boulder, co - dtv/atv repeater coverage · power has not changed from the original repeater. thus...

AN-32 Rptr Coverage.doc ( 9/24/16, kh6htv) p. 1 of 10

Application NoteAN-32copyright

September, 2016

Boulder, CO - DTV/ATV RepeaterCoverage

Jim Andrews, KH6HTVwww.kh6htv.com

The hams in Boulder County, Colorado have had a TV repeater since 1993. It was ananalog, NTSC, VUSB-TV repeater. Recently in September, 2016, the repeater receiveda major upgrade to add high definition (1080P), digital TV capability, both for receiveand transmit [1]. The purpose of this application note is to document the coverage areaof the new DTV/ATV repeater.

While browsing on the internet, I discovered a powerful on-line program for calculatingthe RF coverage areas for transmitters. The program is called CRC-COVWEB and isavailable from the Communications Research Centre in Canada at:http://lrcov.crc.ca/main The program is based upon pioneering research and computerprograms written here in Boulder at NBS in the 1960s by Phillip Rice and A.G. Longley.In addition to COVWEB, there are several other Longley-Rice programs availableincluding SPLAT!, Radio Mobile, QRadioPredict and Pathloss 5.

The Longley-Rice RF Propagation model works for frequencies above 20 MHz. It doesnot include the HF, over-the-horizon, ionospheric effects. However, it does account foratmospheric changes, topography, diffraction and scatter. I do not believe it includesmulti-path effects. It also allows one to specify statistical estimates.

To run COVWEB, one needs to input the following parameters: transmitter location,frequency, transmitter power, antenna height, antenna gain, antenna pointing azimuth,antenna pattern, surface refractivity, dielectric constant of earth, ground conductivity, andthe climatic zone, plus confidence levels. For the receiver, the only parameter input isthe antenna height. The program calculates the electric field strength at the variousreceive locations in dBμV/m. i.e. dB above 1 μV/meter. I used the followingparameters: freq = 423MHz (i.e. Ch. 57), transmitter power = 35dBm = 3 watts (afterband-pass filter and coax cable losses), antenna = DB Products, DB-411, four-elementco-linear ( vertical polarization, 11.2dBi gain, cardioid pattern with -11dB F/B, at 35ft.height and aimed at Valmont power plant, 67o E of true north), climatic zone =continental temperate, surface refractivity = 301, earth dielectric constant = 10 (poor to

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average, i.e. rocky), earth conductivity = 0.001 (poor). I set all the confidence levels toF(50,50) which means the predicted field strength would occur at 50% of the receivers,50% of the time. i.e. no absolute prediction one would always get a useable signal.Sorry ! -- but no such thing as a "free lunch" in the TV propagation world.

For receiving, I used the FCC criteria. This assumes a minimum station consisting of aunity gain (0dBi) antenna at 30 ft. feeding directly into a typical TV receiver with nopre-amp. I also used the FCC definition for their Grade A and Grade B service contoursfor UHF television. Grade A is defined as a field strength of 74dBμV/m F(70,90), whileGrade B is 64dBμV/m F(50,90). (note: most texts abbreviate this to be "dBu"). For aunity gain antenna (0dBi) in the 70cm band, this is equivalent to a receive antenna outputpower of -56dBm and -66dBm. For the new DTV transmitters, the FCC has a UHF-DTVnoise-limited service contour of 41dBu F(50,90) (-89dBm at 70cm). The FCC alsodefines another contour of Principal Community of 80dBu F(90,90). For analog TV,these levels correspond to picture quality ratings of P2 (40dBu), P4 (64dBu), and P5(74dBu). For digital TV, 40dBu corresponds to the typical DTV receiver digitalthreshold. For this particular transmitter installation, the theoretical limits for Grade A &B coverage, assuming ideal free space propagation, would be 4.4 miles and 14 milesrespectively.

The Appendix contains several RF coverage maps covering various areas of the FrontRange of Colorado. These CRC-COVWEB maps use different colors to represent thesevarious service areas. DTV & P2 = gray, P4 Grade B = light blue & P5 Grade A = lightred. Fig. 1 shows the overall coverage area which is the Colorado Front Rangeextending from Denver north to Loveland and Greeley. Figs 2 & 3 show the primarycoverage area which is the Boulder Valley in the eastern half of Boulder County whichlies mostly within either the Grade A or Grade B service contour. There is a smallpenetration into the mountains to the north-west of the repeater site. Beyond BoulderCounty to the east is the weak signal fringe area. Figs. 4 & 5 are a more detailedanalysis of the fringe areas with calculation steps of 12dB and 6dB above 40dBμV/m.

