Re: [time-nuts] Mounting GPS Antenna on Steel Roof
Why not use RS232? Several issues come into play. One is that driving long cable runs with large voltage swings slows down the transition. Another is that many receiver designs use slew rate limiting capacitors in an effort to reduce noise coupling. These capacitors of course introduce delays, that will also drift with temperature and the voltage of the drivers. Basically you are throwing away some amount of timing accuracy when using RS232 for the PPS signal. It is slightly more convenient to use RS232 to drive the PPS signal of course. from web link www wraith sf ca us/ntp/#gps-receiver They are using a modded RS232 board to bypass the RS232 chips. The PPS signal would be the one signal to most benefit this special treatment as far as time delay the serial signal would benefit from the increased distance. Maybe everything is one package ? I know this thread is more about isolation/surge protection but the trade off is the more stuff we add the more chance for variable delay vs static delay, with the variable part adding to error. But the simple route with less stuff also has less too no protection. The antenna protection does protect the GPS receiver, but the first goal may be to keep the surge away from the inside of the building. Maybe a WiFi or Fiber link to the internal network with the network time server, separate power supply and GPS receiver all mounted outside ? Another reason to use a small embedded low power server. Layers of protection as to reduce the damage. Low power would also add solar / battery as an option which would remove the power source as an entry / exit point for any surge. - Original Message From: [EMAIL PROTECTED] [EMAIL PROTECTED] To: time-nuts@febo.com Sent: Saturday, March 8, 2008 8:32:29 AM Subject: Re: [time-nuts] Mounting GPS Antenna on Steel Roof In a message dated 08/03/2008 13:29:42 GMT Standard Time, [EMAIL PROTECTED] writes: The MAX232, like all RS-232 interface chips I have ever come across, inverts the signal. That'll explain it then:-) ___ 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. Never miss a thing. Make Yahoo your home page. http://www.yahoo.com/r/hs ___ 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.
Re: [time-nuts] Mounting GPS Antenna on Steel Roof
In a message dated 08/03/2008 03:57:02 GMT Standard Time, [EMAIL PROTECTED] writes: The inverter is required because the Motorola GPS receiver uses TTL and the PC serial port uses RS232. RS232 uses a positive voltage of +3 to +25 volts to indicate a logic zero, and a negative voltage of -3 to -25 volts to indicate a logic one. --- My Motorola Oncore test rig uses a Max232 to interface the RS232, no inverter, and works fine. regards Nigel GM8PZR ___ 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.
Re: [time-nuts] Mounting GPS Antenna on Steel Roof
The MAX232, like all RS-232 interface chips I have ever come across, inverts the signal. Didier KO4BB -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED] Sent: Saturday, March 08, 2008 2:48 AM To: time-nuts@febo.com Subject: Re: [time-nuts] Mounting GPS Antenna on Steel Roof In a message dated 08/03/2008 03:57:02 GMT Standard Time, [EMAIL PROTECTED] writes: The inverter is required because the Motorola GPS receiver uses TTL and the PC serial port uses RS232. RS232 uses a positive voltage of +3 to +25 volts to indicate a logic zero, and a negative voltage of -3 to -25 volts to indicate a logic one. --- My Motorola Oncore test rig uses a Max232 to interface the RS232, no inverter, and works fine. regards Nigel GM8PZR ___ 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. No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.5.516 / Virus Database: 269.21.6/1316 - Release Date: 3/6/2008 6:58 PM No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.516 / Virus Database: 269.21.6/1316 - Release Date: 3/6/2008 6:58 PM ___ 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.
Re: [time-nuts] Mounting GPS Antenna on Steel Roof
In a message dated 08/03/2008 13:29:42 GMT Standard Time, [EMAIL PROTECTED] writes: The MAX232, like all RS-232 interface chips I have ever come across, inverts the signal. That'll explain it then:-) ___ 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.
Re: [time-nuts] Mounting GPS Antenna on Steel Roof
Well, I plugged my Oncore UT+ into my PC and it didn't work until I put a level shifter in... no damage but no data either. So far I've been lucky in that every device I tried that needed a level shifter wasn't damaged by the lack of one. The normal MAX232 type level shifters include an inverter. So even if the voltage levels work without a level shifter, the signal will be upside down. -- These are my opinions, not necessarily my employer's. I hate spam. ___ 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.
Re: [time-nuts] Mounting GPS Antenna on Steel Roof
Hal Murray wrote: Well, I plugged my Oncore UT+ into my PC and it didn't work until I put a level shifter in... no damage but no data either. So far I've been lucky in that every device I tried that needed a level shifter wasn't damaged by the lack of one. The normal MAX232 type level shifters include an inverter. So even if the voltage levels work without a level shifter, the signal will be upside down. To play safe, if one isnt sure that an inverter is required or not an exclusive OR can be used so that the signal can be inverted or not as required. Bruce ___ 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.
