13
votes
If any "antenna" can be impedance matched to the source, can any piece of metal be tuned to perform the same as a physically tuned antenna?
An antenna that is "the optimum length" for the operating frequency (i.e. "tuned"), will present an electrical resistance to a transmitter circuit that comprises 2 elements (a) the ...
- 466k
8
votes
If electromagnetic waves are indeed created by a changing electric and magnetic field, then why don't we see magnet based antennas?
We are bombarded by EM radiation from many sources.
Here, from https://swling.com/blog/2016/06/steve-points-out-the-itu-r-recommendations-on-radio-noise/, is radio noise from various sources.
At ...
- 4,907
8
votes
Accepted
Do radios need a minimum range to function properly?
Generally, the issue that mainly occurs with very short distances is overloading the receiver with too high input power.
According to the linked datasheet, the receiver at hand has a Maximum Input ...
- 5,087
7
votes
Accepted
How accurate is the antenna reciprocity principle in practice?
This is accurate in itself, you will get the same attenuation of the signal in both directions, even with different antennas at different stations talking to each other.
What is not the same in regard ...
- 9,431
7
votes
Accepted
Simple method to generate nonuniform magnetic radiation in a region of 0.5 mm?
I believe that anti-Helmholtz coils will likely service your needs: -
The beauty of this type of coil is that you can make the coils bigger than the target (more practical) and still get a steep ...
- 466k
7
votes
Accepted
Can we catch signals from a cellphone using an external device?
The first two? Yes.
The third one? Yes, you can search for patterns, and you'll find them, because not all the information is encrypted. The encrypted information probably won't have patterns, or if ...
- 5,580
6
votes
Accepted
If a shipboard antenna isn't "grounded" to the water on a fiberglass-hulled boat, would using the radio (TX or RX) attract more lightning?
The voltages generated by RF transmission are not significant when compared to the 10-100 million volts of a lightning strike so the use of the radio will not be an increased risk. Using the radio in ...
- 10.1k
6
votes
Accepted
Are there advantages to sleeved balun over plain whip for short 2.4GHz antennas?
Yes, there are advantages to the "sleeved balun" antenna designs (which are more commonly called coaxial dipoles), and that is that they are "ground-independent". This means their ...
- 5,909
5
votes
Accepted
Monopole antenna with coil design
advertised to be suitable for operation in the GHz range
Marketing will literally claim anything to sell an antenna; that's very much their job.
An antenna that doesn't come without a plot of ...
- 98.2k
5
votes
Accepted
Why aren't baluns needed for a monopole to unbalanced coax connection?
The antenna that you call a monopole may actually be a coaxial dipole
simulate this circuit – Schematic created using CircuitLab
I apologize for the very crude drawing.
A coaxial dipole has two ...
- 26.1k
5
votes
If electromagnetic waves are indeed created by a changing electric and magnetic field, then why don't we see magnet based antennas?
You could indeed make an EM radiator by moving a magnet -- spinning it cross-axis, say.
The problem is, for the speed to be fast enough to have reasonable (or even detectable?) emissions, no known ...
- 43.2k
5
votes
What's a good way to connect an antenna to a breadboard for experimenting?
High frequency signals and bread boards do not play nicely together. However, since you're maxing out at 7 MHz, I think you can get away with plugging the antenna wire into the breadboard. 7 MHz is ...
- 571
4
votes
If any "antenna" can be impedance matched to the source, can any piece of metal be tuned to perform the same as a physically tuned antenna?
Matching only ensures that a given antenna can actually achieve its potential performance. But it doesn't change the properties of the antenna itself.
An electrically short antenna is still a lousy ...
4
votes
Does an aggregation of two lambda/2 dipole antennas z-axis oriented radiate towards the mentioned axis?
No. The radiation pattern will still be perpendicular to the Z-axis; perpendicular to the length of the antennas. The combined pair will radiate in the x-y plane.
Exactly what that pattern looks ...
- 10.9k
4
votes
Accepted
How can a Faraday cage absorb and reflect waves, yet antennas mostly absorb and can be used on signals?
