Hi Jim,
As part of my research into keeping time on rockets and spacecraft, I joined
this list to see what I could learn from the masters. Of course I'm a
knuckle-head for not assuming that you'd be one of the resident masters
<grin>. Anyway, as my accuracy needs are modest (~10uS across many onboard
computers), have access to GPS most of the time and don't really need to
worry about relativistic effects (yet, anyway <grin>) or radiation effects
(due to redundancy), I thought I'd use a GPSDO that can handle a decent
amount of holdover and then use PTP to distribute time across the vehicle.
Do you, or anyone else, have a recomendation for the GPSDO? Jackson Labs'
(http://jackson-labs.com/) DROR seems like it might work, but I wonder if
there might be better alternatives.
-Kevin Watson
----- Original Message -----
From: "jimlux" <jim...@earthlink.net>
To: <time-nuts@febo.com>
Sent: Tuesday, March 08, 2011 6:20 AM
Subject: Re: [time-nuts] GPS Filter
On 3/8/11 4:24 AM, Pieter ten Pierick wrote:
Hi,
GPS phased arrays aren't new, nor is it necessary to physically steer
the antennae within the aray:
http://www.navsys.com/papers/0005004.pdf
But would such a system help with the LNA overload due to a local
transmitter?
I would expect that using separately steered antennas with good
directivity could prevent this out-of-band LNA overload?
As long as your phasing is done before the one-bit ADC, you can place a
null on the offending interference source. This has been used for
adaptive interference cancellers for decades (for cosited transmitters and
receivers). A friend worked for American Nucleonics back in the 80s when
they were starting to implement digital control loops (but the
cancellation was still done with analog techniques) for this application.
You *might* be able to do it even after the sampler, if the interfering
signal isn't too strong. At a guess, if the total noise power at the
input to the sampler were within about 10dB of the interfering signal,
you'd probably be ok. When the interfering signal gets up to 10-20 dB
over the noise power, it starts to really dominate.
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