W6JD wrote:
> This is all absolutely correct, note, however that turning off "SA"
> (selective availability) will not necessarily obviate the need for
> differential GPS..there are still the problems of ionospheric bending,
> multi-path, etc. to be corrected for high precision measurments.
The ionospheric bending and multi-path can be corrected for, by using
both signals (i.e. both frequencies). Military GPS receivers use
these capabilities, but no civilian unit that I've seen does this.
Someone else (exactly who is not clear) had written:
> Having two antenna's won't help as the error is not related to poor
> reception but to deliberate variations (dithering) applied by DOD to
> the clock time sent as part of their Commercial Service.
Not true. Remember, if you are trying to check which way your beam
is pointed, you only need a relative position difference between the
two receivers. The absolute position indicated by either or both
receiver(s) is of no consequence.
> On the matter of the ham on the other end of the barrel with
> tools...
This story has indeed come a long way. I remember reading it in the
early Seventies, at which time neither I nor the story had been
polluted by ham radio...
Chris R. Burger
ZS6EZ
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