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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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Microphonic SAW transmitter?

I built this very simple SAW transmitter, with a simple "spring" antenna for the right frequency. To test it, I tuned a portable receiver to around 433.92Mhz and fine tuned it until I heard silence. ...
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182 views

RF switch for multiple antennas

I'd like to design an RFID reader with 4 output antenna ports. My RFID reader's module maximum output power is 30 dBm. My target is for the maximum output power in the antenna ports to be 30 dBm. ...
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148 views

bearing ambiguity resolve (direction finding) for multiple sources

I am working on wideband direction finding algorithms for passive sensors. I started with Music algorithm. For practical reasons, the spacing can not be maintained lambda/2. For greater antenna ...
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15 views

Parasitic Passbands in distributed filters

it is known that if we realize a filter (for instance a low pass filter) by using distributed elements (transmission lines), there will be some parasitic passbands (which moreover show a behaviour ...
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27 views

RFI protection for a stepper motor controller

I'm building a remote tuning device for a magnetic loop antenna. It will use a stepper motor to turn the shaft on the mag loop's variable capacitor. The electronics will consist primarily of a ...
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71 views

High SNR FM demodulation

So I need to demodulate the FM signal from a sensor with highest SNR possible, at least 70-75 dB. IF is 10.7 MHz, max. deviation is 200 kHz but I can change those values if needed. Baseband signal ...
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59 views

2.4GHz RF design losing signal

First time poster here, please excuse holes in the plot. I have a simple wireless design made of an MCU (atmega328p) and an NRF24L01 module, powered through a 3.3V regulator, talking to a similar ...
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49 views

Question related to two closely separated signals that need to be analyzed by a spectrum analyzer

Question The settings of a spectrum analyzer are given as following: Center Frequency = 1.89 GHz, RBW = 10 kHz, VBW = 10 kHz and Span = 50MHz. The Reference Level is set to -20 dBm and ...
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73 views

Beam Steering range of a phased array antenna system

What is the beam steering range of a phased array dependent on? For example, if I use an antenna array of Nx1, with a phase shifter resolution of \$\frac{2\pi}{k}\$ and the antenna elements spaced at \...
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71 views

Transfer function of loop-back bias circuit for RF amplifier

I am trying to implement a current mirror as part of a bias circuit for a RF amplifier. I want to do a transfer function of the bias circuit since it creates a loop from the amplifier fet drain to ...
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172 views

Different balun configurations

I am looking for a balun to be used as a single-ended to differential converter, 1:2 impedance ratio, including range 1.5-2.5GHz, SMT and phase balance as good as possible (and return loss). Center ...
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281 views

Does anyone know what the heck this is?

I really hope I'm posting this in the right section. I was strolling down the street and looked up at this massive barrel object mounted to a utility pole. It's hard to tell from the pic, but it ...
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67 views

Is a board with on-board radio disabled an unintentional/intentional radiator?

If a board with the onboard radio (e.g., Bluetooth) chip disabled by software using a jumper, would it be considered to be an intentional or unintentional radiator? That is, the onboard radio can be ...
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1k views

How to find the resonant frequency of a human body?

I've read that the human body has resonant frequencies somewhere around 50MHz. I also think it would be interesting to look for values in other ranges like 10-100 kHz. I'm wondering how to build a ...
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128 views

High Frequency Ferrites for Transformers

There are many Ferrite material grades Available.The optimum frequencies start around 20KHz and extend well into the MHz range.There are also many core sizes to go from watts to Kw .Planar cores are ...
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868 views

Getting the best range with XBee-Pro 900 XSC S3B

I have a pair of 900 XSC S3B xbee pros and a couple 2dBi duck antennas. I just did a simple outdoor range testing and only got about 2,000 feet. I was outdoors without any buildings in the way, but ...
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187 views

Interpreting Data Sheets (“Typical Applications”)

I've recently been researching various transceivers, but I run into trouble as soon as I get to the "typical applications" section of the data sheet. With the Si4464 for instance, the example ...
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20 views

How to find Q of a quarter-wave resonator loaded with a coupled-line coupler

I have a quarter wave resonator at frequency \$f_0\$ and characteristic impedance \$Z_{res}\$, which is coupled to a 50 Ohm load via a segment of coupled-lines coupler whose electrical length is \$\...
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39 views

Are magnetically tunable surface acoustic wave devices commercially produced?

