https://projects.osmocom.org/https://projects.osmocom.org/favicon.ico?16647414092022-07-23T15:02:52ZOpen Source Mobile CommunicationsOCTOI - Osmocom Community TDM over IP - Feature #5626: mechanical + electrical setup for GPS receiver at co-locationhttps://projects.osmocom.org/issues/5626?journal_id=244752022-07-23T15:02:52Zlaforge
<ul><li><strong>Status</strong> changed from <i>New</i> to <i>In Progress</i></li></ul><p>The spare Ericsson GPS receivers I have here are GPS03 (successor of GPS02), attached a MA-700G antenna and loked at the current consumption. The absolute peak was 161 mA during start-up. Once the GPS signal is locked (green led continuously on), it's 97..103mA @ 12V.</p>
<p>At the predicted worst-case loop resistance of 100m CAT5 of 20 Ohms, that would be a 2V voltage drop for the average power consumption, and 3.2V on peak.</p>
<p>Will do some voltage range tests next, and also insert a 20Ohm series resistor.</p> OCTOI - Osmocom Community TDM over IP - Feature #5626: mechanical + electrical setup for GPS receiver at co-locationhttps://projects.osmocom.org/issues/5626?journal_id=244762022-07-23T15:07:31Zlaforge
<ul></ul><p>Reducing the voltage (after lock was acquired) showed operation down to about 6.5V. Current consuption increased to 140mA, so there's some DC/DC converter inside (good).</p>
<p>Cold-Starting the receiver at 7V worked fine; idle current 140-147mA.</p>
<p>In all of those tests the RS485 drivers were open, i.e. not driving any capacitive or resistive load yet.</p> OCTOI - Osmocom Community TDM over IP - Feature #5626: mechanical + electrical setup for GPS receiver at co-locationhttps://projects.osmocom.org/issues/5626?journal_id=244772022-07-23T15:57:06Zlaforge
<ul><li><strong>File</strong> <a href="/attachments/5263">nmea_data.png</a> <a class="icon-only icon-download" title="Download" href="/attachments/download/5263/nmea_data.png">nmea_data.png</a> added</li><li><strong>File</strong> <a href="/attachments/5264">1pps.png</a> <a class="icon-only icon-download" title="Download" href="/attachments/download/5264/1pps.png">1pps.png</a> added</li><li><strong>File</strong> <a href="/attachments/5265">1pps_zoom.png</a> <a class="icon-only icon-download" title="Download" href="/attachments/download/5265/1pps_zoom.png">1pps_zoom.png</a> added</li></ul><p>regarding capacitance, <a class="external" href="https://en.wikipedia.org/wiki/Category_5_cable">https://en.wikipedia.org/wiki/Category_5_cable</a> states 52pF/m so about 5.2nF for 100m. To that we'd have to add the capacitance of the RS422 receiver input, but for sure it's just going to be some pF, so negligable.</p>
So, I set up as follows:
<ul>
<li>22 ohms series resistance between PSU and GPS 03</li>
<li>100 ohms parallel to 4.7nF termination of 1PPS <strong>or</strong> NMEA-Tx pair</li>
<li>current consumption increased from 100mA to 120mA</li>
<li>scope traces of signal looked fine to me</li>
<li>receiver operation down to about 10V PSU output voltage</li>
</ul>
Furthermore:
<ul>
<li>terminating the second transmitter (NMEA Tx) increased current consumption from 120mA to 148mA</li>
<li>operation of receiver still down to 10V from the voltage source</li>
<li>cold start also possible from 10V voltage source</li>
</ul>
<p>So all in all, we can conclude it is safe to operate the GPS03 with the chosen antenna over 100m of CAT5.</p>
