Tagged: rtl2832

Using a LimeSDR and RTL-SDR to Transfer a Text File Over the Air

Over on his blog nuclearrambo has been working on a project that uses a LimeSDR and RTL-SDR to transfer a small CSV text file over the air.

The transmitting side consists of a GNU Radio flowchart that encodes the text file into a binary string, modulates that binary string with Binary Phase Shift Keying (BPSK), and then transmits it using the LimeSDR.

The receiving side uses an RTL-SDR, and is based on another GNU Radio flowgraph that uses a polyphase clock sync block to synchronize the sampling time, a costas loop for fine frequency correction, an LMS DD equalizer block to compensate for multipath effects, and finally demodulation blocks that recover the bits and text file from the BPSK signal.

His results showed that he can almost recover the entire file except for the first few bytes of data which is always lost since it takes time for the clock sync and costas loop block to converge. The post goes into further detail about what each of the blocks do and some of the signal theory math behind everything. The GNU Radio GRC file is also provided if you want to try it out yourself.

LimeSDR Transmitting a CSV file to a RTL-SDR with BPSK modulation.
LimeSDR Transmitting a CSV file to a RTL-SDR with BPSK modulation.

SignalsEverywhere: Testing out NooElecs PCB L-Band Patch Antenna

Over on his YouTube channel Corrosive from the SignalsEverywhere YouTube channel has uploaded a video where he tests out the new US$29.95 NooElec PCB patch antenna for receiving L-band satellite signals. In the video he shows how it can be combined with one of their SAWBird L-band low noise amplifiers in order to receive L-band satellite signals such as Inmarsat STD-C and AERO.

We note that our own RTL-SDR Blog Active L-band patch antenna will be ready to ship out before the end of this month, and while waiting for it we are currently having a preorder sale for US$34.95 including free shipping over on our store. For US$34.95 our patch antenna is fully contained in a waterproof enclosure, includes an LNA built in, and comes with several mounting options, so we believe that it is really a great deal. The patch design is based on the Outernet ceramic patch that was compared against the NooElec PCB patch shown in Corrosives video, so performance will be very similar.

Nooelec NEW Inmarsat Patch Antenna with Airspy SDR

SDR in the Local Newspaper: Investigating an RF Dead Spot for Car Key Fobs

Reddit user [SDR_LumberJack] writes how he was recently featured in his local newspaper [Part2] in Ontario, Canada thanks to his efforts in helping to hunt down the cause of an RF deadspot with an SDR. He began his journey by reading a story in his local newspaper called the [Windsor Star]. The story was about locals having found a ‘dead-spot’ for car key-fobs. In the dead-spot key-less cars wouldn’t start, key-fobs wouldn’t unlock cars, and alarms would go off.

Being intrigued by the story [SDR_LumberJack] investigated by driving around with an RTL-SDR, HackRF and a laptop running SDR#. Eventually he found that there was what appeared to be a WBFM Broadcast radio station interfering at 315 MHz. This frequency happens to fall into the ISM radio band that used by car remotes and key-fobs. The exact source of the interference hasn’t been nailed down just yet though.

While it’s possible a broadcast station is at fault it is also possible that his SDR was just overloading, causing broadcast FM imaging. Perhaps a WBFM filter could be used to prevent signal imaging that could interfere with the investigation.

Hopefully [SDR_LumberJack] will continue his investigation and we’ll get an update on this story.

If you’re interested, back in 2016 we posted a very similar story about the exact same thing happening at a car park in Brisbane, Australia. The conclusion to that story was that the dead-spot only occurred in particular locations in the car park, and this was due to the shape of surrounding building causing the RF signals to reflect off the walls and distort the signal.

SDR_LumberJack in the local newspaper
SDR_LumberJack in the local newspaper

New Product in Store: RTL-SDR Blog Magnetic Whip Antenna Set (Great for KerberosSDR Direction Finding)

We've recently released a new Magnetic Whip Antenna Set in our store. The set consists of a heavy duty magnetic mount antenna base with 2M RG59, a 9.5cm fixed whip antenna (usable from 400 MHz to 2 GHz+), and a 17cm to 1m telescopic whip (usable from 100 MHz - 400 MHz).

Click Here to Visit our Store

The antenna set costs US$14.95 each with free shipping. And if you buy four sets you will receive a 15% discount. Currently available to ship worldwide right now from our warehouse in China, and they will be on Amazon in 2-3 weeks.

One application of our KerberosSDR 4-Tuner Coherent RTL-SDR is radio direction finding. This requires four quality omni-directional antennas. We were disappointed to find that there were no high quality magnetic whip antennas available on the market for a low price that we could use with KerberosSDR so we made our own.