Re: [time-nuts] Mounting GPS Antenna on Steel Roof
Quoth Hal Murray at 2008-03-07 19:59... The normal MAX232 type level shifters include an inverter. So even if the voltage levels work without a level shifter, the signal will be upside down. I'm building my test board with a hex inverter that I'm actually using to buffer the 1PPS signal. I've got spare gates on there so will build the board with jumpers so that I can invert or not invert (that is the question ;-)) As I'm working with two different types of GPS module, and may have others, my development board will have a lot of jumpers so that I can actually patch together something that works before I build the final boards - something that I feel necessary as I always seem to get my TX/RX mixed up! Just to clarify - I don't tend to use breadboards as they tend to take longer to debug than making a PCB. When PCBs are concerned, I tend to use SMDs wherever possible until such time as I find a way of making holes that a) doesn't break my drill every other hole and b) actually lines things up properly. (A CNC XY drill rig would be really nice - better buy a lottery ticket.) Cheers M -- Matthew Smith Smiffytech - Technology Consulting Web Application Development Business: http://www.smiffytech.com/ Personal: http://www.smiffysplace.com/ LinkedIn: http://www.linkedin.com/in/smiffy ___ 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.
Re: [time-nuts] Mounting GPS Antenna on Steel Roof
The inverter is required because the Motorola GPS receiver uses TTL and the PC serial port uses RS232. RS232 uses a positive voltage of +3 to +25 volts to indicate a logic zero, and a negative voltage of -3 to -25 volts to indicate a logic one. Brian KD4FM Bruce Griffiths wrote: Hal Murray wrote: Well, I plugged my Oncore UT+ into my PC and it didn't work until I put a level shifter in... no damage but no data either. So far I've been lucky in that every device I tried that needed a level shifter wasn't damaged by the lack of one. The normal MAX232 type level shifters include an inverter. So even if the voltage levels work without a level shifter, the signal will be upside down. To play safe, if one isnt sure that an inverter is required or not an exclusive OR can be used so that the signal can be inverted or not as required. Bruce ___ 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. ___ 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.
Re: [time-nuts] Mounting GPS Antenna on Steel Roof
Attached is a interface for an Oncore VP receiver. You will have to check - I believe the GT and UT use the same connections as the VP. Brian Kirby wrote: The inverter is required because the Motorola GPS receiver uses TTL and the PC serial port uses RS232. RS232 uses a positive voltage of +3 to +25 volts to indicate a logic zero, and a negative voltage of -3 to -25 volts to indicate a logic one. Brian KD4FM Bruce Griffiths wrote: Hal Murray wrote: Well, I plugged my Oncore UT+ into my PC and it didn't work until I put a level shifter in... no damage but no data either. So far I've been lucky in that every device I tried that needed a level shifter wasn't damaged by the lack of one. The normal MAX232 type level shifters include an inverter. So even if the voltage levels work without a level shifter, the signal will be upside down. To play safe, if one isnt sure that an inverter is required or not an exclusive OR can be used so that the signal can be inverted or not as required. Bruce ___ 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. ___ 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. Oncore Interface.pdf Description: Adobe PDF document ___ 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.
Re: [time-nuts] Mounting GPS Antenna on Steel Roof
Quoth Brian Kirby at 2008-03-08 14:46... Attached is a interface for an Oncore VP receiver. You will have to check - I believe the GT and UT use the same connections as the VP. Thanks Brian - that's pretty close to what I've come up with apart from the fact that I'm putting isolation (TI ISO7231) between the receiver and the rest of the circuit and the receiver is powered by a MeanWell high-isolation DC/DC convertor. And I've got mine running right to left ;-) I've got a something very similar drawn up for my Trimble modules except that the isolation and level conversion is x2, for the two serial ports. Cheers M -- Matthew Smith Smiffytech - Technology Consulting Web Application Development Business: http://www.smiffytech.com/ Personal: http://www.smiffysplace.com/ LinkedIn: http://www.linkedin.com/in/smiffy ___ 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.
Re: [time-nuts] Mounting GPS Antenna on Steel Roof
For isolation of digital signals such as RS-232 (before level translation), it's hard to find something more amazing than the Analog Device ADuM5241 http://www.analog.com/en/prod/0,2877,ADUM5241,00.html It's an SO-8 device, with two digital channels, isolated to 2500V (!) and a built-in power converter that delivers 5V @ 10mA. All in an SO-8 package. The power converter runs at 300 MHz. But wait, it costs $3 in 1,000 pcs quantity. They have other options in the same series, with more channels (in a larger package). After seeing that, the LTC 1535 from Linear Technology, which would be pretty amazing in it's own right, looks pretty dull: http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1007,C1017,P1746 Didier KO4BB -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Matthew Smith Sent: Saturday, March 08, 2008 12:15 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Mounting GPS Antenna on Steel Roof Quoth Brian Kirby at 2008-03-08 14:46... Attached is a interface for an Oncore VP receiver. You will have to check - I believe the GT and UT use the same connections as the VP. Thanks Brian - that's pretty close to what I've come up with apart from the fact that I'm putting isolation (TI ISO7231) between the receiver and the rest of the circuit and the receiver is powered by a MeanWell high-isolation DC/DC convertor. And I've got mine running right to left ;-) I've got a something very similar drawn up for my Trimble modules except that the isolation and level conversion is x2, for the two serial ports. Cheers M -- Matthew Smith Smiffytech - Technology Consulting Web Application Development Business: http://www.smiffytech.com/ Personal: http://www.smiffysplace.com/ LinkedIn: http://www.linkedin.com/in/smiffy ___ 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. No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.5.516 / Virus Database: 269.21.6/1316 - Release Date: 3/6/2008 6:58 PM No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.516 / Virus Database: 269.21.6/1316 - Release Date: 3/6/2008 6:58 PM ___ 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.
