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
  • 24.5k
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
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
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
2 votes
1 answer
205 views

How is impedance matching related to balance and common-mode currents?

Does a good impedance match imply good balance and lack of common-mode currents? Does a poor impedance match imply poor balance and excessive common-mode currenst?
Phil Frost - W8II's user avatar
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I wonder, even in this modern generation why the outdated vacuum tubes are used. In other electronic circuits they have been replaced by more efficient (and small) transistors years ago.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
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
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
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
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
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
244 views

Would a switched RF attenuator be (a)symmetric?

I picked up this 0-80 dB switched RF attenuator at a flea market, with no part number or other useful markings other than the knob settings. I've tested it and confirmed that it works, but there's one ...
Kevin Reid AG6YO's user avatar
  • 24.5k
3 votes
2 answers
241 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 ...
elplatt's user avatar
  • 160
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
2 votes
1 answer
204 views

Connect mobile device with coax cable to SDR board

My goal is to connect mobile devices using a coax cable with a SDR board to be independent from using the air interface and antennas. I don't know how to connect my devices with the SDRs since I'm an ...
k_o_'s user avatar
  • 123
2 votes
2 answers
1k 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 ...
Ben Madison KO4UXC's user avatar
1 vote
3 answers
437 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? ...
Ben Madison KO4UXC's user avatar
1 vote
2 answers
771 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? ...
hotpaw2's user avatar
  • 13.3k
1 vote
2 answers
134 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 ...
Buck8pe's user avatar
  • 989