The magnetic base is designed carefully with conductive metal that is properly connected to the shield of the coax cable. Most cheap antenna bases just leave the shield connection floating and this causes insufficient coupling to the underlying ground plane resulting in poor performance and poor results when it comes to direction finding and reception.

We've tested this set with KerberosSDR and it is known to work well. The antenna can also of course be used for any other receiving purpose if you prefer to use a whip antenna over our multipurpose dipole antenna set.

In the first two images in the image slider below you can see a comparison between a black base that is not properly bonded to the coax shield, vs the RTL-SDR Blog silver base which is correctly bonded to the coax shield. Both tests used the 9.5cm whip antenna. You can see that the RTL-SDR Blog silver base provides a much lower noise floor and higher signal SNR due to the better ground plane. Also we note that when placing the antenna bases on a metallic surface to create a larger ground plane, the black base showed no further improvement, whereas the RTL-SDR Blog silver base did.

The final three images in the slider show the SWR plots of the two whips on the base. We can see that the 9.5cm whip provides an SWR of less than six below 412 MHz. The telescopic whip can be adjusted to provide better SWR for lower frequencies.

RTL-SDR Blog Antenna Base (Coax shield properly connected to base)

RTL-SDR Blog Antenna Base (Coax shield properly connected to base)

Generic Black Antenna Base (Coax shield not connected to base)

Generic Black Antenna Base (Coax shield not connected to base)

9.5cm Whip SWR Plot

9.5cm Whip SWR Plot

Telescopic Whip Collapsed SWR Plot

Telescopic Whip Collapsed SWR Plot

Telescopic Whip Fully Expanded SWR Plot

Telescopic Whip Fully Expanded SWR Plot

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Using a LimeSDR and RTL-SDR to Transfer a Text File Over the Air

Over on his blog nuclearrambo has been working on a project that uses a LimeSDR and RTL-SDR to transfer a small CSV text file over the air.

The transmitting side consists of a GNU Radio flowchart that encodes the text file into a binary string, modulates that binary string with Binary Phase Shift Keying (BPSK), and then transmits it using the LimeSDR.

The receiving side uses an RTL-SDR, and is based on another GNU Radio flowgraph that uses a polyphase clock sync block to synchronize the sampling time, a costas loop for fine frequency correction, an LMS DD equalizer block to compensate for multipath effects, and finally demodulation blocks that recover the bits and text file from the BPSK signal.

His results showed that he can almost recover the entire file except for the first few bytes of data which is always lost since it takes time for the clock sync and costas loop block to converge. The post goes into further detail about what each of the blocks do and some of the signal theory math behind everything. The GNU Radio GRC file is also provided if you want to try it out yourself.

LimeSDR Transmitting a CSV file to a RTL-SDR with BPSK modulation.
LimeSDR Transmitting a CSV file to a RTL-SDR with BPSK modulation.
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SignalsEverywhere: Testing out NooElecs PCB L-Band Patch Antenna

Over on his YouTube channel Corrosive from the SignalsEverywhere YouTube channel has uploaded a video where he tests out the new US$29.95 NooElec PCB patch antenna for receiving L-band satellite signals. In the video he shows how it can be combined with one of their SAWBird L-band low noise amplifiers in order to receive L-band satellite signals such as Inmarsat STD-C and AERO.

We note that our own RTL-SDR Blog Active L-band patch antenna will be ready to ship out before the end of this month, and while waiting for it we are currently having a preorder sale for US$34.95 including free shipping over on our store. For US$34.95 our patch antenna is fully contained in a waterproof enclosure, includes an LNA built in, and comes with several mounting options, so we believe that it is really a great deal. The patch design is based on the Outernet ceramic patch that was compared against the NooElec PCB patch shown in Corrosives video, so performance will be very similar.

Nooelec NEW Inmarsat Patch Antenna with Airspy SDR

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SDR in the Local Newspaper: Investigating an RF Dead Spot for Car Key Fobs

Reddit user [SDR_LumberJack] writes how he was recently featured in his local newspaper [Part2] in Ontario, Canada thanks to his efforts in helping to hunt down the cause of an RF deadspot with an SDR. He began his journey by reading a story in his local newspaper called the [Windsor Star]. The story was about locals having found a ‘dead-spot’ for car key-fobs. In the dead-spot key-less cars wouldn’t start, key-fobs wouldn’t unlock cars, and alarms would go off.

Being intrigued by the story [SDR_LumberJack] investigated by driving around with an RTL-SDR, HackRF and a laptop running SDR#. Eventually he found that there was what appeared to be a WBFM Broadcast radio station interfering at 315 MHz. This frequency happens to fall into the ISM radio band that used by car remotes and key-fobs. The exact source of the interference hasn’t been nailed down just yet though.

