[time-nuts] FASTRAX GPS

Bob Stewart bob at evoria.net
Wed Jul 2 00:30:30 EDT 2014


Are you trying to find out how to hook up a receiver in your office/radio room to an antenna that is some ways away?  Or are you specifically trying to remotely hook up a receiver near your antenna?  If the former, just use RG-6, like for cable TV, with adapters on each end.  RG-6 has such low loss that the impedance change is not an issue.  I've got a 30+ ft run up to the attic to a cheap GPS puck antenna for my setup.  Others have much longer runs and it works OK.


 From: jim s <jwsmail at jwsss.com>
To: Discussion of precise time and frequency measurement <time-nuts at febo.com> 
Sent: Tuesday, July 1, 2014 4:56 PM
Subject: Re: [time-nuts] FASTRAX GPS

I went back thru this thread to look for the answer, and did not see it 
so am asking.  The one of these I have has a threaded female connector 
on it.  One of the ones in Tom's page has a smooth sided connector, FWIW.

I wonder if this would work with one of the 5m SMA male active antenna 
units will work with it?


This one happens to be 5 meters long and is active.  I am guessing 
because the unit has antenna power this is the sort of item to use?

I want a long run because where I plan to use it is some distance from 
clear line of site.

On 6/20/2014 8:31 AM, Tom Van Baak wrote:
> Hi Ernie, Jason, (also Hal, Chris),
> I'm able to get NMEA and 1PPS out of the Fastrax/iTrax130 board now.
> Before I sink any more time into this project, have any of you made 1PPS measurements?
> Compared to ublox, using the same antenna, these units take tens of minutes or even hours to lock. And they have a bad habit of being close to UTC for a few hours but then gradually wandering off by tens or hundreds of microseconds.
> A power cycle puts them back on track (aligned with UTC), so it would seem to be a firmware issue rather than antenna or reception. A similar thing happens on three different boards I have evaluated over the past two weeks.
> Now, when they are working right, the 1PPS has an RMS deviation of around 20 ns, which I've come to expect as typical for cheap GPS/1PPS receivers these days. But the long lock times and unexplained 1PPS drift make them unreliable for GPSDO or serious timing work, even at $12 each.
> It might be me, so I'm asking if you've seen anything similar. The binary command set looks tempting, but I usually don't play with that until the unit can be trusted to give reliable NMEA and 1PPS output.
> Unfinished page: http://leapsecond.com/pages/itrax/
> /tvb
> ----- Original Message -----
> From: "Ernie Peres" <ernieperes at aol.com>
> To: <time-nuts at febo.com>
> Sent: Wednesday, June 11, 2014 4:11 AM
> Subject: Re: [time-nuts] FASTRAX GPS
>> Hi Jason,
>> I figured out a different pin assignments....
>> hold the PCB so that the SMA antenna connector is looking to right and under the PCB.
>> open-   1      2-  Ant power    presently connected to pin nbr 4
>>     TX-   3      4-  Main power  +3 volt
>>      RX-  5      6-  1PPS
>> open-   7      8-  Grnd   power -3 Volt
>> the unit takes about 60mA @ 3,0 volt and comes-up in NMEA mode.. 9600 Baud.
>> I use the FASTRAX_WORKBENCH_522 software.
>> I wonder if anybody has other pin arrangement/connection. The 2 open pins is UNK and also not sure if pin nbr 4 is the main power or perhaps the pin nbr 2......??
>> Rgds Ernie.
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