Questions tagged [equipment-design]

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20 votes
2 answers
15k views

How to detect common-mode currents or “RF in the shack”?

Let's say we already know that if your antenna is not suitably constructed or connected then you can get current on the shield of your coaxial feed line which will flow through the shielding/grounding ...
Kevin Reid AG6YO's user avatar
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14 votes
6 answers
6k views

Why are vacuum tubes still used in amateur radios?

I wonder, even in this modern generation why the outdated vacuum tubes are used. In other electronic circuits they have been replaced by more efficient (and small) transistors years ago. Why they are ...
Sumithran's user avatar
  • 573
14 votes
4 answers
9k views

What does the addition of a shield to a small loop accomplish?

A small shielded loop is an antenna with a loop of wire, smaller than 1/10th of a wavelength in diameter, also surrounded by a shield. Often, they are constructed from coax. There is a gap in the ...
Phil Frost - W8II's user avatar
13 votes
4 answers
1k views

Why do today's transceivers use LC filters rather than crystal filters?

Going through a number of schematics for today's receivers (Elecraft KX3, for example) I note that most use LC circuits for filtering. The wikipedia article for Crystal Filters suggests, however, ...
Adam Davis's user avatar
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12 votes
1 answer
7k views

How is the IF for a superhet selected?

There seem to be almost as many choices for the intermediate frequency (IF) as there are superheterodyne receivers and transceivers out there. The ones I have come across are 455 kHz, 452 kHz, 1.6 MHz ...
VU2NHW's user avatar
  • 2,834
11 votes
6 answers
16k views

Can you use a satellite dish for a ham radio antenna?

Can I use a satellite dish as a ham radio antenna? I was thinking that because there are two unused, working satellite dishes that have all appropriate wires attached conveniently to the roof of my ...
hopefulhacker-Reinstate Monica's user avatar
11 votes
4 answers
9k views

What is dBm and why is it used rather than watts?

Reading through an RF power amplifier datasheet, I found the sheet only referenced dBm output power, rather than watts. What is dBm? How do I convert it to watts? Why, or when, would you use dBm to ...
Adam Davis's user avatar
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11 votes
1 answer
2k views

Why is dynamic range relevant for an SDR?

Sometimes I see dynamic range mentioned as a figure of merit for an SDR. For example, I know that the bits per sample used by the analog to digital converter can affect the dynamic range. Why do I ...
Phil Frost - W8II's user avatar
10 votes
1 answer
7k views

How to design a rubber ducky antenna

I am attempting to design an antenna for a 162.4 MHz omni receive only application and am confident it is going to be difficult if not impossible. I have very tight specs on space(6" diameter by 3" ...
Josh Cox's user avatar
  • 241
9 votes
5 answers
833 views

What limits a PIN diode or varicap from being used in a "Software Defined [Radio] Filter"?

A PIN diode varies its capacitance based on a DC bias, and a Varicap exhibits this effect even more clearly. What limits the use of "solid state variable capacitors" like these for ...
natevw - AF7TB's user avatar
9 votes
1 answer
429 views

How Could Superheterodyne Receiver Ever Work?

I am surprised how the Superheterodyne Receiver still works and is still in use after coming to realise the impact of Image Frequencies on its performance. Basically, I'm curious how engineers make ...
Denis's user avatar
  • 702
8 votes
2 answers
4k views

RF Transceiver for walkie talkie use

I'm close to my EE. BSc finale and I'm looking to play around a little bit with the stuff I've learned. To be honest, I'm a little bit upset that after 4 years of learning communications theory, I'm ...
Santiago's user avatar
7 votes
1 answer
367 views

Simple circuit for acceptably clean CW in homebrew TX?

I'm working on a design for a home-brew 10 metre transmitter for CW. My oscillator is running cleanly, and I need to add a (small, probably 1/2 ~ 1 Watt) power stage to it, and I need to "...
Toby Eggitt'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
  • 7,848
6 votes
5 answers
2k views

Are QRP transceivers only meant for CW communication?

I was just thinking about making a QRP transceiver, but are they only used for CW (Morse code) communication? If it is so, can I modify a QRP for two way audio communication?
Sumithran's user avatar
  • 573
6 votes
2 answers
737 views

Choosing capacitor for high-pass filter with cutoff of about 160 MHz

A strong (100 kW) local FM transmitter causes interference to or overloading of receivers in the VHF/UHF bands. It seems like a single, properly chosen, capacitor could make an effective passive high-...
Jamie Cox's user avatar
  • 163
6 votes
1 answer
6k views

Using standard headphones with the Yaesu FT-60?