Re: [time-nuts] Mounting GPS Antenna on Steel Roof
I will be doing (4) as soon as I've found the time to make up a TTL to RS232 board. I suggest trying it without anything fancy. All the GPS toys I've tried work fine without any conversion gear. The normal TTL to RS-232 chips include an inverter. That will break things unless you add another inverter. (or your gear expects an inverter) The usual switching point for RS232 receiver chips is 1.4 volts. That's the switching point for TTL inputs, 2 diode drops above ground. That works fine for 3V CMOS drivers. -- These are my opinions, not necessarily my employer's. I hate spam. ___ 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.
Re: [time-nuts] Mounting GPS Antenna on Steel Roof
Quoth Hal Murray at 2008-03-06 20:07... I will be doing (4) as soon as I've found the time to make up a TTL to RS232 board. I suggest trying it without anything fancy. All the GPS toys I've tried work fine without any conversion gear. The normal TTL to RS-232 chips include an inverter. That will break things unless you add another inverter. (or your gear expects an inverter) The usual switching point for RS232 receiver chips is 1.4 volts. That's the switching point for TTL inputs, 2 diode drops above ground. That works fine for 3V CMOS drivers. So my Trimble ACE II and Moto Oncore modules will tolerate RS232 levels without conversion? Are we absolutely sure on this - I don't want to fry anything! Cheers M -- Matthew Smith Smiffytech - Technology Consulting Web Application Development Business: http://www.smiffytech.com/ Personal: http://www.smiffysplace.com/ LinkedIn: http://www.linkedin.com/in/smiffy ___ 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.
Re: [time-nuts] Mounting GPS Antenna on Steel Roof
Matthew Smith wrote: Quoth Hal Murray at 2008-03-06 20:07... I will be doing (4) as soon as I've found the time to make up a TTL to RS232 board. I suggest trying it without anything fancy. All the GPS toys I've tried work fine without any conversion gear. The normal TTL to RS-232 chips include an inverter. That will break things unless you add another inverter. (or your gear expects an inverter) The usual switching point for RS232 receiver chips is 1.4 volts. That's the switching point for TTL inputs, 2 diode drops above ground. That works fine for 3V CMOS drivers. So my Trimble ACE II and Moto Oncore modules will tolerate RS232 levels without conversion? Are we absolutely sure on this - I don't want to fry anything! Cheers M Matthew All that has been stated is that the receiver modules wont be damaged when driving an RS232 input. However when an RS232 input drives a 3V CMOS input there are no guarantees. In the latter case a series resistor at the CMOS input can be used to guarantee the COS gate isnt destroyed. In general it would be better to use a CMOS - RS232 converter chip, it can be socketed and used as a fuse (considerable cheaper than using the GPS receiver outputs as a fuse) should anything untoward occur. Also CMOS devices arent rated to continuously drive a short circuit a series resistor to limit potential fault currents to the datasheet maximum is advisable. Bruce ___ 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.
Re: [time-nuts] Mounting GPS Antenna on Steel Roof
On Thu, Mar 6, 2008 at 3:08 PM, Matthew Smith [EMAIL PROTECTED] wrote: So my Trimble ACE II and Moto Oncore modules will tolerate RS232 levels without conversion? Are we absolutely sure on this - I don't want to fry anything! Well, I plugged my Oncore UT+ into my PC and it didn't work until I put a level shifter in... no damage but no data either. So far I've been lucky in that every device I tried that needed a level shifter wasn't damaged by the lack of one. CK -- GDB has a 'break' feature; why doesn't it have 'fix' too? ___ 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.
