ANTENNA TOWER - SPECIAL REPORT
Broadcast Digital TV from Squaw Mtn received metrowide
A DTV antenna licensed to KBDI-channel 12 (PBS affiliate) operating at only 2.4% of allowable power, was received from Parker to Greeley, Roxborough Park to Broomfield. The signal was received as far away as 75 miles by 10 electrical engineers volunteering to assist licensed broadcvast engineer Timothy Cutforth hired by Squaw Mountain Communications in September, 2002.
The study demonstrated that a full power DTV facility on Squaw Mountain would provide excellent coverage of the Denver metro area. Reception was surprisingly clear in shadowed areas of Jefferson County.
Very few isolated locations were found to require an On-Channel Booster where the shadow was not filled by the main DTV signal. Booster repeaters will easily fill significant shadows wherever they might occur. Common indoor antennas received the signal as well as outdoor devices. Most non Line-of-Sight locations will have useable DTV signals from SMC even where multiple obstructions exist.
Mulitpath was not found to be a problem from Squaw Mountain and reception in shadowed areas was found to be significantly better than computed coverage claims of Denver TV stations that prefer to remain 2000 feet lower altitude, in the Mountain Backdrop of JeffCo foothills.
Squaw Mountain Communications provided Denver TV stations and Jefferson County planning department with maps and 1500+ pages of data and analysis of the tests. SMC is a proven alternative site to residential Lookout Mountain or Mount Morrison at 2000 feet lower elevation in the foothills.
KBDI-12 deserves support!
The only Denver TV station willing to loan their FCC-licensed digital spectrum for testing in the metropolitan area was PBS affiliate Channel 12. Many Mount Vernon Canyon residents are boycotting donations to Channel 6 for its tower pollution of the Lookout Mountain Nature Center and Boettcher Mansion and proposed new towers on Mt. Morrison. To support KBDI, call 303-296-1212 or www.kbdi.org
DTV Reception Measurements
Even though the coverage area from Squaw Mountain is greater than that of Eldorado Mountain, Lookout Mountain or Mt. Morrison, the applicants for towers on these sites on have claimed that Squaw Mountain would not be an appropriate site for DTV transmitters.
Specifically, proponents for other sites have said that the foothills between Squaw Mountain and the Denver Metro area would produce multipath reflections that would degrade DTV reception even to areas that have line-of-sight (LOS) to the site on Squaw Mountain. The Hart Report, COMPARISON OF FRONT RANGE RADIO SITES FOR FM, NTSC TV AND DTV BROADCAST SYSTEMS, states that tests should be performed in order to determine whether this is truly the case.
A DTV signal source on Squaw Mountain would make testing very straightforward, but no television station has been willing to place a temporary DTV transmitter on Squaw Mountain even though members of Lake Cedar Group have since 1998 had FCC Construction Permits that would allow such a transmitter.
There are however DTV stations transmitting in the Denver Metro area. FOX is currently transmitting DTV on channel 32 from Lookout Mountain with 223 kW Effective Radiated Power (ERP). This power is 22.3% of the FCC recommended maximum power. KRMA is transmitting low power DTV on channel 18 with 7 kW ERP (0.7% of the FCC recommended maximum power) from the top of the Republic Plaza Building in downtown Denver. These signals have been used as test sources for various receiving sites located in the Denver Metro area.
If grazing incidence reflections off the foothills between Squaw Mountain and the Denver Metro area would cause multipath problems in otherwise suitable line-of-sight coverage areas, these multipath problems should also be evident when viewing signals from the FOX and KRMA DTV transmitters at positions that have intervening grazing incidence scatterers or blockage.
A series of measurements of DTV reception has been made in order to observe any multipath problems that may be caused by intervening terrain or obstructions between receiving sites and the FOX channel 32 and KRMA channel 18 transmitters. Measurements were also made in residential sections of the metro area to see what degradation of reception might be caused by local scatterers such as buildings and trees.
The DTV used for the reception tests was an RCA F38310 television with built-in tuner for over-the-air broadcasts. This was the cheapest locally available DTV with a built-in tuner. Initially, reception was tested with two antennas. A simple dipole antenna to simulate indoor rabbit ears was mounted on a broomstick, and an available directional corner reflector UHF antenna was mounted on a rotatable pole to simulate an outdoor antenna. The corner reflector antenna was vertically polarized. Later a third antenna, a Radio Shack model 15-2160 UHF directional antenna was also added. This antenna was used to check reception with horizontal polarization. A portable generator and the pole for the corner reflector were mounted on a boat trailer pulled by a Chevrolet Suburban that carried the DTV.
