76
votes
Accepted
Why do IR remotes influence AM radios?
This IR signal is indeed ignored by the AM radio. However, an AM radio is very sensitive the radio waves (yeah, DUH! ;-) )
When the IR remote operates (you push a button) the chip in the remote will ...
- 81.2k
58
votes
How did 455 kHz end up being a commonly used IF (intermediate frequency)?
Piecing together information from a number of sources on the web, I believe this is the correct combination of circumstances:
Early amplifiers were not stable much above 500 kHz, so the IF had to be ...
- 177k
39
votes
Accepted
Can I break a radio tranceiving device by operating it with no antenna connected?
You could potentially break some radio transmitters by operating them without the antenna connected.
Several things combine to make this possible.
First, it's difficult to make power at RF frequencies,...
- 171k
38
votes
Accepted
Why does radio reception consume so much energy?
In short: receiving is much more complicated than transmission.
You'll notice that whatever you measure in the real world is overlaid with noise.
The problem "seeing all this noise with a bit of ...
- 98.3k
36
votes
Accepted
What went wrong with my DIY project?
Congratulations on spending time and effort with your son learning the practical aspects of electronics. [Be aware that this may have the effect of turning him into an engineer :-) :-) ].
It is ...
- 151k
31
votes
Accepted
What kind of electronic device is this?
That would be an inductor with a resistor style color code.
Here's a picture from that Wikipedia page showing some similar 100 µH axial lead inductors:
Vahid alpha at English Wikipedia CC BY 3.0, ...
- 41.5k
26
votes
How many watts does a 40 MHz radio frequency signal create?
This is like asking "how bright is a red light?". It's as bright as it is. You can make a bright red light or a dim red light.
As another answer points out, the energy per photon of an ...
- 132k
25
votes
Accepted
Why don't we use lenses for RF?
In optical engineering, the choice between lenses and mirrors often comes down to aperture diameter: less than a few inches and lenses can be made cheaply and with high accuracy. Larger and costs ...
- 17.8k
24
votes
Where is the antenna in this remote control board?
Disclaimer: Any modification to this circuit will likely make it illegal to operate under FCC regulations(in the US), and likely other regulatory bodies in other countries!
The antenna is the section ...
- 890
22
votes
What could this signal at 119.9 MHz be?
This signal is an extremely inefficient use of bandwidth, as you can see because there is an essentially unused area between the center and ±125 kHz. Therefore, I expect that it is almost certainly ...
- 7,581
21
votes
How can the same radio signal be received by 100s of receivers without any loss in it?
... without any loss in it ...
First, physics says there must be some loss, because energy is received at the antenna and is available to be consumed by the receiver.
... be received by 100s of ...
- 46.7k
20
votes
Accepted
Radio frequencies, what are the limits?
Radio waves and light waves are both electromagnetic (EM) waves. Visible light is physically the same thing as radio, just at a different frequency/wavelength. All EM waves are a coupled electric and ...
- 3,552
19
votes
North American Regulations on 433MHz Radio
I have a similiar device, and just wanted to clarify something:
For a low power 433MHz transmitter, those would fall under under the provisions of FCC Part 15.231 for periodic transmission (which ...
- 1,917
18
votes
Accepted
Why can only analog signals pass through air (wireless channel)?
Adding to Tom's answer:
The wording is not very clear, but what this means is that digital signals do not actually exist in reality. All signals are analog.
When we decide that a voltage above a ...
- 80.3k
18
votes
Why don't we use lenses for RF?
i don't know of any rf lens usage case
That can be changed. They are quite common for ku-band and up. Think satellite communications, radar, point-to-point links where you want high but can't use a ...
- 98.3k
18
votes
Why does radio reception consume so much energy?
Well, first off, you're looking at a microcontroller. The datasheet also says it will draw 3.4mA without any radios on, so you can only attribute 3.5mA to radio reception.
And then, if you look at the ...
- 7,948
18
votes
Is there a limit to how much power could be transmitted wirelessly?
Using directional antennas, hundreds of watts have been transmitted to drones. Further, a bit higher in the EM spectrum, lasers have been used to remotely power unmanned aerial vehicles (UAV's).
In ...
- 4,977
17
votes
Why does this AM radio circuit not work?
With components of 1 mH and 20 pF, the minimum frequency you'll be able to tune is about 1.125 MHz. And that's neglecting the self-capacitance of the inductor, which is probably quite significant.
For ...
- 177k
16
votes
Why don't we use lenses for RF?
There is the Luneburg Lens, which can be used for various applications, from optical to RF. Luneburg Lenses are generally spherical, made of concentric shells of material with a stepped refractive ...
- 1,183
16
votes
Why don't we use lenses for RF?
You can make lenses out of metamaterials - see this Phys.org story
A three-dimensional self-supporting low loss microwave lens with a
negative refractive index Journal of Applied Physics 112, 073114
(...
- 2,216
16
votes
Accepted
Is AM radio louder the closer you are to the transmitter?
If you detuned from a strongly received AM radio station transmission, you would immediately hear a lot of background noise. You can even hear the background noise when you receive a weak station that ...
- 467k
15
votes
Can I break a radio tranceiving device by operating it with no antenna connected?
Just to complement the excellent answer of Neil_UK and stress the fact that at RF frequencies voltages and currents don't really behave as those nice entities you know from KCL and KVL.
You must ...
15
votes
What went wrong with my DIY project?
Those two joints look like they were cold soldered to me - the parts moved before the solder had cooled completely. So, bad connection to the circuit.
At the same time, there's a little splatter of ...
- 73.1k
15
votes
What went wrong with my DIY project?
The plastic connector is backwards. The one in the lower right has notches on the board that match up with the notches on the connector. These are keyes that prevent plugging the wrong way around.
- 317
15
votes
Accepted
Where is the antenna in this remote control board?
The antenna is the rectangular loop trace at the top edge of the PCB. Transistor Q1 is the oscillator. L1 is probably used to provide DC power to Q1, and C1 and C2 are part of the matching and ...
- 5,909
14
votes
Hearing only noise and ticking sound with simple AM radio - The art of electronics
The 1N4001 diode will never likely be any good because it can have (manufacturer dependent) a reverse recovery time of up to 30 μs and that makes it ineffective as a signal rectifier above a few kHz. ...
- 467k
14
votes
Accepted
2.4GHz sender cause 433MHz receiver jammed, vice versa
What you are experiencing is called Blocking. It's part of a continuum whereby a receiver is very sensitive to interference on-channel, less sensitive in the adjacent channel, and progressively less ...
- 171k
14
votes
Is AM radio louder the closer you are to the transmitter?
Yes, a crystal AM radio will receive stronger signals louder than weaker one.
You are also correct that nearly all commercially-made AM radios have AGC or Automatic Gain Control to help alleviate loud ...
- 7,967
14
votes
Can two interfering light beams create radio waves?
Yes, however you would need a nonlinear optical medium to get mixing such that sum and difference frequencies are generated.
In a linear medium like air or vacuum, adding and subtracting does not ...
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