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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991 views

NRF24L01 presence detection

I have adapted my RF73/RFM73 library for the NRF24L01. These chips are almost identical, except that the RFM73 has a second bank of registers that must be initialized with some magical values. The ...
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1answer
4k views

RF Via fences/stitching spacing

I'm working on a 4-layer PCB with a U-Blox module and I'm trying to calculate the space between the fencing vias next to the Antenna trace and for the stitching vias. According to the datasheet we ...
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What is the output impedance of HF power amplifiers?

In case it matters, let's discuss solid-state, linear, class AB amplifiers operating below 50 MHz and on the order of 100 W. Here's my confusion: I'd think ideally, the output impedance of the ...
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1answer
752 views

MIPI RFFE software implementation

I'm currently trying to implement the MIPI RFFE (As master) protocol on a simple AVR microcontroller, the specs says that the clock frequency can go down to 32 kHz, so I guess this it should be ...
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605 views

Industry standard measure for coaxial cable stiffness?

Is there an industry standard measure for coaxial cable stiffness? By stiffness I mean the spring force experienced when bending or deforming the cable. In my search for a highly flexible lab test ...
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1answer
263 views

ISM band rules for spread-spectrum: how much do I need to spread?

I'm doing a preliminary study for a 5.8 GHz ISM band data downlink for a cube satellite. I know that spread-spectrum is mandatory for ISM, but the FCC rules seem pretty opaque on how much I need to ...
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3answers
842 views

How can I Amplitude Modulate this?

I recently built this circuit, and could hear a nice full quieting signal on my short-wave radio with a 7.2 megahertz crystal for the 40 meter band. What is the simplest way I could Amplitude ...
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1answer
787 views

Design of cavity filter

I try to design a Chebyshev bandpass filter for 6 GHz as a coaxial cavity filter. I know that the filter can be designed with the aid of the coupling coefficients between the resonators and the loaded ...
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High frequency signal using low frequency micro-controller

How do micro-controllers running at slow clock frequency (under 100 MHz) produce high frequency radio signal (2.4 GHz for example)? For example - ESP8266 runs on a clock speed of 80 MHz but is capable ...
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Can I run 125kHz RF circuit on a breadboard?

I was wondering if making a low frequency RF circuit on a breadboard is viable.
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Is the meaning of a Decibel different when applied to Voltage vs Watts?

If I have an amplifier that provides +3dB, or an attenuator that provides -20dB, then how do I know if that applies to Voltage or power? In other words, if I have a 0dBV signal and I run it though a +...
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What happens when you keep increasing frequency of an RF signal?

I know that radio waves occupy the lowest portion of the EM spectrum and gamma rays occupy the highest. I'd like to know if increasing the frequency of a radio wave can produce visible light and maybe ...
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The reason for using air coils in LC tank circuits

I noticed that in LC tank circuit designs very often people use air coils as the L element as opposed to an axial inductor. I understand that the problem with the axial ones is that they tend to self-...
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RF design stitching vias

Having no past experience on RF design I have recently been taught that placing stitching vias is a good practice. Reading the "definition" of stitching vias I am not sure that I can distinguish ...
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North American Regulations on 433MHz Radio

I'm considering the RFM69HCW 433MHz transceiver radio for use in some RFID-based equipment that we make in low volume. The RFM69HCW is available in 868MHz or 915Mhz as well but those frequencies are ...
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3answers
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How to measure EMI without special equipment?

I have bought a cheap dashcam to play with, only to discover that my GPS receiver stops working when it's on. After I ruled out power supply issues (both devices have batteries), I'm left with a ...
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3answers
604 views

Is information lost when you downconvert an RF frequency?

I am trying to work out what happens when you downconvert an RF signal, such as what happens in an SDR device when tuning to a given frequency. For example if a device using a Zero-IF is tuned to ...
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4answers
10k 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 ...
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2answers
454 views

What does the wifi amplifier exactly amplify?

The question is not exactly about the wifi, but on how does this operate in full duplex, in principle? As an practical example, lets take some commercial amplifier. As we can see from the picture, it ...
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2k views

How did my TV capture neighbour's DVD player's frequency?

The question might be quite confusing since I'm totally new to electronics world. When I was in school, I had a TV that required a TV Antenna to capture free air channels. So one day when I was just ...
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5k views

Can I input a square wave LO into a mixer?

I would like to downconvert a signal at 169.55MHz (10khz bandwidth) into an IF of 20.4MHz. For that purpose, I need a local oscillator of 149.15MHz or 189.95MHz. But... of course, I cannot find a ...
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3answers
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Why would I use a transformer instead of one inductor in a crystal set?

I'm reading up on A Simple Radio Receiver. I have a question about this image: The signal from the antenna (perhaps a few tens of microvolts, or hundreds for a nearby transmitting station) is ...
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650 views

Is sending a signal over 433.92 MHz blocked by plastic?

to be honoust: I never understood radiowaves; how I can receive radio in my house? Transferring a complete video through air from laptop to router? Never a clue. So with that (lack of) knowledge my ...
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1answer
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Why are the capacitors set up this way in this old tube radio?

I'm trying to figure out what's going on with these capacitors, so I can replace them in an old tube radio, but why are they connected in this way? simulate this circuit – Schematic created ...
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2answers
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What RF attentuator would be used for the HackRF?

Background info: The HackRF is an SDR Radio capable of receiving and transmitting frequencies from 10MHz to 6GHz. Michael Ossmann, the creator of the HackRF, states in his wiki that: The maximum ...
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How is signal strength calculated?