<p>some scope traces of the data on the "remote" end of the simulated CAT5:</p> OCTOI - Osmocom Community TDM over IP - Feature #5626: mechanical + electrical setup for GPS receiver at co-locationhttps://projects.osmocom.org/issues/5626?journal_id=244782022-07-23T15:57:55Zlaforge
<ul><li><b>Checklist item</b> <input type='checkbox' class='checklist-checkbox' checked disabled> <i>investigate if 12V phantom voltage via 100m CAT5 (~20 ohms loop resistance) is viable</i> set to Done</li></ul> OCTOI - Osmocom Community TDM over IP - Feature #5626: mechanical + electrical setup for GPS receiver at co-locationhttps://projects.osmocom.org/issues/5626?journal_id=244792022-07-23T16:54:11Zlaforge
<ul><li><strong>File</strong> <a href="/attachments/5266">cat5em_1.jpg</a> <a class="icon-only icon-download" title="Download" href="/attachments/download/5266/cat5em_1.jpg">cat5em_1.jpg</a> added</li><li><strong>File</strong> <a href="/attachments/5267">cat5em_2.jpg</a> <a class="icon-only icon-download" title="Download" href="/attachments/download/5267/cat5em_2.jpg">cat5em_2.jpg</a> added</li><li><strong>File</strong> <a href="/attachments/5268">1pps_new.png</a> <a class="icon-only icon-download" title="Download" href="/attachments/download/5268/1pps_new.png">1pps_new.png</a> added</li><li><strong>File</strong> <a href="/attachments/5269">1pps_new_edge.png</a> <a class="icon-only icon-download" title="Download" href="/attachments/download/5269/1pps_new_edge.png">1pps_new_edge.png</a> added</li></ul><p>Building the entire setup (22R on 12V rail, 100R || 4.7nF on each of the three differential pairs) on a small adapter board (mis-appropriating one of my RJ45 jumper box PCB) looks like this:</p>
<p><img src="https://projects.osmocom.org/attachments/download/5266/cat5em_1.jpg" alt="" /><br /><img src="https://projects.osmocom.org/attachments/download/5267/cat5em_2.jpg" alt="" /></p>
<p>For some reason the waveform of the 1PPS now looks much more reasonable. Maybe I had a bad probe GND connection or something last time. It's a nice 50us square pulse. Rise time has not changed.</p>
<p><img src="https://projects.osmocom.org/attachments/download/5268/1pps_new.png" alt="" /></p>
<p><img src="https://projects.osmocom.org/attachments/download/5269/1pps_new_edge.png" alt="" /></p> OCTOI - Osmocom Community TDM over IP - Feature #5626: mechanical + electrical setup for GPS receiver at co-locationhttps://projects.osmocom.org/issues/5626?journal_id=245782022-08-04T15:22:19Zlaforge
<ul><li><strong>% Done</strong> changed from <i>0</i> to <i>20</i></li></ul><p>the over voltage protection devices for the RS485/422 signals (DCO SD2 MD) have meanwhile arrived. However, the part for 12V was missing from the shipment (despite listed on packing list). Have complained with the supplier.</p> OCTOI - Osmocom Community TDM over IP - Feature #5626: mechanical + electrical setup for GPS receiver at co-locationhttps://projects.osmocom.org/issues/5626?journal_id=246382022-08-14T07:54:01Zlaforge
<ul><li><strong>File</strong> <a href="/attachments/5283">dco_sd2_md_hf5.jpg</a> <a class="icon-only icon-download" title="Download" href="/attachments/download/5283/dco_sd2_md_hf5.jpg">dco_sd2_md_hf5.jpg</a> added</li><li><strong>File</strong> <a href="/attachments/5284">dco_sd2_md_hf5-internal.jpg</a> <a class="icon-only icon-download" title="Download" href="/attachments/download/5284/dco_sd2_md_hf5-internal.jpg">dco_sd2_md_hf5-internal.jpg</a> added</li></ul><p>in case anyone is curious, this is the internals of the "DCO SD2 MF HF 5":</p>