I just got a Yaesu FT-60R handheld, along with the MH-37A4B earpiece. After having it around for a couple days, I think I'd like to be able to connect standard headphones to it, so as to be able to ...
Kevin Reid AG6YO's user avatar
  • 24.5k
6 votes
2 answers
2k views

Dummy load construction and heat dissipation

I'm building my own dummy load, consisting of resistors submerged in liquid paraffin (or something similar, not 100% decided). I had some questions around heat dissipation and how I can calculate ...
David VK2VXK's user avatar
6 votes
2 answers
367 views

Does the waveform of the VFO necessarily have to be sinusoidal?

Looking around for a VFO online, I see most kits/manufacturers make it a point to mention the waveform. Sinusoidal is a fundamental shape, whereas others (sawtooth, square) are a composite. I recall ...
VU2NHW's user avatar
  • 2,834
6 votes
1 answer
455 views

Pentode vs. Triode in Tuned RF Reflex Receiver

I'm planning on building a multi-band vacuum tube receiver. I've got a circuit diagram in hand for a two triode twin reflex with optional regeneration (P.E. Edelman, Reflex Radio Receivers, 1924, Fig....
Zeiss Ikon's user avatar
  • 4,097
6 votes
2 answers
442 views

Purpose and sizing of capacitors placed across RF push-pull power amplifier transformer windings

I keep finding RF push-pull power amplifier designs specified with a small(-ish) capacitor across the primary (or secondary) windings of the coupling transformers. Here's an example: This is one ...
Buck8pe's user avatar
  • 989
6 votes
2 answers
353 views

Why does capacitive loose coupling increase selectivity?

There are multiple ways to couple antennas. It is said that an antenna is capacitive loose coupled if a small capacitor is used between the antenna and the parallel resonant circuit (like C2 in the ...
dudekowsky's user avatar
6 votes
1 answer
1k views

Resonant RF Transformer Substitution

I'm looking at a RF transformer filter design that appears to be using the primary-side transformer inductance as part of a second-order band-pass filter (first schematic). This isn't the only filter ...
W5VO's user avatar
  • 1,901
5 votes
2 answers
3k views

Why do Baofeng radios have such poor reception reliability?

What is the nature of Baofeng radios' poor receiver performance? This brand of handhelds has somewhat notoriously poor receivers. I hadn't noticed this much when using them for short distance simplex ...
natevw - AF7TB'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
278 views

How can Ground Penetrating Radar work?

I was reading about GPR devices recently. Considering the operation frequency of these devices, how they can go that deep (up to 50 feet)? Normally you would only expect a Hz to KHz range signal to ...
Samk80's user avatar
  • 65
5 votes
1 answer
533 views

How different is Q-factor of SMD inductor from regular one?

I am trying to figure out if it is possible to replace inductors like this wound by 0.1mm (diameter) copper wire with multilayer 0805 SMD inductors. Those are supposed to be used inside band-pass ...
k1zmt's user avatar
  • 337
5 votes
1 answer
207 views

Looking for a book that contained a circuit for receiving (literally) underground amateur radio transmissions

In this comment in Earth Science SE I've said: This is a really cool question! I remember (a long time ago) reading about electromagnetic waves inside conductive soil that travelled near but below ...
uhoh's user avatar
  • 543
5 votes
4 answers
2k views

Substitute for 455 kHz Ceramic filters in new designs

I am looking to design a dual conversion FM receiver/power meter for t-hunting similar to the MK4 sniffer using 10.5 MHz and 455 kHz IF. In my research it appears that manufactures have stopped ...
Jason R. Moore's user avatar
5 votes
1 answer
608 views

Why would a VNA not make a good Spectrum Analyzer? Or an SDR a good VNA?

Happy to be corrected where I'm wrong in any of this but in broad strokes my understanding is: Spectrum Analyzer measures input signal strength while sweeping across frequencies, measuring RF ...
natevw - AF7TB's user avatar
5 votes
2 answers
829 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
1 answer
664 views

Receive Data on Specific Frequency

So if I were to build a simple AM radio transmitter just using say, my Arduino, an oscillator, and wire for an antenna (this is all crude I know, but work with me here) and use it to transmit data ...
user2278224's user avatar
5 votes
2 answers
122 views

LOS One-way radio system, 4km with at least 1000bytes/s

In order to track skydivers/BASE-jumpers with flysight I am looking for a one-way radio system to transmit the location data. System needs the following specifications: ...
wittrup's user avatar
  • 153
5 votes
1 answer
130 views

Demodulation based on external frequency source

I saw a design for a walkie talkie that used a mixer that mixed the TX freq to the RX path before demod. Looking at the SA616 chip, demod is acomplished by Gilbert cell quadrature detector that is ...
Ben Madison KO4UXC's user avatar
5 votes
2 answers
3k views

How can the design of an RF filter also encompass impedance matching?

