RF category

RFM69 output power

Bob @ electrobob.com tipped us with his latest article about RFM69 module.

As I was mentioning in my 1000.1000 Hardware selection, I have opted for the cool RFM69HW radio module. Weirdly enough, in quite a few sources (big distributor and ebay) the higher power HW module is cheaper. So there ie no reason not to get the higher power module, given quantity discounts. But I want it to operate at lower power most of times. The datasheet does not show any differences at lower power, so I had no reason not to go for the higher power module. It even says so on the features list on the front page, I can turn the power down to -18dBm.

RFM69 output power – [Link]

Teardown and analysis of microwave (26.5GHz) electro-mechanical step attenuators

Teardown and analysis of microwave (26.5GHz) electro-mechanical step attenuators from The Signal Path:

In this short episode Shahriar takes a close look at a pair of Hewlett Packard microwave electro-mechanical step attenuators operating up to 26.5GHz. Mechanical attenuators offer excellent repeatability, low insertion loss and nearly limitless linearity. The teardown reveals that the construction of both modules is very similar on the microwave path. In fact, the lower-frequency model still uses the same attenuator components. The newer model employs electronic control circuity while the older generation attenuator uses purely mechanically controlled DC path. Both models use a solenoid style actuators for step attenuation control.

Teardown and analysis of microwave (26.5GHz) electro-mechanical step attenuators – [Link]

NUT4NT, Open-Source 4-Channel GNSS Receiver Development Board

Although the industry of professional satellite navigation systems is limited to experts and large companies, Amungo Navigation is working towards bringing this industry to individual developers, small companies, and startups through its new open source platform NUT4NT.

NT1065 chip
NT1065 chip

NUT4NT is a development board which implements NT1065 chip with USB 3.0 interface. NT1065 is a Global Navigation Satellite System (GNSS) receiver designed by NTLab, a fabless microelectronic company. It is the first low-cost low-power RF front-end solution in the world. It also has 4 channels supporting all GNSS systems and bands.

GNSS receivers are electronic devices that receive and process signals from a GNSS satellite. These signals used to provide information about receiver’s position,velocity, and time.

NUT4NT has two different working modes. The first uses dual inputs and acts as a centimeter level precision positioning tool, without the need of high quality antenna. The other mode uses the four inputs and provides an array antenna processing system to simply reduce interference and noise.

Dual Inputs Mode (Left) - Four Inputs Mode (Right)
Dual Inputs Mode (Left)   –   Four Inputs Mode (Right)

Hardware and software specifications of NUT4NT:

  • Receiver chip: NT1065
  • USB 3.0 controller: CYUSB3014
  • Clock rate: 10 MHz
  • RF inputs: two or four, depending on board option
  • RF inputs referred Noise Floor: 1 dB
  • ADC resolution – two-bit
  • ADC frequency – up to 99 MHz
  • Samples transfer – continuous full stream, from 20 to 100 Mbytes/sec
  • Power: 5V @ 0.5 A from USB or external adapter
  • Size: 70x50x20 mm (early board) / 77x122x25 mm (single board)
  • All GNSS systems: GPS, GLONASS, Galileo, BeiDou, IRNSS and future
  • All GNSS band: L1/L2/L3/L5, G1/G2/G5, B1/B2, E1/E5 and future
  • Four-channel synchronous reception for antenna array processing
  • Signal dumper (grabber) software
  • Spectrum analyzer software
  • NT1065 configuration software
  • Supports libusb API
  • Supports native Cypress driver API
  • Software for Windows, Linux, and potentially all other OS’s with libusb

There are two options of NUT4NT boards, the Early Board and the Single Board.

Early Board is for $399 and there are only limited boards to order through the crowdfunding campaign page. It consists of two separated boards: the base board, which has the USB 3.0 controller, and NT1065 submodule board.

Single Board will be available later as a future plan, and it is said to have  only one board instead of two.

NUT4NT Early Board
NUT4NT Early Board

NUT4NT is an open source project. Software sources are available on github and the hardware’s documentation will be available soon.

More information and details about the product with many accessories are reachable on the product crowdfunding page.

VHF Frequency Counter with PC Interface

pic-IMG_8318-600

Scott has published a new build:

This is the general idea behind how this frequency counter works. It’s so simple! It’s entirely digital, and needs very few passive components. sn74lv8154 is configured in 32-bit mode (by chaining together its two 16-bit counters, see the datasheet for details) and acts as the front-end directly taking in the measured frequency.

VHF Frequency Counter with PC Interface – [Link]

Image courtesy of Google

Everything You Need To Know About Bluetooth beacons in A White Paper

Image courtesy of Google

Bluetooth 4.0 introduced the Bluetooth low energy (BLE), which is a version of Bluetooth protocol designed for devices with power constraints like battery powered sensors. Bluetooth low energy beacons are BLE (Bluetooth Low Energy) enabled devices, they repeatedly broadcast radio signals to nearby smartphones, containing a small amount of data.
Mobile apps can listen to the signals being broadcast and trigger an action after analyzing beacon’s information.

Beacons are used for proximity-aware applications like positioning and navigation indoors like anti-lost tracking tags, another application is for location based advertisements.

There is no official Bluetooth Special Interest Group (SIG) beacon standard, so beacons have pseudo-standards. For example, iBeacon standard is used by Apple and Eddystone is used for Google.