While it’s possible a broadcast station is at fault it is also possible that his SDR was just overloading, causing broadcast FM imaging. Perhaps a WBFM filter could be used to prevent signal imaging that could interfere with the investigation.

Hopefully [SDR_LumberJack] will continue his investigation and we’ll get an update on this story.

If you’re interested, back in 2016 we posted a very similar story about the exact same thing happening at a car park in Brisbane, Australia. The conclusion to that story was that the dead-spot only occurred in particular locations in the car park, and this was due to the shape of surrounding building causing the RF signals to reflect off the walls and distort the signal.

SDR_LumberJack in the local newspaper
SDR_LumberJack in the local newspaper
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New Product in Store: RTL-SDR Blog Magnetic Whip Antenna Set (Great for KerberosSDR Direction Finding)

We've recently released a new Magnetic Whip Antenna Set in our store. The set consists of a heavy duty magnetic mount antenna base with 2M RG59, a 9.5cm fixed whip antenna (usable from 400 MHz to 2 GHz+), and a 17cm to 1m telescopic whip (usable from 100 MHz - 400 MHz).

Click Here to Visit our Store

The antenna set costs US$14.95 each with free shipping. And if you buy four sets you will receive a 15% discount. Currently available to ship worldwide right now from our warehouse in China, and they will be on Amazon in 2-3 weeks.

One application of our KerberosSDR 4-Tuner Coherent RTL-SDR is radio direction finding. This requires four quality omni-directional antennas. We were disappointed to find that there were no high quality magnetic whip antennas available on the market for a low price that we could use with KerberosSDR so we made our own.

The magnetic base is designed carefully with conductive metal that is properly connected to the shield of the coax cable. Most cheap antenna bases just leave the shield connection floating and this causes insufficient coupling to the underlying ground plane resulting in poor performance and poor results when it comes to direction finding and reception.

We've tested this set with KerberosSDR and it is known to work well. The antenna can also of course be used for any other receiving purpose if you prefer to use a whip antenna over our multipurpose dipole antenna set.

In the first two images in the image slider below you can see a comparison between a black base that is not properly bonded to the coax shield, vs the RTL-SDR Blog silver base which is correctly bonded to the coax shield. Both tests used the 9.5cm whip antenna. You can see that the RTL-SDR Blog silver base provides a much lower noise floor and higher signal SNR due to the better ground plane. Also we note that when placing the antenna bases on a metallic surface to create a larger ground plane, the black base showed no further improvement, whereas the RTL-SDR Blog silver base did.

The final three images in the slider show the SWR plots of the two whips on the base. We can see that the 9.5cm whip provides an SWR of less than six below 412 MHz. The telescopic whip can be adjusted to provide better SWR for lower frequencies.

RTL-SDR Blog Antenna Base (Coax shield properly connected to base)

RTL-SDR Blog Antenna Base (Coax shield properly connected to base)

Generic Black Antenna Base (Coax shield not connected to base)

Generic Black Antenna Base (Coax shield not connected to base)

9.5cm Whip SWR Plot

9.5cm Whip SWR Plot

Telescopic Whip Collapsed SWR Plot

Telescopic Whip Collapsed SWR Plot

Telescopic Whip Fully Expanded SWR Plot

Telescopic Whip Fully Expanded SWR Plot

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International Space Station SSTV Event Scheduled for October 9 and 10

The International Space Station (ISS) periodically schedules radio events where they transmit Slow Scan Television (SSTV) images down to earth for listeners to receive and collect. This time they have scheduled SSTV images for October 9 09:50 - 14:00 GMT and October 10 08:55-15:15 GMT.

With an RTL-SDR and a simple V-Dipole from our RTL-SDR V3 antenna kit it is possible to receive these images when the ISS passes over. ISS passes for your city can be determined online, and the SSTV images can be decoded with a program like MMSSTV.

AMSAT-UK writes:

Russian cosmonauts are expected to activate Slow Scan Television (SSTV) image transmissions on 145.800 MHz FM from the International Space Station on Wednesday/Thursday, October 9/10.

This is the schedule for the planned activation of the MAI-75 SSTV activity from the ISS.
• Oct 9 09:50-14:00 GMT
• Oct 10 08:55-15:15 GMT

Transmissions will be sent on 145.800 MHz FM in the SSTV mode PD-120. Once received, images can be posted and viewed by the public at http://www.spaceflightsoftware.com/ARISS_SSTV/index.php

ISS SSTV uses a Kenwood TM D710E transceiver which is part of the amateur radio station located in the Russian ISS Service Module.

