Hot answers tagged

18

My understanding is that in at least some telegraph systems, the principle of operation was as in this circuit (where the coils depicted are actually telegraph sounders): simulate this circuit – Schematic created using CircuitLab Thus, your key's shorting switch is, in radio terms, your transmit/receive switch: you close it in order to listen, and ...


17

Mostly, they used RF Ammeters in series with the antenna. The first ones were hot-wire ammeters which were completely mechanical devices. One end of a thin nichrome wire (or other wire of sufficiently high resistance) inside the meter was coupled directly to the pointer shaft (often wrapped around it); the other end was anchored to the meter case. As the ...


15

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 magnetron is still mass-produced, for microwave ovens. Although apparently semiconductor replacements already exist, and soon the magnetron will go the way of the CRT....


10

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 application are essentially from the fact that the tube can be built as a large and sturdy device. Semiconductor devices may fail due to overheating which ...


9

They were created to save time in Morse code communications. From https://en.m.wikipedia.org/wiki/Q_code: The Q code is a standardized collection of three-letter codes all of which start with the letter "Q". It is an operating signal initially developed for commercial radiotelegraph communication and later adopted by other radio services, ...


9

The origins of the amateur radio call sign districts can be traced to 1912 when the Department of Commerce, Bureau of Navigation created nine radio inspection districts to enforce the 1912 Act to Regulate Radio Commerce. Primary foci of the act were to regulate ship to ship and ship to shore radios including those used on the Great Lakes. As a result, all ...


9

The spark gap is a simple, low-tech way of generating high frequencies. It was the only way of generating them before valves and transistors were invented. As C1 charges up through R1, eventually the air in the spark gap breaks down, becoming a short circuit. The breakdown of a spark gap happens over just a few nanoseconds. (It turns off much more slowly ...


9

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 tube amplifier that is more efficient than any solid state amplifier. This is just one example of active research on vacuum tubes.


8

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 decades. Relays are hard to beat for isolation and maximum power ratings. Their downside is relatively slow speed, which prevents really good QSK operation. They ...


7

Land line telegraph keys are fitted with a circuit closer switch. Radio telegraph keys were not but many radio operators used land line keys because they were so readily available. This includes the rather ubiquitous J-38 about which more will be found below. The arcing that occurred at the key contacts of the early spark radios caused radio stations to ...


7

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 amps. I don't know if LF frequencies higher than that are useful for that, but the hams on the 2200m band (137 KHz) use above-ground antennas. A lot of ham ...


6

The ARRL NTS (National Traffic System) is designed to operate from one local area to another local area (say, across the country) by the process of Relaying messages from one station to another. I am a member of several section nets in the northwest area. If I had a message that I wanted to originate from the Seattle area to a destination across the ...


5

[Discovered this via a comment on another answer.] According to their Wikipedia article: Lecher lines were used as frequency measuring devices until frequency counters became available after World War 2. The idea is to short a transmission line after some distance, forming what we now would call a resonant stub. The resonant reflections set up standing ...


5

The US National Bureau of Standards (NBS) had a system for basic measurement of frequencies as early as 1911. They used very basic calculations to determine the resonance of an LC circuit. The math was greatly advanced in 1923 in an article in Radio Broadcast magazine entitled ""Reducing the Guesswork in Tuning". The method involved careful measurements of ...


5

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 much more clearly and deeply than I do the internal physics of a transistor. Further, it's much more comfortable (for me) to think in terms of increasing voltage ...


4

the spark gap's purpose is to very suddenly change the current in the LC circuit to which the antenna is, in fact, directly connected. the sudden change produces a very strong inductive kick in that circuit, producing a suddenly-rising voltage in it. that sudden rise gets filtered by the capacitor and inductor, causing them to resonate at the transmitting ...


4

The switch on the side of the key is or rather was used when tuning up a transmitter. In the old days you had to increase drive and dip the grid of the final amplifier. So this is simply a switch so that the operator can key his transmitter and use both hands for the operation. Today you don't tune like that UNLESS you have a high power amplifier. But ...


