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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How to increase efficiency of antenna without moving antenna far from tree?

I have designed a monopole antenna at 868MHz frequency. Now I would like to attach that antenna to the tree (wood). But, due to Why does placing an antenna far from the wood increase the efficiency of ...
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BNC and SMA cable testing

Are there tools for checking (or that could be adapted to check) if BNC or SMA coaxial cables are in spec for things like proper shielding, impedance (across their bandwidth), etc.? I've found lots of ...
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How to design a class-E amplifier with a more complicated load (tesla coil)

I'm currently trying to build a 4MHz Tesla Coil powered by a Class-E amplifier. I've managed to design and simulate such amplifiers with a load consisting of a resistor and a coil or a capacitor using ...
ismxy's user avatar
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LTE Bandwidth at band edge

If my LTE uplink channel is right on the band 20 edge for example 861.9MHz or 24449 EARFCN and my LTE BW is 10MHz does that mean the final signal would be outside of B20 or 856.9-866.9 ? Or is the ...
Engo's user avatar
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Why does placing an antenna far from the wood increase the efficiency of the antenna?

I designed a monopole antenna at 868MHz frequency. I placed wood as the surrounding material. I noticed that placing the antenna far from the wood increases the efficiency of the antenna. Can anyone ...
Sai's user avatar
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GPS patch antenna feeding line layout issue

When I tried to put Molex GPS ceramic patch antenna 2042860001 on two-layer PCB, I found it's impossible to connect the feed pin to the RF trace on the two-layer PCB if following the recommended ...
Ross's user avatar
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Is it possible to create a device that can decode the EM waves generated from an electronic machine?

I recently watched a movie in which the hero (a robber) invents a device that can capture and decode the EM waves generated from an Automated Teller Machine (ATM) during its use. The movie claims that ...
Sasikuttan's user avatar
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RF interference in high node density 2.4 GHz networks

These days, there are a lot of products that are working on 2.4 GHz RF - mobiles, laptops etc using 2.4 GHz wifi, earphones using BT, home automation products using 2.4 GHz zigbee. Though these ...
Whiskeyjack's user avatar
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Synchronization of remote sensors

I have a project that involves multiple (5+) remote sensor units (custom PCB with a MCU, WiFi Radio, and sensor), that record data for a short test (<60 seconds). Each sensor records data ...
Kyle Hunter's user avatar
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Wireless charging shielding requirements

I have a project where I want to throw a charging coil into the wonderful mix of tiny parts but the problem is, I also need an accelerometer/magnetometer roughly right beside said coil. I believe I ...
OwenTheProgrammer's user avatar
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Help in smoothing signal output from a frequency mixer

I have a circuit with a TFM-3MH+frequency mixer. I need to output a low frequency signal of 10-100Hz. The signals that I'm sending to the input ports from a signal generator are: Sine wave of ...
Nikola Petrovic's user avatar
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Input impedance into center tapped transformers

For a project, I need to find the input impedance into 2 types of transformers at their center frequencies (peak input impedance). Can anyone help me find the peak input impedance? Both L1s are ...
radio_guy's user avatar
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Properly grounding an SMA connector (bottom ground plane only)

I’m currently designing my own breakout board for the RFM95W (LoRa module). I’ll be operating at ~900 MHz. The board has two layers. The top layer contains all the signal tracks (no ground pour). The ...
Miles's user avatar
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Receive GPS with 2 antennas

For an amateur rocket project, I want to receive the GPS signal from 2 antennas placed in the opposite directions, but I'm very beginner in RF domain. So my first thought is to use a signal Power ...
Zskdan's user avatar
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Understanding the input characteristics of an RF power transistor (2SC2237)

I've had this 2SC2237 RF power transistor from Mitsubishi for quite some time and I've finally found a project for it. The datasheet can be found here. The first thing I need to do is figure out its ...
Buck8pe's user avatar
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External Antenna for ESP32-S2-DevKitM-1U

For starters, I'm new to electrical engineering, especially rf applications, so I apologize in advance for anything dumb I say. I currently have an ESP32-S2-DevKitM-1U, and am looking for an external ...
Cygwin231's user avatar
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How to design a matching network for an ASK 315 MHz receiver?

