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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Qucs model for 2.4 GHz matching circuit

I am designing a matching circuit for an EFR32BG13 SoC. The current board layout looks like this: In addition to the visible layers (top and bottom), layer 2 is a solid ground plane and layer 3 is a ...
4 votes
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522 views

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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4 votes
1 answer
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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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4 votes
1 answer
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Sequencing modes for FCC "Intentional Radiator" test

I'm FCC certifying as an "intentional radiator" a product that uses a custom antenna and off the shelf Broadcom WiFi module. The module has an antenna port, so single-modular and limited single-...
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3 votes
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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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3 votes
2 answers
179 views

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 ...
3 votes
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301 views

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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3 votes
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155 views

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 ...
3 votes
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120 views

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 ...
3 votes
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171 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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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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3 votes
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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 ...
3 votes
1 answer
564 views

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 ...
3 votes
1 answer
69 views

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) ...
3 votes
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301 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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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 ...
3 votes
2 answers
521 views

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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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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3 votes
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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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3 votes
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915 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 ...
3 votes
1 answer
238 views

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, ...
3 votes
2 answers
926 views

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 ...
2 votes
0 answers
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Can I compress the dynamic range of ns pulses to better fit ADC range using log amp or mixer?

I have an experiment in which the signal I want to measure is a 1 ns pulse that occurs somewhere around 0-100 ns after a trigger. I want to digitize the pulses to extract the time they occurred and ...
2 votes
0 answers
72 views

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 ...
2 votes
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98 views

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 ...
2 votes
1 answer
39 views

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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2 votes
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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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2 votes
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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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2 votes
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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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2 votes
0 answers
53 views

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 ...
2 votes
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80 views

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 ...
2 votes
1 answer
132 views

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 ...
2 votes
0 answers
71 views

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 ...
2 votes
0 answers
126 views

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 ...
2 votes
1 answer
307 views

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 ...
2 votes
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190 views

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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2 votes
1 answer
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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.
2 votes
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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 ...
2 votes
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186 views

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 ...
2 votes
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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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How to correctly document wireless network choice for a project?

Disclaimer: I have limited wireless knowledge at the moment, I'm currently following the Certified Wireless Network Administrator study guide. I'm working on an RC car and have the following network ...
2 votes
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119 views

Calibrate for an inaccurate 50 ohm load in a DIY Vector Network Analyser (VNA) based on a VSWR RF bridge

I have built a "DIY VNA" using a frequency generator, an SDR receiver, a RF Reflection Bridge and a 50 ohm load. This is used to measure "VSWR values" of antennas to see what frequencies they are ...
2 votes
0 answers
574 views

Why are tv aerial cables so mysteriously sensitive to their positioning and the proximity of people?

Digital TV Reception is not great in our area and sometimes we lose reception when conditions aren't favourable. Being UK Freeview, I'm pretty sure it uses the DVB-T2 standard. Anyway, when ...
2 votes
1 answer
257 views

Thermal Noise in Oscillators

let's consider this circuital model for an LC oscillator in which the parasitic resistance R is affected by thermal noise (represented here with an equivalent noise current source, according to the ...
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