Questions tagged [rf]

Short for Radio-Frequency. Frequencies at which radiation (intentional or not) plays a role. Typically associated with wireless communications, but also relevant for high-speed PCB design.

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When has to be used a ferrite bead in power supply?

I'm designing a PCB with a Telit GL865 GSM/GPRS module. I find this example in Internet and I am wondering why has it got a ferrite bead on 3.3V power supply line. Some extre values from datasheet: ...
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How does a low power device make a direct uplink to iridium satellite?

I was always fascinated by this idea. You are literally able to communicate or open a web browser from anywhere in the world. I am OK with the low power device able to receive data from satellites, ...
6
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1answer
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Impedance matching with only capacitors?

I need to do impedance matching for 33 + j32 ohm source and 16.5 + j0 ohm load. The copper traces adds 99 ohm impedance and 20 degree electrical length. According to smith Chart below, I need to use ...
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Choosing capacitors for Microwave RF application

I've recently been given a project to lay out some PCBs which will contain a few Mini-Circuits RF amplifiers, and their associated biasing components. However, since I need to have several stages of ...
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1answer
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What makes an “rf transistor” different from an ordinary transistor?

I have been looking at various types of transistors that can switch at higher speeds than my clunky but powerful IGBT, and I came across these things called "rf transistors" or "rf mosfets" which can ...
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Is the wrong antenna worse than no antenna?

I have a wireless transceiver. It is programmable to allow both transmit and receive from 1-1000MHz with FSK or ASK. The PCB and components have been chosen for transmission at 433MHz. Another PCB ...
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419 views

Can I run custom firmware on a pre-certified RF module without needing to redo full FCC certification?

I need BLE connectivity in a product, so to save costs on FCC certification, Bluetooth SIG membership, etc. it will use a pre-certified module for this purpose. Usually such modules work in one or ...
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How “pinless” moisture meters work?

I see that there are "pinless" moisture meters on the market, e.g., http://www.omega.com/pptst/HHMM257.html that look like this My understanding is that they measure the amount of reflected RF. ...
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Are there any differences between clamp, twist-on, and crimp coax connectors outside of cost and ease of assembly?

I have recently started working with software-defined radio, and have replaced some connectors on RG-58 coax in preference to using multiple adapters. RG-58 BNC connectors seem to come in three ...
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Chip antenna layout

I am trying to integrate a chip antenna but I'm unable to understand the layout guidelines in the application note. Can any RF experts comment on what this actually means for the PCB layout - is the ...
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How can I make a diy anechoic chamber?

I'd like to make a small anechoic box for RF measurements. I need roughly a 30x30x30cm cube of usable space, and I'd like the reflections from the walls to be attenuated by 10dB or more from 100MHz ...
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197 views

Why does EM radiation travel much further than the magnetic field of an equivalent power electromagnet?

If both fall of as 1/r^2 from the source then why can radio waves travel around the world and still be picked up easily at the right frequency but the field from a powerful electromagnet can not?
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How to minimize characteristic impedance mismatches caused by vias?

This question springs from an answer here. When using stripline configurations for rf signalling, the conductors are routed on an inner layer of the pcb, sandwiched between two ground planes. I ...
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1answer
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Trifilar Transformer Common-Mode Rejection Circuit (Signal Recovery, Hybrid Combiner, RF)

I'm trying to develop a circuit that allows me to effectively subtract two different sources of RF noise from a single signal at the same time. I am planning to use something called a "trifilar" ...
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2answers
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transmit data wirelessly under water?

I am looking into constructing a small submarine with a Raspberry Pi. This is just for a hobby project but my idea is to have it communicate with the surface wirelessly. I know that normal radio waves ...
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1answer
459 views

Help with Matching circuit

I'm using a SAW filter which has balanced input and output. In the datasheet there is shown a matching application for 50ohms balanced output. But plotting the S22 parameters into a Smith Chart and ...
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1answer
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GSM/GPRS antenna noise depending on cable length and position

A board I designed has a noise problem that is caused by an onboard GSM/GPRS module (the Quectel M66 [1]). This module is connected to a Siretta Delta 2C [2] dipole antenna via 20cm coax cable. The ...
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3answers
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Does a 40 MHz radio frequency have any interference to Bluetooth signal?

From my understanding, the Bluetooth signal is using a 2.4 GHz frequency. However, when someone is playing with a 40 MHz RC vehicle, the Bluetooth signal keep on getting interrupted or disconnected. ...
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Does putting a car remote on your chin make it more effective? [duplicate]

Recently asked on Physics.SE: Why does a remote car key work when held to your head/body? And also, similar claims abound. RF engineers know that putting a big conductive thing like a human head ...
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What is the best way to debug a radio?

I am currently programming / configuring an Atmel AT86RF233 radio and trying to get it to communicate with an digi xbee. So far I have set the following fields on the Atmel radio: extended address ...
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What are these metal plates covering parts of PCBs called?

I am trying to fix my wireless router, but one of the parts is under a metal plate. What are these metal plates called? This is what it looks like when it is removed: (The gold coloured plating ...
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Advice on cleaning up 5VDC from a wall-wart

Assumption: I think it's generally true that commercially available AC/DC wall-worts can be expected to be pretty noisy (e.g. you can't count on much better than 5% stability). Background: I'm ...
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How does sender and receiver clock time periods synchronize in data communication?

In asynchronous data communication, Initiation of data communication between two stations(sender and receiver) involves synchronizing their clocks to ensure both stations are agreed upon same bit ...
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simplest FM radio receiver?

As per this building simple radio it is the simplest AM radio receiver. obviously this is very poor AM receiver.(but it was working for someone in comment) I'm wondering what will happen when this ...
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207 views

Why does microwave test equipment use N connectors?

