Thanks to all of you for your feedback on last Wednesday's over-the-air television reception two-part series and my last-Friday follow-up piece. Last Wednesday morning, I had the pleasure of a visit by KTVN's chief broadcast engineer, Jack Antonio, and his assistant Eric Brown. Antonio and Brown brought along with them a full-sized UHF/VHF antenna pre-mounted on a tall metal pole, along with a Sencore AT1506 TV signal analyzer, and a Samsung SIR-T151 ATSC-only set-top box (as you'll soon see in more detail, I own that exact same STB model) and tethered portable CRT TV. As a reminder, KTVN's ATSC (high-band VHF channel 13) broadcast originates from Slide Mountain, ~20 miles away and at a compass heading of ~87° according to AntennaWeb.

At the time of Antonio and Brown's visit, I was unable to receive KTVN's ATSC transmission (or for that matter, KOLO's NTSC channel 8 and ATSC channel 9 transmissions), even though I tuned in KRNV's ATSC channel 7 transmission just fine...and even though all three stations' towers are on Slide Mountain. I'll apologize upfront that, due to limited schedule availability on their part, we were unable to measure the signal strength coming from my Antennas Direct ClearStream 2 antenna. However, I think the data we did gather will still be of great interest to you.

Antonio and Brown began by sticking their antenna up in the air at my outside parking pad. Antonio's general rule of thumb is that a -10 dBmV signal strength is sufficient for a television tuner to reliably lock on, and we were therefore surprised to see that channel 13 (KTVN's ATSC broadcast, which I was unable to receive) measured –5 dBmV on the Sencore AT1506. In fact, KTVN measured stronger than KRNV's channel 7 ATSC broadcast, which came in at –7.5 dBmV (and, again, I was able to receive). However, Antonio's KOLO results correlated with mine; channel 9 measured –16 dBmV, and the Sencore AT1506 wasn't reliably able to lock onto it.

Next, we disconnected my antenna from the front door coax feed and connected KTVN's antenna instead. Then, we went inside and measured signal strength at the end of my sub-60' coax cable run. Channel 7 (KRNV) degraded from –7.5 dBmV to –9 dBmV. Channel 13 (KTVN), on the other hand, was attenuated by my home's wiring from –5 dBmV to –13 dBmV. No wonder I couldn't tune it in! Antonio suggested a preamplifier, along with experimentation of various antenna compass orientations. We didn't measure channel 9 inside the house, since KOLO's signal was already so weak outside.

This doesn't seem to jive with the manufacturer's claim of 'consistent gain through the entire DTV channel spectrum', so I asked for clarification...several times. Finally, my nagging had the desired affect, and here's what I got back from company founder and president Richard Schneider:

We knew in 2009 that a percentage of the DTV broadcasters would revert to high VHF. So 2 1/2 years ago we started work on a new design in an attempt to cover both bands without compromising the UHF performance. This turns out to be a lot harder than it sounds, so we ended up covering each band using different methods.

The TV engineer is correct that the tapered loop element is optimized for the core UHF frequencies, and is almost flat in terms of directivity and beam pattern between 470 -700 MHZ. (The element has some nominal VHF performance), but what we don't show on the graph is the high VHF performance. Since it was not possible to incorporate a VHF element into the design without severe compromises to the UHF performance (electrical coupling and insertion losses), the solution the engineers came up with was a redesign to the PCB balun to allow the feed line to act as a high VHF radiator. This will give modest VHF performance, between 174 -216 MHZ. We have found it to be a significant improvement over our traditional UHF/VHF combination designs.

For people with high VHF reception problems in fringe locations we will offer an add-on high VHF only antenna called the Clearstream 5.

Currently, we have about 1000 Clearstreams in customers' hands, and from the feedback we have received it appears that most people living in a city with high VHF (Dallas, Miami, Tampa etc) will probably be OK without the need for a 2nd antenna to cover VHF.

I hope that helps

Although I'll grant Schneider's point that most VHF transmissions post-NTSC sunset (in just over six months!) will be high-band in nature, I still think it's misleading to refer to the ClearStream 2 as 'designed and optimized for 2009 frequencies associated with the DTV transition'.

Continue reading with Part 2, 'Thin-Air ATSC (And NTSC): Current Conditions, and Comments On Comments'...