Questions tagged [rf]
Short for Radio Frequency, i.e. 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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Impedance matching for an antenna
I've been working on a project for school which involves designing matching networks for antennas (meant to be driven at 2.4 GHz) being connected to a 50 Ω line, and it led me to consider the ...
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Why DDR4 Specs recommend that Address, Control and Clock buses be referenced to VDD?
Micron's Technical Note TN-40-40: DDR4 Point-to-Point Design Guide, page 19, says (emphasis mine):
Timing Budget
Suggested practice is to look at the design from a timing budget
standpoint to provide ...
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RFID reader array using row/column RF switches (multiplexers)
I need an 8x8 grid of RFID readers arranged on an 8"x8" board. The RFID tags will be placed only millimeters above each antenna.
I was wondering if I could use one 1:8 RF switch (e.g. pSemi PE426482) ...
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IIP2 Second Order Intercept Rule of Thumb
I'm faced with the problem of explaining the harmonic production in a system where the second order intercept points of the cascaded components are unknown. As a way to bolster my explanation, I would ...
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How to match an edge launch SMA connector to a pcb with coplanar waveguide with ground?
I'm trying to develop a pcb that is capable of handling signals over 6GHz and created a test board to see how the pcb and connectors perform. The pcb is a relatively low-cost 4-layer FR-4 TG155 board ...
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Why would a non-nichrome resistive element be desirable?
While working on a circuit design the other day, I happened across a datasheet for a high-frequency resistor that specifically mentions that it uses a "non-nichrome resistive element". In ...
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High Frequency Oscillations on Mosfet Gate
I am working on a circuit that drives an inductor at its resonant frequency. However certain models of MOSFET I simulate the circuit with experience oscillations at the MOSFET gates as pictured below. ...
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FSK Modulation in Python
I am currently writing a script that uses I/Q data to do FSK modulation.
My question is about the FFT plot. I expected to have a peak at 1Hz and 2Hz which are the frequencies that represent binary 0 ...
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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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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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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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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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Help identifying UHF RF SMD component
I need some help identifying two components in this RF circuit. I have spent quite a bit of time searching for either, who makes it, or what exactly they do, but no luck. Maybe someone here knows ...
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50 Ohm-Terminated Antenna Oscilloscope Readings
As a follow up to my previous question about measuring antenna performance via amplitude at 88 MHz to 108 MHz on a DSOX1102G oscilloscope, can I trust these new readings? Measurement channel is on 1:1 ...
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Unequal resistive power splitter
I'm looking at a 3-port, unequal resistive power splitter design like the dashed-line box in the diagram.
1 is the source, whereas 2 and 3 are two loads of impedance, say Z0. All 1, 2, and 3 are ...
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Square vs Round Air-core Inductors for RF filters: When would you use one vs. the other?
The Kyocera AS-series Square Core Inductors boast that "the unique square cross section of the air core inductor provides better performance, and offers manufacturing advantages over toroidal ...
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Esp32 rf design review
Preamble: this is the first time I'm working in rf circuit design, I went simple and I hope I didn't make any silly mistakes, but I still have some doubts.
I am currently designing a garden programmer ...
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Questions about RF ground plane and low frequency reflections
Why do RF signals on a microstrip/stripline require a ground plane to propagate within a circuit? When studying DC and low frequency AC circuits in school, it appears that ground is a particular point ...
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Using a single MOSFET as an RF switch
I'm assembling a receiver kit from QRP labs. It is an inexpensive kit designed to cover HF. This kit has a BS170 at the input which I assume is intended to disconnect the receiver when the transmitter ...
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RF signal Multiplier or Chopper
I'm trying to design a circuit that "multiplies" two signals.
I have an electrical unit with two separate circuits. One circuit drives the other one with a square signal. The width of the square ...
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Eliminate reflections on pulse signal transformer
I am trying to isolate an RLC ringdown signal via an RF signal transformer but I'm having trouble maintaining the signal integrity through the transformer. Below is the simple schematic describing my ...
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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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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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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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How can I reshape this PCB antenna so that I can still use it with the given circuit?
I'm borrowing the RF design from the MICRF114 Development Kit.
Here's user guide- http://ww1.microchip.com/downloads/en/DeviceDoc/50002433A.pdf
The circuit I'm using is on p. 35 and the antenna ...
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Gunn vs. VCO in terms of phase noise and THD
I am trying to compare the THD and noise phase of a Gunn oscillator and a VCO. I conducted an experiment where I measured both parameters for both devices and came up with the following results:
(1) ...
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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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Discrete distributed amplifier
I read about distributed amplifiers. I know they are used in MMICs, but I wonder whether it would be possible to build a distributed amplifier with discrete components.
In my opinion, it would have ...
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When are 1:1 baluns worth it?
I am trying to build an antenna to connect to the GOES-16 satellite (downlink at 1690,1MHz, linear polarization) with my SDR. My plans are using a 1m offset parabolic dish with a BiQuad feed, ...
