Classic Pete: Once More, Out To The DTV Fringe
- Published on Saturday, 15 August 2009 16:38
- Pete Putman
- 35 Comments
Recently, I made a third trip to my brother’s house in the hills of southwestern Vermont to finish what I started over two years ago – set up this distant, remote location to receive every digital TV channel from Albany. And I succeeded.
My first visit in May of 2007, chronicled here, showed that a modest suburban UHF yagi (Channel Master’s model 4308) and a low-noise preamp was sufficient to pull in four Albany DTV stations over a 54-mile path by taking advantage of knife-edge refraction of the RF signals, bending over a range of hills about ½ mile to the southwest of the house.
I was surprised at how strong the “bent” signals were, even with moderate multipath distortion. But they came in just fine on a pair of Gen5 ATSC DTV receivers, with minor interruptions in service during periods of heavy rain or dense fog.
Still, I hadn’t resolved the issue of receiving a pair of high-band Albany VHF DTV channels – WXXA-7 (Fox) and WNYT-12 (NBC). That would be addressed during my next visit in early January of this year, and you can read about it here. Trust me; it wasn’t much fun working outside in sub-zero temperatures. And I didn’t have the best antenna for the job, relying on a used Terk TV35 suburban VHF/UHF yagi to pull in the signals, aided by a dual-band, low noise preamplifier.
I knew a third and final tweak to the system would inevitably be in order, particularly to improve the reception of WXXA-DT. Plus, WRGB-DT (CBS), previously operating on UHF channel 39, was scheduled to move back to VHF channel 6 on June 12 as the analog TV shutdown was completed. And another Albany DTV station, WNYA (MyTV), hadn’t even signed on yet- they were still waiting for WNYT to vacate their analog signal from channel 13.
THE FINAL PUZZLE PIECE
The first order of business was to replace the Terk TV35 with a more serious VHF yagi. Fred Lass, chief engineer at WRGB, kindly sent along a pair of Antennacraft Y5-2-6 low-band VHF yagis for the job, but those wouldn’t help me with channels 7, 12, and 13.
Instead, I opted for the Antennacraft CS600 VHF yagi, which would provide reception from channel 2 through 13 and which (according to the specs) was good for up to 40 miles on low-band VHF and 50 miles on high-band VHF. Coupled to the Channel Master #7777 dual-band preamp, I figured it would be enough.
The next step was to check reception from the January installation by recording new spectrum analyzer plots and comparing them to the screen grabs I captured eight months ago. Good news – the 8VSB carriers from the remaining UHF stations (WTEN-26, WMHT-34, and WCWN-43) hadn’t changed any, even with all the nearby trees fully leafed out.
Unfortunately, signals from WXXA-7 and WNYT-12 didn’t look too good, thanks to a broken rear reflector element on the TV35. So, I removed the Terk from the system and assembled the CS600. I also had to install a second, offset antenna mast to clear the rear elements of the CS600 from the deck supports, not to mention a large rose bush which had grown around the mast and TV35!
To make everything fit in this tight space, I drilled a set of new boom-to-mast bracket holes near the rear of the CS600. The antenna is light and sturdy enough to be mounted this way, although I recommend using the standard mounting holes when up on a rooftop mast to balance the antenna and reduce wind load.
From my January escapades, I found that the TV35 worked better when it was offset about 30 degrees farther west from the UHF antenna heading. I chalked that up to different reflections of the knife-edge signal than I had seen on UHF, and initially installed the CS600 at the same height, facing in the same direction.
A quick test with a Zenith DTT901 NTIA converter grabbed WRGB-6, WNYT-12, and newcomer WNYA-13 with no difficulty. But WXXA-7 was intermittent, and now WMHT-34 (PBS) was becoming problematic to receive. This wasn’t going to be easy! (It never is…)
In my January conversations with Fred Lass, he mentioned that the refraction angle for channel 6 could be more severe than that of the UHF DTV stations. That meant I might have more luck if I lowered the CS600…and that’s exactly what happened.
After a night to clear my head and socialize with my relatives, I walked outside early the next morning, connected my spectrum analyzer, loosened the mast bracket, and lowered the CS600 to within a foot of the ground. I also rotated it south to the same antenna heading (230 degrees) that I eventually used to clean up reception of WMHT-34 on the Channel Master 4308.
