Cris Alexander, CPBE, AMD, DRB Crawford Broadcasting Company

KLTT NX50 and MDCL in Colorado

My apologies for not getting a column out last month. Year end is always a challenge around here, and this year was a triple whammy with year end, holiday vacation (hah!) and a transmitter project that I couldn’t keep my hands out of.

KLTT CE Amanda Alexander with her new Nautel NX50 transmitter

The new KLTT Nautel NX50 transmitter arrived on the Wednesday after Christmas, the delivery truck showing up a few minutes before the crew that Amanda had lined up and the forklift! Once everyone got there, it didn’t take us long to get the new rig off the truck and into the building.

We got the transmitter, transformer and ancillary stuff uncrated in short order, then levered everything off the skids onto the floor using a pry bar, the biggest one that Lowes had on hand. We had also purchased three 4-foot lengths of ¾” iron water pipe, and we used that as rollers to get the transmitter across the floor into place and the transformer (1,300 pounds!) into the transmitter.

The electrical work had mostly done the week before Christmas; all that remained, or so we thought, was to make the final connection into the transmitter. As it turned out, there was a safety interlock switch that goes in the 480-volt line that was not mentioned in any of the pre-installation documentation or even the installation manual. That wasn’t a lot of work, however; the electrician mounted it right next to the disconnect and used a short nipple to get the three phases into and out of the safety interlock.

While the electrician was installing the rough electrical the week prior and we had the power off, Amanda and I removed the 7/8-inch transmission line from the old aux transmitter, a Nautel ND2.5, and we punched out the hole in the top of the phasor to 3½ inches and drilled out the six 3/8-inch holes for the EIA flange bolts. We made the new connection inside the phasor and re-plumbed the RF to make the main the aux and vice-versa.

On installation day, by about 2:00 PM we had power to the transmitter and started going through the commissioning checklist. We were making (unmodulated) RF into the dummy load a short time later, cranking it all the way up to the licensed 52.650 kW TPO before shutting it down to start working on control and audio cabling.

The following day we wrapped up the remote control, audio and Ethernet wiring and were ready to modulate. Our first attempt resulted in two separate audio sources modulating the main (analog) carrier, one a second or so out of time alignment with the other. We finally figured out what was wrong and got that cleared up, and in short order we had it sounding great in both analog and digital. In fact, the digital adjustments were a snap and took just a couple of minutes to optimize. KLTT’s digital lock time on every HD radio I have tried is about a second, the fastest in town!

The KLTT NX50 Screen

The following week we activated the Modulation Dependent Carrier Level (MDCL) feature, which in the AMC algorithm reduces carrier power during periods of heavy modulation. The theory is that as long as sufficient carrier is maintained for proper demodulation, you really don’t need a full-power carrier during high modulation. When the modulation is reduced (during quiet passages or periods of silence), the carrier comes back to full power so that the AGCs in receivers doesn’t run up the noise.

The effect of all this is what I can best describe as “extreme carrier shift.” The very thing we worked so hard to prevent all these years is now desirable! We have the AMC carrier reduction set to 3 dB right now, so we see the carrier power drop to a little over 26 kW when the modulation is heavy. The sideband power is not affected by the MDCL operation, so loudness and coverage area are not affected.

We have been operating MDCL on our 50 kW station in the San Francisco market for several months now, long enough to get a read on the power savings. In both November and December, we noted a 21% decrease in power consumption over the same billing period last year. That’s nothing to sneeze at, an $800 per month savings! We look for similar savings at KLTT going forward.

Because demand is such a big part of the electric utility cost, it occurred to me that if we were to operate the Nautel ND50 auxiliary transmitter at full power for more than a very few minutes, we would push our peak demand back up to its old level and that would negate most of the savings we would have achieved with the NX50’s MDCL. So we did a firmware update in the ND50’s exgine and IBOC exciter to incorporate MDCL in that transmitter as well. It works great, producing the same carrier reduction with modulation that we are seeing with the new transmitter.

When walking into the KLTT transmitter building, we notice two things these days: quiet and cool. The NX50 is practically silent compared to the 1995-vintage ND50. And all that waste heat that we could always count on to keep the building comfortably warm in the winter months is now gone. The exhaust air from the NV50 has very low volume and is just a few degrees above ambient. That means that we actually have to run the heat in the building to keep the temperature above 50 degrees when it’s cold outside!

If you want to see some photos of the project, they are available at These were taken with several different cameras and as such are in chronological order by camera, not in straight chrono order from start to finish. The folks in the photo are Cliff Mikkelson (Salem-Denver CE), Mike Kilgore (general contractor), Keith Peterson, Amanda Alexander and yours truly.

(Copper?) Thieves!!
At 2:00 AM on January 12, thieves tried to gain entry to the KLTT transmitter building.

They used bolt cutters to cut the chain on the gate (we know this because they left their bolt cutters on the ground by the gate post). Then they evidently used a hammer to break off the doorknob on the front door, which freed the “realtor box” hanging on the knob.

And they then presumably smashed the realtor box to get to the key inside, then put it in the deadbolt and unlocked it. But they didn’t get in – in smashing the door knob froze the lockset mechanism so that it would not turn. They did, however, rattle the door sufficiently to trip the burglar alarm, and the alarm company called the Adams County Sheriff, who responded to the attempted break-in along with Amanda and her assistant Keith Peterson.

Before they took off, they evidently took a swipe at the door handle on the back door as well, so we ended up replacing both deadbolts and both locksets. We upgraded the exterior lighting, and we are also upgrading the alarm system and expanding it to include the tower base areas. We have never had an attempted break-in or any copper theft at that site (although a prairie dog exterminator did have his unsecured ATV stolen from behind our building last year), but now that the site is “on the radar,” we will beef up security at the site.

If you have news to share with the Rocky Mountain radio engineering community, drop me an email at