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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.

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11answers
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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'...
61
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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 ...
42
votes
2answers
3k views

What is wrong with my 50 Ω grounded coplanar waveguide?

I've been working on a 4-layer design built around the EFR32BG13 Bluetooth Low Energy SoC. While trying to measure the impedance of the antenna to build a matching circuit, I discovered that my short ...
41
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8answers
9k views

Can a radio transmitter somehow detect the number of receivers in its area?

During conversation, a colleague proposed that over-the-air television and radio broadcasters can determine the number of viewers or listeners based on the "load" on their signal. This seems to me ...
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 ...
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 ...
27
votes
5answers
16k views

How come radio signals don't interfere with each other all the time?

I'm a newbie on wireless technologies and I'm trying to understand how they work. One thing I don't understand is this: How come transmissions from different devices don't interfere with each other ...
26
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5answers
4k views

Why do some EMI/RF shields have holes on the top and some don't?

I am not talking about cutouts for tall components. I don't think they are for ventilation as they are often covered with manufacturer labels.
26
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5answers
3k views

Can I build a camera that is sensitive at 2.4GHz?

I want to build a camera obscura as an art project that produces photos of WiFi signals. The idea for now is to build a 125cm x 125cm x 125cm Faraday cage (using fine copper mesh) with a centered hole ...
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 ...
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
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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. ...
24
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5answers
9k views

How could have Banksy kept an RF receiver running for 12 years? [closed]

I'm talking about Banksy's "Girl with balloon" painting that shredded itself at auction. I think the general consensus is that he didn't, and that it was set up before the auction (or a couple years ...
24
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8answers
20k views

What is a 50-ohm antenna? How would you make one?

This is an intentionally very open ended question. What does it mean for an antenna to be a 50-ohm antenna at some frequency? How do you make a 50-ohm antenna for say 433.92MHz? What are the options? ...
24
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3answers
2k views

Why is the reflector on this millimeter-wave antenna spinning?

The WIRED YouTube video Inside Facebook's Quest to Beam the Internet Via Solar Drone and article Inside Facebook’s First Efforts to Rain Internet from the Sky show a dish antenna (starting after 02:00)...
22
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3answers
2k views

Why solder mask are not applied to RF PCBs

I've gone through some of the RF PCB designs. In which solder masking on the traces are not present. Like this one Is there a specific reason or performance issue to remove that?
21
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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 ...
20
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5answers
2k views

How do low price toys implement RF communication

I have seen toy remote controlled cars and other toys available for real low prices. How do they implement RF communication? I mean to say when I search for RF units to buy they come at a pretty high ...
20
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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 ...
19
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4answers
4k views

What does the rectifier do in a crystal radio?

I have been reading up on semiconductors and all of the references that I have found say that the first practical application of the semiconductor diode was in crystal radios, and that semiconductor-...
18
votes
7answers
4k views

Why are RF components and cables still so large?

With the advent of ICs in past decades, circuits have decreased in size exponentially over time. However, it appears RF components and connections, with coax SMA cable, connectors, and components, ...
17
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4answers
4k views

Why are there so many vias on this board?

I was looking at the MMZ09312BT1 development board layout, and I was curious about all the holes they have on the board. Are these vias? What is their purpose (I heard somewhere that they are meant as ...
16
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6answers
69k views

Why do higher frequency waves have better penetration?

In free space, lower frequency signals seems to go farther because the signal is either diffracted by the ground or reflected by the upper atmospheric layers, making it actually go farther. In urban ...
16
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10answers
5k views

Schematics for a simple radio transmitter that can be built only with passive components?

Fantasized in some of the survivalist, post-catastrophic novels, movies or docudramas is the radio built only with handcrafted or scraped components. Beyond the popular appeal of this stories, I ...
16
votes
3answers
6k views

Is there a RF viewer like a thermo camera?

So I know thermo cameras are sold. Police/Fire use them all the time. You point your little hand held black box at a bush and you can see if there is a creature living in there or at a burn zone and ...
16
votes
3answers
12k views

Why is 433 MHz used widely in RF modules?

I was planning to interface an RF module to my PIC16F877A microcontroller and was exploring the web. I came across many modules which use 433 MHz as the standard frequency. Why is it so? Can't we ...
16
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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.
16
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5answers
43k views

433MHz quarter-wave length antenna: longer is better?

