[FOSS-GPS] RTKLib - Constant offset between UBlox NEO-M8T receivers
DavidKelley at ITSware.net
Tue Apr 14 09:22:09 PDT 2015
As general rule (first taught to me by my father an EE who was also a
avoid Ham radio type, but seen myself over decades), you want to place
any antenna roughly 10 wavelengths from other objects to get a far field
effect. But on a vehicle, where flat space is limited, this is not
realistic, however you still want to has the most spacing you can get,
certainly over a wavelength (hence >19cm). You can find in the
literature both reports that say this matters and reports that say it
does not (as well as ones where precise fractions of a wavelength were
used for various bean forming or heading needs).
All these are general best practices, but what can really kill you is to
have two identical devices (in this case uBlox) near each other where
the IF down convert frequency is emitted by one device and received by
another (regrettably the antenna is also at times an inadvertent
transmitter). Because they use the same design and frequency, they can
beat against each other can cause disastrous results to the L band
signal. Sharpe filters may provide attenuation for this, but at times
not, and the jamming signal may be far outside the spec for the SAW
filter used.. (Aside: Typically a splitter has about 30db between each
leg is enough to prevent this in shared antenna configurations) Short
of a lab and a spectrum analyzer there is no good way to "prove" it is
occurring except that further separation distance removes the effect.
Sorry for such a long winded reply.
Regards, David Kelley
On 4/13/2015 9:50 PM, Forrest Voight wrote:
> On Mon, Apr 13, 2015 at 12:40 PM, David Kelley <DavidKelley at itsware.net> wrote:
>> What was the antenna separation distance (one hopes >>19 cm)
> Why should it be more than 19cm (the wavelength of the L1 signal)?
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