Tagged: rtl-sdr

February 10, 2017

Building a DIY Carbon Fibre Yagi Antenna with 3D Printed Parts for 20€

Over on his blog author Manuel a.k.a ‘Tysonpower’ has written about a DIY Carbon Fibre Yagi antenna that he’s built for only 20€. The antenna is very lightweight thanks to a 12mm diameter carbon fibre pipe which is used as the main boom. It also uses 3D printed parts that clamp onto the carbon fibre pipe and hold the metal elements in place. The advantage of the carbon fibre pipe over a PVC one is not only is it lightweight and much easier to hold, but it also stronger, and much less bendy and floppy. The metal elements are welding rods which he found on eBay, and the carbon fibre pipe was sourced cheaply from China with Aliexpress.

A Yagi is a directional antenna with high gain towards the direction it is pointing. You’ll need to hand point the Yagi in the general direction of the satellite as it passes over, but you can expect much higher SNR readings compared to something like a QFH or Turnstile.

Manuel designed his antenna for 2M satellites (NOAA, Meteor M2, ISS etc), and was able to achieve over 36 dB SNR with an RTL-SDR.com V3 receiver, FM Trap and LNA4ALL on NOAA 18 at a 34° max. pass. He writes that the design is easily modifiable for other frequencies too.

To show off the design, construction and performance of his antenna he’s uploaded two videos to YouTube which we show below. The speech is in German, but even for non-German speakers the video is easily followed

[EN subs] Yagi Antenne aus Carbon bauen (140mhz, 3 Elemente) - DIY

Watch this video on YouTube

Über 36db SNR!- Test der DIY Yagi aus Carbon

Watch this video on YouTube

February 10, 2017

First Steps Towards Decoding HD Radio

Programmer Phil Burr wrote in and wanted to share his newest code which is a partial implementation (no audio) of the iBiquity IBOC HD Radio standard. HD Radio is a proprietary broadcast radio protocol and is used only in North America. You may have noticed it before as the rectangular sidebands on the spectrum which surround standard analogue broadcast FM signals.

The audio codec specifications are not public and is thus not implemented here, so this code has very little use outside of being a good learning tool. But Phil does write that if anyone if able to figure out how to decode the codec, then this code may be a good starting point.

Phil writes:

I wrote this because I wanted to learn about digital broadcasts. Despite the fact that the audio codec used is iBiquity’s proprietary HDC codec, I decided that writing a receiver that could decode the air interface would be a great learning experience.

iBiquity’s HDC codec is supposedly based upon some of the same technologies as HE-AAC codec so it may be possible for some audio codec gurus, given access to the raw HDC audio packets, to write a decoder for the codec.

The receiver is somewhat limited. It only decodes FM MP1 profile transmissions (which happens to includes every IBOC FM transmitter in my area). It is also somewhat limited in the Layer2 packet demultiplexing. It likely needs a strong signal in order to decode signals reasonably well. However it is just enough to get access to the main program stream.

HD Radio Sidebands Visible on the Spectrum

February 10, 2017

A Design for a Robust, Selective and Flexible RF Front-End for Wideband Receivers

Recently Sivan Toledo wrote in wanting to share an academic paper he wrote together with Itamar Melamed, both from Tel-Aviv University in Israel. The freely available paper describes the design and evaluation of a second-generation front-end for wideband software defined radios. Their front-end helps SDRs optimize reception by providing filtering, a bias tee for mast head amplifiers and also protects the radio against damage from strong signals with an RF limiter. The abstract reads:

In this paper, we describe the design and evaluation of a second-generation front-end unit for wideband sampling radio receivers. The unit contains a surface acoustic wave (SAW) filter to protect the receiver from strong out-of-band signals, an RF limiter to protect both the filter and the receiver from physical damage due to strong signals, and a bias tee with a DC limiter to provide DC power to a masthead low-noise amplifier, if one is used. The unit allows receivers such as those of the universal software radio peripheral (USRP) N-series type to be effectively used in RF environments with weak signals and strong in-band and out-of-band interferences.

Although the front-end is designed for the USRP SDR, it should also work well with RTL-SDR dongles and other SDRs. The authors also write that their design is uploaded and available for PCB printing on CircuitHub.

February 9, 2017

Reverse Engineering Honeywell 345 MHz Home Automation Sensors with an RTL-SDR

OpenHAB is an open source home automation software program which is designed to interface and manage all the various sensors and systems in an automated house. One problem however, is that many wireless sensors and actuators utilize a proprietary communications protocol that is not supported by OpenHAB.

