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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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RF signal generator, spectrum analyzer measurement questions

I want to test the attenuation characteristics of an RF filter I’ve built into a project, but do not have any experience using RF signal generators or spectrum analyzers. In all of the videos I have ...
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179 views

Why do XC and XL need to roughly match in an LC tank?

In an LC tank circuit, why do XC (XC1 + XC2) and XL need to be roughly similar? For example, in this Colpitts Oscillator taken from https://www.electronics-tutorials.ws/oscillator/colpitts.html, I ...
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71 views

Frequency Hopping 900MHz — Noise Floor Mitigation and Algorithim Design

I've built a few baremetal fixed frequency RF systems, and am working on a long range frequency hopping product using a ARM Cortex M3. So we got some horsepower here! I've got the the TX FCC Part 15....
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49 views

How to test an RF crystal oscillator performance integrated into a Cellular radio?

I have a couple of reference designs with 2 different crystal oscillators integrated into it. These are cellular radio and can generate standard LTE QAM signals out of it. But I do not have access to ...
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118 views

Is this an acceptable 100Mhz OCXO output?

I was looking for a 100Mhz sinwave OCXO output. I picked up a used one and I have the following output: Each vertical square is 1 volt. I was expecting it to look exactly like a mathematically ...
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63 views

Is there a standard that specifies the polarity when using an SMA connector (or similar) to connect a DC power source?

For regular DC power adapters I will see a polarity indicator like the following: However I have seen some RF circuits that indicate a DC power connection to the circuit over an SMA connector but do ...
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58 views

Conversion of Additive Noise to Phase Noise

RF Microelectronics by Razavi contains the following snippet in section 8.7.3 concerning the analysis of phase noise in oscillators: We write \$x(t)=A\cos(\omega_0t)+n(t)\$ where \$n(t)\$ denotes ...
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26 views

Regulated power for radio module HM-TRP. Is config correct?

I'm trying to figure out how to make a nice power supply to the radio module HM-TRP. I heard that running certain voltage regulators with capacitors having high ESR values is a bad idea and will ...
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568 views

Identifying an old RF circuit

I got an old RF circuit (I guess), probably used for pedagogical purposes. Here's the schematic: I chose the positive and ground rails as it seems right to me, looking at transistors and resistor ...
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265 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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106 views

Modeling impedance matching network

Background I'm looking at the RF (LNA_IN) pin of ESP32 as described in esp32_hardware_design_guidelines. According to this document, the output impedance of the RF pins of ESP32 are (30+j10) or (...
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43 views

Decide coherent time and fade duration through empirical studies on the channel and relate them to channel modeling

I. Scenario: TX floating in the lossy heterogeneous medium with undetermined positions within a limited region; RX fixed in the air and closed to the boundary of air-lossy medium; Frequency: 500 MHz ...
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219 views

Impedance Matching: Minimum Reflection vs Maximum Power Transfer

The minimum reflection is achieved when the two "circuits" being connected have the same impedance. This makes sense because all the components of the wave can propagate without needing to be modified....
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Transmittance of a capacitively coupled shunt resonator

I have been trying to understand the expression of |s21| for the resonator mentioned in this article. For a circuit similar to the drawn below, in which R1 is used as the temperature sensitive element,...
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67 views

Use existing WiFi hardware as an RF receiver? [closed]

I have seen mine & many others' (Android) devices nowadays have WiFi hardware capable of connecting with 2.4Ghz & 5Ghz APs. Wanted to know if I could tweak the WiFi driver in the kernel source ...
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28 views

How to do high switched current from small solar

I am working on a small, solar-powered application that makes use of RF and a few higher-power sensors. Those will only be on for a fraction of the time, but might consume 1A-2A at 3.3V. The ...
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77 views

How to select rated voltage of a RF capacitor

For example, GSM low band PA output around 33dBm, I need to put a dc block (33pF) on my design. The cap vendor has rated voltage 6.3V, 25V, 50V. How to choose it? Is 6.3V ok for the design?
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286 views

Can you reuse FCC certification from a pre-certified RF chip and antenna for a new product?

I am in the process of designing a board that turns a Gameboy into a Bluetooth controller. Due to size constraints, I would like to use the ESP32-PICO-D4 standalone chip by Espressif instead of one of ...
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1answer
36 views

Random errors in communication via RFM12B

I am using RFM12B as communication modem with PIC18F4550 on one board as Master board and RFM12B with PIC18F25K50 on two Slave boards. My communication is working but some day when I continue working ...
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75 views

S-Parameters math confusion

S11 for marker 1 says -47.661 dB Two Questions 1st ..... What is | S11 | ^ 2 2nd Is this accurate ? g = 20 log_10(-47.661) dB
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54 views

How to prevent EMI from affecting transistor

I am working on a simple APRS tracker. The schematic is here: It's not on a PCB, but just on a protoboard: The problem: Q1 transistor activates the push-to-talk on a handheld VHF transceiver, "...
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2answers
327 views

Wi-FI Antenna DC Blocking Capacitor

I have a 2.4GHz Wi-Fi design that uses an SMA connector connected to a dipole whip antenna. The issue is the SMA connector mounts to a metal chassis. This causes a potential issue in where someone ...
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69 views

Short antenna feedline

So this was talked about in the comments of a previous question, but not in great detail: I'm using a 2.4GHz ble chip, with a chip antenna. The recommended layout for this chip has a capacitor and an ...
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1answer
64 views

Design of a differential digital signal buffer, 250MHz, 1V output swing

Primarily for academic interest (so please don't suggest ICs to do this, as they won't help me learn how to deal with this kind of problem) I'm attempting to design a buffer circuit to accept a ...
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92 views

Top Ground Copper pour in PCB having three RF Sections

I am designing my second RF board (First one had BLE). This board has LoRa Components (SX1257 and SX1301), GPS (MAX-6) and 4G LTE Module (SIM7600). All the components are on top layer (red layer). My ...
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1answer
71 views

Spectrum Analyzer Mode — TX Duty Cycle With Time Domain?

