Questions tagged [equipment-design]

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Is a 94' dipole antenna fed directly by coax useful for any particular known purpose?

I'm trying to figure out an old handmade antenna I picked up at a swap meet a few years back. It is a dipole (or "doublet"?) that is both made of coax but also fed by a length of built in ...
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2 votes
2 answers
144 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 ...
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2 votes
1 answer
88 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 ...
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1 vote
1 answer
55 views

Current Transformers in Series versus a Single Voltage Transformer

I've read that the commonly used 49:1 (7t:2t) auto transformer for Multi-band End-fed Half-wave (EFHW) antennas has criticisms as not being very efficient. I haven't found any other designs that ...
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3 votes
2 answers
81 views

VHF Balancing, necessary? Methods?

This is a question about power dissipated due to radiation and ohmic heating caused by common mode current in the coaxial shielding, specifically at VHF frequencies. When a balanced antenna (such as a ...
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6 votes
2 answers
132 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 ...
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  • 917
6 votes
1 answer
163 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 "...
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1 vote
1 answer
59 views

multiple pcb trace antennas in the same design. Bad idea?

Since time is money and my PCB home making skills are not the sharpest, I would rather fit my PCB design with two unbalanced antennas (no balun, just impedance matching parts, for 315 / 433 MHz) for ...
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5 votes
2 answers
299 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'...
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1 vote
1 answer
70 views

CW speaker and volume control

I'm building a kit for the LNR precision mountaintopper 3 band qrp radio. I'm having problems wiring a panel mounted volume knob and speaker to hear the cw output. I'm new to home brew electronics ...
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9 votes
5 answers
801 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 ...
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0 votes
1 answer
80 views

Circuit for RF Splitter [closed]

Does anyone know of any resources which describe how to design a circuit with one RF input and multiple (at least 6) RF outputs, whereby the signal strength of each output matches (does not exceed and ...
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1 vote
1 answer
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Need way to indicate when rotary inductor reached its limit switches on a remote homebrew motorized hf tuner

I have a homebrew motorized hf tuner which is controlled by coupling dc from the shack through two BiasTs - one topside, the other in the shack. As I reverse polarity to adjust tuner, will two LEDs, ...
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3 votes
2 answers
419 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 ...
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1 vote
1 answer
288 views

Crystal Oscillator Output Impedance and Output Voltage

I am working on a project designing a 40 MHz radio transmitter, but I need some clarifications. I need to know how to calculate its output impedance. I know how to calculate common collector's output ...
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1 vote
2 answers
453 views

Benefits of AGC?

I note that many popular kit and QRP radios do not include any AGC capability. Thus it must be possible to operate successfully without AGC. Are there difficulties involved in manual gain control? ...
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0 votes
3 answers
119 views

How can the waterfall still be displayed during transmission

I noticed that on some higher-end transceivers, the panadapter/waterwall is still being displayed during transmission. How is this possible? If the panadapter is part of the receiver, it should be ...
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0 votes
0 answers
46 views

Simple minimum component RF Amplifier Design

Looking for advice/assistance in Retrofitting sans Cabinet Antique 2 and 3 Dialer 1920's TRF tube radios to operate with low safe Plate voltages.Both Hollow State and Solid State. The plan is to ...
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1 vote
3 answers
554 views

What replaces the T/R switch in modern transceiver

I have been watching and reading about the time when receiver/transmitter were separated and T/R switches were used. Current transceivers are still sharing a single antenna to transmit and receive. ...
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  • 199
3 votes
2 answers
188 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 ...
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3 votes
1 answer
140 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 ...
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1 vote
2 answers
123 views

RF PCB Design Difference Between Controlled Impedance Track and Impedance Matching Circuit

Im new on RF circuit designing. Im designing an circuit with GSM and GPS capabilities. I know when using high frequency signals the RF traces must be impedance matched. Now what I understand is, I can ...
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8 votes
6 answers
9k 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 ...
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6 votes
2 answers
212 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 ...
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1 vote
0 answers
244 views

LA1185 FM downconverter shows weird behavior

I've built FM CCIR/OIRT downconverter based on Sanyo LA1185 IC. I've used most famous schematics for it with slight modification (added DC blocking capacitor 1 nF rated on the output) Coils L1 and L2 ...
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0 votes
2 answers
118 views

Imaging with radio Frequency

Is it possible to image bones and tissues with radio waves (2.7GHz-5GHz) with a tiny radio frequency source and on one side and a receiver on other side which can image the data through a PC mediated ...
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1 vote
1 answer
146 views

PSR500/Pro106/WS1040 Phase II Upgrade?

