Originally Posted by GaryJC
Because of terrain, my prospects for successful DTV reception didn't seem good. A few weeks back, I searched archives in this forum for threads about local installations.
Inspired by a few threads in the archives, I recently installed an OTA antenna for my Dish 6000 to receive the local Los Angeles DTV broadcasts. I don't have clear line of sight to Mount Wilson, which is 46 miles distant. (For local readers familiar with the area, I'm in hilly terrain above the intersection of Trabuco Road and Lake Forest Drive in Lake Forest.) There's a ridge 0.3 miles away that's 44 feet higher than the elevation at my house, as measured with a GPS. Plus, the ridge has trees and 2-story apartments, offset somewhat since my roof-mounted antenna is 25 feet off the ground. Beyond the ridge, there's nothing else in the way.
I installed a Radio Shack 15-2160 yagi with one of their 30dB mast-mounted pre-amps. I used a Winegard DS-3000 J-pipe mount that's securely bolted to the fascia on the eave of my roof line. This mount is nearly identical to the mounts that come standard with Dish Network SATV dishes, except the pipe is longer and can be cut to length. I found this mount online at dishplace.com. Starkelectronics.com sells them for less, but was out of stock.
I've had mixed results with DTV reception... KABC, KNBC, KTLA(WB) are consistently in the high 70s to high 80s. KCET(PBS) is usually in the low to mid 60s and exhibits occasional dropouts. KCOP(UPN) is often 55 to 65 and also exhibits some dropouts. Most of the time, I can't receive KCBS or KTTV(FOX) at all. I've never received a KCAL9 (local independent) DTV broadcast, but I haven't performed automatic DTV searches since the antenna installation, either. Numerous Hispanic stations have strong DTV signal levels, but these don't interest me. There is some variation in signal consitions, as would be expected.
I'm not confident that my antenna orientation is optumum, either. For work, I occasionally rent a spectrum analyzer. Sure wish I had one now to help with antenna orientation! Or, that Telemann HiPix HTPC card that can show concurrent receive signal levels for all DTV stations!!
Regarding picture quality...
I noticed that even SD OTA broadcasts are significantly better than the corresponding local station broadcasts from Dish Network. I suspect that Dish is compressing signal bandwidth more than the local OTA transmitters.
I believe KABC is broadcasting 720i format while the others are boradcasting 1080i. Right? Does this explain why KABC SD fills the screen while the other stations' SD has bands at the sides?
I'll mention a few antenna complications I encountered. A warning might help others...
1. Until halfway through the installation process, I realized that some stations don't broadcast DTV 24/7 - KCET(PBS) for one, maybe there are other stations. It's hard to find stations that aren't broadcasting!! (duh)
2. I used the u-bolt clamp that comes with the Shadio Rack Yagi, and it was a tight fit over the Winegard mast. This presented some problems. I used a compass to initially aim the antenna boom, then noticed that the azimuth would change when tightening the two u-bolt nuts! Tighten the rear-facing nut, and the antenna boom would turn to the left. Tighten the front nut, and the boom would move right! This was not a minor effect. I had to keep checking azimuth with the compass, and carefully alternate tightening. Even then it was not an exact, known azimuth adjustment.
3. Before mounting the antenna, I used a bubble level to make sure the mast pipe was plumb. I was surprised that this did not assure consistent antenna elevation because of the antenna's u-bolt clamp! After numerous trials with strange results, I discovered that antenna elevation was changing significantly with each azimuth adjustment. Finally, I ended up setting elevation after each azimuth adjustment by (a) loosening the J-pipe at the mounting plate, (b) reading a bubble level laid on the antenna boom while tilting the mast as necessary to get the desired elevation, and (c) tightening the J-pipe mount with an eye on the bubble level to make sure it stays at the desired tilt. Once the J-pipe mount was tight, the elevation was rock solid.
4. Due to problems 2 and 3 above, I wasted two hours making small antenna adjustments with large introduced errors. Only the last few trials had reliable azimuth and elevation settings. Since rain was threatening when I performed my antenna adjustments, I need another round of tests to optimize antenna orientation. Then, I'll consider next steps.
The RS Yagi is quite sensitive to orientation. From my house, the azimuth spread is only a quarter degree to cover all operating DTV stations on Mt Wilson. The KCBS tower is offset from the others (as seen from my house) accounting for roughly half of this spread. This might explain why I rarely "see" KCBS.
The Radio Shack yagi specs do not provide a gain/azimuth plot, but I'd expect this antenna to have a narrow frontal lobe. I am surprised how sensitive some DTV stations are to antenna orientation, while others seem insensitive.
I used the lat-lon coordinates at an online geodetic distance calculator (dead link today) to compute the azimuth to each local DTV antenna. This showed me the spatial relationship between the stations as they range from WNW to NNW, as viewed from my house, which explains how antenna azimuth adjustment might change reception for the various stations.
I have wondered if all these stations are operating at their full licensed output power.
Comment on Radio Shack equipment: In the past I designed products that were sold by RS. Their specifications and acceptance criteria are significantly higher than most people would assume. Their products are probably suitable for many applications, and there's no reason to spend more unless it's necessary. That yagi retails for $21.99, an inexpensive experiment.
I realize my installation my be pushing the envelope due to marginal OTA conditions. If ongoing experiments with antenna orientation don't improve my OTA reception, I might consider a better antenna and/or ChannelMaster UHF-only pre-amp.
All comments welcome...