Questions tagged [radio]

Consider also the rf tag.

96 questions with no upvoted or accepted answers
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69 views

Building a personal RF anechoic chamber in a large walk-in closet?

What would one need (besides many foam absorbers) to build an in-home small anechoic chamber for transmissions in the UHF to L-bands (specifically 500Mhz - 2 Ghz), and what resources would you point ...
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83 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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76 views

'P.V.' marking on 1940's electrolytic capacitors

I am replacing the paper and wax capacitors in a tube radio of 1949 vintage. Puzzled by the initials P.V. where I'd expect to read VAC or VDC. Can anyone explain this puzzling jargon? For some reason ...
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24 views

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 ...
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96 views

Uniden BC780XLT Radio scanner, unknown modification

I recently purchased an old Uniden BC780XLT scanner. It has been modified replacing two smd resistor with THT resistors with different values. I am curious about this modification: what does it do? I ...
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1answer
183 views

Gain of a Dual Gate MOSFET

simulate this circuit – Schematic created using CircuitLab This is the schematic of the circuit but tried to find the gain of this circuit, assuming 50 % of the Duty Cycle for the LO, and M2 ...
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0answers
577 views

Is it possible to make a Raspberry Pi transmit FM on several frequencies at the same time?

I have read a few questions here on transmitting on multiple frequencies at the same time. But all of them was about transmitting the same signal to all frequencies. The PiFM and PiTX projects are ...
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182 views

1968-ish Philips radio components question

I found a Philips radio/record player from I believe 1968 at a garage sale. I picked it up for $5. Sweet deal for me! I researched the cabinet to find it's general manufactured time frame. I've ...
2
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1answer
302 views

What is the End of Train Device RF Path?

A railway end of train (EOT) device is applied to the last car in a train consist. It communicates in the 450 MHz band with a head of train device in the lead locomotive. Modern trains can reach ...
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62 views

Connect headset to radio

I would like to connect a headset to my radio (Cobra AM845.) The Cobra radio has a 2,5mm audio jack and the headset has a 3,5mm audio jack. I made a PCB to connect the together as: When I close ...
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13 views

How do i find the FNBW of a main lobe using a diagram?

Looking at the graph below, i can see that HPBW of the main lobe is around 45 degrees, but when it comes to identifying the FNBW i have trouble understanding it. Reading various articles online i've ...
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119 views

Ratio detector FM demodulator

The aim of the exercise is to design a ratio detector FM demodulator circuit. UPDATE: I changed the circuit: This is my transient analysis in output: I found the information about AC analysis and ...
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62 views

How does one choose a resistance for an AM radio antenna receiver tuner?

[![enter image description here][2]][2] I am using some pretty rough, brute force and novice calculations, so if anyone knows a nicer method I am happy to learn. I want to build an AM radio receiver ...
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1answer
46 views

Formula to calculate the isotropic range of a signal

I am wondering, is there a formula to calculate the range of a signal with a given frequency and output power? For example, how do i find the range of a 580khz AM signal on entirely flat terrain with ...
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13 views

Split loop cavity or Loop gap cavity

I want to make a code for the power vs wavelength for the split loop cavity resonator. Can someone help me with the python code for the same?
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1answer
108 views

Vintage Pocket Radio Transistor Replacement is Oscillating

I have an old pocket radio which uses silicon NPN transistors for the mixer and IF stages. I replaced 2 of the IF transistors and the unit functions, but the new transistors are faster than the old ...
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30 views

LoRa RSSI value is not accurate

I want to use LoRa (SX1280) to locate devices by RSSI and TDOA. I put two LoRa devices on the table (within one meter,) one for TX one for Rx, and the RSSI values change a lot. Then I power off the TX ...
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36 views

Low Duty Cycle (LDC) Mode Issues on RF Transceiver

I am experimenting with Low Duty Cycle Mode (periodical sleep and active state transitions to reduce average power consumption) on the SPSGRF-915 RF Transceiver, based on the SPIRIT1 RF Module, which ...
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47 views

RF transformers in first, second and third IF stages, how and why are they different?

Many websites about RF transformers talk about IF transformers to be implemented in first (green slug), second and third (brown, black or orange slug) 10.7 MHz IF stages. Other than this, I don't see ...
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41 views

Design spec for faraday cage

I need to build a faraday cage to shield from the following source: 8 Watt, 14 MHz. The signal is AM modulated I want to build an metal box enclosing the source. I want it to shield the signal so that ...
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1answer
40 views

How to understand the EIRP criteria in 47 CFR § 15.519 for UWB device?

I have difficulties to understand the EIRP critera in 47 CFR § 15.519 for UWB device.It says, (c)...a device...shall not exceed the following average limits when measured using a resolution bandwidth ...
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1answer
26 views

Current waveform for LTE transmit

I am designing an IoT system which uses the SIM7000A. In the SIM7000 series datasheet it says that the highest possible current for LTE is under 200mA (section 5.4 of SIM7000 Hardware Design_V1.03). ...
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82 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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52 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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1answer
46 views

True near field distance for a short monopole antenna

Antenna properties: Height x Diameter = 3.3 inches x 1.4 inches Test Frequency: 900 MHz (Wavelength = 33 cm or 13 inches) I see some conflicting formulas to calculate the near field distance for ...
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1answer
75 views

Unbalanced RF output to FEM module with balanced input

I have a working ZigBee system based on ATMEGA256RFR2. (Datasheet) On page 33 you can check the RF system of this IC. Now I want to use a FEM module to increase the performance and I found the ...
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444 views

How to switch on PixMob-like led bracelet?