Re: [time-nuts] Mounting GPS Antenna on Steel Roof
So my Trimble ACE II and Moto Oncore modules will tolerate RS232 levels without conversion? Are we absolutely sure on this - I don't want to fry anything! Bruce, Chris, thanks for the confirmation. I'll go back to the idea of using the MAX232 equivalent as originally planned. I'm also putting one of these between the MAX232 and the GPS module: http://focus.ti.com/docs/prod/folders/print/iso7231m.html (That's for the Oncore; it's got two channels in one direction, one in the other, making it ideal for TX/RX+PPS. I'll probably use one of these with a one-each-way for the Trimbles.) The GPS module will also be powered via a high-isolation DC-DC convertor. I don't consider anything that's going to sit between my data network and an antenna overkill! Cheers M -- Matthew Smith Smiffytech - Technology Consulting Web Application Development Business: http://www.smiffytech.com/ Personal: http://www.smiffysplace.com/ LinkedIn: http://www.linkedin.com/in/smiffy ___ 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.
Re: [time-nuts] Mounting GPS Antenna on Steel Roof
Chris Kuethe wrote: On Thu, Mar 6, 2008 at 3:08 PM, Matthew Smith [EMAIL PROTECTED] wrote: So my Trimble ACE II and Moto Oncore modules will tolerate RS232 levels without conversion? Are we absolutely sure on this - I don't want to fry anything! Well, I plugged my Oncore UT+ into my PC and it didn't work until I put a level shifter in... no damage but no data either. So far I've been lucky in that every device I tried that needed a level shifter wasn't damaged by the lack of one. CK The powered down input resistance of a classic 1489 RS232 receiver is 3k minimum. The classic 1488 RS232 driver has a 10mA short circuit current limit. To check if a 10mA current flowing in the CMOS output stage protection diodes compromises the long term reliability of the GPS receive can only be determined by consulting the datasheet for the CMOS output device. In any case, such currents flowing in the logic substrate may alter the chip timing and timing noise characteristics. For example when the inputs of a 74HC04 are overdriven the propagation delay and the associated timing jitter change significantly. Thus although the device may not fail anytime soon due to 10mA currents flowing in the input protection diodes, there is usually no guarantee that the chip will still operate correctly when significant protection network current is flowing. Bruce ___ 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.
Re: [time-nuts] Mounting GPS Antenna on Steel Roof
Matthew Smith wrote: So my Trimble ACE II and Moto Oncore modules will tolerate RS232 levels without conversion? Are we absolutely sure on this - I don't want to fry anything! Bruce, Chris, thanks for the confirmation. I'll go back to the idea of using the MAX232 equivalent as originally planned. I'm also putting one of these between the MAX232 and the GPS module: http://focus.ti.com/docs/prod/folders/print/iso7231m.html (That's for the Oncore; it's got two channels in one direction, one in the other, making it ideal for TX/RX+PPS. I'll probably use one of these with a one-each-way for the Trimbles.) The GPS module will also be powered via a high-isolation DC-DC convertor. I don't consider anything that's going to sit between my data network and an antenna overkill! Cheers M Matthew Using an isolator of some kind is always a good idea to break ground loops and provide some fault isolation, however they do add some jitter (probably insignificant for your application). Such isolators may be inadequate to prevent damage propagation in the the event of a lightning strike. Fibre optic isolators using several meters of plastic fibre will be far more effective in that case. Bruce ___ 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.
Re: [time-nuts] Mounting GPS Antenna on Steel Roof
Quoth Rob Kimberley at 2008-03-05 02:45... You mentioned Time Server..is this your only GPS or do you have other more accurate timing requirements? Unless you are working on nanosecond type accuracy, I don't see that mounting your antenna on the metal roof is going to cause you any practical problems. If all you are interested in is taking time from your GPS over Ethernet using NTP, then all will work fine. Yes, this is all about running a network time server; my other application is a GPS-driven Nixie clock, so that is even less critical. My main concern has been about the receiver getting 'upset', similar to Didier's experience with the Thuderbolt. What I have worked out - mainly from the responses I have received and a little from my own thought processes - is this: 1) Mounting on the ridge should probably be OK. 2) Other parts of the system are more likely to add inaccuracy than multipath. 3) Errors will not be significant in the context of an NTP server. 4) The only way to find out is to try. I will be doing (4) as soon as I've found the time to make up a TTL to RS232 board. I've already found that TrimbleMon will start under Wine, although haven't been able to connect it to any hardware yet. For the purposes of experimentation, I will be putting the antenna up on the ridge of my office roof - a much worse location than the main ridge as it is lower down and has all sorts of other metal to get in the way. (I can get the antenna on my office roof by means of a pole with a bit of Blu-Tak on the end; the main ridge requires someone on the roof and a cable extension.) Thanks again to all who have chimed in on this - really much appreciated. Cheers M -- Matthew Smith Smiffytech - Technology Consulting Web Application Development Business: http://www.smiffytech.com/ Personal: http://www.smiffysplace.com/ LinkedIn: http://www.linkedin.com/in/smiffy ___ 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.
