[time-nuts] GPS Timing in Interference Environment

[Normand Martel]

Hi again...

I forgot one impotrant topic:

Is the interfernce inside the GPS band (1575.42) or
outside it? My last message applies on out-of-band
interference, for which a good bandpass filter will
eliminate the out-of-band interfernce. For in-band
interference the thing is completely different. While
many GPS receivers have some amount of "jam proof"
protection, in-band interfernce should be avoided as
much as possible.

On this point of view, you shall do some
investigation. If the interfernce is relatively weak
and located within a small spot, the best thing to do
is to move the GPS receive antenna away from the
interfernce source. If moving the antenna is
impossible or if the interfernce is too strong,
discussion with the the interference source's owner
shall help. In case of non-agreement or if the
interference is too strong, your last resort is the
FCC. The 1575.42MHz +/- 1MHz band is protected and
reserved to GPS operations and no interference shall
exist within it's limits.


73's de Normand VE2UM
Montreal, Qc. Canada

--- Magnus Danielson <cfmd at bredband.net> wrote:

> From: Phaysal Khan <mortal_f at yahoo.com>
> Subject: [time-nuts] GPS Timing in Interference
> Environment
> Date: Mon, 24 Jul 2006 20:33:14 -0700 (PDT)
> Message-ID:
> <20060725033314.4082.qmail at web53107.mail.yahoo.com>
> 
> > Hi,
> 
> Faisal,
> 
> >   I am new in this group, and wanted to discuss
> something abt GPS timing. I am working on GPS system
> & signals from timing point of view. I want to see
> Effects of Interference(CW) on GPS timing receivers.
> At this stage I am mainly interested on what will
> happen to the timing receiver itself when effected
> by CW interference and the next stage will be to
> find out how this effect could be mitigated. 
> > 
> > What I intend to do now, is to compare the 1 PPS
> pulse from two different rcvrs ( I will be using
> Motorola M12+ Oncore as the subject rcvr and Leica
> CRS1000 as the reference.
> >   
> > Do you ppl have any suggestions?
> 
> The main thing being affected is the C/N factor,
> which has a resulting
> consequences on TDOP. There are several mechanisms
> and they also depends on the
> receiver details. I would monitor the received
> strength while also record the
> PPS output.
> 
> I assume you have read up on the publically
> available material on this.
> 
> There are numerous stories from the real world where
> the GPS steered timing
> fails due to interference or unintentional damping
> of signal.
> 
> Constant logging of signal strengths and evaluation
> of these are a simple and
> straightforward method of detecting a case of
> interference. It does not really
> mitagate it, but many times not pulling the plug is
> worse than being hooked in.
> This is by far not enought thought.
> 
> Cheers,
> Magnus
> 
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