In his home, Dan Englender had several Honeywell 5800 series 345 MHz wireless security door sensors, all of which interface using a proprietary protocol that is not yet implemented in OpenHAB. In order to get around this, Dan decided to reverse engineer the protocol and implement a decoder into OpenHAB himself.

Dan’s four part write up covers the RF capture & demodulation, protocol reverse engineering and implementation into OpenHAB. First he looked up the frequency and bandwidth of the signal via the FCC filing information on fcc.io. Then he captured some packets from a door sensor using his RTL-SDR and GNU Radio, and then wrote a short Python program to decode the protocol and transmit the door open/closed information to OpenHAB. In the future he hopes to optimize the decoder so that it can comfortably run on a Raspberry Pi as the GNU Radio script uses quite a bit of computing power.

The final project is called decode345 and the code is available over on his GitHub.

[Also seen on Hackaday]

February 8, 2017

RTL-SDR.com Broadcast AM Block High Pass Filter Now for Sale

Back in October we released a broadcast FM bandstop filter for removing strong signals in the 88 – 108 MHz region. Today we’re releasing a new broadcast AM high pass filter (BCAM HPF) with a 2.6 MHz cutoff. The cost is the same as the BCFM bandstop filter at $14.95 USD including free international air shipping. Faster shipping options may also be chosen if desired. We’ll eventually have this product on Amazon USA in a few months too, but for now it is only available from our Chinese warehouse.

The filter comes in a 2.8 cm x 2.8 cm x 1.3 cm aluminum enclosure and uses female SMA connectors on each end. Included in the package is also a SMA male to SMA male straight barrel adapter.

Click here to visit our store

This filter is designed to eliminate broadcast band AM (BCAM) stations by attenuating (blocking) any signals below 1.7 MHz. In reality due to roll-off the filter is usable from about 2.5 – 2.6 MHz and above.

The broadcast AM band exists at around 525 kHz to 1.705 MHz. These signals are usually local, and if you live close to a transmitter they can sometimes be extremely strong. Broadcast AM signals that are too strong can overload your SDR or radio, causing poor reception in other HF bands too. The filter also helps attenuate any other strong VLF/LF/MW interference. Note that this filter is a high pass and not a bandstop, so it will also block VLF signals. Specifications are shown below:

Filter Type: LC High Pass Filter
3 dB Cutoff: 2.5 – 2.6 MHz
Attenuation: ~60dB
Pass band I.L: Typically well below 2 dB
Power Levels: RX power only, cannot pass DC

We’ve also uploaded a video below that shows a demonstration of reception when using an RTL-SDR.com V3 dongle in direct sampling mode together with the BCAM HPF. In the video we first compare reception against an upconverter (the Spyverter). It’s worth nothing that the upconverter can receive signals well even without the filter in place. Using the filter does still help the upconverter receive a little bit better but the effect is not shown in the video. Then we simply scroll through the spectrum and listen to a few signals.

RTL-SDR.com V3 Direct Sampling with HPF Demonstration

Watch this video on YouTube

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February 10, 2017

Building a DIY Carbon Fibre Yagi Antenna with 3D Printed Parts for 20€

[EN subs] Yagi Antenne aus Carbon bauen (140mhz, 3 Elemente) - DIY

Watch this video on YouTube

Über 36db SNR!- Test der DIY Yagi aus Carbon

Watch this video on YouTube

Vote

February 10, 2017

First Steps Towards Decoding HD Radio

Phil writes:

I wrote this because I wanted to learn about digital broadcasts. Despite the fact that the audio codec used is iBiquity’s proprietary HDC codec, I decided that writing a receiver that could decode the air interface would be a great learning experience.

iBiquity’s HDC codec is supposedly based upon some of the same technologies as HE-AAC codec so it may be possible for some audio codec gurus, given access to the raw HDC audio packets, to write a decoder for the codec.

The receiver is somewhat limited. It only decodes FM MP1 profile transmissions (which happens to includes every IBOC FM transmitter in my area). It is also somewhat limited in the Layer2 packet demultiplexing. It likely needs a strong signal in order to decode signals reasonably well. However it is just enough to get access to the main program stream.

Vote

February 10, 2017

A Design for a Robust, Selective and Flexible RF Front-End for Wideband Receivers

In this paper, we describe the design and evaluation of a second-generation front-end unit for wideband sampling radio receivers. The unit contains a surface acoustic wave (SAW) filter to protect the receiver from strong out-of-band signals, an RF limiter to protect both the filter and the receiver from physical damage due to strong signals, and a bias tee with a DC limiter to provide DC power to a masthead low-noise amplifier, if one is used. The unit allows receivers such as those of the universal software radio peripheral (USRP) N-series type to be effectively used in RF environments with weak signals and strong in-band and out-of-band interferences.

