Category: Airspy

World Radio TV Handbook (WRTH) Reviews the Airspy HF+

The World Radio TV Handbook (WRTH) is a directory book (or CD) of world radio stations on LW, MW, SW and FM. In addition to the directory they also do reviews of radios/SDRs, and recently they reviewed the Airspy HF+ (pdf). The Airspy HF+ is high dynamic range HF/VHF receiver designed for DXing.

According to the review, WRTH give the Airspy HF+ the award of being the best value HF SDR for 2019. The review takes note of the HF+'s excellent dynamic range and then goes on to validate the manufacturers claimed specifications. Finally they write how they tested it during a contest at 7 MHz, and found no overloading or spurious responses apart from a minor noise floor increase when an extremely strong local CW station was encountered.

World Radio TV Handbook Review of the Airspy HF+
World Radio TV Handbook Review of the Airspy HF+

Black Friday SDR Sales: Airspy 15% Off, SDrplay RSP2 $20 Off, HackRF 20% Off

Airspy

Airspy is currently running a 15% Black Friday sale over on the manufacturers website iead.cc, and on their US distributor airspy.us. The coupon code is BF2018.

This results in an Airspy Mini costing only $84.15, an Airspy HF+ costing $169.15, an Airspy R2 costing $143.65 and a SpyVerter costing $41.65. This is the cheapest we've seen these products to date.  

SDRplay

Over on Ham Radio Outlet, the RSP2 is currently reduced by $20, taking it down to a price of only $149.95. The RSP2 Pro is also reduced down to $192.95. Other SDRplay products, and products on their website appear to be not discounted.

HackRF

Over on SparkFun the original HackRF is 20% off, resulting in a price of only $239.96. It's still double the price of an Aliexpress clone, but it is an original unit. In the UK ML&S are also selling it for 15% off at £219.95. This is the cheapest price we've seen an original HackRF sold for.

Elad FDM S2

At the higher end of the SDR spectrum, we see that the Elad FDM-S2 is currently reduced by $51, resulting in a sale price of $529.

Most of these sales are expected to run until Monday, or until stocks run out.

Have you found any other great SDR deals? Let us know in the comments.

SDR# Update: SpyServer Network Browser now Available

The programmers of SDR# have just released a new version which now includes a SpyServer directory browser. SpyServer is an Airspy and RTL-SDR compatible SDR streaming server for SDR#. It allows you to access your SDR remotely over the internet or a network connection by using efficient data compression techniques. 

The new browser allows you to browse for active and publicly shared SDRs that are running SpyServer. To launch the browser in the latest SDR#, choose "SpyServer Network" in the Source drop down menu, and click on the "..." button. At the moment there are only a few servers listed, and not all work. But we expect more to show up and work as people update their SpyServer software.

For SpyServer users, the latest server version will automatically list your server in the directory, but it can be turned off in the config file.

SpyServer Network Browser
SpyServer Network Browser

Comparing the Airspy HF+ And KiwiSDR on Shortwave Radio

The Airspy HF+ and the KiwiSDR are two HF specialty SDR radios. The HF+ advertises excellent dynamic range and sensitivity, whilst the KiwiSDR has it's strength in it's internet connectivity and 30 MHz wide live bandwidth.

Over on YouTube icholakov has uploaded a video comparing the two SDRs on daytime medium wave and shortwave reception with a W6LVP amplified magnetic loop antenna. It is expected that the two SDRs should be quite similar in easy receiving conditions, but the Airspy HF+ should shine in challenging conditions with strong blocking signals and weak signals being received at the same time. The Airspy HF+ should also be a bit more sensitive in all conditions. It's not clear if there were any strong blocking signals in the tests, but the results appear to confirm the sensitivity expectations.

KiwiSDR and Airspy HF+ comparison

SegDSP: Distributed Cloud Based SDR with SpyServer

Over the last few months Lucas Teske (author of the Open Satellite Project) has been working on a piece of software called "SegDSP". The idea appears to create a web GUI based SDR receiver for SpyServer streams which can be used to create a cloud of channel demodulators, essentially segmenting the DSP computation burden over multiple computers.

