Questions tagged [radio]
Consider also the rf tag.
705
questions
-3
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0answers
58 views
2.4GHz radio transmitter and receiver circuits [closed]
I have a drone which is controlled with remote using 2.4 GHz radio signals
but I don't have the remote so i want to make one on my own but ran into problem with the
radio circuits,
is there any ...
0
votes
2answers
103 views
Why don’t radio waves interfere with each other like other waves? [closed]
I know this question has been asked before, but I still don’t completely understand. I understand that different stations are given different frequencies, but waves are able to interfere with each ...
1
vote
1answer
84 views
Can I replace a 101 ceramic capacitor with a close value one?
I'm kind of new to electronics and sorry if this is a bad question.
I am trying to repair my father's old radio transmitter and I noticed that the PTT won't pick up your voice. I opened it up and ...
1
vote
2answers
72 views
How to preserve signal power in a splitter?
I have a double Yagi antenna setup that I used successfully in the past, with both antenna connected directly to a 4G mobile broadband WiFi router, achieving 50-80 Mbps. The antenna have different ...
0
votes
2answers
85 views
If antennae work best at full, half or quarter wavelengths, why don't received signals at 1, 1/2 and 1/4 wavelengths interfere with each other?
How does a simple radio receiver-antenna differentiate between incoming wavelengths that are the same wavelength as the antenna, one-half and one-quarter?
Or would I just hear static unless I have a ...
0
votes
2answers
100 views
How, exactly, does the 'input signal' wave(s) modify the carrier-wave of a radio signal? [closed]
I cannot find a simple (or really, not-so-simple) explanation of how mixing the high-frequency carrier wave with the lower-frequency input signal works...
Is it entirely due to constructive and ...
0
votes
2answers
60 views
Calculating capacitor capacitance between collector and emitter in radio circuits
In many radio transmitters and receivers there is a capacitor between emitter and collector. As shown in this answer this capacitor gives positive feedback to prevent decay. My question is that, how ...
29
votes
8answers
6k views
Why don't we use lenses for RF?
Radio waves are a class of electromagnetic waves.
Light also is a class of electromagnetic waves.
By shaping a material in which the speed of light changes, we can bend the propagation direction of ...
-1
votes
2answers
68 views
Dipole antenna circuit diagram
I have this circuit :
simulate this circuit – Schematic created using CircuitLab
I am trying to build a radio and I need to build a band pass filter . How do I do that?
0
votes
2answers
88 views
Does it looks like a bandpass matching network?
I am trying to understand this receiver and figure out what does this L-C network is.
I read about matching networks and found this example, I am curious if it is the same thing. is it?
In the ...
0
votes
1answer
56 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 ...
0
votes
0answers
64 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?
0
votes
0answers
44 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 ...
0
votes
0answers
25 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 ...
1
vote
0answers
39 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 ...
1
vote
2answers
73 views
Sensor data transmission without using a microcontroller?
What is the most traditional approach to getting sensor data onto a radio from an embedded device pcb that doesn’t utilize a microcontroller?
Up until now, we’ve been utilizing a convenient firmware ...
0
votes
0answers
19 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 ...
0
votes
1answer
49 views
Strange result when simulating RF low pass filter with Pspice
I'm trying to simulate a RF low pass filter in Pspice. The result don't match with my calculations and a filter simulator I found online.
Does anyone know what I'm doing wrong in Pspice?
My ...
2
votes
0answers
23 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 ...
0
votes
1answer
20 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 ...
0
votes
2answers
28 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 ...
0
votes
0answers
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 ...
2
votes
1answer
71 views
Low cost swarm positioning
I'm looking for a way to make a swarm of sensors know their position using low cost, low power system (ie ESP32.)
Requirement:
low cost per device
low power use on devices
1m accuracy is enough
2D ...
0
votes
1answer
41 views
How to do via fencing of an RF trace with a 5V front copper plane and a GND back copper plane?
Background
I am a building a board to send RTTY via a Radiometrix NTX2B as part of my final year High Altitude Balloon (HAB) project. I have just created a PCB which I uploaded to JLCPCB for ...
2
votes
1answer
56 views
Collpits FM Receiver
I saw this simple schematic for an FM receiver:
https://www.mikroe.com/ebooks/radio-receivers-from-crystal-set-to-stereo/the-simplest-fm-receiver
Moreover, I saw some videos online where people have ...
3
votes
3answers
122 views
How to demonstrate mathematically the conditions of reflection in transmission line?
We are all taught about transmission lines and its associates -- characteristic impedance, reflection, standing wave, etc. It is well known what happens when a transmission line is terminated with ...
0
votes
0answers
43 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 ...
0
votes
0answers
23 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 ...
2
votes
1answer
50 views
What to look for when selecting an RF detector diode
I'm currently diving into the topic of RF detectors and I ask myself which are the key criteria when choosing a diode for a given frequency range.