<p><a class="thumbnail" title="dco_sd2_md_hf5.jpg" href="https://projects.osmocom.org/attachments/5283"><img alt="dco_sd2_md_hf5.jpg" src="https://projects.osmocom.org/attachments/thumbnail/5283/200" /></a>
<a class="thumbnail" title="dco_sd2_md_hf5-internal.jpg" href="https://projects.osmocom.org/attachments/5284"><img alt="dco_sd2_md_hf5-internal.jpg" src="https://projects.osmocom.org/attachments/thumbnail/5284/200" /></a></p> OCTOI - Osmocom Community TDM over IP - Feature #5626: mechanical + electrical setup for GPS receiver at co-locationhttps://projects.osmocom.org/issues/5626?journal_id=246392022-08-14T07:56:32Zlaforge
<ul><li><strong>File</strong> <a href="/attachments/5285">dco_sd2_md_hf5-schematics.png</a> <a class="icon-only icon-download" title="Download" href="/attachments/download/5285/dco_sd2_md_hf5-schematics.png">dco_sd2_md_hf5-schematics.png</a> added</li></ul><p>If I got it right, the schematics look like this:</p> OCTOI - Osmocom Community TDM over IP - Feature #5626: mechanical + electrical setup for GPS receiver at co-locationhttps://projects.osmocom.org/issues/5626?journal_id=246992022-08-22T19:10:06Zlaforge
<ul><li><b>Checklist item</b> <input type='checkbox' class='checklist-checkbox' checked disabled> <i>obtain OVP parts</i> set to Done</li></ul> OCTOI - Osmocom Community TDM over IP - Feature #5626: mechanical + electrical setup for GPS receiver at co-locationhttps://projects.osmocom.org/issues/5626?journal_id=248312022-08-31T18:49:32Zlaforge
<ul><li><strong>File</strong> <a href="/attachments/5305">rs422-ovp-board.jpg</a> <a class="icon-only icon-download" title="Download" href="/attachments/download/5305/rs422-ovp-board.jpg">rs422-ovp-board.jpg</a> added</li></ul><p>picture of the APU-sized RS422 OVP board that goes into the 1U enclosure:</p>
<p><a class="thumbnail" title="rs422-ovp-board.jpg" href="https://projects.osmocom.org/attachments/5305"><img alt="rs422-ovp-board.jpg" src="https://projects.osmocom.org/attachments/thumbnail/5305/200" /></a></p> OCTOI - Osmocom Community TDM over IP - Feature #5626: mechanical + electrical setup for GPS receiver at co-locationhttps://projects.osmocom.org/issues/5626?journal_id=248392022-09-01T06:41:18Zlaforge
<ul><li><strong>% Done</strong> changed from <i>20</i> to <i>40</i></li></ul><p>Did some more testing with the following chain:</p>
<ul>
<li>GPS antenna</li>
<li>GPS03</li>
<li>100m-rj45-resistance-and-capacitance-simulator</li>
<li>rs422 OVP + 12V injection board</li>
<li>USB-RS422 converter attached to my laptop / 1PPS to scope</li>
</ul>
<p>This setup was working fine for hours. It's still missing the DIN-rail OVP next to the GPS03.</p>
<p>I later swapped the 100m-simulator agaist an actual spool of 100m CAT5. Surprisingly, the RS422 signals still look excellent and the NMEA is correctly decoded. However, I think something is wrong with the phantom power, as it looks like the GPS03 is crashing repeatedly. IT does get a fix, but then soon after the first valid standard NMEA sentences, it starts all over again.</p> OCTOI - Osmocom Community TDM over IP - Feature #5626: mechanical + electrical setup for GPS receiver at co-locationhttps://projects.osmocom.org/issues/5626?journal_id=248412022-09-01T09:25:39Zlaforge
<ul></ul><p>laforge wrote in <a href="#note-11">#note-11</a>:</p>
<blockquote>