SpyServer is a SDR server application that is compatible with Airspy products and RTL-SDRs. It allows you to connect to these SDRs remotely over a network or internet connection. The SDR server computer sends the radio IQ data over the network allowing you to perform processing remotely. A major advantage of SpyServer compared to other SDR server applications is that it only sends the raw IQ data for the portion of the spectrum that you're interested in which can save a lot of bandwidth.

One key application that Lucas envisions for SegDSP is using it with cloud clusters of single board computers (SBC) like the Raspberry Pi 3. The philosophy is that there will be specific roles for each SBC machine. For example you might have some SDR machines running SpyServers, some processing machines for demodulating and decoding multiple channels, and a storage machine for recording data. Then you can dynamically spawn / despawn workers when needed (for example only spawning a machine when a LEO satellite with data to decode passes over).

SegDSP development is still in the early stages, and appears to only have the web GUI set up at the moment with a few demodulators. But keep an eye on his Twitter @lucasteske for updates too. Lucas also did a talk at the last CyberSpectrum meetup. His talk can be found at 1:30:00 in the recording.

SegDSP Screenshot Demodulating WBFM
SegDSP Screenshot Demodulating WBFM

 

Cloned SDRPlay and Airspy Units Now Appearing on Aliexpress/eBay

Recently we've found that there are now cloned units of SDRplay RSP1 and Airspy R2 units appearing on Aliexpress and eBay. (We won't link them here to avoid improving the Google ranking of the clone listings). This post is just a warning and reminder that these are not official products of SDRplay or Airspy, and as such you would not receive any support if something went wrong with them. The performance and long term software support of the clones also isn't known. Buying clones also damages the original developers abilities to bring out exciting new products like we've seen so far constantly with Airspy and SDRplay.

SDRplay

We've been in contact with SDRplay for a statement and they believe that the unit is a clone of the older and now discontinued RSP1, and not the RSP1A, despite the listings advertising RSP1A features such as additional filtering. SDRplay note from the pictures of the circuit board that the cloned unit's circuit board looks like an RSP1, and that the listing description is probably just blindly copied directly from the official RSP1A description.

Currently given that the price of the cloned RSP1 is $139, which is higher than the $109 cost of an original and newer model RSP1A, we don't see many taking up the offer.

Airspy

The Airspy R2 has also recently been cloned and now appears on Aliexpress with the lowest price being US$139 without any metal enclosure. Given that the price of an original Airspy R2 with metal enclosure is US$169, we again don't see many taking up the offer of the clone with such a small price difference.

HackRF

The HackRF is a different story in respect to clones. The HackRF design and circuits are open source, so unlike the closed source designs of the SDRplay and Airspy, in a way HackRF clones are actually encouraged and are legal. For some time now it's been possible to find cloned HackRF's on Aliexpress for only US$120 at the lowest, and from $150 - $200 including antennas and TCXO upgrades. This is quite a saving on the $299+ cost of the original HackRF. Reports from buyers indicate that the HackRF clones are actually decent and work well. The advantage of buying the original version is that you support Michael Ossmann, the creator of the HackRF, and may potentially get a better performing unit.

We've also seen clones of the HackRF Portapack on Aliexpress, which is an add-on for the HackRF that allows you to go portable. The clones go for $139 vs $220 for the original. No word yet on the quality.

RTL-SDR V3

We also note that recently there have been several green color RTL-SDRs released on the market with some being advertised as "RTL-SDR Blog V3" units. These are not our units, and are not even actual clones of the V3. These green units appear to just be standard RTL-SDRs without any real improvements apart from a TCXO. Some listings even advertise the V3's bias tee and HF features, but they are not implemented. Real V3 units come in a silver enclosure branded with RTL-SDR.COM.

Final Words

If you know how China works, you'll understand that it's highly unlikely that there is any legal recourse for SDRplay and Airspy to remove these products from sale. Once a product is popular it is almost a given that it will be cloned. It's possible that the clones might be able to be gimped via blacklisting official software, but that the companies would implement this is a stretch, and would probably be easy to get around. In the end while not ethical in a business fairness sense, these clones may be good for the consumer as they force the original designers to lower their prices and improve added value services.

