we want the out of band signals to be low, so smaller signals are better. The Prostick Plus filters our out band signals significantly less, which can be a reason for increased overload. But the amount of filtering performed by the Plus was sufficient together with this 1090 MHz tuned antenna to not cause any overload at max gain.

http://ADS-B%20Comparison

ADS-B Comparison

http://BCFM

BCFM

http://152%20MHz

152 MHz

http://858%20MHz

858 MHz

Test 2: Discone Antenna

In test 2 we show what can happen if the out of band signals going into the Prosticks are really strong. This could especially happen if you are using a wideband antenna that is not specifically tuned to 1090 MHz, or if the out of band signals in your area are exceptionally strong (living near a transmission tower for example). In this test we used the same setup as in test 1, but used a wideband discone as the antenna instead. This means that the natural out of band signal filtering from the FlightAware antenna is not present anymore, and thus out of band signals come into the dongle much stronger.

Here we found that the Prostick Plus produced dismal results. The out of band signals were too strong for the LNA to handle, thus causing overload and significant desensitization of the ADS-B signals. The messages received by the Prostick + Filter was significantly higher. 

In the SDR# screenshots below we can clearly see that the Prostick Plus has very poor ADS-B reception at 1090 MHz with this antenna. The noise floor is much higher due to desensitization and overload from broadcast FM and DVB-T signals. Reducing the gain on the RTL-SDR does not help a lot, since most of the overload occurs in the first stage SKY7150 LNA. This can also be seen in the amount of signal overload that is present when tuned to the broadcast FM and other bands in SDR#.

http://ADS-B%20Comparison

ADS-B Comparison

http://1090%20MHz%20Gain%20Reduced

1090 MHz Gain Reduced

http://BCFM

BCFM

http://BCFM%20Gain%20Reduced

BCFM Gain Reduced

http://152%20MHz

152 MHz

http://415%20Mhz

415 Mhz

http://858%20MHz

858 MHz

Conclusions

The Prostick and Prostick Plus dongles are both excellent low cost ADS-B receivers. If you want to set up a permanent ADS-B monitoring station they are highly recommended. 

So what are the lessons learned from these tests?

  1. If you live in an environment with extremely strong out of band signals you’ll need to place the filter first. So in this case use the Prostick + external filter combination (or Prostick Plus + external Filter).
  2. Otherwise use the Prostick Plus for slightly better performance and lower cost.
  3. To reduce the possibility of overload with the Prostick Plus use an antenna tuned to 1090 MHz.

The table below summarizes the recommendations again.

 

Antenna -> LNA -> Filter
(Prostick Plus)

Antenna -> Filter -> LNA
(Prostick + FA Filter)
Advantages

Noise figure (NF) is dominated by the LNA, thus this method gives minimum NF.

Losses in filter overcome by LNA gain.

LNA will not be susceptible to overloading from out of band signals.

Disadvantages

The LNA can overload from out of band signals since it is not protected by a filter.

The insertion loss (IL) of the filter directly adds to the noise figure (NF). For example a 2 dB IL filter will add 2 dB to the system NF. This may result in a few dB’s lower SNR.

When to use Use this method if you do not have strong out of band signals in your area and/or if you have an LNA with a high OIP3 rating, like with the SKY7150 LNA which is used on the Prostick’s. Use this method if you have very strong out of band signals in your area.

For most people the Prostick Plus should work fine and be the better choice. Also rest assured that if you purchase a Prostick Plus and find that it overloads in your environment, you still always have the option of placing an external filter in front of it. Then you’ll practically have the same performance as with the standard Prostick + Filter combination. A Prostick Plus + External Filter combination may even be more beneficial for users in very very strong signal environments.

Also remember that the Prostick’s are designed to be placed as close to the antenna as possible, without the use of coax cable. You can use USB extension cables, or run the Prostick on a remote Raspberry Pi computing unit to achieve this. If you want to run coax between the antenna and Prostick, you will see heavily reduced performance due to the losses in the coax cable. In this situation you should instead place an LNA like the LNA4ALL or Uputronics ADS-B LNA by the antenna, and use a bias tee to power it.

