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Kinda hard to translate an HD2 that isn’t on the air. KINK HD has been off since July 23rd when tower work started on the Sylvan TV Repack. KXL, KUPL, KLTH, and KXJM have also all been displaced to auxiliary facilities until the new TV antenna is up and connected to transmission line.
Um, yeah. The truth is somewhere in between. The differences noted between KKCW/KFBW and KWJJ have to do with where the digital signal is injected into the mix. My understanding is that KWJJ is low, or mid-level. KKCW and KFBW are combined essentially in the air as the analog and digital signals are injected into the antenna in opposite ends of the hybrids. This method relies heavily on the analog to digital isolation available in the antenna. As the antenna at Skyline was not really designed to do this in the first place, we’re lucky enough that the isolation numbers are in a range that the HD backfeed is even possible at all. HD1 and HD2, running in MP1 mode have the digital carriers further from the analog carrier, and thus get better protection from these poor isolation numbers. When we added the HD3 signals to KKCW and KFBW, we enabled the MP3 mode of operation. This mode of operation adds its carriers even closer to the analog signal, and at a lower injection level than the HD1/2 carriers. If we were able to turn up the power on the digital signals we might see a more stable signal, but this is again where we run into that isolation issue. There is just too much analog signal coming back down the digital transmission path on that antenna system to allow for anything more than -16 operation. I’m afraid we are either going to have to wait until a new master antenna with better isolation numbers is installed at Skyline, or we purchase transmitters capable of enough power to combine the analog and digital at low level.
The first generation gear was really not built solid enough for the environment that it was going to live in. Many transmitter sites run way too hot for the computer motherboards that these things were built on. The primary failure that we had, even at sites that run at about 70 degrees year-round, was the motherboards on the Harris and BE Exporter/Exciter combos. These were the standard leaky power supply caps that plagued many consumer machines for years (thinking Dell GX270s). You could shotgun the caps, or replace the motherboard and get back up and running. Hard drive and GPS modules also failed in a couple of the units we had. Second generation gear just migrated to a new data link (Exgine) for UDP data transport between the Exporter and Exciter. Sadly, this still didn’t address the standard motherboard issues on the Exporters, but it did stabilize the Exciter.
The latest generation of Exporters have greatly improved as they are built on an embedded Linux shell, and do not have any moving parts. We have experienced a little issue with GPS modules on the new Nautel Exporter Plus boxes, but it doesn’t generally take the whole system offline.
I guess one might argue that boxes designed to go at transmitter sites should be more heat tolerant, but you could also argue the other direction. If you run a stable temperature at the transmitter site you are likely to save yourself a whole lot of other equipment wear and tear.
There isn’t enough headroom available in the Sylvan commercial combiner to add KBFF. Even if there was, the suite is already maxed out for heat load and there would be nowhere to locate the filter sections required.
That being said, there would be room to move KBFF over to Skyline if 97.9 moved to Stonehenge. Now if only someone were to move off of the current Stonehenge combined antenna to make room for KLVP…
>>>Do you use the same type of feed at the Sylvan site?
Yes, although the isolation numbers for the antenna are better.
Andy – I wish I could, but it would require a new transmitter as the analog transmitters at the site can’t pass digital carriers at all, and the digital transmitters are too low power to produce the analog TPO required.
102.3 has been running RBDS since it moved to Skyline.
On the topic of the MP3 carriers on the Skyline signals, this is a weakness of the system that is used for the combining of the analog and HD signals. As the digital signals are “backfed” into the combiner system there is no way to fine tune the analog to digital isolation of the antenna. The two signals are being combined in the air so there is no way to keep the stronger signal from stepping on the weak one. If the analog and digital were both being generated by the same transmitter it would be a lot simpler to isolate the analog from the digital, and provide a consistent RF product in the field.
MP3 mode just adds extra carriers closer to the analog carrier. The added bandwidth is in its own ‘container’ so you can’t rob bandwidth from the previous carriers to even out the numbers. In our case, the HD1 is 48 kbps, HD2 is 32 kpbs, and the HD3 is 24 kbps. Unfortunately, because the new carriers are closer to the analog signal, and we are feeding the analog and digital with separate transmission chains, the HD3 carriers are very susceptible to getting stepped on by the analog signal.
From my perspective, the common names within the broadcast engineering circles in town refer to the KGW/OPB site as “Skyline”. The old tower at that site is just that, the old KGW tower. Just SE of that site is the old KATU tower, still referred to as the KATU site. The two towers accessed from Miller Rd. are generally referred to as the Channel 12 tower (east) and the Channel 49 tower (west), even though both stations are now on the east tower of the two. The old Channel 12 tower is in process of transferring back to the land owner as no broadcast facilities use it anymore, and it is so far west on the ridge that it has giant shadow issues into the core population center of Portland.