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Update on Transmitters
Keep in mind that the manufacturers of higher power transmitters also make units that will work great in LPFM applications. For example, Broadcast Electronics offers the STXe for power levels between 70 and 550W (more than enough for any LPFM application). Aside from the integral controller, it has an integral low-pass filter, meaning it can be used as a stand-alone transmitter. It also has an updated GUI, so if the site has IP access, complete remote access is available. SNMP support is also included. With the addition of VPe (Vector Power Enhancement) this exciter can also be used in HD radio applications in FM + HD Radio, or HD Radio only. For those outside the U.S, this exciter can also be used for FM + DRM+ applications.
GatesAir makes the Flexiva series of transmitters and the FAX300 would be appropriate for the many LPFM applications. It includes a direct-to-carrier modulator, with integral stereo generator, and integral low-pass filter, meaning it can be used as a stand-alone transmitter. (The FAX50, FAX150, FAX300, FAX500 and FAX1kW are fully FCC type accepted for LPFM.) Its stereo generator has analog L/R inputs along with two AES inputs, and a built-in RDS generator. AC power input uses between 90Vac and 277Vac. It's 3RU and 20.5" deep. FAX300 comes with an embedded Web interface, SNMP support, and local GP I/O as well. Flexiva 300 can be used for HD Radio or DRM+ as well.
Nautel offers the VS300LP, which is a special version of the VS300, type-accepted for LPFM applications. Like all the other transmitters we've looked at, the VS300LP has an integral exciter; it uses direct-to-channel modulation, and comes with an integrated stereo generator, and SCA and RDS generators. The VS300LP accepts an AES program input, L/R analog inputs, composite, or IP streams such as Shoutcast, RTP, or Livewire. It also supports MPX over AES for a completely digital connection to many audio processors. Maximum power is 330W (analog only), and it's 2RU and about 25" deep with a type-N female connector output. The ac input voltage can operate between 180Vac and 264Vac. Remote access is done via the Nautel AUI, which gives the user complete monitoring and control via IP; parallel control and SNMP access are supported as well.
The evolution of FM transmission continues. After years of using tube transmitters, solid-state has now become commonplace. HD Radio has been thoroughly integrated into new products. The latest trends have mainly to do with the addition of IP access at transmitter sites: Web access, remote control, and the use of streaming audio. As transmitters become more reliable, and require less routine maintenance, they don't require as many hands-on visits, and so the ability to see their operation remotely has become more important than ever. The new design features are indicative of how communication has evolved, with ubiquitous IP access and Ethernet. I hope if you are looking at a new transmitter purchase that you'll embrace these new aspects of the art.
Irwin is RF engineer/project manager for Clear Channel Los Angeles. Contact him at firstname.lastname@example.org.
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