After firing up the DTT901, I was finally done. All eight of the Albany DTV stations were now coming in reliably, free of dropouts. WXXA-7’s waveform, although still somewhat bowed, was considerably cleaner than before. And a modest amount of tilt on WNYT-12 and WNYA-13 was no problem even for the adaptive equalizers in my Gen 5 OnAir Solution HDTV-GT receiver.
In fact, I had enough signal out of the CM 7777 preamp to run a second coaxial drop upstairs to a bedroom, feeding a second DT901 converter box with the same results. Oddly, WRGB’s signal on channel 6 remained consistent through the CS600 at any height and with either of the compass headings I used. The 8VSB carrier wasn’t perfectly level, but the converter boxes and HDTV-GT locked it up quickly every time.
When TV signals bend, they really bend! Knife-edge refraction works so well at this location that I actually received all of the Albany DTV channels with the CS600 resting nose-down on the ground and its rear elements tilted up at a 45-degree angle against the mast! That certainly was cool.
The only weather effects I observed happened the last night of my stay, when dense clouds of moisture formed in the valley right before a strong weather front passed through. The resulting mist and fog caused ABC affiliate WTEN-DT’s signal on channel 26 to break up on a regular basis, while all other channels were unaffected. The next morning, all was well again. (Coincidentally, I’ve observed the same effect at home on Philadelphia’s KYW-DT, also transmitting on channel 26 and otherwise a very strong and reliable signal.)
Because the CS600 sits so low on the mast, I wrapped the longest elements with bright orange electrical tape so no one would walk into it. I also capped the swaged ends of the elements with plastic bolt protectors, glued in with silicone seal. Some new flower plantings around the antenna should keep visitors from accidentally walking into it in the future. (Don’t these problems sound ridiculous?)
Now, my brother and sister-in-law are going to try terrestrial digital TV for a month and see if they still want to pay for their existing DirecTV service. Given how little television my brother watches, I think I know how he’ll cast his vote, but I’m not sure about his wife.
I will say that she showed remarkable enthusiasm for finally having gained access to “free TV,” and she subsequently informed me that there would be a stampede for my services from nearby neighbors who’d also want in on this deal. Maybe it’s a good thing that I live almost 300 miles away?
I’m also amazed at how robust the 8VSB DTV system turned out to be, and how it’s perfectly suited to unusual propagation paths like this one. Granted, I also pulled in analog VHF and UHF TV stations with the earlier antenna setups, but the signals were fairly noisy and had more than a few ghosts, as you might expect.
Digital TV cleans all of that up. All you need is enough signal to get over the required carrier-to-noise threshold (in this case, about 20 dB C/N), and voila – perfect pictures and audio. (Never mind that a few of them were infomercials.) The fact that converter boxes and new integrated digital TV sets are largely using Generation 6 adaptive equalizers is just icing on the cake.
Any disappointments? Well, I never could pull in WYPX-50 from Amsterdam, although it’s strong enough to show up on my spectrum analyzer. The problem is their transmitter location, much farther west than the Helderberg Mountain antenna farm used by everyone else. That would require “sacrificing the good of the many for the good of the one” (to misquote Mr. Spock from Star Trek II: The Wrath of Khan).
Also, I could see another 8VSB carrier on channel 9 from WVER (Vermont Public Television) in Rutland, Vermont. But to receive that station would have required divine intervention, as the signal was coming from the opposite direction, 34 miles to the north/northeast over a tall range of hills, including Mt. Equinox (3,848’ ASL), and ricocheting off the 1300-foot-tall ridge in front of the house. Now, THAT would have been one heck of a billiards shot!
The good news is, if you live in a “tough” DTV reception location, you may not be completely out of luck. It helps if the DTV stations you want to receive are co-located, because having only one antenna heading to deal with is a real blessing. But there’s no reason why you couldn’t succeed with a broader antenna pattern if DTV stations are spread farther part – you just need to get enough signal to the receiver, and you’re home free.
As they used to say in those old Westerns, “Looks like my work here is done.” Time to saddle up, and head off in search of the next fringe…