An ADC0808 directly connected to the GPS antenna? Not even a DC blocking capacitor? So it receives also the 5V antenna supply?
On Wed, Dec 24, 2014 at 7:42 AM, Chuck Harris <cfhar...@erols.com> wrote: > It's Alive!!! > > The MGPS module was saying there was an A-to-D fault > and a Feedline fault. Suspicious of the common element, > I traced the signal path from the GPS antenna connector > to the input of the ADC, and it was a straight DC path. > Sure, there were a few chokes, and capacitors to ground > to filter out any stray 1.5GHz signal, and to keep the DC > circuitry from loading the antenna signal. > > I ordered up a new ADC converter, which was an ADC0808 by > National and TI. A small 28 pin quad J lead surface mount > package. It finally came, and I swapped it out this > afternoon. > > I was rather worried, as the failure mode could have been > simply a faulty converter, or it could be that something > happened on the antenna line that killed the converter. > > It was not evident how the GPS module knew there was an > A-to-D fault. It could have been something like a lack > of an end of conversion flag, or they could have been > using some extras of the 8 analog inputs to measure things > like power, ground, resistor dividers... I really don't > know... > > Powering the GPS module on the bench showed an immediate > improvement: The A-to-D converter fault condition was > no longer set! It was still showing an antenna line fault, > but since I didn't have an antenna connected, that was to > be expected. > > I put the GPS module back into the MGPS chassis, and > installed it in the MFS-209, and as soon as I connected > a good antenna, the antenna line fault indicator went > away.... So far so good. > > Some satellites started appearing on the display, and after > waiting for what seemed like forever, and the almanac was > finally updated. > > And... > > The system status changed to GPS Lock! And reports normal > operation. > > Now to let it cook for a few weeks and see how well this > ancient GPS RbDO performs. > > Thanks to all that offered tips and moral support. > > -Chuck Harris > > Chuck Harris wrote: >> >> And as I feared, the MGPS display is telling the truth, there >> is something wrong with the GPS module's ability to check the >> feed line for shorts and opens, and something wrong with the >> motherboard's ADC module. >> >> At least the communication between the MGPS and the GPS engine >> is working properly... >> >> -Chuck Harris > > _______________________________________________ > 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.