Re: [time-nuts] Mounting GPS Antenna on Steel Roof
Matthew, You hit the nail on the head with item 4! Good luck. Rob K -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Matthew Smith Sent: 04 March 2008 21:17 To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Mounting GPS Antenna on Steel Roof Quoth Rob Kimberley at 2008-03-05 02:45... You mentioned Time Server..is this your only GPS or do you have other more accurate timing requirements? Unless you are working on nanosecond type accuracy, I don't see that mounting your antenna on the metal roof is going to cause you any practical problems. If all you are interested in is taking time from your GPS over Ethernet using NTP, then all will work fine. Yes, this is all about running a network time server; my other application is a GPS-driven Nixie clock, so that is even less critical. My main concern has been about the receiver getting 'upset', similar to Didier's experience with the Thuderbolt. What I have worked out - mainly from the responses I have received and a little from my own thought processes - is this: 1) Mounting on the ridge should probably be OK. 2) Other parts of the system are more likely to add inaccuracy than multipath. 3) Errors will not be significant in the context of an NTP server. 4) The only way to find out is to try. I will be doing (4) as soon as I've found the time to make up a TTL to RS232 board. I've already found that TrimbleMon will start under Wine, although haven't been able to connect it to any hardware yet. For the purposes of experimentation, I will be putting the antenna up on the ridge of my office roof - a much worse location than the main ridge as it is lower down and has all sorts of other metal to get in the way. (I can get the antenna on my office roof by means of a pole with a bit of Blu-Tak on the end; the main ridge requires someone on the roof and a cable extension.) Thanks again to all who have chimed in on this - really much appreciated. Cheers M -- Matthew Smith Smiffytech - Technology Consulting Web Application Development Business: http://www.smiffytech.com/ Personal: http://www.smiffysplace.com/ LinkedIn: http://www.linkedin.com/in/smiffy ___ 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. ___ 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.
Re: [time-nuts] Mounting GPS Antenna on Steel Roof
Matthew Smith wrote: Hi Folks Further to the cable splicing thread, I have been having a discussions off-list with Didier regarding the placement of my antennas on the ridge cap of my roof. There is certain concern that I may have issues with reflections - can anyone confirm whether or not this is the case? Here is a terrible diagram (I cannot for the life of me figure out how to draw solid, straight lines with the Gimp) of the proposed installation: http://www.smiffysplace.com/files/antenna_diagram.jpg The ridge runs just about 15 degrees of an East-West line, is the highest ridge on the building and is the highest point for some distance (there are trees 80m to the South), barring a vertical phased array VHF TV antenna. I can't really see how a signal striking the roof would reach the antenna, working on the basis of angle of refection = angle of incidence. Is this installation likely to case me any problems? I am rather short on other options due to the presence of steel sheds and fences. Getting the antenna clear of all of these would probably require something like a 100m+ cable, either buried or strung overhead, neither of which is practical (nor the cable length). The cable run from the ridge to my office works out at about 10m. I will have a redundant antenna a couple of metres along the ridge from the main, disconnected. If antenna #1 were to fail, I would just unplug the antenna extension cable in the loft from #1 and connect to antenna #2. I have spotted a splitter on eBay that is good for 10-1880MHz and includes power passing on one output - I guess that this means I am still able to power the active antenna as normal provided that at a receiver is connected to that output. Any comments on this would be much appreciated. Cheers M Matthew One has to be careful in assuming that reflections are a simple as you depict especially when the reflectors are only a small number of wavelengths (~ 19cm @ 1575.42MHz) in extent. The presence of any periodic structure in the metal roof (eg corrugations) may cause significant diffraction effects particularly in the near field. Roughness of the finish will increase scattering over that obtained with a smooth surface. Also at least some of the magnetic base antennae are intended to be mounted on a conducting surface. So the preferred mount may be on a ground plane of the recommended size on the end of a tripod a meter or more in height. However since you have a magnetic mount its easy to try your method and see if it causes any observable problems, if it does try a different mounting scheme. Even the experts can get it badly wrong, mounting GPS antennas with choke ring ground planes mounted on concrete pillars can contribute to measurement instability whereas such mounts tend to be very stable mechanically, see: ftp://ftp.ngs.noaa.gov/dist/Jimr/igsframe-igs06.pdf ftp://ftp.ngs.noaa.gov/dist/Jimr/metrologia-2.pdf http://www.geopp.de/media/docs/pdf/gppigs06_pnf_g.pdf http://www.geopp.de/media/docs/pdf/gppigs06_pnf_g.pdf The size of the effects detailed above are only of significance for geodesy and other high precision applications. However, if a choke ring ground plane or equivalent were not used the effects would be much larger. Bruce ___ 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.
