15 votes
Accepted

Why are vacuum tubes still used in amateur radios?

The last mass-produced vacuum tube was the Cathode Ray Tube, Thankfully those are now going the way of the dodo, replaced with much more practical LCD or OLED displays. (Edit: it turns out the ...
user avatar
  • 4,409
14 votes
Accepted

How Could Superheterodyne Receiver Ever Work?

The answer is simple: filtering. For example, let's say the desired signal is at 800 MHz, and the intermediate frequency (IF) is chosen to be 100 MHz. Mixing the 800 MHz signal with a 900 MHz local ...
user avatar
14 votes

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

You can use a satellite TV dish antenna for amateur radio use but how you use it depends on what frequency you want to operate on. The satellite dish antenna is two basic parts, the parabolic ...
user avatar
  • 342
13 votes
Accepted

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

What limits the use of "solid state variable capacitors" like these for dynamically filtering (low power/received) RF signals? The main issue is bandwidth. Although there are some varicaps ...
user avatar
  • 246
10 votes
Accepted

Why is dynamic range relevant for an SDR?

Signal strength and dynamic range Generally speaking, dynamic range is the ratio between the strongest and weakest signal that can be received. In a digital signal, the dynamic range is determined by ...
user avatar
  • 23.1k
10 votes

Why are vacuum tubes still used in amateur radios?

As far as I know, vacuum tubes are used in newly-manufactured radio equipment (as opposed to still-in-use old equipment) for one purpose: high-power amplifiers. The advantages of vacuum tubes in this ...
user avatar
  • 23.1k
9 votes
Accepted

How can Ground Penetrating Radar work?

There is a special adaptation of the Friis equation, called the Radar Equation, that describes the range of a radar system. Here is a basic version that calculates the maximum range of a radar system: ...
user avatar
  • 18.2k
9 votes

Why are vacuum tubes still used in amateur radios?

Vacuum tubes are neither outdated nor less efficient. See https://spectrum.ieee.org/semiconductors/devices/the-quest-for-the-ultimate-vacuum-tube The above IEEE Spectrum article talks about a vacuum ...
user avatar
  • 4,258
9 votes
Accepted

Are QRP transceivers only meant for CW communication?

QRP only means low power, often 1W or less. While you could technically have a 1W SSB transceiver and call it QRP, the practical range of such a radio would be limited. It is much easier to hear a ...
user avatar
8 votes
Accepted

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

SMD chip inductors, compared to larger ones, will generally have: lower Q higher DC resistance higher SRF lower DC saturation current, if they're ferrite cored But read the datasheet and see if they'...
user avatar
  • 8,235
8 votes
Accepted

What replaces the T/R switch in modern transceiver

Receivers and transmitters are still separated today, they are just in the same box. There is still a T/R switch too, integrated in the box. In many radios, it's a relay, same as they have been for ...
user avatar
7 votes

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

As Phil Genera says, the KX3 uses a different type of receiver that requires a different kind of filter. A traditional superheterodyne receiver, which is what you'd find in most older radios, uses a ...
user avatar
  • 171
7 votes

Why are vacuum tubes still used in amateur radios?

There's one more reason vacuum tubes are still used in amateur radios: personal preference of the amateur building the radio. Speaking for myself, I understand what's going on inside a vacuum tube ...
user avatar
  • 3,891
7 votes
Accepted

What are Smart Antennas?

"Smart antennas" are antenna arrays with software-controlled phasing. Antenna arrays are commonly used in the amateur radio hobby, such as in Yagis, four-square antennas, etc. However, the phasing ...
user avatar
7 votes
Accepted

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

Yes, this most certainly was a thing, and people actually did it. This type of communication has been done at ELF frequencies in the 3-30 kHz range. Their linear amplifiers were ordinary Hi-Fi audio ...
user avatar
  • 7,544
6 votes

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

Another way to detect current on the outside of coax is to run your hand up and down the coax wile an analyzer is connected , if you see a fluctuation on the meter then current is following on the ...
user avatar
6 votes

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

Highest frequency stability is generally achieved when the oscillator is kept running while some following stage (or stages) is (are) keyed. However, the very high Q of a crystal-controlled oscillator ...
user avatar
  • 7,693
6 votes

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

There is no such thing as a minimum power level at which a conductor will start radiating. If it radiates at all, then the radiation will be proportional to the power applied. Therefore, the maximum ...
user avatar
  • 23.1k
6 votes

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

Apart from using it as a ham radio satellite antenna (eg. for QO-100) or a microwave terrestrial antenna, you can turn it into a VHF slot antenna. Here is an example: https://w6nbc.com/articles/20xx-...
user avatar
  • 161
5 votes
Accepted

Mic ground vs ground

The problem you could run into is RF feedback into the sensitive mic input. This is particularly a problem if you run "QRO" - high power. It is best to use shielded multi-conductor cable, with the ...
user avatar
5 votes
Accepted

Using standard headphones with the Yaesu FT-60?

I've done some tests with what I have available (now including the CT-44 adapter). With the MH-37A4B Earpiece/Microphone connected, the internal microphone can still be used: whichever mic has its ...
user avatar
  • 23.1k
5 votes

Weird Harmonic Issue on Raspberry PI FM Transmitter

There are many articles which describe how to use a R-Pi to emit (=transmit) a signal. However what most, if not all, articles fail to describe is that this signal is a very rough signal, usually not ...
user avatar
5 votes

Weird Harmonic Issue on Raspberry PI FM Transmitter

You are observing a practical example of harmonics. Harmonics of a Square Wave You do not mention how you are generating the signal with your Pi but it probably uses a simple square wave generator. ...
user avatar
  • 18.2k
5 votes
Accepted

Toroid Coupling Issue in Common-base Amplifier

The problem is most likely the type 43 core material. It is quite lossy at 21 MHz and is a poor choice for the auto-transformer. Unlike a transmission line transformer, the auto-transformer relies on ...
user avatar
  • 18.2k
5 votes

Substitute for 455 kHz Ceramic filters in new designs

Since this platform considers questions asking for products as off-topic, I'll interpret your question as: I have an IF receiver, but there's no good filters for the rather low IF it uses (455 kHz)....
user avatar
5 votes

Are QRP transceivers only meant for CW communication?

A QRP transceiver is just a transceiver that operates on low power (usually less than 5 watts). If you look at the international Q Code, you will see that QRP simply means 'low power', and QRO means '...
user avatar
  • 4,409
5 votes

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

I want to point out an important aspect that is only implicit in the other answers. At the frequencies at which they can be efficiently used, dish antennas are (by design) highly directional. That is, ...
user avatar
  • 151
5 votes

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

Technically, the utility of a variable capacitor in a receive filter depends on the amount of available capacitance variation and its Q - the quality factor, which is the ratio of the capacitor's ...
user avatar
  • 7,693
4 votes
Accepted

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

A "shielded loop antenna" is a very misleading name. It isn't an antenna, with a shield. It's an antenna made from a shield, with a feedline inside it. It's commonly stated that the shield blocks ...
user avatar

Only top scored, non community-wiki answers of a minimum length are eligible