I am trying to conduct an RF project using XY-MK-5V / XY-FS modules: link here My problem is that even though most blogs and Google searches for these modules use a quarter-wave length antenna (...
16
votes
1answer
2k views

Analyze My Homebrew Diplexer

I'm in need of a diplexer that'll separate RF signals from a single feedline to two antennas. What I designed and built was a diplexer that would allow ~38 Mhz and below out port 1, with ~38 MHz and ...
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 ...
15
votes
4answers
30k views

Why the conversion to Intermediate Frequency?

While studying about various communication systems (Superheterodyne receivers and Television receivers, to name a few) I often come across blocks that convert RF signals to Intermediate Frequency (IF) ...
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 ...
15
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3answers
5k views

How does RF anti-jam technology work?

I'm pretty certain that RF jammers work by overpowering the target signal with their own higher powered signal at the same frequency. So the question is, how does anti-jammer technology negate the ...
15
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2answers
457 views

Could a copper RF cavity like this be reasonably expected to have a Q > 7000?

The paper Measurement of Impulsive Thrust from a Closed Radio-Frequency Cavity in Vacuum (H. White et al, J. Propulsion & Power, November, 2016, http://dx.doi.org/10.2514/1.B36120) refers to an ...
15
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2answers
4k views

Can I solder a RG316 coax directly to a PCB instead of using the intended SMA connectors?

I have a length of RG-316 single shield 50Ω coaxial cable carrying a 5.8 GHz signal that I need to connect to a PCB. While cheap relative to most coaxial connectors, SMA connectors are still quite ...
15
votes
6answers
11k views

Free RF Simulation Software

What free tools are there to simulate RF circuits?
14
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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 ...
13
votes
2answers
3k views

Why do only high-end phones support a lot of LTE bands?

Most lower and middle end phone only support 3/4 LTE bands. High end phones, like the iPhone, or flagships from Samsung and LG also support a lot of bands. iPhone 7: 1, 2, 3, 4, 5, 7, 8, 12, 13, 17, ...
13
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4answers
3k views

How is it possible to have a 5W transmitter driving 50 ohms with a 12V supply?

So let's say you have a circuit, which generates a carrier wave at some frequency (let's say 27MHz) and it's connected to a 50 ohm dummy load (which I gather is equivalent to an antenna for circuit ...
13
votes
5answers
6k views

Antennas and Ground Planes

I'm looking at this datasheet for the ANT-433-HETH antenna. In the box labeled "Suggested Board Layout" I see a dimension labeled "Minimum Distance to Ground Plane" of 0.5 inches. I always thought ...
13
votes
4answers
984 views

Eliminating mains hum from frequency modulated RF LC oscillators

I'm trying to build a frequency modulated LC oscillator but all circuits I've tried have terrible mains hum after demodultaion. The oscillator is tuned by capacitive sensor but I'm using a fixed ...
13
votes
1answer
3k views

GPS Design Review (RF Input)

I've designed a PCB in Eagle to host a GPS Receiver module and a GPS patch antenna. The RF input to the module is specified as a 50Ω unbalanced (coaxial) RF input. I used this calculator to calculate ...
13
votes
1answer
1k views

Need help with selecting an antenna for PCB

I have designed a pair of circuits which utilize the QAM-TX2-433/QAM-RX2-433 transmitter/receiver. So far everything is hooked up on solderless breadboards, with just a length of wire for antennas. ...
13
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1answer
1k views

Is it possible to reject noise traveling on the outside of a coaxial transmission line?

Say I have some ordinary coax between a receiver and an antenna. That coax will have three currents in it: the desired signal an exactly equal an opposite current on the inside of the shield (really, ...
12
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5answers
3k views

Forgot to put a via near bypass capacitor, and now the boards have been fab'd - what can I do?

I goofed and didn't notice this until the board was already fab'd and assembled. The board is an RF amplifier; the portion I have pictured is a part of the DC control pat (so no RF is nearby but we're ...
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 ...
12
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2answers
2k views

Should each trace carrying RF be 50Ohm in characteristic impedance? How?

I have to translate a VHF (160MHz) receiver schematic into a PCB. After looking here and there, I am a bit confused. It seems like the main issues with RF are to avoid stray inductors and ...
12
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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 /...
12
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2answers
1k views

How does the plastic-tube inductor in this wireless transmitter work?

This single layer PCB (solder side shown here) is from an old fan remote: The inductor in the plastic tube is not connected physically to any components; however, the two loops of wire surrounding it ...
12
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3answers
2k views

How much power do I need to transmit a radio signal through a solid ice crust 100 km thick?

Imagine I put a floating probe inside the subglacial ocean of Encelado or Europa: how much power should my radio have to be able to communicate from external surface with the probe? Or, in different ...