I've a led bracelet, which was switched on and controlled by concert organizer (the bracelet called 'fanband' and according to the official site controlled either by special remote or by sound). I ...
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1answer
106 views

Using Clear Channel Assessment / CSMA in CC1120

I have two transmitter nodes both running the same firmware, just that the transmitted packet is configured to have a different node ID (you can call MAC address) in it's packet. I see that the ...
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767 views

FM radio Transmitter - frequency drifting

First can someone explain to me how this FM transmitter circuit work? Second, after replacing Q2 with a blt81, I got a Frequency drifting problem. Once it's running for a while, I need to re-tune my ...
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243 views

Radio Electronics

I'm a beginner in radio electronics. I have basic experience building circuits with both passive and active components. I was wondering if it was at all possible to build your own transmitter, ...
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316 views

Superheterodyne receiver with voltage controlled oscillator

I'm new in electronics and I want to create a FM receiver that performs a product of the received RF signal and a local signal (the local signal is also frequency modulated with a Voltage Controlled ...
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47 views

Radio - Amplifier Connection

This is my first post here, so please give me feedback on how I can improve in the future. Background I am trying to reverse engineer a Becker Grand Prix Stereo Radio with an external amplifier. On ...
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4answers
57 views

Signal interference in receiving antenna?

I’ve been scouring the interweebs for some insight into how electrical signals travel in a wire. More specifically, I cannot wrap my head around how a receiving antenna works with hundreds if not ...
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1answer
53 views

433 MHz Transceiver - understanding OOK demodulator parameter 'OokFixedThreshold'

I would appreciate some help to understand a parameter for this device https://www.semtech.com/products/wireless-rf/fsk-transceivers/sx1231h. I'm far from an expert at RF matters and this question has ...
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66 views

Design of a low frequency (80 kHz) voltage-controlled oscillator circuit

I'm working on a project involving low frequency, through-the-earth data transmission from a transmitter in a karst cave system to a receiver on the surface. I've worked out that a SDR can be used for ...
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57 views

CB Radio Effects Unit. Can anyone help with a wiring puzzle?

I’m working on a small CB radio project for a friend, but am having a hard time figuring out some technical details. If anyone has any ideas on how to solve this puzzle I’d be super grateful. The ...
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49 views

TTE low frequency radio transceiver

I'm interested in developing a bespoke through-the-earth (TTE) radio transceiver for a measurement instrument in a limestone cave system. The issue I have is that conventional RF signals cannot ...
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1answer
89 views

Figuring out what this circuit does

I need to understand this circuit (at least to a basic point). I know it's supposed to be a radio but I need to break into stages in my head to get what's happening. I am going to try to describe it ...
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39 views

What will be the simple SPI sequence to transmit packet with cc1101

I'm trying to mimic behavior of my weather sensor with esphome and cc1101. rtl_433 detects ...
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43 views

Typical half-wave dipole antenna parameters

From my bachelors degree, I have learnt the fundamental theory behind antennas. One of the main types is the half-wave dipole antenna. We've studied its radiation pattern (isotropic) and how it varies ...
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1answer
64 views

Characersitics of a traveling wave on a half wave dipole antenna

For a center fed dipole antenna when operated at resonance, the AC electric potential applied at the feed point results in traveling waves of AC current which emanate from the feed point out towards ...
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78 views

Short range FM transmitter

I made this FM transmitter from this video (https://youtu.be/joFourugXvs) but it has a very short range (30 cm). Where's my mistake?
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51 views

How does current flow in unbalanced antennas?

I have been researching and learning more about antennas recently however I am a bit stuck on understanding how balanced and unbalanced lines / antennas function. My understanding is that a balanced ...
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29 views

Filtering Options for an RTL-SDR (DSP and Analog routes)

I have several related questions regarding filtering for an RTL-SDR radio. It's readily swamped by the very, very strong AM and FM radio stations local to me. So much so that your basic passive RC ...
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20 views

Labeling requirements for equipment using off-the-shelf 900 MHz ISM radio

Can anyone tell me or point me to an authoritative reference as to what external labeling is required for an industrial product that uses an off-the-shelf 900 MHz ISM band radio? I understand that ...
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1answer
28 views

Can I replace the 433mhz modules on my homemade remote controller with a nrf24 transreciever

I built a simple 4 channel 433mhz transmitter and reciever because I can't afford a remote controller, the range is limited to 3 feet and nrf24 transreciever have longer range, so my question is can I ...
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2answers
31 views

A question about antenna gain and signal property

I have an antenna with a somewhat constant gain "X dBi (theta, phi)" in the frequency range of interest. With this antenna we receive a radio signal with an amplitude of "Y Volt (t)". The signal is ...
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47 views

How many periods of an electromagnetic signal are required to be detectable?

Lets say you want a receiver circuit to light up an LED when it receives a radio wave pulse. How many periods must the emitted pulse last to generate enough electric current to be detectable and ...
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44 views

How would I calculate the frequency range of this FM radio?

https://abra-electronics.com/index.php?dispatch=attachments.getfile&attachment_id=599 Here are more clear images of the circuit and it’s diagram Any contribution to how this radio works ...
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24 views

RC quality factor increase

simulate this circuit – Schematic created using CircuitLab This circuit has a bandwidth of 0.9Hz but I want even lower bandwidth. I have this RC tuning circuit. If i had an RLC tuning circuit ...