How to match antena network impedance for a certain receiver frequency. Example how below circuit values are calculated to match the SYN470R receiver for 315MHz. Is there a way to further simplify the ...
yeganehhp's user avatar
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Designing a pseudo-Doppler transmitter

I am thinking about creating a CW transmitter based on the pseudo-Doppler effect (educational purposes, nothing special in mind). For this purpose, \$n\$ antennas will be placed in a straight line, ...
user3141592's user avatar
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How should I route the ground plane under a RF trace with a LC balun?

I'm designing a PCB with a ESP32-PICO-V3, with a RF output to a 50 Ohms U.FL (Micro-Coax) connector. The chip supports WiFi and Bluetooth in the frequency range 2.45 +/- 0.45 GHz. Right now, I have a ...
Marc's user avatar
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Impedance transformer, how to measure

I am preparing to do some RF mixer experiments with the SA612 Gilbert cell mixer. I started out with the impedance matching as I understand that the input and output need to be matched. From what I ...
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Help me identify this component in an RF transmitter

This is from a 2-channel RF Transmitter FlySky FS-GT2. I think the antenna's wire should be soldered onto this RF transmitter PCB, flat silver component, however, I do not know where to solder because ...
Octane 663's user avatar
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Can you measure or estimate antenna reflection back into freespace caused by a freespace impedance mismatch?

Consider an antenna as a 2-port reciprocal network such that you may have S11 reflection at the feedpoint, but also S22 reflection back into freespace. S11 is well understood and measured because that ...
KJ7LNW's user avatar
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Can port parameters in one representation (mag-angle, decibel-angle, or real-imaginary) be converted to the other?

I'm trying to figure out what network parameter data would be "best" to use when generating a Touchstone file, or if the different data representations are equivalent in terms of the ...
KJ7LNW's user avatar
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Can an antenna be modeled as a 2-port passive network?

I've been using xnec2c to model antenna characteristics in Linux and the latest version is able to create a CSV by frequency of SWR, Zr/Zi, dB gain, and other metrics. I was thinking it would be neat ...
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Coaxial Transceiver - HF Signal & LF Signal on same cable

I have a project which needs a analog video signal & some control data sent on a coaxial cable, I came up with some ideas and I asked about it and some interesting answers were received (Multi &...
Stefan Merfu's user avatar
2 votes
1 answer
158 views

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 ...
Kinka-Byo's user avatar
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1 answer
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S Parameters Channel Modelling Time domain representation of insertion loss

Below is the insertion loss waveform obtained after S parameter of a channel.The waveform is in frequency domain. May I know what is the equivalent time domain waveform and how to obtain it from this ...
Hari's user avatar
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1 answer
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RF Impedance Matching in Altium

I'm trying to route a LoRa module to an SMA Antenna on my board (first time tracing RF signal). Shown in image below: I adjusted my layer stack up for my 2 layer board, 1.6mm thickness and added an ...
Explorex's user avatar
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3 answers
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How is cutoff frequency defined?

Cutoff frequency is often measured and presented in academic papers, for example, for high electron mobility transistors. How is this defined exactly? Is it defined as a frequency at which the current ...
user207787's user avatar
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2 answers
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Understanding the balun frequency range

I am exploring the balun part for my RF based application. In many part datasheets, I see there is certain frequency range mentioned such as in BD4859N50100AHF part number, 4.8-5.9GHz is provided. I ...
BalkisMM's user avatar
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1 answer
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How do coupled combiners work?

I cannot seem to find this information anywhere.. basically my question is, how are the directional couplers used to combine power? Couplers pretty much take an input and split it into two different ...
user207787's user avatar
1 vote
1 answer
147 views

Protect PCB from RF reflection

I am designing a system on megahertz frequency bands (~ 400-1000MHz.) This device is connected to a variable antenna which does not necessarily stay in match with the circuit so there will be some ...
Anonymous's user avatar
4 votes
4 answers
2k views

Why are the measured and theoretical Q factor of an LC circuit very far off?

I have an LC circuit, where inductance is about 5 mH, and the capacitor is about 1.25 nF. The resistance of the inductor is about 1 ohm. I think the theoretical Q factor should be $$\frac{\sqrt{L}}{R\...
shimao's user avatar
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16 votes
3 answers
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What is this circuit diagram found on an FM transmitter?

