# 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.

162 questions
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### RF Energy Harvesting

Why can energy invested in RF radiation not be harvested fully? What are the main factors that affect this? Is there any significant research nowadays that fully describes this process? I stand on the ...
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### Long range (~15 km) low baud-rate wireless communication in a mountain environment (no LOS)

I'm trying to implement a point-to-point communication system in a mountainous environment where the base station and the client are at least 15 km apart, without any line of sight (LOS). The ...
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### Why is channel capacity a factor of bandwidth instead of frequency?

I'm trying to understand the concept of capacity for a wireless channel. Some help would be appreciated. For a AWGN channel capacity is calculated as: $$C=B \cdot log_2(1 + S/N)\text{ bits/sec}$$ ...
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### Why do characteristic impedances matter only when traces are longer than half a wavelength?

Why are characteristic impedances of traces not considered when the traces are shorter than half a wavelength? I've had the same issue with light diffraction, which happens when pinholes are smaller ...
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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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### What's the cheapest way to link a few microcontrollers wirelessly at low speeds over short distances

What's the cheapest way to link a few microcontrollers wirelessly at low speeds over short distances. I'm looking to keep it ultra-cheap, use common discrete parts and keep it physically small. I don'...
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### How can this FM transmitter modulate?

simulate this circuit – Schematic created using CircuitLab This is a minimalist FM transmitter I've found from http://www.talkingelectronics.com/projects/Spy%20Circuits/SpyCircuits-1.html I'm ...
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### How can I tell if an RF transmitter is transmitting?

In my project, I use a use an RF Transmitter and Receiver. One of the RF components seemed to fail because the connection between my Arduinos no longer works. I cannot determine whether the RF ...
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### How to connect 20 wireless sensors in one receiver with arduino?

I live in a house with many doors and windows and I plan - as an easy project - to be able to detect and see which door/window is open using simple leds. What I do not want to do is to have 2 or 3 ...
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### FCC and CE Testing / Failure Resolution

I'm seriously thinking about (practically committed to) taking one of my products through FCC and EC testing and it's my first time doing so. It's Arduino based electronics running off a 16MHz crystal ...
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### Ferrite or iron powder? How do I tell what an unknown core is made of?

Most times when I need a small inductor, I try to find the necessary core in my junk box. Depending on what I'm trying to build (RF, power, ...), a ferrite core or an iron powder core might be the ...
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### What is the standing wave ratio (SWR)?

In rf electronics, we often characterize a component or antenna by its standing wave ratio (SWR). What is the definition of this parameter and how does it affect a circuit? The motivation for this ...
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### Smith Chart Explanation

I'm working on designing some hopefully simple RF (912 MHz) attenuators. I need a few different levels of attenuation but each different attenuator can be fixed. I have prototyped one using just off ...
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### Very high speed counter (around 1.5 GHz to 2 GHz)

I am thinking of a device that can measure the distance of an object from a sensor using a radio transmitter and receiver pair. I'm thinking of using a counter at the sensor side, with a fixed-...
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### Suggestions for a Point-to-Point reliable Wireless Communication Module

I've to implement a wireless communication system. Details are as follows. Range is about 600m Point-to-point communication No LoS is available. (but not highly obstructed) Won't need much higher ...
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### What does this symbol in the schematic represent?

I know the symbol at the bottom is ground, but I can't get what the other symbol is. It can be a single symbol of two arrows pointing at each other, or two symbols each one a arrow. I also have the ...
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### Why does holding my car's RF remote to my head extend its range?

I'm in my parking lot and just a little too far from my car for the remote to work... But if I hold the remote up to my chin, and then suddenly it works. It sounds dumb until you try it, but it ...
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### Would an RF amplifier be required for an indoors antenna connected via coaxial cable to an outdoor directional antenna (900/1800 MHz)

Sorry, couldn't make the question title any shorter without losing meaning. So, I'm looking to build an outdoors yagi antenna that's connected to another indoors antenna via coaxial cable. The ...
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### What do I need for a basic RF circuit?

I'm looking for any resource that can help me build a very very basic RC circuit. I'm talking as simple as using RF to turn on/off an LED. The purpose of this circuit is for research and education. If ...
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### What connector is similar to U.FL but has no pin?

I am trying to identify this connector style: Look at the two RF micro-coax connectors on the left, just next to the PCB antennas. They look identical to U.FL or IPEX but have no central pin. What ...
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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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### Why is this Arduino RF Receiver changing value back and forth so much?