From my understanding an antenna’s job is converting the freespace
impedance to the feed-point impedance, is it something to do with,
effectively the faraday cage does not have a matched ‘feedpoint’ ...
- 466k
4
votes
Accepted
Can you convert a radio receiver frequency from 315 to 433 MHz by changing the antenna?
No, the antenna is just the means to get from wired to wireless. Different frequencies calls for different antenna designs but it does not set the frequency in this case. The frequency is mainly ...
- 16k
4
votes
If a shipboard antenna isn't "grounded" to the water on a fiberglass-hulled boat, would using the radio (TX or RX) attract more lightning?
If a shipboard antenna isn't "grounded" to the water on a
fiberglass-hulled boat, would using the radio (tx or rx) attract more
lightning?
Lightning almost effortlessly manages to ...
- 466k
4
votes
How accurate is the antenna reciprocity principle in practice?
Local background noise is hardly ever the same. Even not-so-local background noise is often different, since each station in a long-distance contact "sees" a different part of the ionosphere....
- 7,948
4
votes
Why don't people always use 50 ohm resistors when matching impedances?
I want to ask why we don't use a 50 Ohm resistor for impedance matching?
Because
you can't get from any point to any point on the Smith chart using only one type of component; so, the proposal ...
- 98.2k
4
votes
Why don't people always use 50 ohm resistors when matching impedances?
I want to ask why we don't use a 50 Ω resistor for impedance matching?
Real resistors automatically consume power and reduce the signal by at least 6 dB. Using a tuned LC to match doesn't lose any ...
- 466k
4
votes
Accepted
EMF Meter: difference between AC magnetic, AC electric, and RF Measurements
No they are not the same thing.
As a simple first order model:
They are magnetic only waves (B) without electric field (E), electric field only waves (E) without magnetic field (B), and when they both ...
- 164k
4
votes
Monopole antenna impedance measurement
I have one of those antennas somewhere. It was used screwed into a PCI wireless card.
That antenna intrinsically will vary in impedance. Impedance will depend on how much it is bent and will depend on ...
- 1,011
4
votes
Can we use telescopic antenna for RF receivers?
Portable AM/FM radios and televisions with telescoping antennas used to be extremely common, these are receivers.
Spring coil antennas are used when you want the antenna to be short while in use, ...
- 26k
4
votes
Do radios need a minimum range to function properly?
CARE & FEEDING OF 2.4 GHZ LOW POWER TELEMETRY MODULES.
NRF24L01 and the "+" variant and the superset Si24R1 are a VERY variable feast. There is some utter junk out there and some ...
- 151k
4
votes
Why does the Voyager space craft use a 3.7 meter dish antenna?
In spacecraft (but generally, everywhere), decision on how big to make an antenna are trade-offs on a system-level, system being the whole spacecraft. Sure, the team building the comms link would have ...
- 98.2k
4
votes
Why does the Voyager space craft use a 3.7 meter dish antenna?
To a first order approximation, an antenna's sensitivity, that is how much power, or signal it can capture, is directly related to the size of the antenna or, more properly, the size of the aperture.
...
- 10.9k
3
votes
Monopole antenna with coil design
How does the loading coil work in this case? Is it even a loading coil
at all?
At the intended frequencies, this "coil" would have immense inductance, if you considered its inductance alone....
- 26.9k
3
votes
Yagi antenna with 16 dBi gain, is it bottle necked by the power input?
The antenna doesn't care how much power you put into it, as long as it's not so much that it arcs or melts.
When working with decibels they add. So if your amplifier is 5 W, that's 37 dBm.
If you put ...
- 26k
3
votes
Accepted
If any "antenna" can be impedance matched to the source, can any piece of metal be tuned to perform the same as a physically tuned antenna?
Two reasons: efficiency, and bandwidth.
First, every matching network has some inefficiency, because it's made out of real components like inductors, capacitors, and transmission line. Mostly the loss ...
- 7,948
3
votes
GPS signal combiner
Trying to combine signals from multiple antennas, will not work properly in the general case due to lack of a clearly defined phase centre. The only way for this to work reliably is with a single ...
- 7,906
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