23
votes
Accepted
Accidentally downmixed stereo to mono, why does this work?
This can be easier to understand if you look at the waveforms.
In a push-pull, or bridge amplifier both lines are driven as shown below.
Notice \$L-\$ is literally the inverse of \$L+\$
Similarly ...
- 46.5k
12
votes
Accepted
How does tuning in a spectrum analyzer actually work?
A RF mixer doesn't actually multiply two signals, at least not directly. Instead, the signals are first added and then passed through a nonlinear circuit, which ideally has a quadratic relationship ...
- 15.6k
11
votes
Accepted
What's the purpose of the band-pass filter in an RF transmitter?
The output of an AM (Amplitude Modulating) mixer contains a number of frequency components. These components are 1) the modulating signal. This signal is typically audio frequency, and in the diagram ...
- 20.7k
11
votes
What's the purpose of the band-pass filter in an RF transmitter?
Every mixer produces quite a deal of unwanted frequencies.
These include:
frequencies contained in both input signals
the above frequencies multiplied by various integer numbers
all of the above ...
- 8,746
10
votes
Accepted
Radar received RF signal phase-shifted by 90 to obtain I/Q signals
What is idea behind this instead of classical way with shifted LO, what affect this produce, any useful link to read about this approach ?
If done perfectly, it really doesn't matter whether the LO ...
- 162k
8
votes
Accepted
Does a carrier wave need to be sinusoidal?
Square-wave carrier systems are actually not uncommon in cable, fiber optic, or even line-of-sight optical communication systems, but it is important to note that these are closed-channel systems; ...
- 607
7
votes
Volume gets lower when left and right audio channels are combined
Without any further details, the possible reasons why volume gets lower when two channels are combined:
"Combiner" is damaged / unsuitable.
Audio output amplifiers are damaged / fighting ...
- 16.1k
6
votes
Algorithm for mixing 2 axis analog input to control a differential motor drive
Here's a solution that doesn't require complicated if/else chains, doesn't reduce the power when moving full forward or rotating in place, and allows for smooth curves and transitions from moving to ...
- 250
6
votes
Gilbert cell. Understanding the basic
The Gilbert cell is properly viewed as a differential-inputs EXOR gate. With 200 milliVoltsPeakPeak signals on RF and on the LO, the current-source will be strongly steered to one or the other "mixer" ...
- 33.8k
6
votes
Accepted
Feasibility of rat-race as RF mixer without active devices
some sort of active device (sometimes diodes)
This suggests that you deem diodes to be active devices, so presumably a passive device means no diodes. In that case, a structure that's passive will ...
- 162k
5
votes
Why is DC offset from LO feedthrough less problematic in the second mixer stage of a dual conversion receiver?
The first mixer is fed by an LNA with a lot of gain making it more sensitive not only to the signal you're trying to receive, but also to signals you aren't trying to receive, including internal ...
- 40.8k
5
votes
Accepted
DIY mixer - use diodes to prevent input potentiometers influencing each other
You need a simple mixer circuit based on the summing amplifier.
simulate this circuit – Schematic created using CircuitLab
Figure 1. Stereo mixer basic schema.
As Brian Drummand says, you ...
- 171k
5
votes
Accepted
Voltage across tape recorders
The author of that article seems to be confused. The caption says:-
Figure 2. In a matched-impedance system working to the 600 ohm
standard, connecting two tape machine inputs to the same console
...
- 55.9k
5
votes
Accepted
Cost-efficient mixers and/or demodulators for low frequencies
Antonio's suggestion of four switches to make a mixer is an ideal one for low-frequencies like 200 kHz. A local oscillator at 4X frequency (800 kHz) allows I & Q output:
simulate this circuit &...
- 24.4k
5
votes
What's the purpose of the band-pass filter in an RF transmitter?
Before sending the signal to the antena the signal's bandwidth must be limited using a band pass filter in order to avoid interference with adjacent stations.
Most of the RF spectrum is regulated by ...
- 427
5
votes
Self-biasing diode in mixer applications
A 1/4\$\lambda\$ transmission line shorted at the end will act as a short circuit for DC, but as a high impedance at the frequency of interest. This is sometimes used as what's called a shorted stub ...
- 19.6k
5
votes
Accepted
Volume gets lower when left and right audio channels are combined
Contrary to popular belief, the output impedance of an amplifier is not 8 or 15 Ohms. It is very low, typically less than 0.5 Ohms
So connecting outputs in parallel presents close to a short circuit ...
- 539
4
votes
Accepted
Are electret microphones frequency mixers?
No, at that SPL, the microphone will be operating linearly, and not producing any significant harmonics or intermodulation products.
- 170k
4
votes
Audio summing mixer- inverting or non inverting output?
When listening to a single channel, delay or inversion doesn't matter. When the overall audio has multiple signals (stereo has two, for example), then the relative phase or inversion between channels ...
- 312k
4
votes
Why can't this mixer be built with two resistors?
As you've already found out:
$$
a = \frac {R_2} {R_1+R_2} \\
b = \frac {R_1} {R_1+R_2}
$$
Also realise that:
$$
a + b = \frac {R_2} {R_1+R_2} + \frac {R_1} {R_1+R_2} = 1
$$
So \$a\$ and \$b\$ are ...
- 5,751
4
votes
How to make mix mono into stereo audio
No, using diodes does not accomplish what you want. That will partically rectify the additional signal, making it sound like a mess.
You need to actually mix the new signal onto each of the two ...
- 312k
4
votes
Multiple Options for Passive Audio Mixer
For resistor values, I believe the goal here is to attempt to match impedances or to minimize signal attenuation. Model the output and input impedances of your sources and load (just a nominal ...
- 335
4
votes
Accepted
Explanation of 3 Tone Control Circuit
I'm not going to try and give you a full treatise but give you a high-level overview.
simulate this circuit – Schematic created using CircuitLab
Figure 1. A simplified variable gain inverting ...
- 171k
4
votes
Why does a Double-Balanced Mixer Reject the LO?
But what is the reason that LO frequency doesn't show up in the
output?
Those four upper MOSfets are a balanced bridge ideally. In the simple case, they are switches and add no DC component, as you'...
- 24.4k
4
votes
Accepted
Why doesn't the microwave motion sensor make its output negative when the object go away from it?
The module you are using mixes the received reflection with the transmitted signal.
The output is the difference of the two frequencies.
An object moving towards the sensor will cause the reflected ...
- 69.2k
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