I have a basic Rigol spectrum analyzer that sweeps across a range of frequencies and displays the amplitude of the signal. When we go to a testing lab, their expensive spectrum analyzer has a mode ...
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2answers
97 views

What options do I have for an ATSC digital television tuner chip? [closed]

I've found a few ATSC digital TV tuner chips (SiLabs, Maxim Integration, NXP) sold via the typical online parts retailers in the USA but they all seem to require contacting sales and signing a NDA to ...
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1answer
100 views

RF transformer design for a capacitance variation sensor

So I`m trying to design a variable capacitance vibration sensor and the best implementation I came up with is a capacitance-to-phase converter. I used: a PIC16F15323 NCO peripheral to control the ...
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2answers
279 views

BJT vs FET for VHF LC oscillator

In the ARRL (2011) section 9.3.1 about LC oscillator circuits it says that "[t]he N-channel JFET source follower shown appears to be the most popular choice nowadays", but does not explain the ...
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1answer
65 views

Buried microstrip vs Top Layer

I'm making a prototype that uses, among other things, a bluetooth mcu connected to a 2.4GHz chip antenna. Its using a 4 layer PCB, and I'm thinking about what to do with the feedline, whether it ...
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34 views

Increasing isolation in power splitter

I want to use This module\minicircuit Power splitter. I am working on the 2.4GHz to 6GHz band. The isolation parameter on the stated for these frequencies in the "Typical Performance Data" table is in ...
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2answers
166 views

How to increase sensitivity of audio-frequency pickup coil

I am building an instrument intended to pick up weak (~100 picotesla) 25 kHz oscillating magnetic fields with Faraday induction. As shown in the photo, I have a 4-layer solenoid coil for pickup ...
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104 views

NRF24 became noisy after a while

I'm making a gyro mouse using MPU6050, NRF24L01+ connected to STM32F103 board, all soldered to a strip-board. The STM32 reads the sensor and sends data via NRF24 to another NRF24 attached to a USB ...
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106 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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PCB Techniques for RF Circuits

Following this Linear Technology (Analog.com) Application Note AN47FA (1991), I found these kind of RF PCBs, among many others, very similar (fig.32 p.18 and Fig.F10 p.107). (The images are in B&...
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178 views

Signal multiplication in AM transmitter circuit

According to Wikipedia, amplitude modulation is achieved by multiplying the carrier signal with message signal. Where is this multiplication performed in this AM transmitter circuit? It seems to me (...
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139 views

RF Module gets stuck with DC Motors [closed]

I am stuck on a problem with RF Module. I am trying to make an RC Car and facing a lot of problems while doing so. I am using a 433 Mhz RF module, HT12E-D encoder decoder, L293D and 2 BO motors(DC). ...
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Using NPN transistor for constant output current. [closed]

simulate this circuit – Schematic created using CircuitLab In the above schematic i would like to understated that how LED is getting constant current . Here we are using following component: ...
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114 views

Vias Size for Microstrip

if my microstrip trace width is about 50 mil, how large should my via drill size be? Should it also be around 50 mil? Thanks!
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39 views

RF signal on wirebonds

I am curious to know how RF signal is transmitted through wirebonds. I thought that in microwave transmission lines, the energy was stored in electric and magnetic fields inside the dielectric ...
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29 views

Checking for signals above strength threshold over SDR on VHF

So I have a small NooElec Software Defined Radio and I've got it working well with my Raspberry Pi using GQRX as a controller and to visualize the SDR output. My goal though is to use a python script ...
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103 views

2 Layer RF PCB With Chip Antenna

I am new to PCB design and RF and I have some questions on my PCB design for Bluetooth low energy chip CC2540. I just want the board to work as a test board, performance is not a problem right now. ...
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2k views

Why solder mask are not applied to RF PCBs

I've gone through some of the RF PCB designs. In which solder masking on the traces are not present. Like this one Is there a specific reason or performance issue to remove that?
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60 views

Can I decrease the width of microstrip at the pin?

I am trying to connect a 60 mil microstrip to the pin of IC. However, the width is relatively large to the space between pins on the IC. Can I decrease the width of microstrip where I connect it to ...
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2answers
231 views

How to draw microstrip line in EAGLE?

I am trying to connect W3113 antenna to my RFID UHF reader. The datasheet of the reader requires me to use 50 ohm microstrip line. However, I do not find where I can draw microstrip. Is it still the ...
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1answer
104 views

Inside of 2.4 GHz Dipole Antenna

I bought the following dipole antenna: Now I want to add some extra simple reflector and directors next to this dipole to construct a Yagi-Uda antenna. For this aim, I need to know where is its ...
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RF design Stitching vias

Having no past experience on RF design i have recently taught that placing stitching vias it is a good practice. Reading the "definition" of stitching vias i am not sure that i can not distinguish ...
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39 views

Circuit for using two antennas (433 and 915 MHz)

I have a CC1125 Module and I need to connect two different antennas (a 433MHz and a 915MHz SMD chip Antenna). They have to be connected at the same time, so when is needed I can simply change the ...
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538 views

RN2483 PCB Layout

I am designing a board based on RN2483. As i have none experience on RF design i am following the guidelines from microchip's datasheet as the pictures bellow. So my question is about the many vias....
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1answer
59 views

Xbee pro s2c 2.4 ghz 10dbi Antenna and its effect

Just wondreing how to increase the range/distance of communication between two xbee modules operating in API mode, we are considering to replace the 2.4 ghz antenna of 5dbi gain with 10dbi high gain ...