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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.

15
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6answers
3k views

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 ...
6
votes
3answers
8k views

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 ...
9
votes
2answers
6k views

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: $$C=B \cdot log_2(1 + S/N)\text{ bits/sec}$$ ...
28
votes
4answers
4k views

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 ...
5
votes
3answers
2k views

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, ...
77
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11answers
13k views

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'...
12
votes
1answer
2k views

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 ...
14
votes
1answer
29k views

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 ...
4
votes
3answers
27k views

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 ...
25
votes
3answers
3k views

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 ...
22
votes
1answer
13k views

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 ...
12
votes
2answers
6k views

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 ...
8
votes
3answers
2k views

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 ...
5
votes
6answers
8k views

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-...
0
votes
3answers
775 views

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 ...
10
votes
2answers
1k views

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 ...
8
votes
5answers
3k views

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 ...
3
votes
1answer
794 views

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 ...
37
votes
7answers
66k views

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 ...
7
votes
2answers
2k views

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 ...
5
votes
1answer
2k views

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 ...
0
votes
2answers
303 views

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. ...
12
votes
6answers
2k views

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 ...
7
votes
1answer
2k views

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 ...
6
votes
4answers
9k views

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 ...
6
votes
2answers
1k views

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 ...
5
votes
1answer
662 views

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 ...
1
vote
3answers
853 views

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 ...
5
votes
3answers
804 views

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 ...
5
votes
3answers
2k views

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 ...
2
votes
1answer
450 views

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 ...
1
vote
2answers
450 views

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 ...
1
vote
1answer
724 views

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 ...
0
votes
1answer
475 views

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 ...
0
votes
1answer
901 views

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 &...
0
votes
1answer
1k views

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 ...
0
votes
2answers
175 views

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 ...
61
votes
5answers
12k views

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 ...
25
votes
4answers
5k views

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,...
25
votes
3answers
2k views

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. ...
20
votes
8answers
13k views

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 ...
11
votes
4answers
3k views

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 ...
15
votes
3answers
4k views

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 ...
10
votes
4answers
30k views

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 ... ...
8
votes
3answers
3k views

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/...
5
votes
4answers
7k views

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 ...
5
votes
4answers
4k views

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 ...
5
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7answers
20k views

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 ...
16
votes
2answers
13k views

Why do my speakers make a noise when my cell phone gets a call? [duplicate]

It's a very common sound but I've never thought to question why it happens.
12
votes
3answers
9k views

What is a PA/LNA?

I saw a comparison of two similar radio receiver modules. They used the same IC, but one had a greater range due to the inclusion of a "PA/LNA" which I understand to be an abbreviation for "Power Amp /...