This is the circuit diagram on the transmitter at a local FM radio station I clean at (I'm a janitor,) but I'm also studying electrical engineering. I'm puzzled by the circuit diagram on the ...
Jessica Ham's user avatar
3 votes
2 answers
640 views

RF PCB ground plane surface finish

I am designing two boards that are supposed to operate at frequencies 2.45GHz and 5.8GHz. In my design, I use simple microstrip lines (not coplanar) on FR4 substrate. There are some quarter-wave ...
UncannyValley's user avatar
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125 views

Secondary Coil Malfunction in an SSTC Circuit

I’ve designed an SSTC circuit which is based on a different topology and I wanted to accomplish it in real life. The circuit is operating at approximately 1.5 MHz during resonance and inherently, the ...
Karakoncolos's user avatar
2 votes
2 answers
460 views

Decoding a 433 MHz energy monitor

I am attempting to capture transmissions from my own energy monitor, a Watts Clever EW4009 for use with Home Assistant. I believe it is an FSK signal, with 250 um packets. I have captured several ...
Denis S's user avatar
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1 vote
0 answers
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Output back off of a high power amplifier (HPA)

We are selling S-band HPAs for satcom applications. A customer needs to obtain key RF characteristics of the S-Band HPA, specifically the wideband frequency response of carriers as a function of ...
W.Dabbas's user avatar
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0 answers
51 views

Is there an advantage to cover all bands of GNSS constellations when selecting an antenna?

I am shopping for shark-style (or aerodynamic low-profile) antennas to make the most of my GNSS receiver (a Septentrio Mosaic X5). Is there any advantage to cover all bands (i.e. ~1.1GHz to 1.6GHz) of ...
Mister Mystère's user avatar
2 votes
0 answers
93 views

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.
user42875's user avatar
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3 votes
2 answers
189 views

How is the "open" component of the vector analyzer calibration kit made?

I've done some measures of S parameters with a VNA a long time ago. I'm not an expert om this, but I remember the procedure of calibration, which was using, for a single port, the three lumped ...
Kinka-Byo's user avatar
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2 votes
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Why are pull-up inductors biasing the power amplifier output of radio transmitters chips needed?

I have seen many designs where the antenna/PA output is fed DC voltage through an inductor. Why not leave it out and feed the DC bias directly? It is L1a in the diagram below: There are some values ...
kellogs's user avatar
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RF line: routing it orthogonal over SPI digital signal lines

SPI will be kept below 1MHz. RF signal is under 434 MHz. Is this crossing fine through the big zero ohm resistor ? Side question: will the outermost SPI line (it is the chip select one), or any of the ...
kellogs's user avatar
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2 votes
2 answers
533 views

How to protect a cheap RF amplifier from spontaneously dying?

I've bought a few RF amplifiers based on the SPF5189z LNA chip. These have decent performance for their price but there is a common issue where they just kinda die from pretty much any reason. I've ...
derek's user avatar
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2 votes
2 answers
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Safety Capacitors; Is it OK to fit an X1 in place of an X2?

I have a PCB which has a 0.010uF X2 safety capacitor fitted. It seems the exact part is now obsolete. Would it be acceptable to replace this part with a 0.010uF X1 safety capacitor? I believe a ...
313Ctron's user avatar
1 vote
1 answer
604 views

Ground plane placement in relation with LORA spring antenna

I am making a simple lora transciever and absolutely want to fit it on a single side dual layer 0.8mm thick pcb. Which makes impedance matching a bit tricky with 53mil traces... Here the form factor ...
ESD's user avatar
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1 vote
1 answer
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Nonideal RF coupler model, admittance matrix in QUCS simulation

I'm trying to simulate a nonideal directional coupler in QUCS. Unfortunately, the only model available is the ideal one without taking into account the isolation or insertion loss values. Initially, I ...
UncannyValley's user avatar
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1 answer
236 views

Transmission line and input impedance - Smith chart

According to "Smith Chart Supplement - Corrected Jan 2012" when f.e. calculating input impedance (from load impedance) it is necessary to use WLTG (wave lengths towards generator). WLTG ...
Fasset's user avatar
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2 answers
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Matching network and filter design

I am designing matching network at 868MHz frequency. I have a source impedance of Z=15.27-j1.27. In order to match that with 50 Ohm, I implemented LC matching network (red color). After that in order ...
Sai's user avatar
  • 27
2 votes
2 answers
1k views

Why are transmission lines and waveguides needed for high frequency?

At low frequency, we can just use a piece of wire to connect electrical components, but why are special transmission lines and waveguides needed for high frequency circuits? Also I am confused by the ...
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