If readers are interested in a comparison between the clones and original units, please let us know as we may consider an article on it.

Cloned SDRs Roundup
Cloned SDRs Roundup

Testing out the New Airspy HF+ Preselector

The Airspy team have recently been working on a preselector retrofit product for their HF+. The Airspy HF+ already has excellent dynamic range and sensitivity, but by adding a preselector they seek to improve performance enough to claim that the HF+ is as good as or even better than much more pricey SDRs like the Perseus by achieving dynamic range figures of more than 105 dBm.

A preselector is a filter or bank of filters that attenuates out of band signals. This is useful as radios can desensitize if an unwanted signal comes in too strongly. For example, if you are tuned to the 20m band, but there is a very strong MW signal, the SNR of your desired 20m band signal might be reduced. Radios with a natural high dynamic range design like the Airspy HF+ are less affected by this problem, but for the strongest of signals use of a preselector can still help.

The Airspy HF+ preselector needs to be soldered directly onto the HF+'s PCB, and once installed it automatically switches bands using GPIO expansion ports controlled automatically via tuning in SDR#, so no external switching is required.

The expected pricing of the HF+ preselector is US$49, and it will be ready for sale in a few weeks.

Measurements

We received a prototype of the filter a few days ago and have been testing it out. From measurements on a VNA, we found that the preselector features four bands of operation:

  • 0 - 5.2 MHz
  • 5.2 - 10 MHz
  • 10 - 17 MHz
  • 17 - 30 MHz

Airspy have also provided us with a block diagram schematic which we show below.

HF+ Preselector Schematic
HF+ Preselector Schematic

Insertion loss appears to be mostly below 3 dB with fairly steep skirts especially on the lower side. The top three filters do an excellent job at blocking out the broadcast AM band. Below are some VNA plots that show the filter responses.

VNA_180628_175816
VNA_180628_175907
VNA_180628_180008
VNA_180628_180057

Installation

The preselector comes in a small 3.2 x 1.7 cm sized PCB that is fully covered with a metal shielding can. To install it you need to carefully solder it onto the HF+ PCB. This can be a little tricky since the pads are so small, but if you're experienced with soldering it shouldn't be an issue.

  • First you need to open the HF+ and remove R3 from the HF+ PCB, which is a zero ohm resistor.
  • The preselector PCB can then be positioned and the two IN and OUT pads soldered in place.
  • Then you'll also need to connect the power and 2x GPIO lines to the preselector using wires.
  • Now you need to bridge the two shielding CANs with a thick bit of wire. We simply used two cuts of copper solder braid to do this.
  • Finally is also recommended to update the HF+ firmware to the latest version and download the latest version of SDR#.

Once soldered in place the preselector is ready to use, and the HF+ cover can be put back on. It is expected that the commercially sold versions of the preselector will come with detailed installation instructions. 

In the first photo below we removed the shield to see what was inside, and the second photo shows it installed on the HF+ PCB.

hf+presel_PCB
hf+presel_installed2

Using it on a RTL-SDR V3

Whilst the preselector is designed for the Airspy HF+, there's no reason why it couldn't also be retrofitted onto other SDRs, such as our RTL-SDR V3, for use in improving direct sampling mode performance.

The V3 has spare GPIO ports that can be used to control the filter, and 5V for powering the filter could be tapped off the PCB as well. Currently we're considering making a breakout PCB for the filter than might aide with this.

We did a quick test with the preselector connected to the RTL-SDR V3 running in direct sampling mode, and as expected performance is much better, especially above 5 MHz once the second filter kicks in. This is because the second, third and fourth filters all heavily attenuate the MW broadcast AM band, which is the main source of overload issues on HF.

The following screenshots show how much the filter was able to reduce the signal strength of AM broadcast when the second 5.2 - 10 MHz filter was turned on. This reduction was enough to prevent overload on all the higher bands.