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February 9, 2017

Reverse Engineering Honeywell 345 MHz Home Automation Sensors with an RTL-SDR

The final project is called decode345 and the code is available over on his GitHub.

[Also seen on Hackaday]

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February 8, 2017

RTL-SDR.com Broadcast AM Block High Pass Filter Now for Sale

The filter comes in a 2.8 cm x 2.8 cm x 1.3 cm aluminum enclosure and uses female SMA connectors on each end. Included in the package is also a SMA male to SMA male straight barrel adapter.

Click here to visit our store

Filter Type: LC High Pass Filter
3 dB Cutoff: 2.5 – 2.6 MHz
Attenuation: ~60dB
Pass band I.L: Typically well below 2 dB
Power Levels: RX power only, cannot pass DC

RTL-SDR.com V3 Direct Sampling with HPF Demonstration

Watch this video on YouTube

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February 7, 2017

A Pre-Built Raspberry Pi Image for using an RTL-SDR as an APRS RX iGate

Keith Maton (G6NHU) wrote in and wanted to share his new ready to go APRS RX iGate image for the Raspberry Pi. APRS stands for “Amateur Packet Reporting System”, and is a type of packet radio communications system used by Amateur Radio operators. They often use them to transmit short mail messages, weather sensor updates, track vehicles and for various other purposes. An iGate allows APRS messages to be transmitted over the all world via the internet via a signal chain such as: RF->iGate RX->Internet->iGate TX->RF. To run an iGate you should be a radio amateur with a callsign. A global aggregation of APRS broadcasts received by iGates can be seen at aprs.fi.

An RTL-SDR can be used to receive APRS packets easily and many amateur radio enthusiasts have been setting up APRS RX only iGates using the “direwolf” decoding software. Keith’s image simplifies the process of installing and configuring software significantly by proving a plug and play image that you just burn to an SDcard and plug into your Raspberry Pi. His post also explains how to configure the iGate correctly.

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February 7, 2017

RTL-SDR Waterfall on a C.H.I.P

The C.H.I.P is a $9 USD single board computer which is similar to a Raspberry Pi. It is powerful enough to run the RTL-SDR, and in fact the Outernet project use the C.H.I.P together with our V3 dongles in their DIY kit to receive, decode and serve their free L-band satellite data service.

Over on the C.H.I.P forums a user ‘Basketball’ has also submitted a photo showing his C.H.I.P with LCD screen running a Python based waterfall display with his RTL-SDR. His C.H.I.P system has been modified to be portable with a 3D printed case, 10000 mAh battery and 4.3″ LCD screen. Others on the forum have also noted that they have had FreqShow successfully running on their Pocket C.H.I.Ps as well.

So if you’re looking for a low cost computing platform to run your RTL-SDR the C.H.I.P may be a good choice.

Thanks to Mike Ladd for the submitting the forum post to us.

CHIP_waterfall — C.H.I.P Running a Waterfall Display

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February 7, 2017

A Tutorial on Using RTL-SDR with LabView: Creating a Simple FM Demodulator

LabView is a popular visual programming environment often used in industry and by engineers for test, automation and control applications. It is somewhat similar to GNU Radio in that programming is done by connecting a series of various blocks together, each of which performs some function. The RTL-SDR is compatible with LabView via a simple RTL-SDR interface.

Recently Albert Lederer wrote in to us and wanted to share his beginners guide to creating an broadcast FM demodulator with an RTL-SDR in LabView. The tutorial focuses only on demodulating the mono part of the broadcast FM signal structure and provides a fully functional LabeView project file. Albert describes the signal chain implemented below:

1. The signal is received from the rtl-sdr device as IQ data. This is converted to a complex signal and the phase is extraced.

2. The phase correction removes phase discontinuities.

3. The key demodulation component in the chain is the phase derivative. The phase derivative takes the phase of the signal and creates a second signal that is composed only of the changes in frequency. This is then the demodulated signal.

4. The low pass filter is used to filter out frequencies above 15kHz, which do not contain the desired information.

5. The rational resample takes the signal, which is still at the sampled rate (in the examples case 286650Hz) and resamples it to something the sound card can handle. In this case, we are using a decimation factor of 13, which results in a 22050Hz audio stream. Actually, I worked this out the other way around. I wanted a 22050Hz audio stream and checked which sample rate would give me an integer decimation while keeping the RF sampling rate as low as possible.

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