Questions which involve the properties or applications of individual electronic components.
Questions tagged [electronics]
115 questions
19
votes
3 answers
SDR sampling bandwidth - do the bits per sample matter?
I'm looking at data converter chips for a homebrew SDR design, and I see that I can choose not just the sampling frequency, but also the bits per sample.
Obviously the sampling frequency has to be several times the target frequency, but what effect…
Adam Davis
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13
votes
3 answers
UHF FM power amplifier design without expensive software
I'm designing a small UHF data transceiver for the 70cm band, based on a Silicon Labs EZRadioPro Si4463 IC. Modulation is FM, 12.5kHz channel step. The concept is similar to SiLabs' AN656 application note but with a different power amp BJT as the…
philpem
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11
votes
3 answers
Why does "high SWR" damage transmitters, instead of "impedance mismatch"?
In the audio realm, where cable lengths are insignificant compared to the signal wavelength, I would understand an impedance mismatch damaging an amplifier as follows:
Take an audio amplifier that can deliver 100 watts of power into an 8 ohm speaker…
natevw - AF7TB
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10
votes
3 answers
Why are germanium diodes specified in amateur radio designs?
It's somewhat common to find a schematic that calls for a germanium diode in amateur radio contexts. For example:
This is a QSK circuit from the Fldigi manual.
And yet, purchasing a germanium diode is a relatively difficult task. For example,…
Phil Frost - W8II
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10
votes
1 answer
How does a switching mixer multiply the two signals?
I understand what a mixer does, and when I see it in a block diagram it's obvious what purpose it serves and how it fits in the overall design of the radio.
However, when I look at the schematics and see how it's created, I don't understand how it…
Adam Davis
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9
votes
0 answers
Beyond Maximum Stable Gain of a transistor
I was plotting constant-gain circles on the Smith chart the other day for a potentially unstable RF transistor.
I recently read on-line that for a potentially unstable transistor the maximum gain that can achieved is the MSG or maximum stable gain.…
Thomas L
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8
votes
1 answer
What will the *amplitudes* of mixer products be?
The key fact about mixers, which iirc is even part of the FCC amateur radio exam(s) in the USA, is that they output "the sum and difference" of the input frequencies. And iiuc in practice it's usually assumed that besides those products the mixer…
natevw - AF7TB
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8
votes
2 answers
How to reduce VFO sensitivity to the hand capacitance?
I got a little tired of Si5351 and decided to build an analog CW transceiver. It's almost done and works pretty well. However, I discovered one problem. When I reach the VFO control with my hand the frequency shifts a little, about 100 Hz or so.…
Aleksander Alekseev - R2AUK
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7
votes
1 answer
Double power-handling ability of RF amplifier output transformer
I want to base the output network for a 500W push-pull HF amplifier on "A 250W Broadband Linear Amplifier" described in Chapter 17 of the 2014 ARRL Handbook. I need advice on whether and/or how the 1:4 impedance step-up transmission line transformer…
Brian K1LI
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7
votes
7 answers
Is it practical to use a slug-tuned variable inductor in an antenna matcher (aka "antenna tuner")?
I will soon need an antenna impedance match (aka "antenna tuner"), because I'll initially only have a single antenna for my HF rig (needs to cover 80m, 40m, 20m, 15m, and 10m). Obviously, in order to manage SWR, I'll need a matching network, quite…
Zeiss Ikon
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7
votes
2 answers
Water cooling a GS-35B in lieu of air cooling?
Does anyone know how to --or have any experience with-- water or oil-cooling the anode? Since forced-air cooling is required, the sound from the blower and the exhaust air would be too noisy for my ears.
They look similar to an 8877, but have…
Mike Waters
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7
votes
1 answer
How to determine number of turns for a 1:1 balun?
I would like to make a 1:1 balun with М1000НМ ferrite core (magnetic permeability - 1000) and 1 mm thick copper wire using triple bifilar winding. Unfortunately I didn't manage to find a clear instruction on how to determine the required number of…
Aleksander Alekseev - R2AUK
- 4,262
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- 48
7
votes
2 answers
Learning RF electronics
I've been studying and building test circuit for actually several YEARS now, so far with no success. It sounds ridiculous but it's true.
So I feel like I have a good understanding or RLC circuits, I can calculate phase shifts and impedances etc., I…
user13171
6
votes
3 answers
How should this SWR meter's directional coupler work?
I'm wrapping up a "home build" of the MFJ-941EK antenna tuner kit and having trouble getting the wattmeter calibrated. I can't use C4 to get the reflected power reading calibrated down to 0 as is supposed to happen. So now I need to figure out what…
natevw - AF7TB
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6
votes
1 answer
Non-inductive resistors
When we use a "non-inductive resistor" to check the output impedance of say an unun, say 50ohm 1:1, what resistor type is actually non-inductive, or does it not really matter as long as the leads are short and frequency is low? I know there's…
t252
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