So I have a 315Mhz receiver hooked up to an Arduino, and constantly printing the value of the A0 Analog in pin over to the Serial Plotter that is built in to the Arduino software. This is the graph. ...
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### Simulate bad cell phone reception in the lab

I'm currently developing an internet of things device that utilizes a uBlox SARA-U260 gsm/3G modem. In field testing, we have had significant software/firmware issues due to poor cell phone reception ...
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### 50Ω Impedance Matching with Signals Through Vias

I'm working on an IoT board and it is all laid out (LTE, GPS, BLE, WIFI - 30mm x 30mm -- VERY TIGHT). As a design concession, I have to use vias to route some of the RF signals. There's no other way ...
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### Driving an LED/Laser diode with a RF signal up to 20 MHz

I'm trying to design a circuit that will let me drive an LED or Diode laser with a RF signal up to ~20 MHz or so. Since the optical device will need to be biased with a DC current, a bias -t is a ...
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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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### 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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### How to use the same antenna to receive and transmit on the same frequency with an SDR [Half-Duplex]?

Considering that the SDR board has one TX/RX output/input and one RX input, I am wondering how could I use one antenna for a half duplex communications on the same frequency. The idea is to use the ...
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### Method required to enable a toy “vehicle” to follow a “target” wirelessly?

I am trying to create a small robot toy car with the ability to follow a person around, with a range of about 50 m. Ideally the person will be provided with a small transmitter of some kind, and the ...
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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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### Wireless water level sensor, in sump. Installation best-practices for longivity

My wireless water-level sensor is working fine, and when deployed in the sump-well, it is giving me periodic readings quite well. At this stage, I have the circuit still on a breadboard, and now plan ...
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### Shared antenna on multiple 2.4Ghz receivers

I want to use several 2.4 Ghz transcievers (not sure which IC yet, either Atmel AT86RF*** or TI CC) in order to build a simultaneous multi-channel sniffer. The transciever output is differential. I am ...
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### Should there be more clearance on RF vias with microstrip?

I'm routing an RF board ( above 1 Ghz) with microstrip lines. Our plan is to feed it from the backside, take it through the via onto the top layer and continue routing. as part of our rules we pull ...
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### Radiation Resistance of a Straight Wire Antenna

I am new to antenna theory, and I have been reading up on antenna properties to create my own antenna. I want to use a piece of copper wire, maybe around 18 gauge, as a monopole antenna, but it will ...
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### Any Way of Converting Several 2-Port S-Parameters Measurement to 4-Port S-Parameters

I have a bi-driectional coupler and attenuator (att) in which I would like to capture its s-parameters: So I measured 2-port s-parameters between ports 1 & 2, 1 & 3, 1 & 4, 2 & 3, 2 &...
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### Connect SMA to a regular pin/wire

I have an RF signal (5ns pulses every 200ns) coming out from a SMA connector on FPGA board (Spartan 3E Starter Kit). I want to send this signal back to the FPGA using one of the on-board pins. So, I ...
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### Maintaining constant gain through impedance coupling

Para_1 The following discussion is about type of coupling involved to couple rf amplifier with the mixer. The coupling involved is impedance coupling in which Lm provides a shared mutual impedance ...
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### What is impedance?

This is presented as both a resource for the community and a learning experience for myself. I have just enough knowledge of the subject to get myself into trouble, but I don't have the best grasp of ...
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### At what frequencies does PCB design get tricky?

I have designed many mixed-signal PCB's where the highest-frequency component is the microcontroller's crystal oscillator itself. I understand the standard best practices: short traces, ground planes,...
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### What happens at the end of a transmission line?

Let's say I wanted to make a widget containing a relay to switch between two antennas. There is a coax transmission line coming in from the transmitter, and two going out, each to a separate antenna. ...
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### Cheapest way to add wifi to a project [duplicate]

I need low power wifi for a not-very-data-intensive application. What modules or chipsets should I look at? Other than low cost and low power, I have no restrictions. The cheaper the better. This ...
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### What's the best/easiest way to measure an unkown inductance without an RLC meter?

Is there a decent way to measure inductance accurately using an oscope and a function generator? The best method I can find is to build a tank circuit and sweep the frequency until the highest voltage ...
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### How can over 24 GHz communication be possible?

I read the article Google wants the US' wireless spectrum for balloon-based Internet. It says to use over 24 GHz frequency spectrum for communication. Is it ever possible to generate that high ...
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### How exactly are radio waves produced from a current in a circuit itself?

I am 17, and I am new to electronics, and I've learned everything online and expect to continue to do so with all the resources. I have dug around and can't find concise answers on this question ... ...
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### Low-power wireless module strategy

I'm designing low-power sensor modules which will be spread over a reasonably small area. The modules are all battery powered and should operate for a decently long time without having to recharge/...
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### Measuring output impedance

Given I have designed and produced an RF circuit with an output for connecting an antenna. I know this antenna has an input impedance of 50Ω. I now wish to measure the actual output impedance of my ...
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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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### 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 ...