Entercom San Diego, through technical consultants GEO Broadcast Solutions, has built out a significantly advanced Single Frequency Network (SFN) for their 97.3 MHz station, KWFN (FM), “The Fan.” The team added analog-digital hybrid Xperi HD Radio on February 19, 2020 to help KWFN reach an audience that now extends past some significant terrain barriers within their licensed service contour. KWFN, with its sports talk format, hosts the current Padres Radio Network. The SFN includes the booster KWFN-FM1 La Jolla (in the Bird Rock neighborhood), KWFN-FM2 Ramona, KWFN-FM3 San Marcos (from Whitney Peak), and KWFN-FM4 Escondido (from Black Mountain). GEO is working to add the KWFN-FM5 booster in Encinitas that they have an FCC Construction Permit for.
Bill Hieatt, Chief Technical Officer of GEO Broadcast Solutions, the technical development heavyweight of the system, says KWFN has the first multiple booster FM HD system in the U.S. “KWFN is the world’s first all GatesAir HD+FM ever implemented, with four boosters going to five, that actually works exceptionally well, FM and HD.”
“The GEO team configured its Chicago-based lab to duplicate the KWFN system, providing engineers with a reliable testbed for the coverage modeling. This was particularly important given the challenge of predicting HD Radio coverage alongside FM, enabling the team to resolve configuration issues prior to deployment. The technical staff at Entercom San Diego played a key role in finding and resolving issues outside of the lab environment.”
KUSC-FM built a single HD hybrid booster using Interplex for FM synchronization and Nautel in 2016, but it was different in its nature that it had more significant terrain blockage to aid in its design. And because of the distance and lack of population in the interference zone, the precision-timing was less demanding.
Implementing a hybrid analog-digital booster system such as this isn’t for the timid. Your goal is to get a region served where you can pass in an automobile between any combination of coverage zones and the originating signal without even a blip of interruption to the audio. In the end, your transmitters need to be synchronized and in phase down to the individual zero-crossing, taking into account propagation delay and the maddening loss and reordering of packets through the wild, wild internet. If you don’t have a disciplined fiber internet service available, you may have to recruit a local wireless internet service provider (WISP) that can actually do business-class provision and care about your just-in-time, 24/7-don’t-miss-a-single-packet node. You need to delay your primary audio and digital to match the site with the most propagation delay. You have to do some on-the-fly buffering, error-correction, filling packet loss with error correction or substituting lost packets from internet provider A with found packets from provider B, and then some packet re-alignment on receipt. “Hey, you there—get in line–quickly!” All this is done synchronized to GPS.
GEO chose an end-to-end GatesAir system of Interplex point-to-point codecs and Flexiva transmitters. An advantage of single-sourcing is that it reduces finger-pointing when technical challenges arise. GEO started by installing analog-only booster systems and then getting the packet losses and errors down to zero. It took enormous cooperation from the ISPs and GatesAir to finally deliver an error-free service.
By the way, you can drive around to test the system. Pay attention to the RDS identification that is unique for each site. It should silently change as you pass from zone to zone. And forgive the team if your HD reception is weak as you get farther from the transmitter. That is a product of the hybrid digital system as it exists in the U.S. You can only get so much energy to the receiver when your HD sidebands are down 10 – 14 dBc from your low power booster carrier.
Erik Peterson GEO Broadcast Solutions in Chicago did the site procurement and project management. Vern Egli managed all of the details of technical implementations. They’re working on similar coverage extension systems for Boston, Chicago, and San Francisco.
As a matter of full disclosure, I was involved in some of the build-out of the SFN at several sites and we brought in Vic Soelberg for tower rigging services. Mike Prasser and Bill Eisenhamer of Entercom San Diego manage the system remotely. This is a remarkable team of smart people to work with.
The next task for GEO is “Zonecasting.” They intend to have the capability to provide ads delivered to individual zones. This will require specialized automation, data routing, and a change in FCC regulations that allow this in cable delivery but not over-the-air.
Edited 3/3/2020 to add the paragraph quoting Bill Hiaett telling more of the story about the lab simulation.