CGC #1128

by CGC on March 22, 2012



                        THE CGC COMMUNICATOR

                              CGC #1128

                      Thursday, March 22, 2012


                  Robert F. Gonsett, W6VR,  Editor

     Copyright 2012, Communications General® Corporation (CGC)



  This newsletter is devoted exclusively to continuing
  yesterday's discussion of Forest Service ("FS") Appendix G
  applicable to FS radio communication sites.



  Those of you who have read Appendix G realize that more than anti-
perching devices are involved.  For example, the Forest Service states 
that, "New towers shall be the same or lesser tower height as existing 
towers at the site and no more than 199 feet above ground level (AGL)...."  
A 199 foot height limitation on new Mt. Wilson towers makes no sense.  
Much taller towers are routinely used at that location and allow the 
consolidation of communication facilities -- an important goal of the 
Forest Service.

  Concerning bird protection, the question remains as to why the 
Forest Service is concerned with radio facilities at all.
Is the basic issue avian exposure to RF fields?  If so, what studies 
did the Forest Service reply upon in determining unacceptable RF 
exposure levels for birds?  According to Radio World, cats are 
responsible for 42% of avian deaths due to outside sources, collisions 
with buildings and windows take another 42% while communication towers 
are only responsible for 0.3% of the deaths.  See the second URL below 
for a link to the Radio World story that reflects data just released 
by the FCC.

  Another concern with Appendix G involves undefined terms such as 
"anti-perching materials."  The lack of a clear definition leaves 
interpretations open to local Forest Service officials with the 
likelihood of arbitrary and inconsistent determinations.  For example, 
are plastic owls bona fide anti- perching devices?  Are 950 MHz open-
grid dishes considered "microwave dishes?"  All microwave dishes must 
now be covered by radomes under the Appendix G mandate, but radomes 
are not even manufactured for open-grid dishes as far as we know.
Radomes installed on open-grid dishes more than quadruple the wind 
loading according to a leading dish manufacturer.
A covered dish would literally be ripped off a tower in a windstorm 
with the brackets unable to hold the increased load.

  If metal spike strips are used to deter bird perching, there is a 
huge likelihood that loose strips, rubbing wires and/or electrolysis 
will generate significant levels of harmonics and intermodulation 
products that will degrade on-site receiver performance.  RF-
conductive anti-perching strips attached to antennas or tower 
structures can also warp RF radiation patterns depending on the 
dimensions and placements of the strips.  This could amount to a 
de facto modification of your FCC license.

  One good way to proceed would be to have a face-to-face meeting with 
Forest Service officials at the Forest Supervisor's office in Rancho 
Bernardo, CA.  Let's talk about our concerns.
Perhaps a well respected organization such as the Southern California 
Frequency Coordinating Committee (SCFCC) could take the lead.  If 
individual users start installing metal spike strips (or insulated 
strips that act like conductors at RF frequencies), the communications 
industry is likely to suffer serious long-term consequences 
particularly at multi-user sites.

  For background information on this story, CGC contacted two 
officials at the Rancho Bernardo Cleveland National Forest 
Supervisor's Office.  We were told that even receive-only microwave 
dishes would be required to have radomes and anti- perching devices 
because of the way Appendix G is written; however, users are allowed 
to request exemptions.  CGC recommends that all affected parties 
(particularly those notified of pending facility inspections) either 
request exemptions or ask that Appendix G be stayed until the 
technical issues are ironed out.

  CGC supports the idea of a stay.  Even if the problems are resolved 
verbally, the questionable language will remain in place and will be 
interpreted differently when the next round of Forest Service 
personnel arrive.  The results of any verbal agreements need to be 
memorialized in writing and be legally binding.

  Please forward a copy of this newsletter and our previous newsletter 
(CGC #1127) to any contacts you may have in the southern California 
land-mobile and cellular/PCS industries.
The use of metallic or insulated but RF-conducting spike strips could 
cause serious long-term technical problems as outlined above.  The 
higher the radio frequency field strengths, the more intense the 
interfering signals will become.  Even strips that are not conducting 
at DC but are advertised to "not interfere with electrical or 
communication transmissions" need to be independently tested at all 
applicable RF frequencies in order to verify the claim -- and this 
process will only add to the costs.

  As one client put it, "We are already paying huge fees to the 
Forest Service.  Now this."  (Appendix G)  (Avian mortality data)

                       LETTERS TO THE EDITOR


  Letters to the Editor of the CGC Communicator should be posted on 
the Tech Letters Website.  Here is the URL to see the most recent 
postings and to make new postings (all letters and comments are 
moderated and are posted after review):

  Please contact the moderator, Steve Blodgett, if you are having 
trouble viewing or posting: sblodgett (at)




  The CGC Communicator is published for broadcast engineering
  professionals in so. California by Communications General®
  Corporation (CGC), consulting radio engineers, Fallbrook, CA.

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_________________________    End   _______________________________ 

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