Questions tagged [electronics]
Questions which involve the properties or applications of individual electronic components.
115
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Zero resistance inductor
I have RF schematic and there is one inductor with no inductance value, but with this.
Where and how I can buy this inductance? I searched an can't find inductance with 0ohm and 1%. What 1 % does ...
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votes
3
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72
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Serial Inductors in Tuned Circuit - Elenco AM780K AM Radio Kit
I'm trying to understand a component of an AM radio kit that I have. (There is a document available here: https://www.elenco.com/wp-content/uploads/2017/10/AM-780K_REV-K-2.pdf describing the build ...
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What's the maximum possible "DC input to radiated RF" energy efficiency of a radio transmitter system?
It's simply a bromide amongst hams that you need to match the output impedance of a transmitter to the input impedance of an antenna, but I never thought through the implications of this until I came ...
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112
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How much does a RF amplifier use of its input power?
I've been casually aware that signal gain can be added in "stages" but never really considered how that might actually work in practice. And it seems that some RF amplifiers really prefer to ...
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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'...
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23
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Ferrites losses calculation
I am new on RF design. I would like to know more about ferrites. I am looking for information about how to calculate ferrite losses and saturation points for a given application. I also would like to ...
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58
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How do I test if three turns are better than 4 turns?
I built a class ab amplifier kit to use with my qrp radio. 2 watts in creates 50+ out.
This was the pa 70 amplifier kit.
It is a kit with no instructions, but a whole suite of internet videos and ...
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164
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What is a diode for in a JFET-based audio mute circuit?
I've build the following audio mute circuit:
It works fine. However in many circuits I've seen people add an extra diode on the gate of Q1:
For instance, see "QRP Classics" page 120 / page ...
2
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1
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57
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How can a low-impedance load can damage a FET final amplifier?
I believe I understand how an excessively high impedance can damage a final output power MOSFET (voltage rises until avalanche breakdown). But how does an excessively low impedance do that? If the ...
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68
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Does a filter or inductor's power rating matter in its passband, or only in the attenuated frequency range?
I would like to build a high-pass filter that would block reception of signals from the United States' FM broadcast range (88–108 MHz) while still allowing me to transmit VHF ham signals (around 146 ...
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99
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Jennings variable vacuum capacitor
I have a Jennings CVDD 500 vacuum capacitor which is not working. Think it's a mechanical problem because I have another one and it works.
The symptom is that it is always electrically shorted.
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287
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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 ...
- 667
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77
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What is a marker unit?
Sorry to ask what may be a basic question. I have a used Icom 745. It has a "marker unit" option installed. The manuals says how to adjust it and use it, however it does not say what it ...
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393
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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 ...
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Is it beneficial to boost the transmit power from a transmitter past 2W around 2.4GHz?
I have a ready-made transmitter that outputs 2W of RF power at 2.4GHz carrier frequency (I'm trying to transmit TV using DVB-S2) into the antenna, and I was wondering if it made sense to add a power ...
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79
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IF derived AGC: how to choose the best block diagram?
I've built several transceivers in the past. I never implemented IF derived AGC, so I decided to give it a try in the next project.
I choose to build a superheterodyne receiver, which will probably ...
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Acoustic Communication issues [closed]
[![I've attached schematic, I am connecting transducer directly to that header pins on receiver side. On transmitter side I am connecting op-Amp to boost voltage to +10v -10v.][1]][1]I am working on ...
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Diagnosing IC-7100 Drive Amp Bias | PA Won't TX
A faulty in vehicle DCDC charger has fed 16V or so into my brand new IC7100, killing the main board and preventing it from transmitting. I've replaced the mainboard with a brand new one however I'm ...
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455
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Choosing a Relay for HF Applications
As part of my 20m transceiver build I'm looking for a relay to by-pass an RF amplifier in the front-end board. So, to be clear, that's after the 20m broad bandpass filter and before the RF mixer (it'...
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201
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What causes an AF amplifier to make popping sounds in a superheterodyne receiver?
Recently I've made a simple single IF superheterodyne SSB receiver for 40 meter band. The schematic is available here [PDF]. VFO and BFO are based on Si5351, the AF amplifier is LM386. It works OK but ...
4
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Looking for origins of a crystal filter schematic used in uBITX
Here is a crystal filter used in uBITX transceiver:
I've never seen such a topology in any other transceiver and decided to invest some time in exploring it. Turned out it's quite interesting. Eight ...
3
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1
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125
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Is this "floating" output single-ended or differential and against GND or VCC?
I'm looking at a simple FM transmitter output (see picture). It is from the collector of a transistor and it goes through a DC blocking capacitor before the antenna would be connected. The entire ...
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564
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What is an expected IF level of SA612?
I tried to use SA612 as a frequency mixer. Since it's a Gilbert cell, it has a high input impedance. Thus I added a pair of transformers as "Experimental Methods in RF Design" book suggests:
...
4
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236
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Design of oscillator
I'm looking for a good tutorial about oscillator design (electronically) for transmitter. The problems with current tutorials are almost all provide only schematics, some explain how it works. But ...
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251
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How to estimate input and output impedance of an amplifier?
I'm trying to figure out how to design power amplifiers which input and output are properly matched to 50 Ohm. My thinking was that the most bullet proofed approach would be to model an amplifier in ...
4
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2
answers
817
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How to measure quartz crystal motional parameters using a VNA?
I want to measure quartz crystal motional parameters with a VNA. Unfortunately all Google searches I've done have lead me to nothing in concrete. I know how to get an impedance curve and measure the ...
