TheEC: BRICs Through the Air

Jun 17, 2016

UBNT radios on the roof balcony of the Omni Hotel. RIPR's studios in 1 Union Station are at the bottom. The WELH "Main Studio" is behind the tree the arrow points to.
Credit Aaron Read RIPR

This week we have crossed a new milestone for our Studio/Transmitter Links (STL) for WELH 88.1FM.  Longtime EC readers know that we've had, well, "issues" with the STL for a long time.  One of the original PAS circuits, leased from Verizon, was highly problematic...and after much effort and coordination with The Wheeler School, we successfully installed a 950MHz Microwave STL that beamed audio from 216 Hope Street on College Hill (Wheeler's "Main Studio" for WELH) to the transmitter site in Seekonk.

And of course, less than a year later, Verizon discontinued offering the PAS circuits at all; retiring any copper-wire-based telecommunications technology in favor of fiberoptic tech instead.  Unfortunately, the fiberoptic stuff is quite pricey (it would've added a zero to our monthly costs) so we elected to use Comrex BRIC Links, connecting over the public internet, while working on a more long-term solution.

The long-term solution ended up being placing several Ubiquiti wireless ethernet radios/antennas, each the size of a hardcover book, on the roof of 1 Union Station (our studios), the roof of the Omni Hotel in downtown Providence and the top floor windows of 216 Hope Street (again, where the WELH "Main Studio" is located).  These sites each have line-of-sight to each other, and essentially they function like a really, really long ethernet cable; extending our studio's local network out to distant locations.

The Loco M900's built-in spectrum analyzer, sampling the local RF scene on the roof of the Omni Hotel. Note the presence of a fairly strong signals on 894MHz, 921MHz, 924MHz, and 931MHz. Plus a lot of little signals gathered around 927.5MHz. "Strong" is a relative term here, they're all at least -50dBm which is pretty weak overall. But UBNT radios work at very small power levels, so care must be exercised about what frequency you use.
Credit Aaron Read RIPR

These Ubiquiti radios are Nanostation Loco M900​ units, operating on 900-920MHz.  They're remarkable devices!  Able to transmit at least 20Mbps, even 100Mbps, over 5, 10 or even 20 miles.  (!!!)  Yet they require no license to operate, they're only about the size of a hardcover book (roughly 7 x 10 x 2in), and are entirely self-contained.  The radio is inside the antenna housing, and the whole thing needs only one CAT5 cable thanks to Power Over Ethernet.   Best of all, they're very cheap for what they do; you can buy them for about $130 each.  At that price, it's easy to get a few spares.

We still use the BRIC Links to turn the actual audio into data that travels over the network, but now instead of going over the wild wild web on the public internet, where anything and everything can, and does, happen.

Of course, we're not ones to put all our eggs in one basket, no matter how reliable it's supposed to be.  So we have a separate pair of BRIC Links connecting over our Cox fiberoptic internet connection (at the studios) and Comcast Business Cablemodem (at the tower).  Still over the public internet, but it's just a backup.  And if things really go down the drain, we can rebroadcast our 102.7FM signal via a high-quality Inovonics AARON640 - how could I not get one?? :) the 88.1FM tower site in Seekonk.   All of these can be manually controlled, but they'll automatically switch after 10 seconds of silence, too.

UBNT's AirLink web software, for planning your wireless ethernet path.
Credit Aaron Read RIPR

The end result of all this is that hopefully we'll have more reliable audio delivery from our studios in 1 Union Station to the listeners of 88.1FM!

The next step is to install a higher-gain antenna on the roof of the Omni Hotel to boost signal levels a bit, and thus improve our bandwidth.  With that, I can use the BRIC Link to send uncompressed audio at the highest possible audio fidelity: 16 bit, 44.1kHz sampled full stereo AES digital audio.  I may even be able to eventually recognize the dream of an all-digital audio path from soup to nuts.  No analog anywhere in there, and crystal-clear audio all the way.  That'll be sweet!