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RF amplifier not working
I designed an RF amplifier that should amplify signals in the FM band of 88 to 108MHz. The circuit is as shown below:
The input to the circuit is connected to an USRP through an SMA cable. The output ...
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In PCB RF layouts, should low-pass elements be oriented parallel or perpendicular to the feed?
This is a portion of a 900 MHz 50 Ω controlled-impedance layout for a radio antenna feed.
The above layout is based roughly on something like this Pi filter:
simulate this circuit – Schematic ...
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When should an unmatched antenna be measured with a cable length in even multiples of a half-wavelength?
A few years ago someone told me that if you use a cable which has a length of an even half-wavelength multiple for the frequency being tested, then the impedance measured at the end of that cable will ...
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Why does isotropic radio transmission appear to be better than optical for communications?
I have a walkie-talkie that supposedly has a range of 5 km in open country, line of sight, that puts out 1 W in all directions.
Now, if I replaced that RF transmitter with a 1 W light source and the ...
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Transistor impedance
According to LDMOS transistor AFT05MS031N datasheet at p. 13 " ZSource - Test circuit impedance measured from gate to ground" for 155 MHz is
Z = 4.31 + j.7.54
https://www.nxp.com/products/...
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Crystal Radio Troubleshooting
I am learning radio starting with the basics, and I had a question about the behavior of my set up. I made a crude schematic below, the antenna is a 14 AWG random wire that I hung from a tree (using ...
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Why 7 dB power increase after combining identical strength signals?
I have signals from two transmitters that are combined via a power combiner (link).
Both signals are at 7 dBm when fed into the combiner on their own. When combining both, the meter either reads 7 dBm ...
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What is the link between conjugate matching efficiency and amplifier efficiency?
In the design of a class AB amplifier, there is part of the understanding that I miss. It is well-known that the maximum power transfer is achieved when the load impedance is the complex conjugate of ...
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How to prototype with sensitive electrical components without a PCB?
Right now I'm trying to get consistent radio operation with an NRF24L01+ and a Teensy 3.6, however in my experience working with radios they have extremely inconsistent connectivity when using ...
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Maximum RF power for microstrip
Microstrip line have couple parameters that we can change. It's track width (W), copper thickness (t) & substrate thickness (h).
The question is "How much RF power we can transfer by this ...
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SX1262 Matching impedance
I want to build a LoRa node from SX1261 which works on the frequencies of 868Mhz and I found at the manufacturer the following assembly ms I did not find more details on the different passive ...
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Tips on how to increase the gain and lower the noise factor of a LNA
Hey guys I am designing a LNA biases by a 3.3 V source and tuned to 2.5 GHz.
Here is the schematics, the testbench and some results (s parameters analysis). I would like to know if there is a way of ...
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Friis Transmission Equation for Wideband Transmission
it's known the following Friis transmission equation:
$$P_{rx} = P_{tx} \cdot G_{tx}(f) \cdot G_{rx}(f) \cdot \left(\frac{c}{4 \pi R f}\right)^2$$
It's nice but, as far as I'm concerned, it works only ...
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What are the connectors for GND and power supply on these RF LNAs?
What connectors are these? They seem to be widespread on LNAs.
Bonus question: is it a reliable connection? I am planning on using them on a large RC car so it is going to be shaken quite a lot.
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RF PCB Layout for 915Mhz + BLE: Which is better?
I am designing a small board with a 915Mhz transceiver IC breakout (based on the CC1101 + CC1190 chipsets), controlled by an STM32. I have used the popular nrf24l01 chipset in the past, but was ...
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De-embedding ceramic filters
I want to design a diplexer using two ceramic filters.
S2P files of the filters are not provided. Therefore, I designed a PCB which can be shown below to obtain their S2P parameters.
In the first ...
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How would you design a power divider with 50-Ohm unbalanced input and 4x 100-Ohm balanced output impedances to send RF down a CAT6 cable?
A CAT6 cable has 4 balanced pairs, each at 100 Ohm. I'm wondering if I can make a 50-Ohm coax unbalanced input and split the power to 4x 100-Ohm balanced output (and then merge it back together the ...
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What metal(s) are old game console RF shields made of and coated with?
I'm restoring my old game consoles (like NES) and am having trouble finding what the RF shields are made out of and coated with so I can sand out the corrosion and re-plate them.
I thought it might be ...
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Need help understanding RF radio parameters
I am experimenting with the SPSGRF-915 RF transceiver, particularly with the different center frequencies.
My question mainly revolves around the situation where multiple devices can transmit at the ...
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Anything obviously suboptimal about this design?
RF novice here, this is the first PCB I've designed and I'm just wondering if anyone more experienced than I (which is most people) sees anything glaringly wrong/bad/in need of improvement with this ...
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HB100 range extension with dish antenna
I have interfaced an HB100 sensor with an ATMega microcontroller. It easily detects my hand movement upto 5-6" away only.
I want to extend the range of the sensor so that it detects movement upto ...
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