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254
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Can't identify old Chinese(?) and American radio/telephone
I have searched image banks and Googled period radios, but I can not identify these old units. I picked them up overseas in SE Asia and I got them as projects to teach myself enough to challenge the ...
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5
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4k
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Significance of 1/4 wavelength with respect to antennas
I am a new to the radio design field.
My question is, 'What is so significant about 1/4 wavelength with respect to antennas.'
From the information I have gathered from various sources, it is my ...
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4
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223
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Identification of valve
My favorite receiver used for 40 m AM broadcasts has a cracked valve, but the valve type normally printed on the glass has rubbed away. Can anyone tell me what the numbers for this valve are ?
The ...
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154
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Where am i supposed to ground the audio path?
Where does the ground of the audio path go in this schematic?
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51
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Clocking A and N in a Dual-modulus PLL Prescaler
In an effort to "up my game" attempting to build a VFO for my DIY transceiver, I've been looking at PLL theory and circuits. Many of my research references are quite old and I understand that many of ...
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172
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How can i adjust the IF strip in a single conversion SSB receiver which has a product detector?
I have an analog 27 MHz transceiver which i am planning to convert to 10 m. The radio is an AM / SSB unit with a single conversion superhet receiver with an IF of 7.8 MHz using a crystal filter. This ...
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257
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Unknown kit from DK0TV
When my father - who became a ham years after I did - passed away, I found an unstarted project (board + components), which I only re-discovered again years later.
The board is marked DK0TV-001, and ...
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4
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What is unique about a Low Noise Amplifier (LNA)?
What is so special about a low noise amplifier? If I were to design an amplifier, I would always design an amplifier with low noise anyway.
Why is it emphasised as being “Low Noise”?
What are the ...
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305
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What does "HF-QUARTZ 4.19 MHz" on a ~1980s wall clock mean?
I have a wall clock from the 1980s or early 1990s. Probably 1980s. It has a black box behind/"inside" it which powers the whole thing. It's made by Quartz.
On the black box, it says "HF-QUARTZ 4.19 ...
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2
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135
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voltage rating for RF filter components
I want to design a PCB for a diplexer for Satellite operations. I want to use SMD capacitors and possible inductors to get some experience with soldering SMD components. What should the voltage rating ...
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71
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Had +5VDC and GND swapped, feeding a GPS receiver. Source is +5VDC output @ DB9 port on Yaesu FT-2600M, now showing 0V. Did I fry something?
Basically, I connected +5VDC to the ground of a GPS receiver, and now have no power from the power source.
Is it possible to mess something up by doing this?
I feel like this is more of a basic ...
0
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1
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79
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Can i use an anaolgue IC switch to change a 10 m yagi's directivity by somehow combining received signals with different variable phase?
Can i use an analogue IC switch being triggered at the same frequency I am receiving on to change a 10 m yagi's directivity by somehow combining received signals with different variable phase either ...
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5
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326
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ARRL handbook as a reference for all your radio learning needs?
Looking to take up learning understanding everything from basic electronics to how today's wideband radios work, so that I can build my own radio systems (not just ham radios), and talk radio concepts ...
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125
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How is frequency selection (tuning) accomplished in a direct conversion receiver?
How is frequency selection (tuning) accomplished in a direct conversion receiver ? A crystal filter can't be used is that correct ? Because there is no IF to mix with the incoming frequency band ...
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406
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What are the advantages for a receiver that uses an IF compared to direct conversion?
What are the advantages for a receiver that uses an IF compared to direct conversion ?
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164
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If I parallel two crystal filters together, will that double the bandwidth? [closed]
Will the bandwidth be doubled ?
And will the impedance be halved ?
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369
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Dipole increased CM current using choke balun
My 20 meter inverted vee dipole is fed with 56 feet of 50-ohm coax. The SWR measures 1.2 at the center of the band. According to http://arrl.org/grounding a balanced antenna doesn't need a ground, so ...
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758
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How does the Maximum Power Transfer Theorem relate to RF power amplifiers?
The Maximum Power Transfer Theorem says that maximum power transfer occurs when the source impedance equals the load impedance, when the power transferred to the load is 50%, the other 50% being ...
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4
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1k
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Why does an RF Amplifier fail when the SWR is high?
Exactly why does an RF output transistor fail if the SWR is bad ?
Is it A because the impedance mismatch between the transmission line and the antenna results in maximum power not being transferred ...
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4
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Voltage vs. Current Balun for Dipole
I'm a new radio amateur setting up a half-wave 10-meter inverted vee antenna fed by 50 ohm coax. I understand that the inverted vee lowers the normal 72 ohm dipole closer to 50 ohms, so I only need to ...
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4
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249
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How is working on DC high voltages as in a tube radio different from 120VAC?
Suppose that I am familiar with the safety procedures for working on 20 A 120 VAC 60 Hz household lines.
What should I be prepared for before working on high voltage DC circuits (say, 800 volts) as ...
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Is it practical to use a magnetic amplifier as an AM modulator in a transmitter?
If I'm building a vacuum tube HF transmitter (say, 40 m band), obviously the simplest mode to build is CW; it's common to key the oscillator input to the final (in order to keep the oscillator running ...
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Are jammers relate to electronics or electrotechnics , why? [closed]
Are jammers relate to electronics or electrotechnics , why ?
Please ,tell me the main difference between electronics and electrotechins and why we can classify jammers as electrotechics or ...
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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:...
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