https://arstechnica.com/science/2018/09/a-new-antenna-using-single-atoms-co…
A new antenna using single atoms could usher in the age of atomic radio
The team tested their device by recording themselves singing "Mary Had a Little Lamb"
Jennifer Ouellette - 9/19/2018, 6:18 AM
Enlarge / Zapping a vapor cell of excited cesium atoms with lasers makes an excellent detector of radio waves.
Rydberg Technologies
In the 1950s, atomic clocks revolutionized precision time-keeping. Now we may be on the verge of so-called "atomic radio," thanks to the development of a new type of antenna capable of receiving signals across a much wider range of frequencies (more than four octaves) that is highly resistant to electromagnetic interference.
An antenna is typically a collection of metal rods that pick up passing radio waves and convert their energy into an electrical current, which is then amplified. One might argue that the good old-fashioned radio antenna has served us well since the dawn of the 20th century, so why do we need anything to replace it?
According to David Anderson of Rydberg Technologies, those antennae are wavelength-dependent, so their size depends on whatever wavelength of signal they are trying to measure (they need to be about half the size of whatever wavelength they are designed to receive). That means you need antennae of several different sizes to measure different radio frequencies.
Anderson is a co-author of a new paper posted to the arXiv describing a novel alternative to conventional antennae, based on vapor cells filled with a gas of so-called "Rydberg atoms." That just means the atoms are in an especially excited state, well above their ground (lowest-energy) state. This makes them especially sensitive to passing electric fields, like the alternating fields of radio waves. All you need is a means of detecting those interactions to turn them into quantum sensors.
"You can design the receiver to operate at whatever frequencies you want and avoid intentional electromagnetic interference much more easily."
The Rydberg Technologies team realized they could zap their vapor cells filled with excited cesium atoms with laser light tuned to just the right critical frequency. This saturates the atoms so they can't absorb any more light, such that a second laser beam can pass right through them, effectively making the gas transparent. The critical frequency at which this transition happens will change in response to a passing radio wave, so the light from that second laser beam will flicker in response. The vapor cell becomes a purely optical radio wave detector, with no need for any wires or circuitry.
Plus it's capable of measuring pulsed and modulated RF fields, according to Anderson, which is how information is transferred across the airwaves. They have already tested the concept with AM and FM microwaves to transmit recordings of various team members singing "Mary Had a Little Lamb"—a nod to Thomas Edison, who sang the same song when he invented the phonograph in 1877.
The all-optical nature of the vapor cells means that even if they are hit with a massive burst of electromagnetic radiation, like that from a solar flare, they won't be permanently damaged because there is no circuitry to fry. This is a major concern for the electrical grid or certain defense systems and satellites. An atomic antenna would also be less vulnerable to the recent spate of suspected microwave attacks at US embassies in Cuba and China. And the cells are ideal for secure communications. "You can design the receiver to operate at whatever band or whatever frequencies you want and avoid intentional electromagnetic interference much more easily," says Anderson.
The detector cells are quite small, merely millimeters in size, with potential to scale them down even more. However, they require a significant backup system to operate, which has not been miniaturized. "You're not going to have a radio receiver that fits into a car dashboard today," says Anderson. "But the atomic clock paved the way for what we now call quantum technologies," and they began as large tabletop devices. Eventually scientists figured out how to make them small enough to fit into commercial systems.
Anderson foresees a similar trajectory for atomic radio. Within the next couple of years, he is confident they will have a suitcase-sized system that would fit neatly into an airplane or a ship, for example—vessels that would welcome the added protection from interference and electromagnetic pulses conferred by these detector cells. And perhaps one day these vapor cells will replace those pesky car antennae with something a bit more aesthetically pleasing.
[h/t: Technology Review]
-------- Forwarded Message --------
Subject: [socal-hamnet-users] Mesh Network cameras and brushfires
Date: Tue, 18 Sep 2018 15:58:12 -0700
From: Orv W6BI <orv.beach(a)gmail.com>
Reply-To: socal-hamnet-users(a)groups.io
To: VC_HAMMESHNET <VCHAMMESH(a)groups.io>, socal-hamnet-users(a)groups.io
Earlier this afternoon we had a brushfire in the northeastern corner of
Simi Valley. VCFD jumped on it with lots of resources and got it
snuffed out before it got much beyond about 50 acres.
In spite of it being windy and jiggling the camera, and having to zoom
way in, I got some fairly decent screenshots from the mesh network
camera on the north end of Sycamore Road here in Simi Valley. A few of
them are attached. I streamed it for about 30 minutes to Youtube, too.