The DTV has a menu selection titled Antenna Info, that produces a number for Signal Strength. It was found that the signal strength never registered higher than 94, even when the antenna was placed a few hundred feet from the FOX transmitter. With weak signals, the lowest indicated numerical rating for signal strength was 22, and weaker signals had an indicated signal strength of --. In general, signal strength greater than 34 resulted in reception of both picture and sound.
At each site, measurements of signal strength were recorded for all antennas, with each antenna pointed in the direction that yielded the highest signal strength. Presence or absence of picture and sound were also noted. GPS coordinates and a brief description of the site were recorded, as well as whether the site had visible line-of-site (LOS) to the transmitter. For some of the measurements presence of LOS could not be determined in the field due to darkness or smoke from the Snaking Fire near Bailey.
Terrain profiles indicating the height of terrain between the transmitter and receiver are given for all sites where the FOX Channel 32 transmitter was used as the test signal. Terrain profiles between the lower Squaw Mountain site and various receiver sites are also included in order to compare these profiles with profiles from the FOX transmitter that resulted in good reception without evidence of multipath.
In the lower left corner of each terrain profile is a number (usually 3.2x) that indicates the elevation exaggeration of the individual profile. This is the magnification of the elevation axis on the plots with respect to the horizontal distance. In order to make accurate comparisons of profiles, this number should be the same for all profiles. Due to limitations in the software used to make the plots, some of the profiles (particularly the longer distance ones) do not have an exaggeration of 3.2x. The profiles also do not take into account the curvature of the earth, so longer distance profiles that show LOS may actually have intervening terrain.
RESULTS AND GENERAL COMMENTS
DTV signal reception was found to be very robust. Many sites with no LOS still had very strong signal strength. Low sites as far as 43 miles from the FOX transmitter where even the highest peaks of the Rockies had disappeared over the horizon still had good reception with signal strength higher than 90. In Strasburg, 50 miles from the FOX transmitter, the FOX signal was received with signal strength of 76 with the dipole antenna, and 88 with the corner reflector. This was in a residential neighborhood, with no LOS and homes and trees between the antenna and transmitter.
The channel 18 transmitter was received with a signal strength of 52 on the Radio Shack antenna at the Watkins-Front Range Airport exit 295 on I-70, twenty-one miles from the transmitter with no LOS. The channel 18 transmitter was also received on Squaw Mountain, 27 miles away with a maximum signal strength of 70. This is pretty impressive considering that the transmitter output is only 0.7% of the FCC recommended maximum power for DTV transmission!
Only one site with LOS to the transmitter did not receive a strong enough signal to produce both picture and sound. This site (#57, on Squaw Mountain) is in a null of the directional FOX antenna. All sites with LOS to the east of the FOX antenna, and all sites with LOS (in all directions) from the channel 18 transmitter produced both picture and sound with a directional antenna.
One site exhibited evidence of possible degradation due to multipath. This site (#55) was in front of the Morrison Post Office. The Channel 18 broadcast from Denver was received with a signal strength of 48 using the Radio Shack antenna pointed at the gap where Morrison Road passes through the Hogback. It was found that the antenna could be pointed away from the gap (toward the top of the hogback) and the signal strength increased to 60, but the audio went away.
A direct line from the channel 18 transmitter to the receive site passes through the hogback approximately at the position the antenna was pointed for maximum signal strength. This was the only site where a signal level greater than 34 did not result in reception of both picture and sound, and the antenna had to be oriented in a specific direction in order to cause failure to receive the audio portion of the broadcast.
Squaw Mountain should not be ruled out as a viable site for DTV broadcast based on the assumption that intervening terrain between Squaw Mountain and the Denver Metro area would cause unacceptable multipath reflections. These measurements have shown no evidence that similar terrain profiles between the FOX antenna and test sites caused degraded DTV reception.
Jefferson County should not dismiss Squaw Mountain as a viable alternative site unless actual tests of signals transmitted from Squaw Mountain prove that it is inappropriate for DTV broadcasting.
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Many documents and details are available at www.c-a-r-e.org.