Radio Definition and 691 Threads

In a lecture (at 10:24) on the birth of the laser printer, Gary Starkweather mentions that a HAM radio license was required to use early lasers (he finished undergrad in '60). Why was this? (All the following questions are just filling out the primary question.) What were the...

In the 1970s, did transistor radios have RF receive sensitivities down to the 1 microvolt level? If not, what is the highest microvolt it could resolve? But how could it do that? Even modern amplifiers have much noises. For example, at 100kHz, and a very quiet circuit with total noise of...

I've been working on a personal project to connect my old H10 series david-clark headset to my UV-5R radio. Up to this point, I've been using the headset purely as a set of headphones to listen in, but I want to be able to transmit with it as well. The problem I'm running into is that the...

https://www.wired.com/story/tetra-radio-encryption-backdoor/

We are attempting to penetrate 1m of water featuring dissolved ions ( assume salinity of sea water) using radio waves. Aside for using wavelengths of very low frequency radio or below, what would be the best frequency for achieving this task?

I’ve read that the Ca2+ channels in neurons can be manipulated through the use of certain radio wave frequencies. And the resulting internal/external charge differential will cause the neurons to fire. Does anyone have any more insight into that?

Hi everyone I'd like to set an ImageView background for a menu screen that uses ScrollView, ConstrainedLayout and Radio Buttons. This is possible if I hardcode the width and height of the ImageView, but I don't want to do this because it might ruin the formatting on some models of phone. I'd...

What does the output of a radio telescope look like? I suppose it is not an image like that of a telescope observing visible light

The solution pretends that the ship is a two point source emitter, one h above the water, and one h below the water. The one below the water is out of phase by half a wavelength. I don't understand why then d sin θ = λ - wouldn't it be d sin θ = (1/2)λ since it is out of phase? Thank you.

I wonder if anyone could help me identify a short story I read back in the 1960s. It might have been in an old (1950s) copy of Astounding Science Fiction magazine. I think the story involved a sea journey but the main thing I recall is that that radio wave communications was interpreted as...

Homework Statement:: I would like to write a science fiction story on how alien quantum communication could work and how scientist on Earth build the first "radio" receiver, entangling Quantums over big distances randomly. Relevant Equations...

It's been stated that the index of refraction of materials varies with frequency throughout the EM spectrum. What are the index of refraction for various materials in the radio frequency?

I seem to hear about huge astronomical events that generate radio waves seem to come from objects with huge magnetic fields, such as neutron stars and black holes. Does that mean magnetic fields only come from the radio end of the spectrum, and not higher frequencies, like IR, UV, X-rays, etc?

I have searched the internet and spoken to the manufacturer of my equipment and can not find an answer. I am using RFExplorer (test equipment) to measure the power generated by my ham radio antenna. The only options for displayed power is mV/m or nW/m2. I am trying to find out how to convert...

I saw on another forum mention of Alcyoneus radio galaxy and have been google searching but can't find any information on it from any reputable astronomy related websites. Is it real or just fake news?

Hello Guys! I'm studying radio waves and I can't understand the following: Radio waves propagates through Earths surface as a ground waves, line-of-sight waves or skywaves. There is a phenomenon that occurs with line-of-sight waves (and maybe with ground waves?) known as height gain, in which...

Paper: N. Hurley-Walker, X. Zhang et.al, A radio transient with unusually slow periodic emission (Nature, 26 January 2022) Abstract: The high-frequency radio sky is bursting with synchrotron transients from massive stellar explosions and accretion events, but the low-frequency radio sky has...

Treating water as having a conductivity of ##\sigma \sim 5 \ \mathrm{Sm^{-1}} \gg \omega \epsilon_0 \epsilon_{\mathrm{r}}## then Maxwell ##\mathrm{III}## implies\begin{align*} \nabla \times \mathbf{H} = \sigma \mathbf{E} + \epsilon_0 \epsilon_{\mathrm{r}} \dot{\mathbf{E}} = -i \omega \epsilon_0...

Any clue how to make sure that the radio is alive on a satellite that has just reached orbit? Can you transmit at full power although you're not sure whether the satellite antenna is deployed or not? What if you do and the satellite antenna turns out to be stowed? How could you have avoided that...

I am very confused as to how diffraction even happens. I am thinking that radio transmitters are those tall towers. (My country doesn't have those, our lines are underground). Where is the 2nd antenna, and how does the diagram look like? Does it look like: (The dashes are to fill up space)...

Hi everyone! :) While i watched rc jet exhibitions on youtube, i find that the most fast of this RC reached +700 Km/h. When i browse more information about the tourbine, i realized that for a hypothetical supersonic RC the mechanical system of the tourbine must have a complete air compressor...

If my eyes were sensitive to radio wavelength instead of visible wavelengths (and were large enough to resolve an image), what would the world look like? I assume that my brain would interpret different frequencies in a way that is analogous to colours, such that I could distinguish them from...

\begin{Form} Let f be the function given by $f(x)=300+x^3$. On which of the following intervals is the function f increasing?\par \ChoiceMenu[radio,radiosymbol=\ding{108}, name=b] {\textcolor{white}{}}{ } $(-\infty,-10]\cup[10,\infty)$ \par...

How close to "antenna" was the metal barbell thing which was part of Heinrich Hertz' apparatus? Did he know in theory how to build a radio but just didn't have the right components to do it? I know someone around that time referred to the problem of radio in terms of needing proper sustained...

Ever since I learned about FM something's been bugging me, which is that the PLL error correction acts on the encoded data, seeming to leave open the possibility of the shape of the data itself interfering with the PLL's interpretation of what the carrier frequency is. It seems dangerous to mix...