73
Orv W6BI
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SBARC DMR users:
This came out in the ARRL letter today. DMR hotspot usage is interfering with amateur radio satellite users! If you have a hotspot, please, please, please be sure you are operating on an appropriate simplex frequency.
When picking a simplex frequency to operate a hotspot on it is important to maintain good operating practice. The important consideration here is not as much the 10 mW hotspot devices themselves but the 5W handheld transceivers and the 25W-50W mobile DMR units transmitting on the hotspot frequency. As there are NO suitable hotspot frequencies in the 435-450 MHz band segment, we suggest starting at the lower edge of the 431.00-431.60 MHz segment. Specifically 431.0125 MHz, 431.025 MHz and 431.0375 MHz are three good hotspot simplex channels that conform with the local SoCal 70cm bandplan. If you have neighbors close by who are using these frequencies already or you are on a promontory, you might consider using higher frequencies between 431.0375 and 431.600 MHz in 0.0125 MHz (12.5 KHz) increments.
LCM
Digital Mobile Radio Hotspots May Be Interfering with Satellite Uplinks, AMSAT Reports
This week, AMSAT News Service (ANS) cited an August 27 report from AMSAT Vice President-Operations Drew Glasbrenner, KO4MA, saying that a digital mobile radio (DMR) signal has been interfering with the AO-92 (Fox-1D) satellite's 435.35 MHz uplink frequency. Glasbrenner said hotspots, repeaters, terrestrial simplex, and "anything not satellite" should never transmit in the segments 145.8 - 146.0 MHz or 435 - 438 MHz by international band plan.
Well-known satellite enthusiast Patrick Stoddard, WD9EWK/VA7EWK, told ARRL that one DMR hotspot operating on the AO-92 uplink frequency in the St. Louis area has shifted to another frequency. But, he added, "I think there are still issues, since not all hotspots will report their frequencies and positions to websites such as BrandMeister or via APRS, where they appear on other sites such as http://aprs.fi."
"There are others surely operating near satellite uplinks," Stoddard added. "For many, the 435 - 438 MHz satellite subband is a big piece of quiet real estate in a busy part of the 70-centimeter band for weak-signal work, repeater links, amateur TV, and other possible uses."
Patrick Stoddard, WD9EWK, does a satellite demonstration at the Palm Springs Hamfest in 2017.
Stoddard points out that FCC Part 97 addresses Amateur Radio operation in these segments, although regulations in many other countries may not be as detailed. §97.3(a)(7) defines auxiliary stations as, "an amateur station, other than in a message forwarding system, that is transmitting communications point-to-point within a system of cooperating amateur stations."
Stoddard said this would include remote bases, EchoLink and IRLP nodes, and hotspots used for digital voice modes, as well as stations using these hotspots and nodes. Auxiliary stations may not transmit in the 145.8 - 146.0 and 435 - 438 MHz satellite subbands (among others in the 2-meter and 70-centimeter amateur bands), per §97.201(b). Further:
§97.3(a)(40) defines a repeater as, "an amateur station that simultaneously retransmits the transmission of another amateur station on a different channel or channels." Stoddard said that because most hotspots operate on a discrete frequency, they would not qualify as repeaters, even if they operate like a repeater, per §97.205(b).
§97.101(a) stipulates, "In all respects not specifically covered by FCC Rules, each amateur station must be operated in accordance with good engineering and good amateur practice." Stoddard remarked, "Whether the hotspot is interfering with a satellite downlink in a particular area, or it is interfering with the satellite uplink affecting a much larger area, this would not be good amateur practice."
In addition to subbands where hotspots are not permitted, Stoddard said, §97.101(b) is also relevant. It states, "Each station licensee and each control operator must cooperate in selecting transmitting channels and in making the most effective use of the Amateur Service frequencies. No frequency will be assigned for the exclusive use of any station."
Stoddard noted that frequencies used by satellites are usually incapable of being changed and are coordinated in advance of launch, while hotspots typically are frequency agile, and the frequencies used by those systems can be changed to avoid potential interference to satellites and other stations. -- Thanks to AMSAT News Service, Patrick Stoddard, WD9EWK/VA7EWK
LCM
Levi C. Maaia, K6LCM
Director at Large | Co-Chair, Telecommunications Services Committee
Santa Barbara Amateur Radio Club, Inc.
a 501(c)(3) nonprofit public benefit corporation
www.levi.maaia.com
+1.805.604.5384
By the way gang, here are those gorgeous coils. Jack Goodearl WA6DQK included the instruction sheet with the sale. It’s time I put them to use.
K6VML
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