How is the signal strength calculated in case of cell phones ? How will the signal strength be calculated in case of WiFi networks ? I am not certain if the question I am asking is the same as QoS ...
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243 views

How do wireless receivers reject noise created by the original signal reflecting off walls?

When a transmitter emits an RF signal it reflects and bounces around all over. If a receiver is line-of-sight with that transmitter then the original signal will hit it first but signals bouncing off ...
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1k views

How do compact AM radios establish a ground?

I am trying to construct a radio and, at the first stage, I have finally detected circuit a signal. My previous attempts have failed and I have discovered that it is because it was not properly ...
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3answers
1k views

Frequency spacing and the doppler effect

Suppose that I'm working on a system which needs to use a transceiver with an FM signal. If that system moves very fast (i.e. it is a satellite or whatever) in which the maximum doppler effect can be ...
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2answers
1k views

868 MHz frequency standard

I am wondering whether I am free to use any transmit/receive methods on this particular frequency or do I need to stick to some standards. I am willing to buy a chip with PHY layer of 868 MHz and we ...
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3answers
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Measuring Distance using Phase Shift

I'm trying to make a pair of devices which can measure their distance from each other (within 50 ft., irrespective of orientation). The basics of a robust solution are described in this comment, but I ...
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2answers
2k views

Matching RF traces

The datasheet for this part states the input and output are internally matched to 50 ohms. However what exactly does this mean? For example the output, would I still need a 50 ohm microstrip to ...
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1answer
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Are core and prepreg dielectrics interchangeable?

This is a followup to an earlier question. In my experience, PCB fab houses always default to using prepreg and foil on the surface layers. For example, on a six-layer board, the stackup would be ...
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1answer
28k views

Definition and Explanation of Insertion Loss and Return Loss

I'm trying to understand the physical meaning on Insertion Loss and Return Loss on a transformer, specifically RF transformers. The values are often quoted as figures of merit in datasheets, but I'm ...
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Communication - 2 Battery Powered Circuits, 1 Conductor, no common ground

TL;DR I need to do is successfully transmit a wave across a single conductor between two battery powered circuits with no common ground. I already know how to create the wave and detect the wave when ...
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5answers
12k views

Circuit to remove noise from digital communication line

Carrying on further from my previous post and drilling down to specifics, I am trying to figure out the right way to implement "glitch remover", or "noise remover", using electronics (i.e. not in ...
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2answers
3k views

When is impedance matching necessary? Isn't it much less efficient on all other aspects?

I understand that discontinuities of the physical properties of conductors create reflections much like dioptres reflect a bit of light, but : in which cases does impedance matching become ...
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How Reflex Klystron works

I have a doubt on how exactly a reflex klystron works(as an RF source). In wikipedia it says that, The electrons are fired into one end of the tube by an electron gun. After passing through the ...
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1answer
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How do you determine antenna gain from a polar radiation plot?

Using the plot from the Wikipedia Patch antenna page as an example, how is the 9dBi value obtained? It looks like the radiation is barely higher than 0dBi at the strongest location.
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what is transparent operation on rf?

Whenever I am searching Rf module, I have seen transparent operation on some module.I have searched meaning of transparent operation, but I could not find anything. My questions are What is the ...
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What are the functional differences between a digital sampling 'scope and a digital spectrum analyzer?

I'm interested in measuring the spectral amplitudes / frequency content of RF frequencies up to 30 GHz. This can be done using a digital sampling oscilloscope (I'll call it a SO) with FFT or a digital ...
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4answers
8k 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 ...
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2answers
1k views

How good is coaxial cable?

My question relates to the accumulated AC voltage that will appear on the screen of a length of coax: If the cable is properly terminated at one end and fed with data (or any signal) at the other end,...
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2answers
608 views

Is there any relation between Watt and Decibel

I really don't know much about radio signals. But I want to know that is there any mathematical relation between antenna dB and the output of an RF circuit (I have heard they say this circuit is ...
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1answer
4k views

Bluetooth vs Bluetooth Smart (Low Energy)

Im trying to decide between Bluetooth and Bluetooth LE. My device needs to transfer 375 bytes per second. Bluetooth LE can send packets of 20 bytes max, so this boils down to about 20 packets per ...
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344 views

Actual Implementation of a Multiplier

In school I have learned in both systems and communication about multiplication blocks. I have been taught that these blocks create a sum and difference frequency and can be filtered to get just the ...
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1answer
88 views

Phase Noise In a Voltage Controlled Oscillator

I am particularly new in VCO design. I am required to build a negative gm oscillator with f=7.4 GHz with a tuning range of 300 MHz. The phase noise should be -110 dBc/Hz at 1 MHz offset. I sized the ...
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2answers
737 views

Tube transmitter tuning

I am trying to tune/tweak/repair this transmitter for a friend of mine. It is oscillating, and it has rf power on the antenna, but it just doesn't seem as "strong" as it should be. The diagram says ...
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How to design wide band amplifiers?

I've been designing microwave power amplifiers and LNAs for school, I design in microstrip and my matching networks usually consist of stub/line sections or similar arrangements, I have also designed ...
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RF Ground Stitching in Proteus Ares 8

I am using Proteus Ares 8 to create a PCB for a simple RF circuit. I have a double sided copper board, filled with groundplane on both sides, with a single 50 Ohm microstripline across the board to ...

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