Radio For Everyone: Testing Several ADS-B Antennas Under $50

Over on his blog ‘Radio for Everyone’ Akos has shared results submitted to him by FlightAware forum user ‘Nitr0’ which compares several ADS-B antennas that cost under $50 USD. The antenna that we most recommend for ADS-B is the FlightAware antenna, but for European buyers there are also many lower cost alternatives available on eBay, most of which are made by fellow radio hobbyists or hams. The tests use the six antennas listed below, comparing each one against the ‘reference’ FlightAware antenna.

  1. The FlightAware Antenna – $45 USD
  2. A Bulgarian made antenna by LZ3RR – $31 USD + shipping
  3. A Slovakian made collinear antenna by stanislavpalo130 – $25 USD + shipping
  4. A Slovakian made 5/8 antenna by stanislavpalo130 – $24 USD
  5. RTL-SDR stock antenna – Included with generic RTL-SDRs
  6. A 3.5 dBi loaded whip – $3 to $15 USD

In summary the tests seem to show that nothing beats the FlightAware antenna, with the closest in performance being the Bulgarian made antenna. We should mention however, without knowing the real radiation patterns, SWR and various other factors it is hard to say which one will work best for everyone. Different locations/obstacles/mountings could mean that antennas with different designs and therefore radiation patterns work better than others. But it seems that the FlightAware antenna is the top performer in the common scenario of being able to mount the antenna on a roof with a good view of the horizon.

Two ADS-B antennas being tested by Akos.
Two ADS-B antennas being tested by Nitr0.

dumpvdl2: A Lightweight VDL2 Decoder

The VHF Data Link mode 2 (VDL2) is a relatively new wireless transmission mode used on aircraft for sending short messages, position data (similar to ADS-B) and also for allowing traffic controllers to communicate to pilots via text and data. VDL2 is an evolution of ACARS and is eventually supposed to replace it entirely. The advantage over ACARS is that VDL2 can transmit data 10 times faster, and supports a much wider range of services. The main default channel is at 136.975 MHz, but channels could exist on other air band frequencies too.

Over on GitHub Tomasz Lemiech (szpajder – also the author of RTL-Airband) has uploaded a new VDL2 decoder called dumpvdl2. This is a lightweight command line Linux based VDL2 decoder and protocol analyzer. The features include:

  • Runs under Linux (tested on: x86, x86-64, Raspberry Pi)
  • Supports following SDR hardware:
    • RTLSDR (via rtl-sdr library)
    • Mirics SDR (via libmirisdr-4)
    • reads prerecorded IQ data from file
  • Decodes up to 8 VDL2 channels simultaneously
  • Outputs messages to standard output or to a file (with optional daily or hourly file rotation)
  • Outputs ACARS messages to PlanePlotter over UDP/IP socket
  • Supports message filtering by type or direction (uplink, downlink)
  • Outputs decoding statistics using Etsy StatsD protocol

In a previous post we showed how VDL2 could be decoded with MultiPSK on Windows. But the advantage of dumpvdl2 is that it allows you to set up a lightweight monitoring station on something like a Raspberry Pi. dumpvdl2 can also be interfaced with PlanePlotter, and statistics can be graphed with another program such as Grafana.

dumpvdl2 running.
dumpvdl2 running.

Radioforeveryone New Posts: PiAware Step-By-Step Guide and a Guide to Feeding Other ADS-B Aggregrators

Akos from the radioforeveryone.com blog has recently uploaded some new posts. The first post is a tutorial on setting up a PiAware server with an RTL-SDR. PiAware is the official ADS-B feeder software from FlightAware.com, which is a web service that provides real time tracking of aircraft. Most of the flight data comes from volunteers around the world running a PiAware server with an RTL-SDR, ADS-B antenna and Raspberry Pi. The installation is fairly simple, involves burning an SDcard with the PiAware image, setting up the WiFi and then seeing your receiver online on the PiAware website. From there you can then configure the device further.

In the second post Akos describes how to feed other tracking websites, e.g. not just FlightAware, but also similar sites like Planefinder.net and flightradar24.com. Akos has also mentioned that a single Raspberry Pi can be used to feed all three aggregators simultaneously.

FlightAware vs FlightRadar24 vs Planefinder Plots
FlightAware vs FlightRadar24 vs Planefinder Plots

Radio For Everyone New Posts: Building an ADS-B Station, Easy Homemade Beginner ADS-B Antennas

Akos the author of the radioforeveryone.com blog has recently added two new articles to his blog. The first post is a comprehensive guide to setting up your own ADS-B station. The guide focuses on creating a system that is easy to use, has good performance and is value for money. In the post he shows what type of computing hardware is required, what software can be used and what RTL-SDR dongles work best. He also shows what choices are available when it comes to amplification and filtering to improve signal reception and goes on to talk a bit about adapters and the antennas that work best for him.