Apple iBeacon Advertising Packet
Apple iBeacon Advertising Packet

As you can see in the above image, there is one byte (power) value indicating the iBeacon’s calibrated output power in dBm measured at a distance of 1 meter.
So Beacons can be used to calculate the proximity distance between the beacon and the receiver of beacon’s information. This calculation relies on a comparison of a Received Signal Strength Indicator (RSSI) to a beacon’s transmit (Tx) power to approximate the distance to the beacon.
The calculated distance can’t be very accurate, since RF signals fade unpredictably according to real-world environmental factors like walls. Future versions of BLE will solve this by using Angle-of-Arrival (AoA) and Angle-of-Departure (AoD) which allow a multi-antenna Bluetooth device to accurately determine the spatial location of another Bluetooth device.

Beacons typically use non-connectable advertising, providing all of useful information in the advertising packet itself. So the radio can be shut off immediately after advertising hence this will save power.

A white paper from Silicon Labs covers a lot of informations about Beacons. The paper examines beacon applications, provides a short description of how BLE work, contains further description of iBeacon and Eddystone standards and highlights SoC solutions for BLE from Silicon Labs such as BLE112 and BLE113 which can have fully standalone applications through a simple scripting language called BGScript developed by Silicon Labs.

BGScript iBeacon example code for the BGM111 Bluetooth low energy module
BGScript iBeacon example code for the BGM111 Bluetooth low energy module

References:

Developing Beacons with Bluetooth Low Energy (BLE) Technology

Beacons: Everything you need to know

Reading “Getting Started with Bluetooth Low Energy by Kevin Townsend, Carles Cufí, Akiba, and Robert Davidson (O’Reilly)” is advisable for anyone like to know more about who BLE works which is a corner stone to understand how beacons work.

OpenCellular – An Open Source Wireless Access Platform From Facebook

Promised projects from Google and Facebook may change our world connectivity. We saw previously Loon project from Google and the Internet drone Aquila from Facebook.

Facebook this time is trying to find a general solution to improve the connectivity infrastructure. The project called OpenCellular.

This new project is a software-defined wireless access platform, and this gives it the ability to support everything from 2G to LTE networks.

opncel_ap

The system consists of general-purpose and base-band computing subsystem with integrated power and housekeeping system and a RF with integrated analog front-end. According to the announcement, Facebook plans to open-source the hardware designs to public, along with necessary firmware and control software.

OpenCellular designed to have various power sources: PoE (power-over-ethernet), solar, DC, and external batteries and internal battery (lithium-ion).

opencel_DB

The problem which Facebook try to solve in this new project is to extend network access in both rural and developed communities. The ecosystem cellular networks still constrained, where the infrastructure is very expensive, making it difficult to deploy it everywhere and for smaller organizations or individuals.

opencel_HW

OpenCellular still under lab tests; “we are able to send and receive SMS messages, make voice calls, and use basic data connectivity using 2G implementation on our platform.” according to the announcement.

Via: Facebook

5 Tips on designing RF PCBs

Michael Ossmann shared some of his practical experience and insights in designing RF PCBs, Michael designed a lot of RF PCBs like HackRF One, which is an open source SDR (Software Defined Radio) platform.

Michael tips don’t include talking about Smith charts, Q factor, S parameters …etc which need a lot of academic knowledge, instead we will take “the simple way” as he said in his presentation.

The presentation consists of three parts: 5 rules for RF circuit design, some examples from Michael’s boards and how to select the components for the RF circuit design.

Michael tipped us with his 5 rules for RF circuit design:five_rules

Rule One: Use Four Layers

It’s not obligatory to use 4 layers in RF design, “you can do 2-layer design but you better start reading” Michael said.  if you don’t like to do an advanced RF study of your circuit, then use 4-layer design and follow the signal stack below.

rule1

Rule Two: Use Integrated Components

Always try to find an integrated component that meets your application. for example, use transceiver ICs like: CC2650, CC1310, ADF7242, AT88RF215, nRF24L01+… etc.
Also use passive components like filters in a shape of integrated component which is much easier than design a discrete one.

Rule Three: Use 50 ohm everywhere

The reason to use 50 ohm is to do impedance matching. This include microstrip impedance calculation to know it’s resistance and Michael showed us how to calculate that using online tools.

Rule Four: Follow The Manufacturer recommendations

Some times, the manufacturer will provide you with a reference circuit to match the impedance of output to 50 ohms, just follow this circuit!

rule4

Rule Five: Route RF First

Keep RF traces short and direct and keep other signals away from RF.

Via: hackaday

Inverter crystal oscillator

figure2-600x463

Vasily Ivanenko build some discrete chip oscillators with 74HC series logic gates and tests them on his oscilloscope. He writes:

In numerous RF synthesizer chips lies an inverter with input and output pins for making a reference crystal oscillator clock. I built some discrete chip inverter xtal oscillators with 74HC series logic gates to better examine them. You’ll quickly recognize the oft-used Pierce oscillator topology with 1 trimmer capacitor to tweak the fundamental frequency which might vary from factors like crystal aging and gate, crystal, crystal holder + board reactances. I determined the 27 pF and trimmer cap values through experiments and measures.

Inverter crystal oscillator – [Link]

VXO – based PLL frequency synthesizer for 7 MHz

vxo1-600

Vasily Ivanenko made a VXO-based synthesizer:

To make a VXO to mix with a ~7 MHz VCO, you’ll need a crystal that is higher in frequency than the highest frequency you want to synthesize. Some rummaging revealed a bag of 21.4773 MHz crystals that I could divide by 3 to garner 7.159 MHz.
To afford a reasonable delta F, three were placed in the super VXO fashion and I applied the smallest amount of series inductance that would ensure a reasonable delta F with solid frequency stability.

VXO – based PLL frequency synthesizer for 7 MHz – [Link]