4

Are there any cellular bands that are close enough to amateur allocation for off-the-shelf cellular modems/filters/antennas to work? Yep, thanks to the fact that what is a GSM band in Europe is the American 33cm band. Does any relatively modern generation of cell technology have enough public datasheets for home/hobby use? Well, 2G and later standards ...


4

A panadapter is a device that adapts the narrow (typically 4kHz) bandwidth of a traditional receiver into a much wider bandwidth, perhaps the entire band. The pan- prefix means all, as in panoramic, pandemic, or Pangaea. A waterfall display isn't a panadapter, though a panadapter may have a waterfall display built in. A spectrum analyzer can also make a ...


4

The process of alignment involves optimizing the settings of variable inductors and/or trimmer capacitors in the set to maximize sensitivity and selectivity. It usually involves feeding the set a series of precise signals and adjusting particular components, in sequence, in each case to maximize output volume or voltage at a particular test point. This was ...


4

This is tough to nail down since even the term transceiver is subject to interpretation. It is also often the case that a given answer may only be applicable for a specific geography. But with those caveats in mind, from a US perspective, I believe the RCA 5 meter ATR-213 introduced in the 1930's might be one of the earliest entries in the US market. It ...


4

Mainstream hams first started to appreciate SWR in the 1940's. In that era some of the first SWR meters started to come on the market. But their accuracy and frequency range was quite limited. Toward the end of the 1940's military surplus coaxial cable was hitting the ham market. Up to that point, ladder line was typically used for most ham antenna ...


4

I don't know much about this, but for what it's worth I do have a rather distant memory of doing this long ago, before transistor RF power amps became affordable and before I had a way to measure SWR or harmonic content of the transmitter output. The transmitter was a very basic VFO, buffer and a 6V6 RF final, maybe 3 or 4W RF output max. The antenna was ...


4

It's more complicated than that. One of the things you do in an alignment is like what you describe, making sure that all of the fixed and adjustable frequencies inside the rig are correct and agree with what's on the dials. This might involve mechanical or electrical adjustment. But in addition to that you do things like Adjusting the tuned filters for ...


4

The challenging propagation experienced during the 2019 ARRL Field Day exercise answers your question with a resounding, "Yes, Relay is still relevant!" Many hams are unable to erect directional antennas on tall towers and power them with legal-limit amplifiers. Others simply prefer to complete contacts with modest antennas and lower power. We will not be ...


3

The methodology needed to accurately calculate the radiated r-f power needed to generate a given field intensity at some distance along a terrestrial path is highly complex — probably beyond the practical possibility of posting in an answer here, even in outline form. However, the U.S. FCC has developed a set of propagation charts relating to this topic, ...


3

We have some clues from a historical perspective. In the January 1917 edition of The Radio Experimentor, author H. Winfield Secor noted that approximately 50 kW (kilo-watts) of transmitter power was required to reach a 3,000 to 4,000 mile range with CW. He then went on to note that 10 μA (micro-amperes) is considered a weak receive signal while 20 μA is a ...


3

Here's a quote from https://en.wikipedia.org/wiki/Q_code . The original Q codes were created, circa 1909, by the British government as a "list of abbreviations... prepared for the use of British ships and coast stations licensed by the Postmaster General".[citation needed] The Q codes facilitated communication between maritime radio operators speaking ...


3

No attempt was made to reject the image response of the superheterodyne. This suggests that the designers wanted nothing to phase-shift RF signals...important in an interferometer - everything between antenna feed and the 10 MHz I.F. amplifier would be quite broad-band. And gain (actually loss) of diode mixers is fairly well-controlled. Keeping those two RF ...


2

Step 1, short out the spark gap. Step 2, lots of current flows through the inductor L, building up magnetic lines of flux (magnetic field) around the inductor L. Step 3, remove the short. Step 4, the current stops flowing through L, causing the magnetic field to collapse, causing a massive reverse voltage across the coil (Back EMF), charging the capacitor ...


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