LETTERS TO THE EDITOR ON
  GPS, LPFM, ULS AND, OF COURSE, POWER CORD 101

  MAY 2000

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  RE: "ANYONE WANT TO BUY A FM DGPS RECEIVER?"

Don't chuck or boat-anchor it yet, Joel.  USCG (and others) will
continue to broadcast DGPS signals, and the accuracy with Selective
Availability (SA) discontinued should be 1 meter or less!  Not a
bad thing.

Anyone report improved Z-axis accuracies?

Peter Moncure, President, RadioSoft, pmoncure@radiosoft.com 

[Ed note:  An interesting chart claiming to show horizontal
and vertical positioning errors with SA turned on & off is:

http://www.cnde.iastate.edu/staff/swormley/gps/sa_trans.gif 

URL courtesy of Jeff Staigh, WA6EQU, KMEXTV@aol.com]

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One of my stations carries the DGPS signal from a company called DCI.
I spoke with Jim Bradley at DCI to investigate the impact of (shutting
off SA).  According to Jim, it will have some impact on his business, but
not as much as you might expect.  With DCI's DGPS, the accuracy is 1 meter.
He states that sun spot activity and the ionospheric fluctuations impact
the accuracy of the GPS even if the SA is off.  The overall accuracy with
the SA off is still only 10 meters at best.

So, if you need greater than 10 meter accuracy, don't cancel your DGPS
subscriptions!

Bob Malsbury, rmalsbury@slonebroadcasting.com 

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Turning off SA will not render differential GPS obsolete.
There are several other sources of GPS error, such as ionospheric
effects, satellite position error, satellite clock errors, etc.,
which differential techniques will reduce or eliminate.

IIRC the specification for the circular error of the civilian
signal without SA is that horizontal positions are within 15 meters
95% of the time.

DGPS can reduce the real time error to 1 to 3 meters on good
hand held consumer receivers.

I suspect the FCC will still require DGPS techniques to be used
in AM proofs which use lat long as the only point descriptor.

Gray, Gray Frierson Haertig & Assoc., gfh@haertig.com 

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  USE OF GPS IN MEXICO

FYI, we use GPS in Mexico along the border for microwave path
studies.  Accurate topo maps are not always available in these areas.
(The improved GPS accuracy with SA turned off) will be very useful
to us.

Robert Haggerty, Haggerty Communications Group, robert@haggerty.com 

[Ed note:  Many of you will remember Bob in his role as a field
inspector for the San Diego FCC office years ago.  Bob is now
extremely busy and successful with his own business of engineering
cross-border microwave links.]

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  GPS FREQUENCY STANDARD SHOWS IMPROVED ACCURACY

The 2 Datum GPS frequency references that I use for the off air
frequency measurement service has gone from under 50xE-12 to
under 1 to 5xE-12.  I don't see them moving around like they used to.

Up to this point I've not really been using GPS for navigational use.
Now that the S.A. has been removed I'm sure I will start using it.
It will help with radial runs but I still like stable visual
descriptions if possible.  I realize in the desert it's difficult
to use a particular cactus or dessert turtle as a marker.

Burt Weiner, K6OQK, biwa@pacificnet.net 

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  AN AID TO DETERMINE LPFM SITE COORDINATES

I'm sure there must be others, but the address-to-coordinates converter at

http://www.geocode.com/eagle.html-ssi 

is a useful supplement to the new FCC LPFM channel finder you described in
CGC #388.  Discovered that there are no channels available in the SF Bay area
but several in Mendocino!

Winston Tharp, TV Engineer, SF State Univ. CATS, k5hsj@sfsu.edu 

[Ed note:  Use address-to-coordinates converters with caution; some
produce significant errors.  Nevertheless, converters can be helpful
in initial/cursory studies.]

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  COMMENTS ON USING THE FCC'S UNIVERSAL LICENSING SYSTEM (ULS)

Despite Steve Weiner's message to Tim Schultz, I was able to register my TIN
and callsign using Netscape Communicator 4.5 with the FCC _without_ the "FCC
Smart Update" plug-in module.  That plug-in is, however, required to use many
of the ASR (antenna structure registration) features.  For example, if you
want to search for a tower registration number by geographic coordinates, the
plug-in is required.  In addition to the plug-in being browser dependent
(Netscape only), it is also platform dependent.  The plug-in is available
_only_ for the Windows versions of the Netscape browsers.  Macintosh and
Linux users cannot directly access the FCC ASR database query system.

I find that the tower registration query system to be dreadfully slow.  I've
complained to the FCC about it several times, and their response has been
"we'll fix it in the next revision of the plug-in".  I suspect that the
glacial speed of the system is due in part to its extensive use of java and
the use of encryption (https).  Am I the only one, or does anyone else
experience sluggish response when using the FCC's one-line ASR query system?

Bob Weller, Hammett & Edison, Inc., rweller@h-e.com 

  ******

  POWER CORD 101

Depending on the design of the equipment, power line cleanliness can have
an effect on the audio.  We all understand the need for a technical ground in
large analog audio facilities.  In home hi-fi, large power amps ask for lots
of current.   Many serious audiophiles run dedicated AC service from the
breaker box to their systems.

Greg Strickland, KLVE/KTNQ, 74331.2645@compuserve.com