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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 ...
Scott Earle's user avatar
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15 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 ...
progrmr's user avatar
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14 votes
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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 ...
Phil Frost - W8II's user avatar
13 votes
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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 ...
Neil_UK's user avatar
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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 ...
Kevin Reid AG6YO's user avatar
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9 votes
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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: ...
Glenn W9IQ's user avatar
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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Vacuum tubes are neither outdated nor less efficient.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 ...
user10489's user avatar
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9 votes
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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 ...
Phil Frost - W8II's user avatar
9 votes
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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 ...
Phil Frost - W8II's user avatar
8 votes
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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'...
tomnexus's user avatar
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8 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 ...
Zeiss Ikon's user avatar
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8 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-...
filo's user avatar
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8 votes

Why do Baofeng radios have such poor reception reliability?

You get what you pay for. The Baofeng radios take a number of shortcuts in their design to make them cheaper, including leaving out front end filters. The result is that the radio is marginal on ...
user10489's user avatar
  • 6,533
7 votes
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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 ...
Phil Frost - W8II's user avatar
7 votes
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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 ...
Mike Waters's user avatar
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7 votes
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Why do homebrew designs wrap toroids instead of using off the shelf inductors?

Broadly, the thing about about inductors (and transformers) is that it is very easy to make them by hand, compared to most other components, and they are relatively rarely used in mass-produced ...
Kevin Reid AG6YO's user avatar
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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 ...
De Bohannan KC5ULU's user avatar
6 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)....
Marcus Müller's 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 ...
Brian K1LI's user avatar
  • 7,878
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 ...
Kevin Reid AG6YO's user avatar
  • 24.7k
6 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 ...
Brian K1LI's user avatar
  • 7,878
6 votes
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Why would a VNA not make a good Spectrum Analyzer? Or an SDR a good VNA?

A VNA generally does not have to worry about a multitude of input signals as it controls its own test signal generation. A SA has to be able to show small signals even in the presence of large other ...
erik's user avatar
  • 76
5 votes
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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 ...
Glenn W9IQ's user avatar
  • 18.6k
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. ...
Glenn W9IQ's user avatar
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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 ...
Edwin van Mierlo's 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 '...
Scott Earle's user avatar
  • 4,619
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, ...
nanoman's user avatar
  • 151
5 votes
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How can the waterfall still be displayed during transmission

I don't know what the specific devices you're referring to do, but a couple of things are all technically possible without great effort: the ADC that is used to calculate the waterfall in receive-...
Marcus Müller's user avatar
5 votes

Why do Baofeng radios have such poor reception reliability?

A big clue is that the short ducky antenna seems to allow better reception than the higher gain Yagi. So it could be that the receiver input is overloaded, possibly by signals outside the band of ...
hotpaw2's user avatar
  • 13.5k

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