Preselector OFF

Preselector OFF

Preselector ON

Preselector ON

Preselector OFF

Preselector OFF

Preselector ON

Preselector ON

HF+ Results

For the HF+ we tested by injecting a strong signal into two HF+ SDRs, one with the filter installed and the other without. The HF+ with the filter was routinely able to withstand much higher signal powers without any signs of overload occurring, and no degradation due to insertion loss was observed.

The screenshots below show an experiment with a weak desired signal injected at 14.2 MHz, and a strong unwanted signal being injected at 1.5 MHz. With the unwanted signal at 5 dBm, the filtered HF+ showed no signs of overload, whilst the unfiltered HF+ had the AGC kick in to increase the front end attenuation, reducing the signal strength by about 20 dB and raising the noise floor.

Filtered HF+

Filtered HF+

Unfiltered HF+

Unfiltered HF+

Other Reviews

Other reviewers have also received the preselector and have been testing it. Fenu radio has uploaded a short review, and plans to write more in the future. He's also made his HF+ with preselector available for public use via SpyServer (details in his post). In the video below Leif SM5BSZ reviews the preselector and runs through several tests while comparing it against the Perseus. His results seem to show that the Persues gets a +25 dBm IP3, whilst the HF+ with the latest firmware and preselector is able to obtain a respectable +10 dBm IP3. 

hfpluspresel2

Conclusion

For most people, the dynamic range of the HF+ is probably already more than enough, but if you are receiving very strong signals, the preselector can help get you get more performance out of the HF+. Of course the preselector cannot help if you have strong signals within the filter bands.

If you're looking to get the most out of your HF+ then the filter at only $49 is a pretty good deal. Just take note that you'll need to open the HF+ and be comfortable with soldering onto the PCB. 

World Radio TV Handbook (WRTH) Reviews the Airspy HF+

The World Radio TV Handbook (WRTH) is a directory book (or CD) of world radio stations on LW, MW, SW and FM. In addition to the directory they also do reviews of radios/SDRs, and recently they reviewed the Airspy HF+ (pdf). The Airspy HF+ is high dynamic range HF/VHF receiver designed for DXing.

According to the review, WRTH give the Airspy HF+ the award of being the best value HF SDR for 2019. The review takes note of the HF+'s excellent dynamic range and then goes on to validate the manufacturers claimed specifications. Finally they write how they tested it during a contest at 7 MHz, and found no overloading or spurious responses apart from a minor noise floor increase when an extremely strong local CW station was encountered.

World Radio TV Handbook Review of the Airspy HF+
World Radio TV Handbook Review of the Airspy HF+

Black Friday SDR Sales: Airspy 15% Off, SDrplay RSP2 $20 Off, HackRF 20% Off

Airspy

Airspy is currently running a 15% Black Friday sale over on the manufacturers website iead.cc, and on their US distributor airspy.us. The coupon code is BF2018.

This results in an Airspy Mini costing only $84.15, an Airspy HF+ costing $169.15, an Airspy R2 costing $143.65 and a SpyVerter costing $41.65. This is the cheapest we've seen these products to date.  

SDRplay

Over on Ham Radio Outlet, the RSP2 is currently reduced by $20, taking it down to a price of only $149.95. The RSP2 Pro is also reduced down to $192.95. Other SDRplay products, and products on their website appear to be not discounted.

HackRF

Over on SparkFun the original HackRF is 20% off, resulting in a price of only $239.96. It's still double the price of an Aliexpress clone, but it is an original unit. In the UK ML&S are also selling it for 15% off at £219.95. This is the cheapest price we've seen an original HackRF sold for.

Elad FDM S2

At the higher end of the SDR spectrum, we see that the Elad FDM-S2 is currently reduced by $51, resulting in a sale price of $529.

Most of these sales are expected to run until Monday, or until stocks run out.

Have you found any other great SDR deals? Let us know in the comments.

SDR# Update: SpyServer Network Browser now Available

The programmers of SDR# have just released a new version which now includes a SpyServer directory browser. SpyServer is an Airspy and RTL-SDR compatible SDR streaming server for SDR#. It allows you to access your SDR remotely over the internet or a network connection by using efficient data compression techniques. 