BuildingADS-Bstation
Building a ADS-B station

 In the second post Akos shows more on how to build your own beginners antennas for ADS-B reception. The post focuses on showing how to modify the stock magnetic mount antenna that comes with most RTL-SDR dongles, and how to build a half-wave ‘spider’ antenna entirely out of coax cable. The post is full of easy to follow images which make it great for beginners.

EDIT: It’s been pointed out in the comments by antenna experts/enthusiasts that the 1/2 wave ground plane antenna described by Akos in his tutorial may not be technically correct. A 1/2 wave antenna has a huge impedance which requires some sort of matching. Without matching there is going to be about 10 dB of loss due to the mismatch, and so the antenna will perform poorly. We recommend sticking with a 1/4 wave design, which is essentially the same as Akos’ 1/2 wave ground plane antenna, just with the element lengths halved.

FlightAware Prostick vs FlightAware Prostick Plus: Review

Recently the FlightAware Prostick Plus was released. The Prostick is a modified RTL-SDR with a LNA built into the dongle. It is optimized for ADS-B reception and works very well due to the low noise figure of the SKY7150 LNA which is used as the first stage LNA. However, due to the increased gain from the LNA it can easily overload from strong out of band signals, such as broadcast FM, DAB, DVB-T and GSM. To eliminate this problem FlightAware recommend using their 1090 MHz filter in front of the dongle. 

The FlightAware Prostick Plus is the same as the Prostick, but the Plus also incorporates a 1090 MHz SAW filter into the dongle itself. The overall cost is about $15.95 USD cheaper than buying the Prostick + Filter combination. See below for a tabulated comparison between the two units.

  FlightAware Prostick + Filter FlightAware Prostick Plus
Price

USA: $16.95 + $19.95 = $36.9 (Buy Prostick) (Buy Filter)

Worldwide: $48.99 + $18 Shipping = $66.99
(Buy Prostick + Filter)

USA: $20.95
(Buy Prostick Plus)

Worldwide: $29.99 + $12 Shipping = $41.99
(Buy Prostick Plus)

LNA + Filter Arrangement Filter -> SKY7150 LNA SKY7150 LNA -> Filter
Filter Specs Type: LC
Passband:
980 – 1150 MHz
Insertion Loss: 1.65 dB
Attenuation: 40 – 50 dB
Type: SAW
Passband:
1,075 MHz – 1,105 MHz
Insertion loss: 2.3 dB
Attenuation: 30 dB 
TCXO Old batches NO.
New batches YES.
YES
Current Draw 330 mA 300 mA
The new Pro Stick Plus RTL-SDR based ADS-B Receiver from FlightAware.
The new Pro Stick Plus RTL-SDR based ADS-B Receiver from FlightAware.

The first thing we notice is that the filter arrangement between the two units is reversed. On the Prostick the filter is external and must be placed before the LNA. This has the advantage of excellent rejection of out of band signals, but increases the noise figure (NF) of the system slightly. A higher noise figure means the ADS-B signal will end up being weaker, resulting in less range and reports. However, the FlightAware 1090 MHz filter has low insertion losses and should only increase the NF by 1-2 dB.

The Prostick Plus on the other hand uses a SAW filter positioned after the LNA. SAW filters at 1090 MHz typically have an insertion loss of anywhere between 2-3 dB’s. But since it is placed after the LNA the losses are almost completely eliminated by the gain from the LNA and thus the total NF remains low. The attenuation of the SAW filter is less, but it has a smaller pass band. The small pass band may be useful for people who live near an airport and suffer issues with interference from the 1030 MHz interrogation pulses or from GSM at 950 MHz.

In theory, the Prostick + Filter should operate better in environments with very strong out of band signals (any signal outside of 1090 MHz). And the Prostick Plus should operate better in environments with weaker out of band signals. The theory is that since the LNA is placed first in the signal chain on the Prostick Plus, it is more susceptible to overloading from the strong signals as it has no protection from a filter. The LNA used in both Prosticks is a SKY7150, which has a very high OIP3 rating. High OIP3 means that its performance in the presence of strong signals is excellent, and it will not overload so easily. However, even a very high OIP3 rated LNA cannot withstand the strong broadcast signals in some locations.