I have been reading up on studies of magnetically tunable surface acoustic wave devices, in general they note the relative velocity change or in some cases a frequency shift if it is part of an ...
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49 views

Has anyone designed a low noise amplifier in the ISM band (24 GHz) using the discrete fet CEL CE3520K3?

I have been trying to design an LNA in the 24 GHz ISM band using CE3520K3. The FET is inherently unstable and one cannot use resistor loading at the input, resistive loading at the output, source ...
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18 views

Unitary property of scattering matrix

From s-parameter lossless network definition , The sum of the incident powers at all ports is equal to the sum of the reflected powers at all ports. But how do we derive the above unitary property ...
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40 views

Measured doppler shift error biggest on direct flight on target

Following scenario: There is a radar on a plane which emits a CW Signal and outputs the measured doppler shifts from the reflection of a static target. I can see from the data, that the error of the ...
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62 views

Does regularly spaced via stitching contribute to standing waves on an RF PCB?

Should vias be irregularly spaced? Can consistent spacing between ground vias create standing waves. Has anyone ever heard of this? I've been doing this for awhile and I've never heard this and ...
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57 views

GPS PCB RF Design and Performance Impact

I have designed a vehicle tracker for two-wheelers which is installed in 500 bikes. I am facing an issue with GPS performance (lock percentage is quite low for more than 75% bikes). This makes me ...
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81 views

Low latency wireless audio transmitter

I am working on a project that requires low latency wireless point to point audio transmission at short distance using a digital transmission technique (ideally 24bit 96khz audio, 30 metre max) at a ...
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33 views

NFC Antenna Feed Lines

I've designed a number of boards in the past that use NFC but I don't think the RF performance has ever been exceptional. These boards have an NFC chip (generally the STM M24SR64-YMN6T/2) connected to ...
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107 views

First PCB project design critique requested (RF) EDITED

This is my first ever RF PCB project and it'd be great to receive some guidance to make this project 'first-time-right'. It's purpose is to transmit and receive signals at two different frequencies: ...
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28 views

Realizing a prototype filter in ADS or any other simulator

I'm trying to design a stub-filter, and I'm stuck on realizing the filter design using Richard's transformations and Kuroda identities. I'm building a 5th order Chebyshev LP-filter for 2.6 GHz pass-...
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113 views

On purpose shorted capacitor in schematic

I've come across this schematic from an RF device where I've spotted some weird configuration of capacitors. There are, all around the schematic, some shorted capacitors which I can't figure out what ...
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27 views

What causes the fail-safe bit to be set in the SBUS protocol?

What causes the fail-safe bit to be set in the SBUS protocol? I know that the when the link between the transmitter and receiver is lost, the fail-safe bit is set, however, what constitutes a 'lost ...
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97 views

Noise floor raising at high RF input power after filtering

I have a USRP b205mini with AD9364 transceiver. When it receives a very high RX input of about -5 dBm at different frequencies, not in the original RX range, the noise level raises slightly. The RX is ...
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62 views

Discrepancy between simulation and measurement for a voltage doubler/ rectifier design at 5.8 GHz

I am designing a pretty straight-forward voltage doubler at 5.8 GHz with MACOM's MA4E1317 diode, which I have used before and know from previous experience that matches pretty well with the spice ...
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110 views

Impedance matching of a RF power amplifier based on the s2p file

I'm designing the input/output impedance matching circuit for a RF power amplifier, based on the vendor supplied s2p file. I designed separately the input/output matching circuit at the given working ...
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62 views