The new browser allows you to browse for active and publicly shared SDRs that are running SpyServer. To launch the browser in the latest SDR#, choose "SpyServer Network" in the Source drop down menu, and click on the "..." button. At the moment there are only a few servers listed, and not all work. But we expect more to show up and work as people update their SpyServer software.

For SpyServer users, the latest server version will automatically list your server in the directory, but it can be turned off in the config file.

SpyServer Network Browser
SpyServer Network Browser

Comparing the Airspy HF+ And KiwiSDR on Shortwave Radio

The Airspy HF+ and the KiwiSDR are two HF specialty SDR radios. The HF+ advertises excellent dynamic range and sensitivity, whilst the KiwiSDR has it's strength in it's internet connectivity and 30 MHz wide live bandwidth.

Over on YouTube icholakov has uploaded a video comparing the two SDRs on daytime medium wave and shortwave reception with a W6LVP amplified magnetic loop antenna. It is expected that the two SDRs should be quite similar in easy receiving conditions, but the Airspy HF+ should shine in challenging conditions with strong blocking signals and weak signals being received at the same time. The Airspy HF+ should also be a bit more sensitive in all conditions. It's not clear if there were any strong blocking signals in the tests, but the results appear to confirm the sensitivity expectations.

KiwiSDR and Airspy HF+ comparison

SegDSP: Distributed Cloud Based SDR with SpyServer

Over the last few months Lucas Teske (author of the Open Satellite Project) has been working on a piece of software called "SegDSP". The idea appears to create a web GUI based SDR receiver for SpyServer streams which can be used to create a cloud of channel demodulators, essentially segmenting the DSP computation burden over multiple computers.

SpyServer is a SDR server application that is compatible with Airspy products and RTL-SDRs. It allows you to connect to these SDRs remotely over a network or internet connection. The SDR server computer sends the radio IQ data over the network allowing you to perform processing remotely. A major advantage of SpyServer compared to other SDR server applications is that it only sends the raw IQ data for the portion of the spectrum that you're interested in which can save a lot of bandwidth.

One key application that Lucas envisions for SegDSP is using it with cloud clusters of single board computers (SBC) like the Raspberry Pi 3. The philosophy is that there will be specific roles for each SBC machine. For example you might have some SDR machines running SpyServers, some processing machines for demodulating and decoding multiple channels, and a storage machine for recording data. Then you can dynamically spawn / despawn workers when needed (for example only spawning a machine when a LEO satellite with data to decode passes over).

SegDSP development is still in the early stages, and appears to only have the web GUI set up at the moment with a few demodulators. But keep an eye on his Twitter @lucasteske for updates too. Lucas also did a talk at the last CyberSpectrum meetup. His talk can be found at 1:30:00 in the recording.

SegDSP Screenshot Demodulating WBFM
SegDSP Screenshot Demodulating WBFM

 

Cloned SDRPlay and Airspy Units Now Appearing on Aliexpress/eBay

Recently we've found that there are now cloned units of SDRplay RSP1 and Airspy R2 units appearing on Aliexpress and eBay. (We won't link them here to avoid improving the Google ranking of the clone listings). This post is just a warning and reminder that these are not official products of SDRplay or Airspy, and as such you would not receive any support if something went wrong with them. The performance and long term software support of the clones also isn't known. Buying clones also damages the original developers abilities to bring out exciting new products like we've seen so far constantly with Airspy and SDRplay.

SDRplay

We've been in contact with SDRplay for a statement and they believe that the unit is a clone of the older and now discontinued RSP1, and not the RSP1A, despite the listings advertising RSP1A features such as additional filtering. SDRplay note from the pictures of the circuit board that the cloned unit's circuit board looks like an RSP1, and that the listing description is probably just blindly copied directly from the official RSP1A description.

Currently given that the price of the cloned RSP1 is $139, which is higher than the $109 cost of an original and newer model RSP1A, we don't see many taking up the offer.

Airspy

The Airspy R2 has also recently been cloned and now appears on Aliexpress with the lowest price being US$139 without any metal enclosure. Given that the price of an original Airspy R2 with metal enclosure is US$169, we again don't see many taking up the offer of the clone with such a small price difference.