The Prostick Plus also has some other enhancements like a TCXO. ADS-B is very tolerant to frequency drift, so a TCXO won’t really improve decoding performance, but the cost of a 28.8 MHz TCXO purchased in bulk is under $1 USD, so they may have decided to add it anyway. They appear to also be using TCXO’s on the new production batches of the Prostick as well. The Plus also only draws 300 mA of current compared to the Prostick which draws 330mA. This may be due to the removal of the LED (Although the new batches of the Prostick might also have the LED removed as they advertise a power draw of 300 mA.) On the image of the PCBs below you can see the difference. The SAW filter is just underneath where the LED used to be.

Again, as we mentioned in our previous review of the Prostick it is a bit odd that the 39 dB OIP3 SKY7150 only appears to be drawing 60 mA, when it should be drawing 100 mA. The lower current usage is probably because they run it from 3.3V instead of 5V. The lower current use probably means that the OIP3 rating is reduced slightly by ~5 dBs.

The Prostick Plus and Prostick PCBs
The Prostick Plus and Prostick PCBs

Real World Testing

Here we test the Prostick and Prostick Plus in a signal environment with lots of strong interfering BCFM, DVB-T and GSM signals around. We’ve seen reports on the FlightAware forums that some users have seen improved performance with the Prostick Plus, whilst others have seen dismal or reduced performance. In these tests and review we are able to show when each stick will perform at its best. We do not test the Prostick without the filter, as without the filter we are unable to receive any ADS-B messages at all due to overloading.

Test 1: Flight Aware ADS-B Antenna

First we set up a test using the FlightAware ADS-B antenna, a 2-way signal splitter and the Prostick Plus and Prostick + Filter. We used Modesdeco2 as the ADS-B software, and ran the test for 45 minutes.

The results show that the Prostick Plus edges ahead of the Prostick + Filter by a small amount. It seems that the 1-2 dB loss in the external filter does not contribute to a huge reduction in ADS-B messaging, but the results do show that the Prostick Plus will give you better results in an environment with favorable reception conditions.

In this test we used the excellent FlightAware ADS-B antenna. This antenna is tuned specifically to 1090 MHz, and performs some rejection of the out of band signals. This rejection is enough to allow the Prostick Plus to work well in our test area without overloading.

In the image slider below we first checked ADS-B reception in SDR#, to see if there was any noticeable visual difference. The reception seemed identical. In the remaining images we checked to see how the reception was on out of band signals with the two units. In these tests we want the out of band signals to be low, so smaller signals are better. The Prostick Plus filters our out band signals significantly less, which can be a reason for increased overload. But the amount of filtering performed by the Plus was sufficient together with this 1090 MHz tuned antenna to not cause any overload at max gain.

http://ADS-B%20Comparison

ADS-B Comparison

http://BCFM

BCFM

http://152%20MHz

152 MHz

http://858%20MHz

858 MHz

Test 2: Discone Antenna

In test 2 we show what can happen if the out of band signals going into the Prosticks are really strong. This could especially happen if you are using a wideband antenna that is not specifically tuned to 1090 MHz, or if the out of band signals in your area are exceptionally strong (living near a transmission tower for example). In this test we used the same setup as in test 1, but used a wideband discone as the antenna instead. This means that the natural out of band signal filtering from the FlightAware antenna is not present anymore, and thus out of band signals come into the dongle much stronger.

Here we found that the Prostick Plus produced dismal results. The out of band signals were too strong for the LNA to handle, thus causing overload and significant desensitization of the ADS-B signals. The messages received by the Prostick + Filter was significantly higher. 

In the SDR# screenshots below we can clearly see that the Prostick Plus has very poor ADS-B reception at 1090 MHz with this antenna. The noise floor is much higher due to desensitization and overload from broadcast FM and DVB-T signals. Reducing the gain on the RTL-SDR does not help a lot, since most of the overload occurs in the first stage SKY7150 LNA. This can also be seen in the amount of signal overload that is present when tuned to the broadcast FM and other bands in SDR#.

http://ADS-B%20Comparison

ADS-B Comparison

http://1090%20MHz%20Gain%20Reduced

1090 MHz Gain Reduced

http://BCFM

BCFM

http://BCFM%20Gain%20Reduced

BCFM Gain Reduced

http://152%20MHz

152 MHz

http://415%20Mhz

415 Mhz

http://858%20MHz

858 MHz

Conclusions

The Prostick and Prostick Plus dongles are both excellent low cost ADS-B receivers. If you want to set up a permanent ADS-B monitoring station they are highly recommended. 