I have a simple detector using a 1N916, which works ...
0
votes
0answers
108 views
Capacitor put the wrong way by manufacturer - is this on purpose or is this a problem?
I am about to change the electrolytic capacitors of a Soviet Selena radio from 1988. I noticed that a few of the capacitors are put with the oposite polarization in respect to the board, e.g. this one ...
2
votes
1answer
68 views
FM modulation, amplitude problem
I'm trying to make an FM modulation with a Hartley oscillator that oscillates at 45MHz. The problem is that it's supposed to have an unitary gain. I can't find a good adjustment between a really low ...
1
vote
1answer
73 views
Frequency modulator won't oscillate
I'm student and I'm working on a school project. The project is a radio transmitter.
My question here is only about the frequency modulator part.
Here is my circuit :
Here is my output signal (...
0
votes
2answers
35 views
How to mitigate change in amplitude when transmitting signal from coil?
I connected 2 equal coils, one from a function generator and the other to an oscilloscope. The signal is transmitted OK, but the amplitude varies with frequency. How can I mitigate this change in ...
0
votes
0answers
48 views
Transmitting sinewave from function generator wirelessly
I am trying to transmit wirelessly a sine wave signal of frequency from 50 to 200kHz. This signal is coming from a dedicated laboratory function generator. How can I transmit this signal and how can I ...
2
votes
0answers
49 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 ...
1
vote
1answer
37 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 ...
0
votes
2answers
70 views
Crystal radio question [closed]
I plan on trying to make some crystal radio sets. The only place I can do this is on the second story, do I have to add anything to the wire coming up from the ground because I'm on the second story?
0
votes
0answers
51 views
Fm receiver circuit doubt
I was trying to simulate an FM receiver circuit on LTSpice.
The circuit is given on this website
I want to know how the correct current/voltage will look around the speaker (modelled as 8-ohm ...
0
votes
0answers
34 views
How do I set up serial communication between two Holybro Telemetry Radios?
I have two USB Holybro 915 MHz Telemetry Radios. These are usually used with Mavlink for communication between drones and ground stations, but I would like to use them to send small amounts of data - ...
0
votes
0answers
51 views
What is the continous power consumption in milliwatts of this circuit?
Also, I want to add a button switch to it. Can I also remove the microphone? I just need to deliver a signal basically like a car key except in a room with several walls (should be strong enough?) I ...
2
votes
1answer
67 views
Is there any country where the 868 MHz or 915 MHz ISM band cannot be used?
The product I am working on (Electronic Shelf Label) uses the 915 MHz radio frequency band and is currently being deployed in Asia. I am gathering the list of countries that the 915 MHz frequency is ...
-1
votes
2answers
56 views
Radio signals detection circuit
What kind of radio signals can I detect with this antenna/tuner circuit?
simulate this circuit – Schematic created using CircuitLab
How can I amplify the incoming signal? I guess I must use a ...
0
votes
1answer
90 views
Diode on crystal radio in odd place?
I'm trying to understand these earings from ebay.
Here is my attempt to reverse engineer the schematic:
If this is correct, I don't understand the function of the diode. If the diode is for ...
1
vote
2answers
106 views
AM modulation stage for small transmitter
I am trying to build an AM radio transmitter. I have built a Colpitts oscillator with a 7 Vpp output and an audio stage with a 1 Vpp output. I am trying to build the amplitude modulation stage I am ...
0
votes
2answers
46 views
Plotting a 20 MHz RF wave in Excel
How can I plot "F1(t) = 20MHz" in Excel?
I will eventually put it into mathcad. The amplitude would be a variable as well but lets pick 4.5 for now. Just get the 20 MHz wave to look how it should.
...
0
votes
1answer
47 views
Can a diplexer connect two antennas with 2.4GHz signal to one transceiver?
I'm looking at using a single transceiver to handle multiple 2.4GHz signals. Think like 2.4GHz mouse or game controller.
A diplexer can easily take two antennae and plug them into one RF signal port ...
0
votes
1answer
42 views
Bluetooth power standard values
Let´s say I have a device with a bluetooth (BLE) 5.1 radio and I would like to know when, using a mobile phone, the power received from the device is good enough to stablish a reliable communication ...
1
vote
1answer
53 views
Why don't these even/odd mode transmission line results math up?
In Pozar's Microwave Engineering, he analyzes the Wilkinson power divider using even-odd mode analysis. His results match the expected values and power conservation is satisfied. Similar derivations ...
0
votes
1answer
60 views
Query regarding RF [closed]
I have few questions about RF.
In the RF they will mention the term "transmitting power." What does it exactly mean, if the transmitting power is more then what will happen?
If they mention a ...
1
vote
2answers
64 views
Does an antenna still receive signals without a resonator?
I want to amplify the signal before separating the frequencies out but I don’t know if the antenna even receives signals without being connected to a resonator. I want to connect the antenna directly ...
