Posts Tagged ‘VLA’
Repeater work on Sandia Crest
I had the opportunity of a lifetime to traverse through the nation’s most RF dense mountaintop towersite, and possibly reduce my chances of having children by a large amount…in any case, today’s work was bucket loads of fun.
|Towers lining the crest. [Wikimedia user Skoch3, Photo]|
The work at the site was simple — some regular maintenance to the W5MPZ D-STAR repeater and gateway.
So, I got up early and headed off to Ed’s (KA8JMW) place to pick up the caravan to the peak. We packed the truck with some server rack shelves and tools, and headed to pick up Brian (N5ZGT), then Chris (NB5T).
And then, the 10,768 ft (3,255m) summit.
The road was blocked by the Forest Service since the park was closed due to fire danger. Thanks to some prior planning, we had no trouble getting past.
And not two turns in to the curvy mountain road, we meet our first deer, head on. Thanks to Ed’s quick foot on the break (maybe he was practicing for QLF?) the deer zipped across the road, perhaps only with a bruised tail.
We were warned that with the lack of humans, nature tends to take over a bit
The one thing I though of going up the road is, what if you had this road all to yourself (like we did then) with a nice, fast rally car?
I think deer would have a problem with that.
Anyway, we got to the top, and met the first obstacle:
Chris dispatched the lock on the well-signed gate and we were in. At that point, we had entered the danger zone; the steel forest. With at least 26 FM stations, almost half being over 20 kilowatts, 33 TV stations, more than half over 100 kW, and an uncountable number of microwave dishes, log periodics, yagis, verticals, radomes, funny looking phased arrays and dipoles supported on dozens of massive towers, I swear I could hear KOB in my teeth.
After driving through the entire site, we arrived at our final destination: the Sandia Nat’l Lab’s personal radio playhouse.
The guys began working on equipment, while I snapped photos and gazed in awe of the city of Albuquerque all within my field of view.
|Chris, Ed, and Brian “working.”|
Brian took the job of tightening the D-STAR antenna, which he did adamantly, without falling, thanks to his fancy harness. It’s funny how dinky that antenna seems, but being over 3,000 ft ( 914m) above the rest of the world, it can see almost 100 radio miles (150km). With my 40w mobile radio, it comes in full signal in Socorro, NM, 75 miles (50km) away.
The team was successful of getting things done, cleaning up the shelves of an obtrusive monitor, keyboard and mouse (by going SSH only) and installing a NetIO internet-controlled AC power killswitch.
|After. Notice the new black box on the top right. That controls power for the whole thing via the web.|
The work was complete right on the dong of noon, and we had ribs for lunch. YUM! After that, Chris’s wife treated us to some homemade ice cream at his place, and we toured his shack, nestled on the edge of a HOA-restricted subdivision. That doesn’t stop him from loving ham radio!
Next on the list is to move this stuff to its permanent home on server racks. Sadly, I won’t be here, with only two weeks left in my VLA internship. I don’t wanna leave! 🙁
I would like to thank Ed James KA8JMW, Chris Aas NB5T and last but not least, Brian Mileshosky N5ZGT for taking me on this mighty heighty outing. Perfect timing for knocking another thing off my New Mexico to-do list.
The only part I forgot on that list was to bring a spectrum analyzer up there. It would have probably blown up in my hands.
|Me, Ed, Chris and Brian on the edge of the crest.|
Fire, Lightning, Wind and Dust: New Mexico Weather
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.
Don’t play Ingress at Radio Observatories
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!
What I’m up to at the VLA
Back last November I was offered this internship to work for up to 8 months at the Very Large Array, as you see pictured behind this post. The VLA is the worlds most prolific radio observatory, having the most citations in of any radio observatory in all of science. I could not turn this offer down/
The VLA is a well oiled machine of 27 cassegrain feed parabolic reflectors each 25 meters, or 82 feet wide, that send concentrated RF to massive feedhorns at its vertex. One VLA dish covers all frequencies from 1-50 GHz, and has two extra bands at 74 and 350 MHz using extra antennas. Together, they can make a dish that theoretically measures over 20 miles in diameter!
|Apex of a Dish Showing the Cassegrain Subreflector, 350MHz cross-dipole at the center of it, and the new strut-straddling sleeve-dipoles for 74MHz around the edges being installed|
My primary job at the VLA is to learn. Everything RF exists here, so I’m soaking up as much as I can. I’ve learned more about microwave RF design, Radar, synthetic aperture synthesis, correlation, radio astronomy, antenna design, transmission lines, test equipment, RFI, and much more that I have ever (and perhaps will have ever) at college.
Learning is a sort of meta-job. What I really do is two-fold.
The first fold is Interference Protection. The IPG specializes in the detection, location, analysis, and mitigation of radio frequency interference that has the potential of ruining and/or corrupting observations of the radio sky. The VLA is located in a lake bed, 20 miles away from any town, 90 miles from Albuquerque, surrounded by 360° of mountains that buffer the observatory from radar, wifi, cellular, aircraft, and other terrestrial sources of RFI. Satellites are also a source of RFI, so they must be documented and their transmissions well understood so that the VLA Correlator can learn how to discern orbiting transmitters from galactic transmitters.
On IPG, we’ve done a few RFI Site Surveys at places like the Magdalena Research Observatory on South Baldy and at the Pie Town VLBA site. Unfortunately, a Verizon 4G LTE cell tower exists on a hill only 5 miles from the center of the array. The signal it produces isn’t bad — it’s the amount of visitors who show up with a full signal, assuming it’s okay to use their smartphones to upload photos, videos, sprout WiFi APs, and cause all kinds of problems. That’s when we break out the CELL PHONE DESTROYER 6000.
|THE CELL PHONE DESTROYER 6000 is nothing more than a 1.8-2.4 GHz feedhorn attached to a spectrum analyzer, which is directly integrated into the neural cortex of this RFI Seeking Unit known only as Mert.|
For quieter RFI, like satellites and terrestrial transmitters, we use a big-ugly 10-foot dish with a wideband conical-log spiral feedhorn to determine bearings to RFI:
Along with intentional radiators, unintentional transmitters like microprocessors, screens, TVs, and other electronics produce noise that can be detrimental to the RF environment. Such electronics need to be tested in the Reverberation Chamber, and shielded if necessary.
The second fold is Front End — Front end of receivers that is. On the FE group, I’ve been tasked of removing old low-band receivers (74 and 350MHz) and installing new consolidated ones along with about 200 feet of heliax and control cables for them. I’ve also been building and improving antenna designs for the LBRs, including the new strut straddling dipoles pictured above. I’ve come across a cool 74MHz widebanded antenna design that may or may not be patentable, so we’ll see from it’s creator if I can get acknowledged in a paper or something 🙂
The LBRs are located in the apex, also pictured above. It’s fun becoming a grease monkey while getting a view of the VLA few have seen.
|Such a view|
So how did I get this job? Ham radio of course! My boss actually e-mailed me after an unsuccessful run through career fairs and internship searches for this summer. He noted my experience with the Missouri S&T ARC, W0EEE, as a big kicker on my resume. At S&T I’ve done a lot of work mitigating RFI, fixing repeaters, learning about radio, and having fun with it. He himself is a ham, albeit inactive, but still understands the value a license can have at such a job.
Ham radio gets jobs! (Girls? No.)
Today Paul Harden (NA5N) and I will be installing a few new LBRs in antennas 18 and 20. The weather looks beautiful for it too! Check out Paul’s personal website, chock full of receiver data, photos, and the history of the area.
That’s about the gist of it. 73 for now!