Re: [time-nuts] Mounting GPS Antenna on Steel Roof
Hi Matthew: Some antennas are receptive to signals coming up from below. Since the signal is circularly polarized the first reflection is supposed to be down something like 20 dB, but the second reflection will be much stronger, so you would also need to look at those. Have Fun, Brooke Clarke http://www.prc68.com/P/Prod.html Products I make and sell http://www.prc68.com/Alpha.shtml All my web pages listed based on html name http://www.PRC68.com http://www.precisionclock.com http://www.prc68.com/I/WebCam2.shtml 24/7 Sky-Weather-Astronomy Web Cam Matthew Smith wrote: Hi Folks Further to the cable splicing thread, I have been having a discussions off-list with Didier regarding the placement of my antennas on the ridge cap of my roof. There is certain concern that I may have issues with reflections - can anyone confirm whether or not this is the case? Here is a terrible diagram (I cannot for the life of me figure out how to draw solid, straight lines with the Gimp) of the proposed installation: http://www.smiffysplace.com/files/antenna_diagram.jpg The ridge runs just about 15 degrees of an East-West line, is the highest ridge on the building and is the highest point for some distance (there are trees 80m to the South), barring a vertical phased array VHF TV antenna. I can't really see how a signal striking the roof would reach the antenna, working on the basis of angle of refection = angle of incidence. Is this installation likely to case me any problems? I am rather short on other options due to the presence of steel sheds and fences. Getting the antenna clear of all of these would probably require something like a 100m+ cable, either buried or strung overhead, neither of which is practical (nor the cable length). The cable run from the ridge to my office works out at about 10m. I will have a redundant antenna a couple of metres along the ridge from the main, disconnected. If antenna #1 were to fail, I would just unplug the antenna extension cable in the loft from #1 and connect to antenna #2. I have spotted a splitter on eBay that is good for 10-1880MHz and includes power passing on one output - I guess that this means I am still able to power the active antenna as normal provided that at a receiver is connected to that output. Any comments on this would be much appreciated. Cheers M ___ 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.
Re: [time-nuts] Mounting GPS Antenna on Steel Roof
Brooke Clarke wrote: Hi Matthew: Some antennas are receptive to signals coming up from below. Since the signal is circularly polarized the first reflection is supposed to be down something like 20 dB, but the second reflection will be much stronger, so you would also need to look at those. Have Fun, Brooke Clarke Brooke The interaction between the antenna and the roof is a near field problem and its more complex than one may at first suspect. To achieve reasonable accuracy you need to either measure the effects or use EM modeling techniques. Bruce ___ 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.
Re: [time-nuts] Mounting GPS Antenna on Steel Roof
Matthew, Height of antenna is not important, but being clear of obstructions and large metallic objects are. Can you mount it on a pole at the end of the garden? As long as the antenna can see a large chunk of sky you should be OK. If you have a handheld GPS then check out the best site for maximum satellites. Rob Kimberley -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Matthew Smith Sent: 04 March 2008 05:08 To: Time Nuts List Subject: [time-nuts] Mounting GPS Antenna on Steel Roof Hi Folks Further to the cable splicing thread, I have been having a discussions off-list with Didier regarding the placement of my antennas on the ridge cap of my roof. There is certain concern that I may have issues with reflections - can anyone confirm whether or not this is the case? Here is a terrible diagram (I cannot for the life of me figure out how to draw solid, straight lines with the Gimp) of the proposed installation: http://www.smiffysplace.com/files/antenna_diagram.jpg The ridge runs just about 15 degrees of an East-West line, is the highest ridge on the building and is the highest point for some distance (there are trees 80m to the South), barring a vertical phased array VHF TV antenna. I can't really see how a signal striking the roof would reach the antenna, working on the basis of angle of refection = angle of incidence. Is this installation likely to case me any problems? I am rather short on other options due to the presence of steel sheds and fences. Getting the antenna clear of all of these would probably require something like a 100m+ cable, either buried or strung overhead, neither of which is practical (nor the cable length). The cable run from the ridge to my office works out at about 10m. I will have a redundant antenna a couple of metres along the ridge from the main, disconnected. If antenna #1 were to fail, I would just unplug the antenna extension cable in the loft from #1 and connect to antenna #2. I have spotted a splitter on eBay that is good for 10-1880MHz and includes power passing on one output - I guess that this means I am still able to power the active antenna as normal provided that at a receiver is connected to that output. Any comments on this would be much appreciated. Cheers M -- Matthew Smith Smiffytech - Technology Consulting Web Application Development Business: http://www.smiffytech.com/ Personal: http://www.smiffysplace.com/ LinkedIn: http://www.linkedin.com/in/smiffy ___ 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. ___ 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.
Re: [time-nuts] Mounting GPS Antenna on Steel Roof
Quoth Rob Kimberley at 2008-03-04 19:29... Height of antenna is not important, but being clear of obstructions and large metallic objects are. Can you mount it on a pole at the end of the garden? I can, but the end of the garden is some 50 metres from the house, which brings back my concern of excessive cable lengths. We're in a bit of a weird situation - it's a rural location, but there are sheds, water tanks and all sorts dotted around and cables can only really be run along (steel) fences as vehicular access is required all around. (Think of a farm and you wouldn't be far off.) I had thought about putting the time server in the big shed and running an underground Ethernet cable (this is a fairly reasonable proposition) until the reflection issue came up - the shed (also steel) has a North to South roof, so the problem would be even worse. Cheers M -- Matthew Smith Smiffytech - Technology Consulting Web Application Development Business: http://www.smiffytech.com/ Personal: http://www.smiffysplace.com/ LinkedIn: http://www.linkedin.com/in/smiffy ___ 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.
