[opendtv] My Return to OTA
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Thu, 10 Jul 2008 11:29:29 -0400
Interesting approach, to create a much smaller antenna than you'd normally get
with VHF/UHF models.
"I combined an Antennas Direct Model DB4 two-bay UHF bow-tie antenna having 14
dBd gain with an AntennaCraft Model Y5-7-13 VHF high band antenna having 7 dBd
gain. I then used a 3 dB combiner to feed a 16 dB gain Channel Master Model
Titan 2 mast-mounted preamplifier."
And you don't need a diplexer.
Bert
--------------------------------
http://www.tvtechnology.com/pages/s.0082/t.14400.html
My Return to OTA
A broadcast engineer goes 'back to the future'
by Dane Ericksen, 7.09.2008
Editor's Note: Dane Ericksen, a senior engineer with Hammett & Edison in the
San Francisco area and longtime SBE National Director, relates his experiences
in setting up a terrestrial DTV system in his Sonoma County home.
SONOMA, CALIF.
After almost 20 years of cable TV, I decided that it was finally time to return
to over the air.
Since my house is more than 60 km north of the Sutro Tower in San Francisco,
and almost 70 km from San Bruno Mountain, another multi-DTV station
transmitting site, this meant installing a rooftop antenna (Fig. 1). That, in
turn, meant adding a support mast, bringing in a down lead cable, and routing
the cable through existing walls so the feed could be accessed by my living
room TV. Not impossible tasks, but not trivial tasks, either.
My house is a single-story residence in Sonoma County, just outside the Sonoma
city limits. As shown by the satellite photo in Fig. 2, it's a nice quiet
neighborhood with a fair number of trees. I was a little apprehensive that
after taking all the antenna-installation steps I might not have useable DTV
reception. This is because as shown by Supplemental Figure S1 my house lacks
line-of sight to Sutro Tower and to the San Bruno Mountain antenna farm just
south of San Francisco (for interested readers, all of the supplemental figures
are available for viewing on the H&E Web site, www.h-e.com). However, the
Terrain Integrated Rough Earth Model (TIREM) predicted service from both San
Bruno Mountain (Fig. 3) and from the Sutro Tower (Fig. S2). So, I decided to
make the hardware investment that would allow for OTA.
THE INSTALLATION
My first discovery was that no manufacturer makes a VHF high-band/UHF-only
rooftop antenna; since there are no VHF low-band DTV assignments in the San
Francisco Bay Area, I didn't want to deal with the greater element and boom
lengths of a conventional VHF-UHF rooftop antenna.
So as shown by Fig. 4, I combined an Antennas Direct Model DB4 two-bay UHF
bow-tie antenna having 14 dBd gain with an AntennaCraft Model Y5-7-13 VHF high
band antenna having 7 dBd gain. I then used a 3 dB combiner to feed a 16 dB
gain Channel Master Model Titan 2 mast-mounted preamplifier. Since I wanted the
ability to experiment with DTV reception from several sites, I also installed
an AntennaCraft Model TDP-2 rotator.
As shown by Fig. S3, an existing gable above my garage made a convenient
mounting for an 8-foot mast, which gets the antennas just above a beautiful
cherry tree that occupies my front yard. Plus, from the street, you have to
look hard to even spot the antennas (Fig. S4). The coax and rotor control
cables were brought into my attic using a RadioShack wall feed-through tube,
part number 15-1200A.
There is pass-DC 3 dB splitter in my attic, with one leg going to my living
room, where a power supply inserts its DC voltage up to the coax to power the
preamplifier. The other leg goes to a guest bedroom. As shown by Fig. S5, an
F-fitting antenna discharge unit (ground block) was installed at my roof gable,
and a ground wire was connected to an existing utilities ground wire next to
the side of my house. While lightning is rare in Sonoma, prudence and Section
810 of the National Electrical Code require that a rooftop antenna be grounded.
Since I had one mast mounting bracket left over, I used that as a pipe clamp. I
was going to trim off the unneeded legs, but decided that the clamp looked sort
of neat as installed, and so left the legs on.