A mobile field survey was done in 2013 to determine the actual coverage area of theanalog TV repeater. The new repeater still has the same transmit antenna and the outputpower has not changed from the original repeater. Thus we did not expect major changesin the coverage area, except for DTV enhancements of P5-digital vs. P2-P3-analog in thefringe areas. The ATV transmitter output power is +40dBm (10 watts pep). The newDVB-T transmitter output power is +36dBm (4 watts, rms avg).

A new mobile field survey has been recently performed in September, 2016 to verify thecomputer predictions for the DTV service area. Fig. 6 shows the predicted coverageareas using a mobile receiving installation with an antenna height of only 1.5 meters. Forthese tests, the repeater was transmitting continuous "live" video & audio using DVB-T,QPSK modulation (8K FFT, 3/4 FEC Code Rate, 1/16 Guard Interval). The mobile useda Diamond model NR2000NA, 2m/70cm/23cm whip antenna. It's gain at 423MHz was2.2dBi [2]. The DVB-T receiver was a Hi-Des model HV-120A with an ARR modelP432VDG pre-amplifier. The pre-amp had a gain of +19.8dB. The HV-120A sensitivity


was -95dBm alone, or -99dBm with the pre-amp. Using the HV-120A's On-Screen-Display (OSD), it was possible to actually record both the received power in dBm and thesignal quality, signal to noise ratio (s/n) in dB (23dB best, 7-8dB loss of signal lock).The HV-120A has a fixed offset error of 14dB at 70cm. This offset and the pre-amp gainneeded to be subtracted from the OSD to determine the actual power from the antennainput to the receiver.

Data was recorded for both "in motion" and "fixed" locations. At fixed locations, theactual OSD values for dBm and s/n were recorded along with GPS latitude and longitudeFor the in-motion situation, the nominal value and the max./min. values in the OSD werenoted while driving in particular areas. The coverage area of the repeater is the easternhalf of Boulder County with predominantly prairie land with rolling hills. Due to thetransmitter location, it's signal does not penetrate into the mountains in the western halfof the county. While driving through relatively flat, rural areas without a lot of trees, thesignal level was fairly steady. In urban environments with lots of houses and trees,signal variations of up to ± 10dB were very commonly encountered. While driving, thevehicle sometimes reached speeds up to 65mph. In strong signal areas, no dropouts wereobserved even at high speeds. In no case was a signal weaker than -92dBm ever able toproduce a picture. This was 7dB worse than the sensitivity of the receiver measured in aperfect signal, lab environment. The 2013, mobile field coverage survey of the ATV repeater confirmed that P2 coverageextends well out onto the prairie to Ft. Lupton, Denver International airport (DIA), andthe fringes of Ft. Collins and Greeley. It also confirmed that there is a 50% probabilityof receiving an excellent P5 picture almost anywhere in the city of Boulder. The soleexception being the downtown Pearl St. mall area due to the tall buildings. P4 coveragewas available along the path of Boulder creek out to the eastern part of the county andalso along the diagonal highway to Longmont. Coverage was very spotty in Longmontand did not exist west of Hygiene along CO-66. It was also spotty along US-36 north ofBoulder towards Lyons. It was noted that the towns of Lafayette, Louisville and Superiorare well shielded by Davidson Mesa and could expect at best P2 pictures and usually nopictures.

The new, 2016, mobile field coverage survey of the new DTV repeater confirmed theprevious 2013 ATV measurements and that DTV reception is almost guaranteed in mostlocations within the Grade A and Grade B service contours (light red & light blue areas).DTV reception was found to be possible in the gray shaded areas, including all the wayout to DIA at a distance of 34 miles. DTV reception in the DTV service contour areas(gray shaded areas) was however extremely marginal and most often non-existent. Theprobability of receiving a DTV (or P2-ATV) signal was far less than the F(50,50)prediction for the gray areas. It was much less than 10%. The areas most likely toreceive DTV in the gray shaded regions were hill tops and bridge overpasses.

Obviously, at locations with the possibility of P2-ATV or weak signal DTV coverage,significant improvements can be made in the receive station over that used for the mobilefield survey. These include using a high-gain, directional yaggi antenna on a much


higher tower, low loss coax and using a good low noise pre-amplifier. Likewise toaccess the repeater, much higher transmitter power is required than from within the gradeA or B service areas. To further enhance the probability of success, a Google Earth pathprofile should be run to determine if a true "line-of-sight" path exists [3]. Without a line-of-sight path in the gray areas, no DTV reception is possible.

The DTV data recorded at locations where the car was stopped was further processed tocalculate the actual received signal strength and then to compare it against the theoretical,free space, ideal propagation conditions. The difference being considered "excess pathloss". The data was broken into three different categories. The first being thoselocations that had a true, unobstructed, line of sight path to the repeater. The second beinga rural environment of prairie with rolling hills. The third was an urban environmentwith lots of buildings, trees, etc. to interfere with the propagation. This urban data wastaken in the city of Boulder, within the predicted Grade A & B service contours (light red& blue shading on map). The urban area was also the area where the "in-motion" testsshowed the most variation.

In summary, the mean excess path loss measured was:1. Locations with true Line-of-Sight path, the excess loss mean was -7.9dB with astandard deviation (σ ) of 4.5dB for 13 observations. Worst case was -16dB, Best was+4dB (meaning 4dB higher enhancement than predicted for free space propagation)2. For Rural (prairie) Areas the excess loss mean was -13.9 dB with a σ of 7.8dB for 47observations. Worst case was -29dB, Best was +4dB. 3 For the Urban (Boulder) Area, the excess loss was 21.8dB with a σ of 10.7dB for 37observations. Worst case was -39dB, Best was +2dB.

CONCLUSIONS:1. The CRC-COVWEB maps are overly optimistic when compared to real worldmeasurements. They paint a too broad paintbrush over localized geographicobstructions, etc. 2. The COVWEB maps are however useful in predicting where one mightpotentially be able to receive a signal. Residing within a Grade A or B coverage zone,will assure one of receiving a picture, but probably with a lot less signal strength thananticipated. Outside of the gray areas, it is impossible.3. As a general rule of thumb, starting with the free space path prediction, oneshould anticipate an excess path loss of: -8dB for a good, line of sight path, -14dB forrural environments and -22dB for urban environments.

REFERENCES:1. "Digital & Analog TV Repeater", Jim Andrews, KH6HTV Video ApplicationNote, AN-31, Sept. 2016, 24 pages2. "Antennas for Ham TV", Jim Andrews, KH6HTV Video Application Note,AN-4, Sept. 2011, 3 pages3. "TV Propagation & Multi-Path Effects", Jim Andrews, KH6HTV VideoApplication Note, AN-7b, rev. Oct. 2014, 7 pages


APPENDIX: Boulder TV Repeater Coverage Maps

Fig. 1 Overall coverage area - Denver north to Loveland & Greeley - FCC ContoursRed = Grade A, Blue = Grade B, Gray = fringe area >40dBμV/m (Rptr Coverage-11 crop.jpg)


Fig. 2 Repeater coverage of Boulder Valley, up to Longmont - FCC ContoursRed = Grade A, Blue = Grade B, Gray = fringe area >40dBμV/m (Rptr Coverage-13 crop.jpg)


Fig. 3 Repeater coverage of Boulder Valley south-east to Broomfield - FCC ContoursRed = Grade A, Blue = Grade B, Gray = fringe area >40dBμV/m (Rptr Coverage-14 crop.jpg)


Fig. 4 Weak signal, fringe area analysis - 12dB steps (Rptr Coverage-15 crop.jpg)

Dark Blue = Grade B >64dBμV/m, Light Blue >52dBμV/m, Grey = 40dBμV/m


Fig. 5 Weak signal, fringe area analysis - 6dB steps (Rptr Coverage-16 crop.jpg)

Dark Blue = >52dBμV/m, Light Blue >46dBμV/m, Grey = 40dBμV/m


Fig. 6 Mobile Field Survey Predicted Coverage Area, Antenna height = 1.5 metersRed >= 74dBμV/m, Blue >= 64dBμV/m, Grey >= 40dBμV/m (Mobile Coverage-20&21.jpg)

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