Questions tagged [electronics]

Questions which involve the properties or applications of individual electronic components.

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19 votes
3 answers
7k views

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 ...
Adam Davis's user avatar
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13 votes
3 answers
345 views

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 ...
philpem's user avatar
  • 131
12 votes
3 answers
5k views

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 ...
natevw - AF7TB's user avatar
10 votes
3 answers
1k views

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 ...
Phil Frost - W8II's user avatar
10 votes
1 answer
3k views

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 ...
Adam Davis's user avatar
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9 votes
0 answers
555 views

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 ...
Thomas L's user avatar
  • 193
8 votes
2 answers
468 views

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 ...
Aleksander Alekseev - R2AUK's user avatar
8 votes
1 answer
261 views

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'...
natevw - AF7TB's user avatar
7 votes
7 answers
2k views

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 ...
Zeiss Ikon's user avatar
  • 4,097
7 votes
2 answers
455 views

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 ...
Mike Waters's user avatar
  • 7,958
7 votes
2 answers
698 views

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 ...
user avatar
7 votes
1 answer
5k views

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 ...
Aleksander Alekseev - R2AUK's user avatar
7 votes
1 answer
1k views

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:...
Brian K1LI's user avatar
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6 votes
1 answer
334 views

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 ...
t252's user avatar
  • 697
6 votes
2 answers
1k views

Feed-through Capacitors

I'm in the "information gathering" phase of a RF Power Meter project and the design I fancy (W7ZOI Power Meter) calls for a feed-through capacitor at the output port. I understand that a feed-through ...
Buck8pe's user avatar
  • 989
6 votes
2 answers
2k views

Is there a best ratio of L to C in a resonant circuit?

When designing a resonant circuit, for example as a local oscillator, the product of $L$ and $C$ determine the resonant frequency according to $$f_{res} = \frac{1}{2\pi \sqrt{L C}}.$$ This means that ...
DK2AX's user avatar
  • 624
6 votes
3 answers
8k views

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 ...
natevw - AF7TB's user avatar
6 votes
0 answers
388 views

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 ...
Aleksander Alekseev - R2AUK's user avatar
5 votes
2 answers
607 views

Share wide band antenna with multiple transceivers

I'm trying to incorporate several transceivers on my board design; I need WiFi (2.4 GHz) SatCom (~1.6 GHz) RF (~900 MHz) and GNSS (~1.5 GHz). I need to combine them into one antenna. I found a wide ...
Jedi Engineer's user avatar
5 votes
3 answers
382 views

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 ...
eecs's user avatar
  • 159
5 votes
2 answers
442 views

In the context of the mixer in my radio, what does balanced and unbalanced mean?

I'm trying to understand how the mixer in a radio actually works, at a physics level. When looking at this article and studying the first schematic I realized I really don't understand what balanced ...
flickerfly's user avatar
5 votes
3 answers
4k views

How to find or derive the maximum safe input power to a receiver?

A number of my RF devices have a specified safe maximum input power, for example: "The maximum RX power of HackRF One is -5 dBm. Exceeding -5 dBm can result in permanent damage!" source "If you look ...
natevw - AF7TB's user avatar
5 votes
1 answer
277 views

Are there an MTTF/MTBF/MTTR data on the typical tubes used in the FT-101/TS-520?

I browse ebay.com for used rigs in good condition and approaching my shoe-string and ... There appear to be a decent quantity of boat anchors out there - FT-101, TS-520, TR-4 to name just a few. By ...
VU2NHW's user avatar
  • 2,834
5 votes
1 answer
788 views

Do vacuum variable capacitors have higher Q than air variable capacitors?

Do vacuum variable capacitors have higher Q than air variable capacitors? They are not commonly seen in tuners or crystal sets. But they are mentioned as superior to air variables for resonating ...
Paul's user avatar
  • 1,455
5 votes
2 answers
827 views

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'...
Buck8pe's user avatar
  • 989
5 votes
3 answers
4k views

Good FM receiver single-chip IC for simple VHF receiver?

