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|
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.|
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|
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!