So what are the lessons learned from these tests?

  1. If you live in an environment with extremely strong out of band signals you’ll need to place the filter first. So in this case use the Prostick + external filter combination (or Prostick Plus + external Filter).
  2. Otherwise use the Prostick Plus for slightly better performance and lower cost.
  3. To reduce the possibility of overload with the Prostick Plus use an antenna tuned to 1090 MHz.

The table below summarizes the recommendations again.

 

Antenna -> LNA -> Filter
(Prostick Plus)

Antenna -> Filter -> LNA
(Prostick + FA Filter)
Advantages

Noise figure (NF) is dominated by the LNA, thus this method gives minimum NF.

Losses in filter overcome by LNA gain.

LNA will not be susceptible to overloading from out of band signals.

Disadvantages

The LNA can overload from out of band signals since it is not protected by a filter.

The insertion loss (IL) of the filter directly adds to the noise figure (NF). For example a 2 dB IL filter will add 2 dB to the system NF. This may result in a few dB’s lower SNR.

When to use Use this method if you do not have strong out of band signals in your area and/or if you have an LNA with a high OIP3 rating, like with the SKY7150 LNA which is used on the Prostick’s. Use this method if you have very strong out of band signals in your area.

For most people the Prostick Plus should work fine and be the better choice. Also rest assured that if you purchase a Prostick Plus and find that it overloads in your environment, you still always have the option of placing an external filter in front of it. Then you’ll practically have the same performance as with the standard Prostick + Filter combination. A Prostick Plus + External Filter combination may even be more beneficial for users in very very strong signal environments.

Also remember that the Prostick’s are designed to be placed as close to the antenna as possible, without the use of coax cable. You can use USB extension cables, or run the Prostick on a remote Raspberry Pi computing unit to achieve this. If you want to run coax between the antenna and Prostick, you will see heavily reduced performance due to the losses in the coax cable. In this situation you should instead place an LNA like the LNA4ALL or Uputronics ADS-B LNA by the antenna, and use a bias tee to power it.

New Low Power RTL-SDR’s for Stratux ADS-B Receivers

Stratux is an RTL-SDR based project that gives small plane pilots access to ADS-B data, without having to purchase an expensive commercial ADS-B installation. It consists of software that runs on a Raspberry Pi, and two RTL-SDR dongles to receive both 1090 MHZ ADS-B, and 978 MHz UAT. The decoded data is then streamed via WiFi to a tablet running navigation aide software with charts for pilots.

Typically Stratux kits come with two standard ‘Nano’ styled RTL-SDR dongles. However, users of the Stratux system have been reporting problems with overheating, and with the Pi struggling with the high current demands of a typical setup which includes two RTL-SDR dongles, active WiFi broadcasting, a GPS unit and an optional cooling fan. A typical RTL-SDR dongle draws 280 mA, so two dongles are already pulling 560 mA.

Chris, creator of the Stratux software and seller of Stratux kits has just released a new low power RTL-SDR dongle (kit with antennas). The cost is $35 USD for two dongles (one for 1090 MHz and one for 978 MHz). The dongle obtains its low power feature by using a switching regulator instead of a linear regulator as the main 3.3V power regulator on the PCB. Normally you would not want to use switching regulator for the main regulator in an RF device because they are very noisy in terms of RF interference generated. However switching regulators are much more efficient compared to linear regulators, and thus save a lot of current wastage. Other dongle manufacturers like ThumbNet have actually gone the other way, removing the secondary 1.2V switching regulator from the standard dongle design, and using a linear regulator instead. The ThumbNets end up with lower noise, but draw 400 mA of current. 

With the switching regulator the new Stratux dongles only draw about 185 mA, a saving of almost 100 mA. They also generate 0.5W less heat. Users of the Stratux system have so far been impressed with them and have not noticed any appreciable difference in ADS-B performance. We think that these low power dongles might also be of interest to people using them on mobile phones or battery/solar powered remote installations.