Re: [time-nuts] Mounting GPS Antenna on Steel Roof
I hope we aren't running Matthew around in circles here for nothing. Multipath in a GPS situation is a problem where the differences in path length are significant relative to the time accuracy desired. If you are trying to make a measurement on a city sidewalk with large reflective objects above you, the differences in path lengths could be hundreds of meters. An antenna mounted less than a meter above a reflective ridge cap should be no problem. I suspect the time errors introduced, if any, will be much, much less than the other errors in the system. Also remember that you could solve one problem (potential multipath error of a few nanoseconds from a nearby reflector) but add another (differences in propagation speed of coax over temperature) by moving the antenna far away. Regards, Keith -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Matthew Smith Sent: Tuesday, March 04, 2008 1:36 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Mounting GPS Antenna on Steel Roof Quoth Rob Kimberley at 2008-03-04 19:29... Height of antenna is not important, but being clear of obstructions and large metallic objects are. Can you mount it on a pole at the end of the garden? I can, but the end of the garden is some 50 metres from the house, which brings back my concern of excessive cable lengths. We're in a bit of a weird situation - it's a rural location, but there are sheds, water tanks and all sorts dotted around and cables can only really be run along (steel) fences as vehicular access is required all around. (Think of a farm and you wouldn't be far off.) I had thought about putting the time server in the big shed and running an underground Ethernet cable (this is a fairly reasonable proposition) until the reflection issue came up - the shed (also steel) has a North to South roof, so the problem would be even worse. Cheers M -- Matthew Smith Smiffytech - Technology Consulting Web Application Development Business: http://www.smiffytech.com/ Personal: http://www.smiffysplace.com/ LinkedIn: http://www.linkedin.com/in/smiffy ___ 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. ___ 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.
Re: [time-nuts] Mounting GPS Antenna on Steel Roof
Matthew, You mentioned Time Server..is this your only GPS or do you have other more accurate timing requirements? Unless you are working on nanosecond type accuracy, I don't see that mounting your antenna on the metal roof is going to cause you any practical problems. If all you are interested in is taking time from your GPS over Ethernet using NTP, then all will work fine. Rob Kimberley -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Matthew Smith Sent: 04 March 2008 09:36 To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Mounting GPS Antenna on Steel Roof Quoth Rob Kimberley at 2008-03-04 19:29... Height of antenna is not important, but being clear of obstructions and large metallic objects are. Can you mount it on a pole at the end of the garden? I can, but the end of the garden is some 50 metres from the house, which brings back my concern of excessive cable lengths. We're in a bit of a weird situation - it's a rural location, but there are sheds, water tanks and all sorts dotted around and cables can only really be run along (steel) fences as vehicular access is required all around. (Think of a farm and you wouldn't be far off.) I had thought about putting the time server in the big shed and running an underground Ethernet cable (this is a fairly reasonable proposition) until the reflection issue came up - the shed (also steel) has a North to South roof, so the problem would be even worse. Cheers M -- Matthew Smith Smiffytech - Technology Consulting Web Application Development Business: http://www.smiffytech.com/ Personal: http://www.smiffysplace.com/ LinkedIn: http://www.linkedin.com/in/smiffy ___ 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. ___ 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.
Re: [time-nuts] Mounting GPS Antenna on Steel Roof
My experience is that when severe multipath occurs, even when short distances are involved, the GPS receiver seems to get utterly confused and won't provide a solution. When I had my GPS antenna only about 2 feet away (above and to the side) from the top of a signal generator on the top of a cabinet (offering a 19x24 reflective surface to the South-East of the antenna), the Thunderbolt receiver had a hard time performing a self survey and had extended hold-over periods. When I moved the antenna up and aside to the West by another 2 feet, the problem went completely away. There was no other significant metal object in the area. The problem could be reproduced, so it was not a one time event. This was when I was using an inexpensive GPS antenna (not mag-mount, but similarly priced), I have not verified that the Symmetricom or the Trimble Bullet antenna in the same location would have the same problem. Didier KO4BB Keith Payea [EMAIL PROTECTED] wrote: I hope we aren't running Matthew around in circles here for nothing. Multipath in a GPS situation is a problem where the differences in path length are significant relative to the time accuracy desired. If you are trying to make a measurement on a city sidewalk with large reflective objects above you, the differences in path lengths could be hundreds of meters. An antenna mounted less than a meter above a reflective ridge cap should be no problem. I suspect the time errors introduced, if any, will be much, much less than the other errors in the system. Also remember that you could solve one problem (potential multipath error of a few nanoseconds from a nearby reflector) but add another (differences in propagation speed of coax over temperature) by moving the antenna far away. Regards, Keith -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Matthew Smith Sent: Tuesday, March 04, 2008 1:36 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Mounting GPS Antenna on Steel Roof Quoth Rob Kimberley at 2008-03-04 19:29... Height of antenna is not important, but being clear of obstructions and large metallic objects are. Can you mount it on a pole at the end of the garden? I can, but the end of the garden is some 50 metres from the house, which brings back my concern of excessive cable lengths. We're in a bit of a weird situation - it's a rural location, but there are sheds, water tanks and all sorts dotted around and cables can only really be run along (steel) fences as vehicular access is required all around. (Think of a farm and you wouldn't be far off.) I had thought about putting the time server in the big shed and running an underground Ethernet cable (this is a fairly reasonable proposition) until the reflection issue came up - the shed (also steel) has a North to South roof, so the problem would be even worse. Cheers M -- Matthew Smith Smiffytech - Technology Consulting Web Application Development Business: http://www.smiffytech.com/ Personal: http://www.smiffysplace.com/ LinkedIn: http://www.linkedin.com/in/smiffy ___ 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. ___ 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. ___ 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.