My attempt: I think ##x## is the path difference so by using trigonometry, I got ##x=d \sin \theta## But my teacher said the answer is ##d \cos \theta## What is my mistake? Thanks Edit: Sorry, I found my mistake. My ##x## is not the path difference

Audio recordings of radio traffic from famous incidents (e.g. 9/11, various shootings) are difficult to understand - at least those I find on YouTube are. Is there something about the way radio traffic is recorded that degrades it? Often the beginning of a sentence is cut off. Could this be a...

Hello, I'm interested in using a choke inductor as a receiving antenna for long-wave radio signals (300kHz). What are the "obstacles" in comparison with a standard ferrite rod antenna used in AM radios? So far I'm registering these: 1) low Q at the desired frequency available chokes seem to...

The Hubble space telescope has tracked down a few FRBs that originate in the spiral arms of galaxies. The NASA video on YouTube: Text version if you prefer: https://scitechdaily.com/magnetic-monsters-hubble-tracks-down-location-of-mysterious-radio-signals-from-intergalactic-space/ Cheers, Tom

This is probably a trivial or even a stupid question, the reason I am writing here is I couldn't find something satisfactory online. I am a new amateur radio operator. Currently enjoying listening to SW and MW bands. I have a nice radio receiver with a long telescopic antenna. I have noticed...

Hello I've made a small program that does FFT, Fast Fourier Transform on a signal from radio receiver (RTL SDR), and parabolic antenna. Of course, the output is amplitude depending on frequency. I want to use it to detect and measure 1420MHz radiation from space. But I'm not sure on what's the...

Hello everyone, I'm not sure I write in the right part of the forum. If not please point me somewhere. Query: I noticed some of the phone chargers interferes with digital radio. I checked some forums and I found reasons like that: It is a low-quality charger and it generates a huge amount of a...

This is the FM demodulation "discriminator" circuit. It is one of the simplest analog demod setups one could think of. An RF (FM) voltage signal is applied at V12 and the voltage at ' a' ' is supposed to contain the AF signal in its amplitude. The idea behind the circuit is that it resonates at...

https://www.scientificamerican.com/article/alien-hunters-discover-mysterious-signal-from-proxima-centauri/?fbclid=IwAR0HOFRU-cvFaU66Wbqql-hoo91hA1WnCl9Azwqa84ly-zS6cjBiDFzlK8o Excerpt: Most curiously, it occupies a very narrow band of the radio spectrum: 982 megahertz, specifically, which is a...

Hey guys, I'm new to the physicsforums. I wanted to share some videos I made and see if anyone was interested or wanted to discuss what they see. In this video I show in a manner in which is VERY easy to see, that a reflective surface will reflect not just light but also radio waves (and most...

FRBs apparently from "...a “run-of-the-mill” magnetar. Astronomers labeled it SGR 1935+2154..." About 30,000 light years away. https://news.mit.edu/2020/ultrabright-radio-flashes-detection-1104 The research paper is behind a paywall, but Abstract at...

Hello, this is an assigment form the 4th grade high school physics in Croatia, concerning electromagnetic waves. Radio waves of wavelength 12m propagate from the source. The source is on the surface of the water and two waves propagate from it: one through the air and the other through the...

Hello, first from all, I am completely new and uneducated in physics. But from nothing I have had idea how to make this invention. And I have quite strong need to share it. My mind found out how we can communicate with no delay through out our universe. Seems quite fancy, isn't it? Yes, quantum...

Anyone have more information...here is Scott Manley report...not good!

So I discover that a human body can affect a radio receiver. When I get close to a receiver, the radio produces buzz sound, which means that the radio signal is disturbed. However when I touch the plastic case of the receiver, the receive becomes normal. This phenomenon does not happen every...

I would like to estimate the magnitude of a radio signal received from a transmitter by first principles: Transmitter antenna length ##L=1## m Transmitter antenna area ##A=1\hbox{ cm}^2## Number of electrons per unit volume in antenna ##n_e=10^{28}## Radiation resistance of antenna ##R_R=10\...

Why SAR value at body is allways higher than at head?

I haven't been building electrical circuits for quite a while, but I'm now trying to create a circuit that produces RF random noise. I found this webpage with some information about it. http://www.n5ese.com/noise.htm There is this diagram there: I have an LM324D SMD op amp with pins...

https://www.sciencealert.com/check-out-this-amazing-plan-to-turn-a-crater-on-the-far-side-of-the-moon-into-a-radio-telescope Original article from NASA: https://www.nasa.gov/directorates/spacetech/niac/2020_Phase_I_Phase_II/lunar_crater_radio_telescope/

Let's assume the following sine signal sent by a low frequency (100 kHz) transmitter. I think with the information that the sending power is 1 watt and the starting phase is 0 the signal is fully described. Are the following assumptions correct?: 1. The frequency of all photons leaving the...

Hello all: I hope all are fine and well in their houses As I am looking into ways to fill my empty time other than reading undergraduate physics books I start to look around and wonder about giving online lessons for public school students , which they are now without a school , but I found...

i have ts832 transmitter and a rs832 receiver. i tried to build a radio receiver to pick up radio signals from the ts832 transmitter,. i measured the ts832's antenna. it was 8.8 centimeters. so i cut a piece of copper wire 8.8 centimeters long. i connected the bottom of the copper wire to two...

I have never seen ray model of light being considered for radio waves, or waves of larger wavelengths. I have a feeling that this model does not apply to them. Am I right?

Is the carrier wave modulated or in other words "modified" with the information signal? If so how exactly is this done? I can't find or maybe I am looking at the wrong things but I don't understand how this is done. I know that AM is modulated with the amplitude and FM is modulated by the...