On Fri, Feb 20, 2015 at 1:10 PM, Tom Miller <[email protected]> wrote:
> > ----- Original Message ----- From: "Jim Lux" <[email protected]> > To: <[email protected]> > Sent: Friday, February 20, 2015 10:25 AM > Subject: Re: [time-nuts] Looking for advice to get a submillisecond setup > > > On 2/20/15 6:30 AM, Chris Albertson wrote: >> >>> I think the easiest cable to make really long, if one must be long is the >>> antenna cable. Use 100 meters of the kind of cable they use for cable >>> TV. It comes double shield and has those compression type F connectors. >>> The cable can cary both the GPS signal and power for the amplifier that >>> is >>> built into the antenna. If the cable is very long, You would need >>> another >>> in-line amplifier, again powered by the cable itself. >>> >> >> that's fine if you have a separate antenna(w/preamp) and receiver.. >> >> But something like the Garmin GPS-18x and other similar inexpensive >> receivers have integrated antennas. >> >> >> >> >> >>> And yes, a gps antenna needs a good view of the sky, but the receiver >>> itself can be 100+ meters away from the antenna >>> >> >> >> I think you're getting into receivers that are well into the hundreds of >> dollars range, if bought new. >> >> For an inexpensive "NTP for few hundred dollars to get better than a >> millisecond" end of things, I think the integrated GPS antenna/receiver >> with a suitable computer right next to it is the way to go. Then you're >> just running a network cable and power. >> >> >> 4 pair Cat5 sometimes works ok with RS232, sometimes not. At the 4800 bps >> of the garmins, it would probably work ok. >> At least you're sending power from the same place as you're >> generating/consuming the signals, so you don't have the common mode voltage >> difference problem. >> >> I like that idea in general.. a pair for power, a pair for TxD, a pair >> for RxD and a pair for 1pps. I'm not sure you'd want to connect the >> "ground" at both ends of the signal pairs, though. What does the supply >> current to the GPS-18x look like? Maybe it really doesn't make any >> difference. Hopefully your computer's RS232 "input" isn't drawing 10s of mA. >> _______________________________________________ >> > > One needs to be careful with extending the 18X "RS232" signal. It really > is not true RS232 but more like a 5 volt CMOS like signal. > > If you are using it in a wood frame house, it might work fine indoors. But > in a steel/concrete multi-story commercial or industrial building, I would > be more surprised if it worked than not. > I've had poor luck extending "fake" RS232 using cat5 wire. It works well if you use differential signaling Convert the cos level serial to RS422 and you can go almost a mile using cheap cat-5 wire. And I've also have worse luck extending a 1PPS plus using cat-5. The solution is RS422 signaling for the plus. But I finally gave up as running a longer antenna cable has easier. > tm > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. > -- Chris Albertson Redondo Beach, California _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