Is there an IC out there that implements all, or most all, of a simple FM receiver in the VHF range? I'm interested in doing some experiments with using DTMF over the air for tele-commands and the ...
mindcrime's user avatar
  • 163
5 votes
2 answers
217 views

New to Amateur Radio [closed]

I'm new to radio, and I'm trying to get into the electronics aspect of it. I was wondering if it was at all possible to build your own transmitter, receiver, etc. (basic radio components) as good ...
rmutalik's user avatar
  • 151
5 votes
2 answers
135 views

Stacked shell inductor — what's its function/use?

I have a device of copper and iron (about 8 kg) which looks like two shell inductors joined so that there is some coupling but high leakage. The windings seem to be identical. Each is a single ...
Merlin3189's user avatar
5 votes
2 answers
930 views

What is Norton's transform?

This article from Itchen Valley Amateur Radio Club describes an interesting technique called "Norton's transform": This results in a negative capacitor, but in a circuit where there are other ...
Phil Frost - W8II's user avatar
5 votes
2 answers
1k views

Adapting an antenna coupler

I've built AA5TB's antenna coupler: I left out C2 because I didn't understand why I would need it - why would I? It works fine without. Unfortunately, when I started tuning for a 5W 20m transceiver, ...
user avatar
5 votes
0 answers
887 views

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: ...
Aleksander Alekseev - R2AUK's user avatar
4 votes
2 answers
462 views

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 ?
Andrew's user avatar
  • 3,685
4 votes
2 answers
1k views

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 ...
S.s.'s user avatar
  • 153
4 votes
3 answers
633 views

Why is coax loss logarithmic?

With DC hookup wire, losses are directly proportional to length. If the resistance of 100m of wire is 10 ohms then the resistance of 200m of wire will be 20 ohms. But we measure coax loss in decibels ...
natevw - AF7TB's user avatar
4 votes
3 answers
318 views

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 ...
RainerJ's user avatar
  • 141
4 votes
4 answers
2k views

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 ...
Andrew's user avatar
  • 3,685
4 votes
4 answers
6k views

What are some equivalents of a BF199 transistor?

I'm planning to build an FM radio receiver using the instructions on http://www.instructables.com/id/Build-your-own-Crude-FM-Radio/ The schematic uses a BF199 transistor which is marked "obsolete" by ...
Alexander Churanov's user avatar
4 votes
2 answers
485 views

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 ...
Peter Buxton's user avatar
4 votes
2 answers
307 views

Is using a DDS chip directly a viable way to transmit 2FSK and PSK on HF?

I'm thinking of building an HF transmitter for data (AX.25 or PSK31). Rather than using an IF stage, I'm thinking of generating the RF frequencies (or phases) directly with a Direct Digital Synthesis ...
watkipet's user avatar
  • 659
4 votes
1 answer
71 views

How to properly simulate a crystal filter being pulled?

After reading k1zmt's answer to the question of how to change the resonant frequency of a quartz, I wondered how to simulate a quartz filter to check that result. I went with the following model of a ...
Marcus Müller's user avatar
4 votes
1 answer
1k views

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 ...
Aleksander Alekseev - R2AUK's user avatar
4 votes
1 answer
256 views

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 ...
user5349's user avatar
  • 251
4 votes
1 answer
264 views

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 ...
Andrew's user avatar
  • 3,685
4 votes
1 answer
343 views

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 ...
Zeiss Ikon's user avatar
  • 4,097
3 votes
3 answers
900 views

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 ...
Andrew's user avatar
  • 3,685
3 votes
3 answers
261 views

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 ...
Aleksander Alekseev - R2AUK's user avatar
3 votes
1 answer
880 views

Series resonant circuit, how to calculate voltage across the capacitor?

This is question a3i3-1 from the practice questions in the book "amateur radio Exam Secrets": A series resonant circuit has 10V peak across it when at resonance. At that frequency the resistance of ...
Pablo Fernandez's user avatar
3 votes
5 answers
6k views

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 ...
Newbie's user avatar
  • 171
3 votes
1 answer
371 views

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 ...
jcoppens's user avatar
  • 699
3 votes
3 answers
151 views

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 ...
Jared's user avatar
  • 201