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@aol.com
To: time-nuts@febo.com
Sent: Wednesday, June 11, 2014 4:11 AM
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?

http://www.ebay.com/itm/321295751672

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.

thanks
Jim
On 6/20/2014 8:31 AM, Tom Van Baak wrote:

Jim,

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.

Bob

From: jim s jwsmail@jwsss.com
To: Discussion of precise time and frequency measurement time-nuts@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?

http://www.ebay.com/itm/321295751672

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.

thanks
Jim
On 6/20/2014 8:31 AM, Tom Van Baak wrote:

time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Bob,
I was being a bit lazy.  The 15' distance gets from a couple of spots in
the room with my systems and lab, and also is already terminated, and
there is no issue with the power since it would be totally contained in
the unit.

But your suggestion and some work making the cables would work best.

To you and Hal who suggested it, is this unit suitable for outputing a
1pps timing signal?  Wouldn't the long serial option Hal suggestion mess
that up, vs. using this method to put the Fastax as close as possible to
a system which which would have the systems gpio and serial ports attached?

Thanks to you both for answering.
jim

On 7/1/2014 9:30 PM, Bob Stewart wrote:

I tried using a long serial cable.  Just because I had some 100 feet
of cat-5 wire already installed.  It did not work reliably I was using
a MAX232 chip as a driver.  I could have made it work by using
differential drivers/receivers at each end but I had some good antenna
lead, pulled that into a closet space and used a shorter serial cable.

The advice to use the cable TV wire for antenna lead is good.  Yes it
is 75 not 50 ohm but even the Trimble user manual says it works best.
Those compression type F connectors are 100% water proof, the cable is
double shielded and inexpensive.

On Tue, Jul 1, 2014 at 10:17 PM, jim s jwsmail@jwsss.com wrote:

--

Chris Albertson
Redondo Beach, California

I noticed on Toms info page, (very good along with the two emails for
info) that there is no connection called out for the antenna power.

There are two power in pins, Primary and Backup power.  Since I'm going
to use an active antenna, can I send the 5 v up the antenna power, or
will the Primary power propagate and power the antenna?

The Antenna power is pin 1.

thanks
Jim

On 6/20/2014 8:31 AM, Tom Van Baak wrote:

Jim,

I'm a rather junior member of the list, but I wouldn't try to move 1PPS over that kind of distance; especially when it's so easy to put the receiver right next to what needs the 1PPS.  The pros are too small and the cons are too great.  There are a couple of vendors on ebay who sell "F" to "SMA" adapters.  But, a warning: from experience I have found that the RG6 is stiff and the SMA male adapter is fragile.  While moving your unit around, it's all to easy to snap the adapter off your unit.  It's a few more bucks, but consider getting a short "F" female to "SMA" male pigtail instead of just a machined adapter.  I assume that it's not a problem on the antenna end, since you're not connecting to a bulkhead connector.

In my house, I put the antenna in the attic, and snaked the RG6 through the same opening that the DirecTV cable came through.  I changed the wall plate to add another F connector.  From there is a short run of RG6 to my splitter, and then a few feet of RG316 to my receiver.

Bob

From: jim s jwsmail@jwsss.com
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Wednesday, July 2, 2014 12:17 AM
Subject: Re: [time-nuts] FASTRAX GPS

Bob,
I was being a bit lazy.  The 15' distance gets from a couple of spots in
the room with my systems and lab, and also is already terminated, and
there is no issue with the power since it would be totally contained in
the unit.

But your suggestion and some work making the cables would work best.

To you and Hal who suggested it, is this unit suitable for outputing a
1pps timing signal?  Wouldn't the long serial option Hal suggestion mess
that up, vs. using this method to put the Fastax as close as possible to
a system which which would have the systems gpio and serial ports attached?

Thanks to you both for answering.
jim

On 7/1/2014 9:30 PM, Bob Stewart wrote:

time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

I appreciate the advise.  I bought one of the cheepo units just to see
it work (hopefully) but to run better location I'll probably pull 2 or
more of the better wire, so I can run multiple receivers. I also have
two different books, one off top of my head is Pasternak Enterprises, so
I can get a feel for what can adapt to what, and either buy it from them
or someone else.

I only am on here because of owning and at one time playing with a pile
or Truetime 468DC's which are now gathering dust.

I manage to charm Paul Swed (excuse the caps :-) into a design he did to
allow them to again display time, but am only now getting to where I may
attempt to use his design and convert mine.

Thanks to Tom for letting me in, and I've learned a huge amount from
everyone here.

thanks
JIm

On 7/2/2014 9:42 PM, Bob Stewart wrote: