CGC #1108

by CGC on December 6, 2011

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                      THE CGC COMMUNICATOR

                            CGC #1108

                   Tuesday,  December 6, 2011

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                Robert F. Gonsett, W6VR,  Editor
                

    Copyright 2011, Communications General® Corporation (CGC)

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  THE KSCI ANTENNA TRAGEDY IS AN IMPORTANT CASE STUDY

  We sometimes hear about 2,000 foot towers collapsing, but broadcast 
antennas falling off towers are very rare; hence, the unusual interest in 
the KSCI case.


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                ABOUT THE KSCI ANTENNA THAT FELL
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  THE ANTENNA STRUCTURE CONSISTS OF A MONOPOLE + AN ANTENNA
                     BACKGROUND INFORMATION

  The KSCI UHF-TV antenna structure consists of a 20 foot monopole 
(essentially a pipe) with a 60 foot pylon-type Andrew slot antenna 
stacked on top (data from KSCI, lengths approximate).
In photographs of the collapsed antenna structure, the monopole is 
sticking up in the air and the antenna itself is resting down in a 
canyon.

  To the untrained eye, the antenna looks like a bunch of large 
diameter stacked pipes or monopoles.  In fact, there are a number 
of precision slots cut in those pipes and the slots are the driven 
elements that radiate the signal.

  The slots are covered with raydomes, making the slots invisible.  
The raydomes seal the slots against the elements.
The raydomes have broken off the upper-most antenna slots and those 
slots are visible in one of the photos.  Click on the second to the 
last photo here and look to the left:

  http://www.earthsignals.com/press/?p=1245

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  ORIGINAL (DECEMBER 1) KSCI PHOTOS NOW PERMALINKED

  The original photos of the fallen KSCI UHF-TV antenna and 
supporting monopole have been permalinked at the URL below.
Thanks to Marty Shostrom, Chief Engineer of KPXN(TV), for 
providing those great shots.

  If you click on the fourth picture for an enlargement, you will see 
the grey "stump" where KSCI's monopole had been attached to the tower 
structure:

  http://www.earthsignals.com/press/?p=1245

  Find the tall orange antenna in the left portion of the picture.  
From the very top of that antenna, look to the right just a hair and 
you will see the grey stump with the flange on top.  Actually there 
should be two flanges bolted together because the KSCI monopole broke 
just above its base flange according to reports.

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  BILL WELTY DISCUSSES THE KSCI ANTENNA COLLAPSE

  Bill Welty, Chief Engineer of KSCI(TV), took a few minutes to 
discuss the KSCI antenna collapse with the CGC Communicator.
A summary of his comments follows:

  o  We think the tip of the antenna hit the ground first,
  then the monopole dented the ice shield (see discussion below),
  then the antenna settled in the canyon and everything rolled
  as a unit and stopped just inches from the microwave rack.

  o  Regarding the cause of the collapse, the monopole end
  flange did not break loose (contradicting earlier speculation).
  The monopole broke about 1/2 inch above the flange according to
  our reports.  Perhaps the monopole was weakened by the factory
  weld and wind-induced metal fatigue took its toll over the
  years.

  o  One possible "lesson learned" is to have your antenna
  inspected regularly and carefully for any signs of metal
  fatigue.

  o  We will know much more after the critical component parts
  are brought down to ground level for a close examination.

  o  For the record, the antenna collapsed at 6:30 AM on
  Thursday, December 1, 2011.

  o  If we replace the Andrew antenna with an Andrew/ERI, the
  factory is quoting four months for delivery.  Meanwhile, our
  auxiliary site is working well and we are particularly
  pleased with the Harris DTV transmitter.

  o  We are so fortunate that the fallen antenna didn't damage
  other people's equipment.  The antenna couldn't have dropped
  in a better place.

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  NEW PHOTOS (DECEMBER 2) OF THE KSCI ANTENNA COLLAPSE

  Dennis Doty has provided a new batch of pictures of the fallen 
KSCI(TV) broadcast antenna and its supporting monopole.
The photos are available at the URL below and these particular 
photos add to our understanding of the situation:

  o  Photos 284, 295 and 297 support the contention that the
  monopole broke above the flange weld.  Note that there are no
  weld marks on the monopole end.

  o  Photo 292 shows the proximity of the antenna structure
  to Mt. Harvard's microwave dishes.  That was one close call.

  o  Photos 287, 304 and 305 show minor damage to an ice
  shield on the site.  In photo 287, note the horizontal I-beam
  in the lower left portion of the photo.  There is a little ding
  on top of the beam -- see it?  That's the only damage to the
  site.  Photos 304 and 305 are sideways close-up shots.

  http://mtwilson.net/pictures/


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                    OTHER WIND-RELATED ISSUES
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  CLEAR CHANNEL RADIO L.A. SURVIVES AND DOES WELL

  Clear Channel Radio, Los Angeles, apparently did pretty well in 
last week's windstorm.  There were no obvious issues at their three 
AM stations.  However, we understand that at KOST(FM), the power 
generator quit about 4AM Friday.  Within minutes KOST switched to 
their backup facility at Briarcrest.

  The generator issue was resolved and KOST was back on the air from 
Wilson around 1PM Friday.  The winds at the Briarcrest site were 
said to be nothing short of amazing.
Fortunately, Briarcrest had only one momentary power glitch and 
remained on commercial power.

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  THE KPCC-FM OUTAGE

  KPCC-FM on Mt. Wilson found themselves without audio for about an 
hour and a half Wednesday night even though their transmitter 
remained on the air.  They couldn't switch to the backup transmitter 
by remote control because of logic damage inside the TX probably 
caused by a power surge.

  Even if KPCC could have switched transmitters, it wouldn't have 
done any good.  The UPS feeding the audio processor that fed both 
transmitters reportedly "blew up."
Immediate solution: Drive to Wilson and bypass the UPS.
(Info courtesy of Pablo Garcia.)

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  WILSON/HARVARD POWER OUTAGE SYNOPSIS

  Here is a time and event log reconstructed from various
  e-mails.  All times approximate and rounded to the nearest
  hour:

  o  Wednesday, November 30, 9 PM:  All commercial power to
  Wilson and Harvard is lost.  Both main and backup power lines
  go down.  Southern California Edison ("SCE") needs to "fly the
  lines" for visual inspections before re-energizing the wires
  but high winds are a problem and SCE has tons of other
  critical customers with power outages.

  o  Friday, December 2, 4 PM:  SCE writes: "...Thanks to the
  information about the down lines CBS sent, our work [to]
  restore your service may be shortened...."

  o  Saturday, December 3, noon:  Power is restored to Wilson
  and Harvard via the old reliable 16 kV circuit.  The 33 kV
  backup line is still down.

  o  Sunday, December 4, 8 AM:  Edison reports finding a
  "broken crossarm" on the 33kV line and will institute repairs.

  There are two big problems on Wilson/Harvard caused by a prolonged 
loss of commercial power -- the need to coordinate fuel deliveries 
for generators (often under adverse weather
conditions) and the need to periodically take generators off-line 
for servicing.  Generators running 24/7 accumulate incredible mileage.


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                           RANDOM NOTES
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  INVITED LETTER ON THE COMPATIBILITY OF MDCL WITH AM HD RADIO

  Preliminary tests at WOR 710 in NYC indicated that the BBC AMC 
algorithm with -3dB carrier reduction @ peak modulation was 
compatible with AM IBOC and with Arbitron PPM data.  Russ 
Mundschenk from iBiquity is doing further tests to confirm full 
compatibility.

  Other algorithms such as ACC with -6dB carrier reduction @ 0% 
modulation did cause dropouts in HD Radio.  AMC @ -3dB provided 
best compatibility and greatest power savings of 37%...

  Geoff Mendenhall
  VP Research and Technology
  Harris Broadcast
  December 2, 2011
  Sent mobile

  [Thanks to our readers for a wealth of related information
  on this important topic.  We believe that Geoff's letter gives
  a good snapshot of the current state of affairs.   -Ed.]

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  GENERAL NOTE FOR RADIO & TV

  o  Re Franken FMs and LPTV-to-Ed FM interference:
  http://tinyurl.com/LPTV-ED-FM-etc


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                       LETTERS TO THE EDITOR
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  TECH LETTERS

  Letters to the Editor of the CGC Communicator should
  be posted on the Tech Letters Website at the URL below.
  Recent Tech Letters postings are as follows:

  o  Richard Rudman (Vice Chair, CA EAS SECC) comments on
     Dr. Mustoe's Radio World EAS posting, and

  o  Dan Ramos comments on ending AM IBOC.

  If you are a registered Tech Letters user, post your letter
  via email to Steve Blodgett.  All letters and comments are
  moderated, and are posted after review.  Also contact Steve
  if you have trouble viewing or posting:
  sblodgett (at) earthsignals.com.

  http://www.earthsignals.com/press/


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                            OFF TOPIC
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  HIGH STANDARD OFF TOPIC MATERIAL

  o  Temecula: Promenade mall unplugs cellphone tracking
  technology for now:
  http://tinyurl.com/PromenadeUnplugs

  o  A ham's Christmas poem:
  


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