Creating a balanced dipole from two monopole chip antennas for use on small PCBs

I'm trying to use a monopole chip antenna on a PCB much smaller than the one recommended in the datasheet. I am wondering if I can get away with a much smaller board by using two monopole antennas ...
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39 views

Near-me area network embedded emitters with a Raspberry Pi server receiver

I am making a toy for 4-year old children with 10-20 pieces in wood, as in this picture with four wooden boards with names: The goal is that each wooden board triggers a sound, such as "Hello" or "...
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62 views

Electro magnetic interference with Arduino Uno and a portable radio

I'm surprised when I'm working with Arduino Uno, by just sitting beside a portable radio, like when I was powered on both Arduino & Radio and when they are close to each other I got some noise ...
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32 views

2 tone test with RF mixer

I am designing a system that uses RF to probe the nonlinearity of a target. It works as follows. Transmitter sends out 2 RF frequencies, such as 900 and 910MHz. The target/reflector has a ...
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45 views

Generate ultrashort rise times with photoconductive switch or photodiode

I am trying to produce voltage pulses with very short rise time (<15 ps), medium width (20 ns) and amplitudes up to 15 V. As a promising candidate I selected photoconductive switches and ultrafast ...
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25 views

CST Studio Space State Matrices

I am new to using CST Studio and I am trying to figure out how to see the state space matrices (A,B,C,D) of a designed antenna to describe its radiation pattern in other software. Any help on the ...
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28 views

Load Impedance Derivation

I'm having some trouble deriving this equation for transmission line theory: From: http://www.antenna-theory.com/tutorial/txline/transmission3.php When I sub the Telegrapher's equations into eqn ...
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100 views

Amplitude Modulating a simple Laser using an RF transformer

I know I can modulate a laser using an audio transformer see pic and website below. Pen Laser website I was wondering if it’s possible to modulate a simple pen laser using RF signals in the RF range ...
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184 views

LoRa RX-Single Mode Inconsistent RX-Timeout Interrupts

I'm trying to implement LoRa communications using an SX1276 module (DRF1276G) and an ATmega328P on a custom PCB. I've got it mostly working but I'm having a strange issue with the timeout interrupt. I'...
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87 views

Reflection on a matched transmission line

A matched load with source using a transmission line (assume real load and matched using quarter wave transformer) should not have any reflection ideally. But we can see that the load impedance is ...
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46 views

Active phased antenna array for Wi-Fi efficiency compared to a directional antenna?

I'm interested in mesh networking of poorly controllable autonomous aerial vehicles (like blimps), so i wonder whether it is viable to use a phased antenna array versus a few traditional directional ...
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539 views

Spectrum Analyzer vs. RF Power Meter?

I own several spectrum analyzers and build various RF boards at all kinds of frequencies. I was looking over a BLE FCC test report for emissions, and I saw this lab uses a RF power meter to measure ...
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109 views

Help decoding line code

I have collected a burst signal from a radio device using an RTL-SDR and gnuradio and demodulated the FSK, but am having trouble deciphering what the line code is. Signal is at 151.3MHz Here is the ...
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140 views

LoRa radio transceiver for PtP mesh?

So after being informed on the Amateur Radio Exchange this isn't quite HAM/Amateur Radio, posting here. So I'm, well, very new to general RF/radio in general other than basic WiFi, but I'm looking at ...
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Interfacing LoRa SX1301 IC to third-party RF front-end

I am reading the datasheet of SX1301. I got struck at SX1301 RX operation using a third party RF front-end topic (Page 22). The page (22) says: In that mode the ...
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142 views

Self Resonant Frequency VS Package Size for capacitor

In general belief, smaller capacitors have better charactristic(more capacitive behaviour) in high frequency than bulky capacitors. On contrary in one of my RF project (8.5GHz - 9.5GHz) when checking ...
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63 views

How to go about decoding baseband from RF?

I'm designing the avionics portion of an ADS-B transponder and have everything done except the one thing I just can't figure out is decoding and encoding the baseband signal. I'm kind of under the gun ...