Posts Tagged ‘Long wavelength Array’
It’s always been a dream of mine to put on glasses that allow you to see only waves of RF emitting, reflecting and illuminating the world around you…this would make my job so much easier too!
Well, there just so happens to be such a thing that allows you to see RF…it only requries about 3 acres and 250 antenna elements, a supercomputer and a fast internet connection.
|The LWA near the VLA|
The Long Wavelength Array is a seemingly random assortment of crossed dipole pairs with a frequency response of 10-88 MHz. Every antenna is separetly fed into a giant computer that correlates and beamforms the array into a giant RF eye looking at the sky.
|LWA Dipole Detail with the VLA in the background|
And by eye I really mean it sees the RF world above it in real time:
Above is a real time view of the sky above the LWA (hit F5 to refresh, I dare ya!). During the day you can see the sun and several radio sources like Cas A, Tau A, and Cyg A which are galaxies, pulsars, and other nebulae of ridiculously “loud” RF emitters. Also, at the top and top left, you can see RFI from the VLA site, which is one of the things we’re working to alleviate.
Another cool thing it can do is plot spectrum over the whole day:
This shows the intensity at all frequencies between 10 and 90 MHz over a 24 hour period starting at 17:00 PST 11 July 2012. You can watch the nighttime MUF drop between 00:00 and 06:00 PST, and surge again at sunrise. Other strange and interesting patterns exist as well — check out the index at http://lwalab.phys.unm.edu/lwatv/ovro and see what you can find.
New Mexico is dry. I was floored when it rained three days ago. But for 11 months out of the year, the air is dry, the sun is bright, the clouds are facetious, and everything’s on fire.
|Smoke plume from the 30,000 acre Silver fire|
|Smoke fills the horizon|
Such is life in NM. The 10% humidity caused me some pain and suffering for a while, but I seemed to got used to it. I used a lot of normal lotion, which wasn’t the best idea for being out in the sun so much.
Currently, a large chunk of the Gila mountain range is on fire, but thankfully few people live in the area. The Silver fire (named because its near Silver City, NM) is currently at 32,000 acres, making it the biggest fire in the US. From atop a VLA dish, you can see the smoke plume and the long trail of smoke being carried by 30-40 mph surface winds. It’s quite dark in Truth or Consequences.
Aside from the fire, the plains of central New Mexico have a variety of weather, typically involving some kind of dust and lots of wind:
|Dust carried aloft by 40 mph winds|
We even have tornadoes of dust! (Seriously, some of them are big enough to cause damage):
|A particularly strong dust devil with a well defined center column|
Then, all of a sudden, it storms:
|A snowstorm to the north…it’s a rare event to see precip actually get to the ground.|
Above, you see it’s snowing. Snowstorms in the southwest isn’t a myth after all! Just last year, a snowstorm dumped 2′ of snow on Socorro, NM.
Typically though, the air is so dry that any precipitation just evaporates before it hits the ground. This phenomena is called virga, and is the sole reason why the clouds are so facetious. What does hit the ground are tendrils of lightning, graupel — basically mini snowballs from the sky — and hail.
|A tendril of lightning betwixt two VLA dishes|
In 2004, hail fell with a vengeance:
So its dry, its dusty, windy and usually boring (minus the bits of hail, getting caught in a haboob, and waking up to lightning barrages)…but now is the season for rain. And we’re in dire need. NM has been in a 10 year drout, and wells are drying up like int he community of Magdalena, NM, just east of the VLA.
Locals believe that July 4 is the day which marks the start of the monsoon season…don’t take monsoon to seriously though, it’s not like the monsoons of India and Asia. They may dump 2″ of rain, but that gets sucked up so quickly by the dry, absorbent dust and flora of the mountain ranges that it was like it never happened the next day.
We’ll see what the skies bring.
A few weeks ago, the IPG got some curious email from some ABQ-ians asking if they could play Ingress at the VLA to capture some GPS-based portals. If you’ve never heard of Ingress, think of it as geocaching with a Virtual Reality spin. Check out their website here.
Ingress is played on smart devices, which require data connections to operate. These data connections are fine and dandy unless you’re at the world’s greatest radio observatory; here they aren’t so dandy.
Below is a screencap of our RF-EMS (Radio Frequency-Environmental Monitoring System) which captured two WiFi access points (the darker blotches) from an RV containing a Verizon 4G hotspot and another router for something else.
|Your VLA on WIFI|
In the last blog I described the 10′ dish for pinpointing RFI. We also have a (usually) 24/7 monitor that uses some pretty nifty antennas and preamps on a 50′ tower, sending it to an HP 70000 Spectrum Analyzer in a RF-shielded room from which we can record and upload plots like the one above, every day for the past 5+ years.
|RF-EMS Tower and Bunker|
The biggest downfall is adequate locating of interfering transmitters. Currently, I’m designing a method which will allow the IPG to quickly and accurately pinpoint people with any kind of transmitter, be it a cell phone, hotspot, or vehicle keyfob (if we wanted to locate such things). My idea is based on multilateriation, which uses multiple receivers around the site which compare arrival times to calculate a four dimensional location. Keeping the bill of materials as low as possible, simplicity, ease-of-use and network integration (without causing RFI itself) a prime focus.
It may be overkill, but it gives me something to do in the free time.
Other Doin’s: Testing out and Debugging the 74 MHz System
When I’m not having free time, this is what I’m doing. A new feature of the Expanded-VLA is observations on the 4 meter band. The current system in place uses these simple crossed dipoles hoisted a few meters below the sub-reflector.
The cross dipoles connect to our receiver, which hooks up to the rack that magically digitizes the signal and turns it into pulses of light which the correlator feeds upon.
One of the problems we face are things broken that don’t have to do with our antennas and receivers. For example, the first test we do to examine the receivers performance is a band pass plot. Often times, we see something like this:
|A bad bandpass plot caused by a faulty relay in the T301.|
This is ugly! What we want to see is this:
|A beautiful bandpass! You can see 4 band on the left, and P-band in the middle with RFI spikes all over.|
First we go digging in the LO-IF and FE racks for a place to stick a spectrum analyzer to…
|Eric the BAMF next to the LOIF and FE rack. Our culprit is on the left, in the middle of the top rack of modules|
And from that we figure its’ this T301 which does the first IF up-conversion from 0-1GHz to 1-2GHz.
We get a new one, stick it in, turn it on and voila, it’s alive!