A NEW DTV WORLD REVEALED
I purchased a Samsung Model DBTH260F 8-VSB tuner, which has a fifth-generation
chip set (Fig. S6). Programming the tuner was straightforward, and the initial
channel search returned 16 DTV signals with 46 program streams-impressive. The
Sutro Tower UHF DTV stations showed 8 out of 10 bars in the signal strength
display mode. The KNTV D12 signal from San Bruno Mountain was weaker, at only 3
bars, but that has proven sufficient to give only rare (and momentary) freeze
frames.
As shown by Fig. 5, taken using a Rhode & Schwarz Model FSL6 spectrum analyzer,
the receive carrier levels for the UHF signals are around Ð60 to Ð70 dBm. As
shown by Fig. S7, D12 from San Bruno Mountain was significantly weaker, at Ð98
dBm. Note the DTV pilot feed through from KCBA-DT, D13, Salinas, transmitting
from Fremont Peak, 193 km to the south, and feed-through of the KOVR-TV, N13,
Stockton, visual carrier. KOVR-TV transmits from a 610-meter tower near Walnut
Grove, 86 km east of Sonoma.
Fig. S8 shows two mountain ridges between my house and the Walnut Grove
antennas, so it's surprising that any N13 signal is seen. Plus, the Figure S7
spectrograph was taken with my rooftop receiving antennas aimed south, not east.
As an unexpected bonus, I found that not only could I also receive the Monument
Peak/Mt. Allison DTV stations, but that the long over-the-bay paths shown in
Fig. S9 didn't seem to bother my reception. And, the antenna orientation for
all four sites was the same from my location. The only disappointment was no
signal from KFTY-DT at Mt. St. Helena, 42 km to the north. That path has only
one relatively minor blockage, so knife-edge refraction should provide plenty
of signal. But, nothing. A check of the CDBS shows an out-of-core D54 license
for 30 kW ERP and an in-core FCD32 CP for 19.9 kW ERP. Given this relatively
modest D54 ERP, and the presence of a co-channel NTSC station, KTEH, at
Monument Peak, I suspect that no KFTY reception will be possible until that
station shifts from D54 to FCD32.
CECBs
I ordered a Sansonic Model FT-300A coupon eligible converter box (CECB) and a
RCA Model DTA800B CECB. The Sansonic CECB worked great, and has the same
excellent sensitivity as my Samsung tuner. Like the Samsung, setup of the
Sansonic CECB was easy (Fig. S10).
The RCA CECB (Fig. S11) was a disappointment; it had markedly less sensitivity,
and had difficulty holding lock on the weaker KNTV D12 signal. Indeed, the RCA
CECB was right in the nether region between a perfect DTV signal and no DTV
signal. The RCA CECB remote control was also much worse, requiring a kluge
approach of entering your TV receiver's remote control code for audio control.
Because of its excellent performance, the Sansonic CECB is now doing service in
my guest bedroom, where a second antenna outlet was installed. The RCA CECB
should be suitable for use at my daughter's San Francisco apartment; even using
an indoor, back-of-set low-gain antenna should provide sufficient signal for
this sensitivity-challenged CECB.
SUMMARY
So, to paraphrase the famous MasterCard commercial: UHF antenna, $59.99; VHF
high band antenna, $19.99; pre-amplifier, $56.99; antenna rotor, $64.99; mast
and mounting hardware, $60; coax and rotor cables, $30; handyman charge to
install antennas, $200 (I am recovering from a motorcycle accident broken leg,
so ladder climbing is a no-no for now); Sonoma Phone Man charge to route cables
through existing walls and add coax outlets, $234; Samsung HDTV tuner, $179.99;
Sansonic CECB, $19.99 (after coupon); RCA CECB, $19.99 (after coupon); total,
$946. The ability to not worry about my local cable company telling me that it
will be turning off the analog signals on my cable service and that I will have
to start renting digital cable set-top boxes: Priceless.
Mr. Ericksen is a senior engineer with Hammett & Edison, Inc. Consulting
Engineers, near San Francisco. He is a registered professional engineer (P.E.),
and holds SBE CSRTE, 8-VSB and CBNT certifications. Mr. Ericksen is Chairman of
the ATSC TSG S3 Specialist Group on Digital ENG and serves on the SBE
Certification Committee. He is in his sixth term as a SBE National Director and
is currently the SBE Chapter 40, San Francisco, Secretary.
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