Please note that SSTV events are dependent on other activities, schedules and crew responsibilities on the ISS and subject to change at any time. You can check for updates regarding planned operation at:
ISS Ham https://twitter.com/RF2Space
ARISS Status https://twitter.com/ARISS_status
ARISS SSTV Blog https://ariss-sstv.blogspot.com/
AMSAT Bulletin Board http://www.amsat.org/mailman/listinfo/amsat-bb

Read the MagPi article Pictures from space via ham radio
https://www.raspberrypi.org/magpi/pictures-from-space-via-ham-radio/

ISS SSTV info and links https://amsat-uk.org/beginners/iss-sstv/

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An Introduction to Pagers with the HackRF PortaPack and an RTL-SDR

Over on YouTube user HackedExistence has uploaded a video explaining how POCSAG pager signals work, and he also shows some experiments that he's been performing with his HackRF PortaPack and an old pager.

The Portapack is an add on for the HackRF SDR that allows the HackRF to be used without the need for a PC. If you're interested in the past we reviewed the PortaPack with the Havok Firmware, which enables many TX features such as POCSAG transmissions.

POCSAG is a common RF protocol used by pagers. Pagers have been under the scrutiny of information security experts for some time now as it is common for hospital pagers to spew out unencrypted patient data [1][2][3] into the air for anyone with a radio and computer to decode.

In the video HackedExistence first shows that he can easily transmit to his pager with the HackRF PortaPack and view the signals on the spectrum with an RTL-SDR. Later in the video he explains the different types of pager signals that you might encounter on the spectrum, and goes on to dissect and explain how the POCSAG protocol works.

Intro to Pagers - POCSAG with HackRF

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SDR# 1717 Officially Released: Dark Mode and Other Skins now Available

Release 1717 of the popular SDR# software that is commonly used with RTL-SDR dongles has just officially been released (actually already up to r1722 at the time of this post). This release brings with it UI theme customization including a very nice looking dark mode. Over on the Airspy/SDR# groups.io board programmer Youssef wrote:

We are pleased to announce the release of SDR# r1717 with the Telerik User Interface.

This is quite a big jump from the old UI components that will allow us to add many fancy features in the upcoming revisions.
For now, the functionality of the software was ported "one to one" with full support of the existing plugins.
A new Plugin API for the tool bar was added which allows plugin developers to add/remove special buttons for quick access.

Despite a slightly longer loading time at the startup of the application, many performance improvements should be noticed in run time, especially the CPU usage.
The package is now distributed with a set of skins/themes you can select in the control panel under "Display". Later on, we will add custom skins loading capability so you can customize the look and feel of the whole program.

Please note that some themes have slower rendering than others. You will have to experiment until you settle with something that is acceptable for the eye candy and the CPU usage / UI reactivity.

Some older plugins may not support the "Dark" themes and will have some rendering problems. The last unskinned version of SDR# will be still available for download in case you really need it. In any case, plugin developers are invited to support the new skins by either using Telerik UI components or at least setting the display properties of the old components so they render properly.

SDRSharp Dark Theme
SDRSharp Dark Theme
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G8JNJ Reverse Engineers and Reviews the MLA-30 HF Loop Antenna

Last month we posted a collection of reviews about the MLA-30 which is a budget magnetic loop antenna designed for receiving HF signals. The overall consensus from the reviews was that it worked decently for the price, but of course could never live up to the high end loops that cost hundreds of dollars.

Recently Martin (G8JNJ) reverse engineered the active circuit used on the loop from photos taken by M0LMK and has made some observations on it's performance, noting that it's design isn't very good. First he notes that the amplifier chip is a Texas TL592B two stage video amplifier which isn't that great for this application. His measurements show an OIP3 of 20dBm, a P1 saturation of -3dBm and a noise figure of 12dB.

Of interest, he explains that the creator of this loop has designed it poorly as the impedance match of the loop to low pass filter is very wrong, resulting in a very poor amplitude/frequency response. He shows how the response can be improved with a few termination resistors, but is still not great.

MLA-30 Frequency Response. Ideally should be flat.
MLA-30 Frequency Response. Ideally should be flat.

If you're interested in a cheap magnetic loop antenna, Martin suggests DIYing the M0AYF design which he says works a lot better.

We note that the "YouLoop" design is also in the works as a product that will apparently sell at close to manufacturing cost. The YouLoop is a passive loop idea by the creator of the Airspy that consists only of a simple 1:1 transformer and coax cable as the loop. It works best with high sensitivity radios like the HF+ Discovery.

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