Posts Tagged ‘c-band’

Excited Cesium Atoms and the Radio Antenna

Wednesday, September 19th, 2018

Fascinating read about an atomic receiver for AM and FM radio communication, able to operate from the C- to the Q-bands, which may someday bring quantum physics into the world of satcom receivers.

Here’s more from MIT Technology Review

The secret sauce in the new device is Rydberg atoms. These are cesium atoms in which the outer electrons are so excited that they orbit the nucleus at great distance. At these distances, the electrons’ potential energy levels are extremely closely spaced, and this gives them special properties. Indeed, any small electric field can nudge them from one level to another.

Radio waves consist of alternating electric fields that readily interact with any Rydberg atoms they come across. This makes them potential sensors.

But how to detect this interaction? A gas made of Rydberg atoms has another property that turns out to be useful—it can be made transparent by a laser tuned to a specific frequency. This laser essentially saturates the gas’s ability to absorb light, allowing another laser beam to pass through it.

However, the critical frequency at which this happens depends crucially on the properties of the Rydberg atoms in the gas. When these atoms interact with radio waves, the critical frequency changes in response.

That’s the basis of the radio detection. Anderson and co create a gas of cesium atoms excited into Rydberg states. They then use a laser tuned to a specific frequency to make the gas transparent.

Finally, they shine a second laser through the gas and measure how much light is absorbed, to see how the transparency varies with ambient radio waves.

The signal from a simple light-sensitive photodiode then reveals the way the radio signals are frequency modulated or amplitude modulated.

And that’s it: an antenna consisting of a cloud of excited cesium atoms, zapped by laser light that flickers in time to any ambient radio waves. They call it atomic radio.

Very cool — and no electromagnetic interference!

DIY Friday: Backyard Flying Saucer

Friday, January 16th, 2015

We like upcycling. When it includes old satellite dishes, we love it!

Using a couple of old C-band mesh antennas to make an alien spacecraft in your backyard is brilliant and worth sharing.

The idea for this project had been milling around in my brain for awhile… I had visualized taking two satellite dishes, preferably 2 of the fiberglass type and slap them together like 2 pie plates to form a traditional saucer shape. The first task I had was to find suitable dishes to salvage for the project. I drove around whenever I had time to watch out for candidates, and I watched Craigslist and other sources of ads on the Internet. I live just outside the city limits, and had plenty of countryside to travel around. I also kept my mind open to the possibility of using the metal mesh dishes as well, thereby doubling my chances of finding what I needed.

Eventually, I placed an ad on Craigslist asking for a dish, and voila! I got a bite! It turned out to be a mesh dish in the city but just a few minutes away. I went over on a Sunday afternoon and it took an hour and some elbow grease to dismantle the dish and load it into the back of my pickup. I should mention that even if I couldn’t use the mesh dish, I could always take it to the recycling center and get some cash out of it! Ironically, I found a fiberglass dish about a mile from home, and after a couple of tries, I finally met the home owner, who said his wife had been asking and asking and asking him to remove the dish. Sounded like I arrived just in time! This one took about TWO hours to take off the mount and take it down to 2 halves and strap them down to my utility trailer. Note: It helps if you have some assistance to dismantle these things, they are HEAVY as all get out! After bringing them home and laying them out in the back yard, I pondered what to do about the situation, as time was marching on and I was tired of looking for dishes.

Get out there and make your own!

Elliptical C-band Uplink Antennas

Friday, October 24th, 2008

Via Doug Lung’s RF Report:

In some cases, it isn’t possible to install an uplink dish that meets the FCC off-axis antenna pattern envelope. In the past, the FCC allowed operation of uplinks with non-compliant antennas upon a showing by the licensee that the effective isotropic radiated power (EIRP) would be reduced enough to keep the energy in side lobes below the level that would have existed using an uplink with a compliant dish at maximum power. This required a detailed engineering showing that often slowed FCC processing.

In the Eighth Report and Order and Order on Reconsideration (FCC 08-246), the FCC adopted an off-axis EIRP envelope approach as one method for applicants to apply for fixed satellite service (FSS) Earth stations using small antennas operating on conventional C and Ku-band frequencies.

It states, "This off-axis EIRP approach gives earth station applicants the flexibility to reduce their power levels to compensate for a small antenna diameter. Thus, using these envelopes as criteria for licensing should enable us to license more earth station applications routinely, expediting the provision of satellite services to consumers and enhancing the types of services available, without increasing the likelihood of harmful interference to adjacent satellite operators or to terrestrial wireless operators."

The Order adopts rules that facilitate the use of elliptical C-band uplink antennas. While the new rules do not specifically state that the major axis of the elliptical antenna be aligned with the geo-stationary orbit plane, the Order notes that "that starting the off-axis EIRP envelope at 1.5 degrees off-axis within the GSO orbital plane, and at 3.0 degrees outside that plane, has the same effect as requiring elliptical antennas to be aligned with the GSO plane in most cases."

The Satellite Industry Association (SIA) claimed that it is not possible to develop an off-axis EIRP envelope for analog video signals because the power density of such signals fluctuates. SES Americom opposed new analog regulations because the current rules are working well. The FCC decided to retain the current regulatory framework for analog services at this time. It dropped plans for eliminating analog video transmission over satellite entirely, noting, "The record in this proceeding has shown convincingly that requiring the transition from analog to digital video transmissions proposed in the Third Further Notice would be unreasonably expensive and burdensome."