<p>I later swapped the 100m-simulator agaist an actual spool of 100m CAT5. Surprisingly, the RS422 signals still look excellent and the NMEA is correctly decoded. However, I think something is wrong with the phantom power, as it looks like the GPS03 is crashing repeatedly. IT does get a fix, but then soon after the first valid standard NMEA sentences, it starts all over again.</p>
</blockquote>
<p>false alarm. I introduced an overcurrent situation due to a bad connection, triggering the PTC fuse. The setup is now working fine with 100m of CAT5 on a spool.</p> OCTOI - Osmocom Community TDM over IP - Feature #5626: mechanical + electrical setup for GPS receiver at co-locationhttps://projects.osmocom.org/issues/5626?journal_id=248592022-09-05T16:03:00Zlaforge
<ul></ul><p>so with the end-to-end setup with icE1usb and the RS422 daughter board by <a class="user active" href="https://projects.osmocom.org/users/12">tnt</a> in place, I'm seeing brown-outs when feeding the 12V phantom supply to the GPS03 over the 100m cable :(</p>
<p>When feeding 12V at the input, I'm seeing about 7V with dips down to 5V on the GPS03, which then makes the 5V output side of its DC/DC converter dip.</p>
<p>Adding a 47uF tantalum capacitor on the 12V input of the GPS03 looks like it helps a bit, but doesn't make the brownout go away.</p>
<p>I don't want to add capacitance to the output side of the DC/DC as that might make it unstable.</p>
<p>Increasing the PSU voltage to 14V resolves the problem: The nominal 12V input to the GPS03 is about 8V with occasional dips to 7.1V. No scope-visible dips in the 5V DC/DC output rail of the GPS03.</p>
<p>So either we increase the 12V to 14V and hope it's ok, or we feed the 12V locally on the roof from a DIN rail PSU. I think the second is actually the safe option without relying on any hacks.</p> OCTOI - Osmocom Community TDM over IP - Feature #5626: mechanical + electrical setup for GPS receiver at co-locationhttps://projects.osmocom.org/issues/5626?journal_id=248602022-09-05T16:04:11Zlaforge
<ul></ul><p>I likely didn't see those brownouts in my existing testing as I only attached RS422 transceivers to Rx/Tx pairs but not to 1PPS.</p>
<p>Driving only either 1PPS or GPS-Tx seems to work even in the current end-to-end setup with 12V, so we are apparently just pushing it over the edge.</p> OCTOI - Osmocom Community TDM over IP - Feature #5626: mechanical + electrical setup for GPS receiver at co-locationhttps://projects.osmocom.org/issues/5626?journal_id=248742022-09-06T16:11:14Zlaforge
<ul><li><b>Checklist item</b> <input type='checkbox' class='checklist-checkbox' checked disabled> <i>end-to-end setup with OVP, GPS, antenna, etc. at laforge</i> set to Done</li></ul> OCTOI - Osmocom Community TDM over IP - Feature #5626: mechanical + electrical setup for GPS receiver at co-locationhttps://projects.osmocom.org/issues/5626?journal_id=249042022-09-15T15:24:01Zlaforge
<ul><li><b>Checklist item</b> <input type='checkbox' class='checklist-checkbox' checked disabled> <i>clarify mechanical mounting (antenna, din-rail) at co-location</i> set to Done</li></ul> OCTOI - Osmocom Community TDM over IP - Feature #5626: mechanical + electrical setup for GPS receiver at co-locationhttps://projects.osmocom.org/issues/5626?journal_id=249552022-09-23T08:33:46Zlaforge
<ul><li><strong>Status</strong> changed from <i>In Progress</i> to <i>Resolved</i></li><li><strong>% Done</strong> changed from <i>40</i> to <i>100</i></li></ul><p>new hub is fully deployed, GPS 1PPS arrives in the rack and icE1usb reports err=0 most of the time, i.e. the 2.048 MHz clock runs at 1PPS-disciplined 2048000 Hz.</p>