The new Stratux low power RTL-SDR dongles.
The new Stratux low power RTL-SDR dongles.

During testing, Chris found that there was no significant noise floor increase visible on the 978 MHz  & 1090 MHz frequencies. Most of the switching noise increase appears to be on the lower frequencies, but those frequencies are not relevant for the Stratux use case anyway.

Chris was kind enough to send us some samples of the new low power dongles. First we ran a noise floor scan with rtl_power to determine the effect of the switching regulator. The results show that the spurs and noise floor readings have definitely increased by a significant amount, with an especially large noise floor rise below 400 MHz. In SDR# wandering switching noise spurs are also visible throughout the spectrum, but they tend to weaken in strength once an antenna is connected.

Stratux vs Standard Dongle vs V3 Dongle Noise Floor Scan
Stratux vs Standard Dongle vs V3 Dongle Noise Floor Scan

Fortunately, ADS-B is very tolerant to spurs and is generally not affected by this type of noise. We’ve only given the Stratux a quick test on ADS-B so far, but when compared against another ‘nano’ styled dongle the Stratux performed nearly identically (in fact even a little better) in terms of messages received. The two dongles were connected to the same antenna via a splitter and we logged the number of messages received in 10 minutes.

Quick ADS-B Reception Test
Quick ADS-B Reception Test

In conclusion the Stratux RTL-SDR set out to solve the mobile power issues suffered by people using the Stratux system. It has achieved that with an over 100mA saving in current use. The new Stratux dongle is much noisier, but the noise does not appear to significantly affect ADS-B reception as seen by our results and from the reports from Stratux users who beta tested this dongle.

Chris has also created a post on Reddit /r/stratux which talks a bit more about the new dongle.

RTLSDR4Everyone Four New Posts: FlightAware Pro Stick Plus Review, Avoid FlightAware Ripoffs, Review of two BCFM Filters, Getting Started with Outernet

Akos from the RTLSDR4Everyone blog has recently uploaded four new articles. The first article reviews the new FlightAware Prostick Plus. The Prostick Plus is an RTL-SDR dongle optimized for ADS-B reception. It contains a LNA and 1090 MHz filter on board the dongle. In his review Akos tests the FlightAware Prostick Plus and compares it against the regular Prostick with external filtering. His results show that the Prostick Plus gets 18.45% more position reports and 5.4% extra max range in his location. His second post continues with the Prostick topic and warns customers to look out for sellers reselling, or relisting the Prostick for much higher ripoff prices.

FlightAware Prostick vs Prostick Plus
FlightAware Prostick vs Prostick Plus

In his third post Akos reviews our RTL-SDR.com broadcast FM filter and compares it against another similar filter from another seller. His test results show that both filters can improve performace.

Two BCFM band stop filters tested by Akos.
Two BCFM band stop filters tested by Akos.

Finally in his fourth post Akos writes a tutorial on getting started with Outernet reception. He bought the full Outernet bundle which comes with a battery bank, CHIP single board computer, E4000 with bias tee RTL-SDR, LNA with filter and patch antenna. His post describes what each component is, then shows how to use them to receive Outernet. His results also seemed to show that our V3 dongle significantly outperformed the E4000 dongle at Outernet reception. The V3 received the Outernet signal with a SNR of 6.39 dB vs only 2.58 dB with the E4000.

Some Outernet Components
Some Outernet Components

RTLSDR4Everyone: Review of the FlightAware ADS-B RTL-SDR

Akos from the RTLSDR4Everyone blog has recently uploaded a review of the FlightAware ADS-B ProStick RTL-SDR dongle. The FlightAware (FA) dongle is a standard RTL-SDR with SMA connector, but with a very low noise figure LNA built into the front end. This low noise figure helps improve the SNR of ADS-B signals, resulting in more decodes and further range. We previously reviewed the FlightAware dongle in our own review available here.

In his post Akos reviews the FA dongle on its use as a general RTL-SDR as well as an ADS-B receiver. His review is initially critical to some of the misinformed advertising claims made by FA. He then goes on to show some noise floor scans and some ADS-B reception comparisons. Finally he shows some modifications that can be made to improve the cooling of the PCB.

He concludes that the FA ProStick works very well on improving ADS-B performance, but that overloading due to the increased gain is common.

prostickreview_akos2