Almost all of the microwave test equipment I've ever seen and used has N connectors, with exception of some scopes that use either custom fancy BNCs (keysight does/used to do this)) or SMA. ...
5
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486 views

40 GHz spectrum analyzer with N-type coax input?

We have an old Rohde & Schwarz FSEK 30 that is advertised as having a range from 20 Hz to 40 GHz, with an N-type input connector. My conundrum is that a type-N connector with air dielectric ...
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Best way to send sensor readings over simple RF connection

I have bought a pair of simple 315MHz TX/RX modules. I want to use these to connect a battery powered ATTiny85 to an Arduino base station. The ATTiny needs to regularly wake up and send a sensor ...
5
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2answers
938 views

MCU clock drift and radio frequency drift - are they the same?

Let's assume that I have two sensor nodes, one with crystal oscillator running at 24 MHz frequency, the other at 24 MHz + 10 ppm frequency. To my understanding, in system-on-chip (for example, Texas ...
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3answers
852 views

Is antenna length for a baseband signal infinity?

I am studying RF communications and learned that antenna length is proportional to a wavelength of a signal. And many literature say that a high frequency is preferred in wireless communication ...
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427 views

What is the purpose of diodes after RF power amplifier and before LPF?

I am planning to build an RF transmitter using an integrated PA module (RA30H1317M1). While studying schematics of similar transceivers, for example IC-2200H (that also has a PA module) I see all ...
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Buying RF metal shields [closed]

Where can I find those metal shield cans that you can solder directly on a pcb for EMI shielding? Just like the ones on the back of XBee modules? I'm not having any luck searching on farnell, perhaps ...
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348 views

How does this coupler work?

I've bought a few 50MHz-6GHz directional couplers (SEDC-10-63+,) each for 75$. Here is a picture of this expensive coupler: Unfortunately one of these couplers was not working from the beginning so I ...
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Insight into cavity resonators

Modes of a waveguide As shown in the link above, they show how these modes work for various values of m, n, and p. However, where is the antenna/ source of radiation placed within the cavity? From ...
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How come esp8266 is able to generate 2.4 GHz wifi signals

I am wondering how it is possible to generate 2.4 GHz, if its core clock frequency is much lower than GHz scale.
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How to know (or estimate) the range of a transceiver?

I'm trying to decide between different wireless transceivers, where my main requirement is furthest range for a given frequency band. Is there a way to relate the frequency, data rate, power output, ...
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Non-metal cases

This question is really aimed at computer cases, but I suppose it also applies to other PCB cases. Most of the Computer cases I come across are aluminium, or else some other metal; As I understand it ...
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373 views

Strange-looking FM transmitter circuit

I found this simple FM transmitter circuit: I built it an it works rather nicely. There are many simple FM transmitter circuits on Google, most of which look basically like this: These work by ...
5
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1answer
210 views

Why do spectrum analyzers generate X-Rays

Most, if not all, old HP spectrum analyzers say X-Rays generated in this intsr are sufficiently screened Why do they generate x-rays at all. The HP 8565E I am looking at can only measure up to 50 ...
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1answer
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Why do cables that carry RF have 2 leads

I just got a ham radio license, and I am trying to figure out the mystery of RF. From the output on your transceiver to an antenna or an RF amp, there is a 2 lead coax cable. If antennas only have ...
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267 views

Visual understanding of EM fields within a rectangular metal container

I have the following scenario setup inside a rectangular metal container. The container size is 12.03m by 2.39m by 1.84m (lxbxh). Additionally, inside the container I have placed 4 antennas equally ...
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451 views

RFID protective case metal selection

There are various RFID tags that are designed to work in close proximity to metal but generally they hope for free space or at least limited loading in close proximity. As a work around for RFID tag ...
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666 views

Why put vias underneath an IC?

Several designs I've seen have a load of vias underneath high frequency or analog ICs. For instance, this is a part of a PCB design for a DDS unit: Design from http://rudius.net/oz2m/ngnb/dds.htm ...
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894 views

Robot following you; what's the best way?

I built a human-sized robot that can follow anyone wearing an IR beacon. It works quite well indoors and it's quite precise, but outdoors it is completely blind due to sunlight infrared. I have a ...
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What type of antenna does the Xbox One controller use and how can you disable it?

I recently cracked open an Xbox One controller, the impetus for doing so was two-fold: First and foremost the engineer in me likes to see how things work under the hood as I learn a great deal that ...
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Does an RF receiver constantly consume power?

I'm building a battery operated robotic arm and would like to use a cheap, short distance RF transmitter/receiver kit to trigger it. However I would like to know whether the receiver will constantly ...
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How do arcs generate radio-frequency

When I have an electric arc, and put an AM radio nearby, I hear a crackle and the station that I previously heard goes away. I am wondering what is going on with the electricity through the air to ...
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100W Low Pass Filter

Currently I have a 60W amplifier for the 400-500MHZ band with a 50Ω impedance. In order to prevent jamming other frequencies I will need a low pass filter to block any frequencies above 500MHZ. I just ...
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Similar books to “High Speed Digital Design: A Handbook of Black Magic”

I am really enjoying reading this book, "High Speed Digital Design: A Handbook of Black Magic", in particular the more in-depth material covered than in undergrad courses and the practical approach ...
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Characteristic impedance of a trace

I'm trying design a video transmitter around an 5.8GHz Airwave module. The documentation says the trace to the antenna must have a characteristic impedance of 50 ohms. How do I calculate the ...
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4answers
616 views

Why should a receiving antenna be impedance matched to 50 ohm instead of a lower impedance?

I'm in the process of getting to grips with RF design and am having some trouble understanding why we should always match antennas to \$50\Omega\$. I understand from the maximum power transfer ...

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