[time-nuts] KS-24361 "NO GPS" - again

Bob Camp kb8tq at n1k.org
Sun May 31 02:32:03 UTC 2015


Hi

Quick “front end” check list:

The old Oncore modules were not the greatest for sensitivity. Compared to what you get today, they are a bit deaf. What that 
turns out to mean is that you need a bit more antenna gain with them than with a newer module (either a newer Oncore or a newer
part from somebody else). Something around 30 db of antenna pre-amp gain with < 10 db of coax loss is about right for them. They 
will overload if you get up to the 39+ db preamp range and < 3 db of coax loss. How much they overload depends on the crud in 
your local environment. 

The Lucent boxes (like just about all similar gizmos) put out +5V to the antenna . There are indeed antennas that need > 7V to do their
thing. How well they work / if they work at 5V - who knows. I would not try it. 

Since you get a “40 - 50” db signal to noise once you lock on to a sat, the preamp gain is a bit weird. It very much impacts satellite 
acquisition, and has less impact once you are locked on. A marginal antenna gain can give you a “long start”, but then lock on to 
a number of sats once things get going. That can make it tricky to spot the problem.

Bob

> On May 30, 2015, at 9:38 AM, Martin VE3OAT <ve3oat at storm.ca> wrote:
> 
> Ulli,
> Sorry that I haven't been following your correspondence so I am coming into the middle of this.  The fact that you receive so few satellites says to me that there is a problem at the front end.  You said you had changed the cable to the antenna and the antenna itself so those parts seem OK at least.  Are you using an active antenna and does the unit provide the required voltage for it?  Sorry if you have already checked that.
> ... Martin    VE3OAT
> 
> Ulli wrote :
> > At least, i saw 1 or 2 satellites from time to time.
> 
> 
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