// HACKER NEWS — CYBERSECURITY
RF Cafe
In 2015 we would hardly think of electromagnetic
radiation in the 5 cm wavelength realm as being 'quasi-optical' as far as circuit-based
manipulation is concerned.
Optical wavelengths begin at around 6,300 Å for red light, which is 6.3x10-5 cm,
or 630 nm. The 5 cm wavelength used an example in a 1932 article in
Short Wave Craft magazine is equivalent to 6 GHz. 6 GHz was an
extraordinarily high frequency to be using for communications back then, and the
author did not intend to liken it to anywhere near visible light. Instead, his terming
its properties as 'quasi-optical' referred to how the waves interacted with physical
objects; e.g., reflection, refraction, absorption, and scattering. Barkhausen
oscillations were a popular subject of the era, as I pointed out recently in the
article "The Spook - Another Weird Effect to Haunt TV..."
Mac's Radio Service Shop: Telephone Pickups and Other
Subjects
At least in the U.S., laws regarding the
recording of telephone conversations seem to be constantly changing and vary
from state to state. Violation penalties - including imprisonment - can be
severe in both cases. Some states require that all parties in the conversation
be apprised of the recording, while others only require that at least one party
(obviously the one doing the recording) be aware of it. As mentioned in this
1954 "Macs Radio Service Shop" story, some areas require that an audible "beep"
be sounded at regular intervals while recording is occurring. With the
ubiquitous use of smartphones featuring built-in recording capabilities,
opportunities for recording and being recorded are constant...
Here is an advertisement for Electro-Voice
Manufacturing Company
microphones that I scanned from page 101 of my copy of the February 1943
QST magazine. As with many companies during the World War II era, this
one's theme is the service their products are providing to America's servicemen.
Per the ad: If you were receiving radio messages from men in the midst of earsplitting
battle noises, you'd hear crisp speech undistorted by background sound effects.
Electro-Voice Microphones, in military service, are helping to make it possible.
Similar microphones, designed to achieve such results, will be available for specific
commercial applications ... after our wartime job is done...
It would be more than a decade after the
publishing of this article before the first
direct-to-home satellite television broadcasts would be a reality, so it shows
how long plans were being made for such systems. Rural landscapes are still peppered
with the large vestigial C-band (~4 GHz) satellite dishes, many with faded
eyeballs and other clever (and ugly) artwork on them. Before coaxial cable was strung
beyond suburbs, country dwellers who either could not pull in over-the-air broadcasts
from downtown locations or just wanted more viewing options paid dearly for satellite
service. Equipment and installation costs on early systems could run into the $30k
realm. Today's satellite TV systems use...
Robert Taylor claims - without contention
from what I can find - to have invented the concept of "super-modulation,"
whereby the normal "splatter" created by greater than 100% amplitude modulation
(AM) can be mitigated through use of specialized circuits. As with many
paradigm-changing discoveries, much was made of super-modulation in the late
1940s through early 1950s, and then it pretty much dropped off the charts. The
cause might have been that the sophistication of circuitry needed to keep
everything tuned and tracking properly to prevent harmonic and sideband was
deemed not worth the trouble once frequency modulation (FM) came on the scene.
FM quickly gained...
By now, most people involved in science and
engineering have seen the iconic photos of cosmic rays and other
subatomic particles leaving a signature of their presence as streaks in a cloud
chamber. Invented by Scottish physicist Charles Wilson, the c