HackRF

The HackRF is a different story in respect to clones. The HackRF design and circuits are open source, so unlike the closed source designs of the SDRplay and Airspy, in a way HackRF clones are actually encouraged and are legal. For some time now it's been possible to find cloned HackRF's on Aliexpress for only US$120 at the lowest, and from $150 - $200 including antennas and TCXO upgrades. This is quite a saving on the $299+ cost of the original HackRF. Reports from buyers indicate that the HackRF clones are actually decent and work well. The advantage of buying the original version is that you support Michael Ossmann, the creator of the HackRF, and may potentially get a better performing unit.

We've also seen clones of the HackRF Portapack on Aliexpress, which is an add-on for the HackRF that allows you to go portable. The clones go for $139 vs $220 for the original. No word yet on the quality.

RTL-SDR V3

We also note that recently there have been several green color RTL-SDRs released on the market with some being advertised as "RTL-SDR Blog V3" units. These are not our units, and are not even actual clones of the V3. These green units appear to just be standard RTL-SDRs without any real improvements apart from a TCXO. Some listings even advertise the V3's bias tee and HF features, but they are not implemented. Real V3 units come in a silver enclosure branded with RTL-SDR.COM.

Final Words

If you know how China works, you'll understand that it's highly unlikely that there is any legal recourse for SDRplay and Airspy to remove these products from sale. Once a product is popular it is almost a given that it will be cloned. It's possible that the clones might be able to be gimped via blacklisting official software, but that the companies would implement this is a stretch, and would probably be easy to get around. In the end while not ethical in a business fairness sense, these clones may be good for the consumer as they force the original designers to lower their prices and improve added value services.

If readers are interested in a comparison between the clones and original units, please let us know as we may consider an article on it.

Cloned SDRs Roundup
Cloned SDRs Roundup

Testing out the New Airspy HF+ Preselector

The Airspy team have recently been working on a preselector retrofit product for their HF+. The Airspy HF+ already has excellent dynamic range and sensitivity, but by adding a preselector they seek to improve performance enough to claim that the HF+ is as good as or even better than much more pricey SDRs like the Perseus by achieving dynamic range figures of more than 105 dBm.

A preselector is a filter or bank of filters that attenuates out of band signals. This is useful as radios can desensitize if an unwanted signal comes in too strongly. For example, if you are tuned to the 20m band, but there is a very strong MW signal, the SNR of your desired 20m band signal might be reduced. Radios with a natural high dynamic range design like the Airspy HF+ are less affected by this problem, but for the strongest of signals use of a preselector can still help.

The Airspy HF+ preselector needs to be soldered directly onto the HF+'s PCB, and once installed it automatically switches bands using GPIO expansion ports controlled automatically via tuning in SDR#, so no external switching is required.

The expected pricing of the HF+ preselector is US$49, and it will be ready for sale in a few weeks.

Measurements

We received a prototype of the filter a few days ago and have been testing it out. From measurements on a VNA, we found that the preselector features four bands of operation:

  • 0 - 5.2 MHz
  • 5.2 - 10 MHz
  • 10 - 17 MHz
  • 17 - 30 MHz

Airspy have also provided us with a block diagram schematic which we show below.

HF+ Preselector Schematic
HF+ Preselector Schematic

Insertion loss appears to be mostly below 3 dB with fairly steep skirts especially on the lower side. The top three filters do an excellent job at blocking out the broadcast AM band. Below are some VNA plots that show the filter responses.

VNA_180628_175816
VNA_180628_175907
VNA_180628_180008
VNA_180628_180057

Installation

The preselector comes in a small 3.2 x 1.7 cm sized PCB that is fully covered with a metal shielding can. To install it you need to carefully solder it onto the HF+ PCB. This can be a little tricky since the pads are so small, but if you're experienced with soldering it shouldn't be an issue.

