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The Very Large Array


The Very Large Array (VLBA) is a large network of antennas that operate as a single telescope.


The VLA

The VLA is located on the planes of San Augstin in New Mexico. They provide a large, flat, and high altitude area that is well suited to the operation.

Picture of the VLA and its railroad track.

Railroad Track

A custom built transporter regularly moves the antennas around on a double railroad track. The transporter is unusual in its ability to make a right turn. It will stop at the cross track, lift itself up with some hydraulic feet, turn the bogies 90 degrees, and sits back down. This was substantially less expensive than using traditional switch tracks for every antenna pad.

Picture of the VLA and its railroad track.
View of cross track at VLA

It is hard to respect the size of these antennas without walking underneath them.

Looking up at a VLA dish.

Looking over the edge

The view over the side of the dish can be a little frightening. Remember that it is safer to just hold a camera over the edge.

Looking over the edge of an antenna.

Azimuth Gear

The VLA antennas sit on a fixed base and have a bearing to allow for rotation. A large geared drive system then moves the antenna. Be sure to lock out the antenna drives prior to putting your hand near the gears.

VLA Azimuth gear

Counterweight

Each VLA antenna has a large counterweight to balance the load on the elevation axis.

Counterweight on a VLA antenna.

VLA FRM

The focus and rotation module (FRM) of the VLA antennas differs only slightly from that of the VLBA. They both serve the same purpose: position a subreflector to focus the beam on one of the receivers.

Apex of a VLA antenna.

Feed horn defrosters

Being at an elevation of about 7000ft the VLA has cold winters. Frost, snow, and ice on the feed horn will interfere with the signal. So defrosters are installed to clear it off.

Defrosters on a VLA antenna.

VLA Electronics Rack

Each receiver cabin has a couple racks of support electronics. Each antenna has to correctly synchronize its clock to the master clock, it has to receive and convert the RF signal, and it has to send the signal to the correlator.

In the original VLA an analog signal was sent back via waveguide. With the EVLA upgrade the signal is now digitized in the antenna and sent back over fiber optic cables.

Picture of VLA electronics rack.

VLA Receivers

NRAO designs and builds most of the receivers used in the antennas. Three of them can be seen here.

VLA receivers

VLA control building

The VLA control building houses the correlator and the control room.

View of the VLA control building from an antenna.

Spare Modules

Spare modules are always kept on hand, and failed modules are diagnosed and repaired. With the recent EVLA upgrade project many of the older electronics were replace with newer ones, so many of these modules are now outdated.

Spare VLA electronics

Old VLA correlator room door

Radio interference is a constant concern at the VLA. While a lot can be removed by the correlator, it is still very important to minimize interference from site electronics. Modern digital electronics generate large amounts of interference at the frequencies the VLA observes at. Shielded rooms such as this are often used to house station computers, preventing interference.

Old VLA correlator room door

VLA RF test chamber

The VLA has a test chamber for determining what interference a device emits. This chamber uses a combination of reflective walls and an omnidirectional antenna.

Inside the VLA RF test chamber

Omnidirectional antenna

This is the omnidirectional antenna used inside the test chamber.


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© David C. Hunter, 2014
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