# Tag Info

## Hot answers tagged history

8

These were common abbreviations in use for Components, Radio equipment, and Printed publications in the 19th and most of the 20th century. Mfd = microfarad or μF kc = kilocycles or kHz. 1,000 cycles per second. μμf or mmf = pF (picofarad) Frequency The change from kc to kHz and mc to MHz were done because someone though that Heinrich Hertz ought to be ...

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 ...

3

Yes, in the early spark days, the fundamental frequency of the transmitter was largely determined by the self-resonance of the antenna system. Any sort of spark generator naturally generates RF energy at many frequencies, but those close the self-resonance of the antenna would be more likely to be effectively radiated. Receiving antenna self-resonance isn't ...

2

As far as your question regards components: T/R switching is usually done with either relays, reed relays (often faster than other types of relays; also more quiet), or PIN diodes (even more quiet and faster). Where high voltages and/or currents are present (and fast switching is needed) vacuum relays are also used. Circuitry may involve circuits that ensure ...

2

As both previous answers mention, the T/R switch functionality is just something that moved into existing boxes, not something that disappeared. The only ways to make that functionalies disappear would be making the receive end tolerant of the transmit power and still a sensitive receiver (practically impossible at any significant power – the difference ...

1

A dipole is resonant on every frequency where it is an odd multiple of (slightly less than) $\lambda/2$. So normally we talk of half-wave dipoles, but 1.5-wave, 2.5 wave, and 3.5-wave dipoles are similarly resonant. They all have a feedpoint impedance of about (72+0j) ohms in free space. For monopoles, being half a dipole, the resonances occur at (slightly ...

1

I wouldn't say that SMA is "the" standard RF coaxial connector, I would say that it is one standard among many. No connector has emerged as the best for all uses, which is why there are many standards. Other connectors such as the "UHF" (badly-named because its performance is terrible at UHF), BNC, F, and N connectors were invented ...

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