I'm installing an antenna which will require a matching network. (A fixed network: the load will not change.) I'm also building some low-pass filters to reduce transmitted harmonics. It would be a ...
Phil Frost - W8II's user avatar
4 votes
2 answers
5k views

Choosing a wideband antenna design

On a previous question I asked about proper antenna design for wideband SDR receiver and ways to improve signal/noise ratio. Ideally the reciever has a range of 100kHz-2GHz. Keeping in mind is ...
Luca's user avatar
  • 329
4 votes
2 answers
474 views

Building a low-power simple RF frequency (433MHz or 900MHz (but not both)) detector effective at 5m with a 10mW signal

I am looking for a simple schematic for building an effective RF detector which can trigger a GPIO. The goal is to (passively?) detect a 10 mW RF signal (10% duty cycle) and have that raise voltage on ...
Kenn Sebesta's user avatar
4 votes
1 answer
500 views

Will I get cleaner keying by keying the oscillator, or interrupting the amplifier B+?

One of my goals as a new ham is to homebrew my own transmitter (using vacuum tubes, aka valves). Initially I'll stick with CW for the transmitter, though over time I might build an AM modulator or ...
Zeiss Ikon's user avatar
  • 4,097
4 votes
1 answer
3k views

What advantages does dual-conversion have over single-conversion superheterodyne?

I've seen a variety of radio block diagrams, and some have two mixers inline with the signal. If the signal is already in a frequency range suitable to work with, what does the second conversion/...
Adam Davis's user avatar
  • 12.1k
4 votes
1 answer
173 views

Looking for criticisms on my VNA-like SWR meter I am designing

I am in the process of building a SWR meter with VNA-like features. I'd be really interested to hear from fellow hams any input, suggestions, or tips they have regarding this before I go get it mass ...
Jeffrey Phillips Freeman's user avatar
4 votes
4 answers
490 views

Should the capacitance or inductance be varied to achieve resonance?

A resonant circuit is typically composed of some resistance and reactance, the latter being provided by inductors and capacitors. The resonant frequency being calculated as the inverse square of their ...
VU2NHW's user avatar
  • 2,834
4 votes
1 answer
2k views

How would this RF field strength meter be calibrated?

I'm interested in an RF field strength meter that doesn't have to be lab quality, but still gives enough information about the RF field to know if an area exposed to RF is above the safety limits ...
Adam Davis's user avatar
  • 12.1k
4 votes
2 answers
494 views

What is the difference between Yaesu noise blanker (analog IF) and Icom noise blanker (perhaps digital)

What is the difference between the Yaesu (say FT DX 5000) and Icom (say IC 7700) noise blankers? I understood that the Yaesu NB is an analogue one while Icom uses a digital solution.
Nicola's user avatar
  • 41
3 votes
2 answers
816 views

SSB Transceiver Architecture - USB with Crystal Filter

I'm planning to build a 20m SSB transceiver and I want to get the overall architecture straight in my head first. Here's what I'm thinking so far, a single conversion superhet design with a 9MHz IF ...
Buck8pe's user avatar
  • 989
3 votes
2 answers
3k views

HF SWL antenna wire? Will plain 16-Gauge copper wire work well enough?

Planning to set up a HF antenna for RX-only. However, I can't decide what kind of wire to use. I want to buy something new. My first thought is to buy a spool of 16 Gauge copper wire, but am hoping ...
Tech2025's user avatar
3 votes
4 answers
4k views

Bluetooth headset for transceiver?

Is there a way to use a Bluetooth headset with my transceiver to eliminate all the wires, like a Bluetooth adapter? It seems like all the Bluetooth applications require a smartphone in the loop ...
K9WIS's user avatar
  • 31
3 votes
1 answer
1k views

Using wirewound resistors in a dummy load

I have a bunch of high-wattage 50 ohm resistors lying around, but they are wirewound. If I use them as a dummy load for transmitters 144 MHz and down, how bad would that be? Since they probably will ...
Skyler 440's user avatar
  • 7,600
3 votes
1 answer
1k views

Mic ground vs ground

Why do most radios have a microphone ground as well as a Ground? I have found that simply using one ground and tying the microphone as well as the PTT (and audio out, 5v out or whatever else is in ...
Skyler 440's user avatar
  • 7,600
3 votes
1 answer
471 views

Multi-band Crystal Receiver?

I'm just getting into radio (inspired by YouTube videos), and like many, I plan to start by building a crystal set (or multiples) before moving up to vacuum tubes (which I prefer over transistors). ...
Zeiss Ikon's user avatar
  • 4,097
3 votes
1 answer
714 views

How can I use the 455kHz IF signal?

As I own a PL-660, I saw a post that 455kHz IF signal can be obtained by connecting a wire to the board. I wonder, if I can tune to any signal by using this IF signal by SDR? And what are some common ...
Harold Chan's user avatar