Re: [time-nuts] Mounting GPS Antenna on Steel Roof
Brooke Clarke wrote: Hi Matthew: Some antennas are receptive to signals coming up from below. Since the signal is circularly polarized the first reflection is supposed to be down something like 20 dB, but the second reflection will be much stronger, so you would also need to look at those. Have Fun, Brooke Clarke Brooke Surely the response of antenna to a reflected circularly polarised wave depends on whether wave the is reflected from behind or in front of the antenna? When viewed in the opposite direction to the wavefront propagation an RHCP wave looks like an LHCP wave. Also imperfect reflectors tend to scatter the wave and only partly convert the polarisation direction. Bruce ___ 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.
Re: [time-nuts] Mounting GPS Antenna on Steel Roof
Brooke Clarke wrote: Hi Bruce: Yes. There was a prior thread about using X band offset parabolic TV antennas with a stock GPS antenna. The idea being to aim the beam at a WAAS GPS satellite. I heard it worked well even though cross pol should have made for poor results. How to find out about where the WAAS GPS sats are located and if the M12+T will work with them? Have Fun, Brooke Clarke Brooke Some idea of the complexities introduced by nearby reflectors/obstacles can be found in: http://www.uni-stuttgart.de/gi/research/schriftenreihe/quo_vadis/pdf/hannah.pdf WAAS The receiver will receive WAAS satellite data if and only if it can process the PRN codes and message formats used by such satellites. some dated WAAS info: http://www.gpsinformation.net/exe/waas.html Bruce ___ 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.
Re: [time-nuts] Mounting GPS Antenna on Steel Roof
I use a Fiber Optic Antenna Link FOL-100 from Truetime. However, I don't know of anything else out there does something similar. -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Matthew Smith Sent: Tuesday, March 04, 2008 3:36 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Mounting GPS Antenna on Steel Roof Quoth Rob Kimberley at 2008-03-04 19:29... Height of antenna is not important, but being clear of obstructions and large metallic objects are. Can you mount it on a pole at the end of the garden? I can, but the end of the garden is some 50 metres from the house, which brings back my concern of excessive cable lengths. We're in a bit of a weird situation - it's a rural location, but there are sheds, water tanks and all sorts dotted around and cables can only really be run along (steel) fences as vehicular access is required all around. (Think of a farm and you wouldn't be far off.) I had thought about putting the time server in the big shed and running an underground Ethernet cable (this is a fairly reasonable proposition) until the reflection issue came up - the shed (also steel) has a North to South roof, so the problem would be even worse. Cheers M -- Matthew Smith Smiffytech - Technology Consulting Web Application Development Business: http://www.smiffytech.com/ Personal: http://www.smiffysplace.com/ LinkedIn: http://www.linkedin.com/in/smiffy ___ 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. ___ 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.
Re: [time-nuts] Mounting GPS Antenna on Steel Roof
Consider a television tripod and mast to elevate the GPS antenna above the roof... Jack Hudler wrote: I use a Fiber Optic Antenna Link FOL-100 from Truetime. However, I don't know of anything else out there does something similar. -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Matthew Smith Sent: Tuesday, March 04, 2008 3:36 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Mounting GPS Antenna on Steel Roof Quoth Rob Kimberley at 2008-03-04 19:29... Height of antenna is not important, but being clear of obstructions and large metallic objects are. Can you mount it on a pole at the end of the garden? I can, but the end of the garden is some 50 metres from the house, which brings back my concern of excessive cable lengths. We're in a bit of a weird situation - it's a rural location, but there are sheds, water tanks and all sorts dotted around and cables can only really be run along (steel) fences as vehicular access is required all around. (Think of a farm and you wouldn't be far off.) I had thought about putting the time server in the big shed and running an underground Ethernet cable (this is a fairly reasonable proposition) until the reflection issue came up - the shed (also steel) has a North to South roof, so the problem would be even worse. Cheers M ___ 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.