I want to know if one can upgrade the hardware chips/ the CPU/DSP inside police scanners to do Phase II. I know they cannot do Phase II due to hardware/software limits but if whistler can upgrade ...
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5 votes
1 answer
176 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 ...
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  • 521
5 votes
1 answer
119 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 ...
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-1 votes
2 answers
175 views

At what watt level is it safe to use metal strips for modulated signals?

In my working design, I have a transceiver TX on low power; Then boost it in a preamp phase in the back. The way I'm sending the signals (RX and TX) through the radio is by a network of 1/8 to 1/4 ...
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2 votes
1 answer
113 views

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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5 votes
3 answers
298 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 ...
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1 vote
1 answer
71 views

Can the transmit and receive functions of a boat anchor transceiver share the tank circuit?

I'm starting design work on a two-tube (two-valve, for those who prefer that term) reflex-regen receiver that I hope will cover AM broadcast through 160m-10m -- both amateur bands and those "in ...
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  • 3,881
7 votes
1 answer
823 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:...
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1 vote
2 answers
175 views

What are Smart Antennas?

What are smart antennas? How are they used in amateur radio, and how might they better than conventional antennas?
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6 votes
5 answers
1k 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?
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  • 563
1 vote
2 answers
1k views

How to convert a crystal controlled tranceiver to VFO (aka Unbinding from the Rock)?

If you look at the circuit diagram for a Colpitts crystal oscillator, it's pretty simple -- a crystal, load resistor, and capacitive voltage divider, with the positive supply feeding the control ...
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  • 3,881
14 votes
6 answers
5k 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 ...
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  • 563
1 vote
1 answer
616 views

Raspberry Pi rpitx for SSB with filter?

Using rpitx, we can transmit SSB using a single GPIO port from the Raspberry Pi. This of course uses square waves so creates a lot of harmonics. If I were to use a ...
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  • 157
2 votes
4 answers
2k views

What is a simple kind of amateur radio transceiver I could try to build, as a beginner?

I am new to amateur radio, and I'm trying to learn the basics of the hobby. I would like to build a simple radio transceiver from scratch (i.e. not from a kit). I have searched the Internet for ...
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  • 563
2 votes
2 answers
674 views

How does keying a CW transmitter work?

In my handbook it talks about keying the transmitter to produce the dots and dashes. Does this mean that the operator is turning the transmitter on and off, or does this mean that the key is turning ...
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4 votes
1 answer
345 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 ...
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  • 3,881
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 ...
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1 vote
2 answers
107 views

Toroid Coupling Issue in Common-base Amplifier

I'm working on an old school VFO for the 15 meter band based on a JFET Hartley oscillator. The plan is to follow the oscillator section with a JFET buffer, then a CB amplifier (for increased reverse ...
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6 votes
1 answer
335 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....
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  • 3,881
3 votes
1 answer
369 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). ...
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  • 3,881
1 vote
3 answers
399 views

What kind of ham radio license should I get?

I have an interest in studying and researching how radio technology can be used in other fields of electronics. What kind of license should I look into so I can carry out some experiments or research? ...
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2 votes
1 answer
1k views

Receiver using a NE602 oscillator-mixer not working

I built a CW receiver using NE602 for the 20m band. Unfortunately, I do not receive any CW or SSB signals, only some noise and sometimes broadcast stations. The schematic here shows the circuit that ...
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5 votes
1 answer
475 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 ...
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  • 275
9 votes
1 answer
356 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 ...
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