  • First you need to open the HF+ and remove R3 from the HF+ PCB, which is a zero ohm resistor.
  • The preselector PCB can then be positioned and the two IN and OUT pads soldered in place.
  • Then you'll also need to connect the power and 2x GPIO lines to the preselector using wires.
  • Now you need to bridge the two shielding CANs with a thick bit of wire. We simply used two cuts of copper solder braid to do this.
  • Finally is also recommended to update the HF+ firmware to the latest version and download the latest version of SDR#.

Once soldered in place the preselector is ready to use, and the HF+ cover can be put back on. It is expected that the commercially sold versions of the preselector will come with detailed installation instructions. 

In the first photo below we removed the shield to see what was inside, and the second photo shows it installed on the HF+ PCB.

hf+presel_PCB
hf+presel_installed2

Using it on a RTL-SDR V3

Whilst the preselector is designed for the Airspy HF+, there's no reason why it couldn't also be retrofitted onto other SDRs, such as our RTL-SDR V3, for use in improving direct sampling mode performance.

The V3 has spare GPIO ports that can be used to control the filter, and 5V for powering the filter could be tapped off the PCB as well. Currently we're considering making a breakout PCB for the filter than might aide with this.

We did a quick test with the preselector connected to the RTL-SDR V3 running in direct sampling mode, and as expected performance is much better, especially above 5 MHz once the second filter kicks in. This is because the second, third and fourth filters all heavily attenuate the MW broadcast AM band, which is the main source of overload issues on HF.

The following screenshots show how much the filter was able to reduce the signal strength of AM broadcast when the second 5.2 - 10 MHz filter was turned on. This reduction was enough to prevent overload on all the higher bands.

Preselector OFF

Preselector OFF

Preselector ON

Preselector ON

Preselector OFF

Preselector OFF

Preselector ON

Preselector ON

HF+ Results

For the HF+ we tested by injecting a strong signal into two HF+ SDRs, one with the filter installed and the other without. The HF+ with the filter was routinely able to withstand much higher signal powers without any signs of overload occurring, and no degradation due to insertion loss was observed.

The screenshots below show an experiment with a weak desired signal injected at 14.2 MHz, and a strong unwanted signal being injected at 1.5 MHz. With the unwanted signal at 5 dBm, the filtered HF+ showed no signs of overload, whilst the unfiltered HF+ had the AGC kick in to increase the front end attenuation, reducing the signal strength by about 20 dB and raising the noise floor.

Filtered HF+

Filtered HF+

Unfiltered HF+

Unfiltered HF+

Other Reviews

Other reviewers have also received the preselector and have been testing it. Fenu radio has uploaded a short review, and plans to write more in the future. He's also made his HF+ with preselector available for public use via SpyServer (details in his post). In the video below Leif SM5BSZ reviews the preselector and runs through several tests while comparing it against the Perseus. His results seem to show that the Persues gets a +25 dBm IP3, whilst the HF+ with the latest firmware and preselector is able to obtain a respectable +10 dBm IP3. 

hfpluspresel2

Conclusion

For most people, the dynamic range of the HF+ is probably already more than enough, but if you are receiving very strong signals, the preselector can help get you get more performance out of the HF+. Of course the preselector cannot help if you have strong signals within the filter bands.

If you're looking to get the most out of your HF+ then the filter at only $49 is a pretty good deal. Just take note that you'll need to open the HF+ and be comfortable with soldering onto the PCB. 

GQRX and gr-osmosdr now with support for SpyServer

Thanks to the work of Lucas Teske, GQRX is now able to connect to SpyServer servers. SpyServer is the IQ streaming server software solution developed by the Airspy SDR developers. It can support Airspy and RTL-SDR devices, and can be used to access these SDRs remotely over a network connection. It is similar to rtl_tcp, but a lot more efficient in terms of network usage, meaning that it performs well over an internet connection. On a previous post we have a tutorial about setting up a SpyServer with an RTL-SDR.

The code modified by Lucas is the gr-osmosdr module, and Lucas' code can be downloaded from his GitHub at github.com/racerxdl/gr-osmosdr. It doesn't yet appear to have been merged into the official osmocom branch. The gr-osmosdr module is a generic block used to access various SDR hardware, so any software that utilizes it (such as GNU Radio) should be able to connect to a SpyServer connection too.