N017RW said:
Where do you see this information?
From what I read abut the NEO-6Q the backup battery (if connected or not dead) is there to maintain the RTC and RAM only.
Also, by classification, TCXOs are not contained in an 'oven' to maintain a constant temp.
They contain additional elements to measure and 'pull' or adjust the oscillator's output accordingly.
It sounds like your describing an OCXO or oven-controlled crystal oscillator.
I don't see any reference to that in uBox's data sheets.
But I'm always open to new or updates to information so please share if you wish.
The Temperature Controlled Xtal Oven is a Temperature Controlled frequency standard. Al least, that is how it functions in the communications gear I used on NTIA spectrum that had to meet frequency stability specs. Keeping the TCXO hot assured stability at power up. Some design aproaches used a warm-up period to come up to temp and resulting stability. I first thought that the TCXO could be drawing the battery down, as the gear I had been using for comms kept it hot all the time. The most simple way to diagnose a stability panel was to feel the side panel that the TCXO was under to see off was working. Cold was a nogo situation.
After pouring through most of the NEO-6 documents, I contacted them with a series of questions to try to understand a little more about the configuration. My correspondence corrected some incorrect assumptions and confirmed some others.
Their implementation of the TCXO is a frequency standard for the RTC. It is only brought to temperature when the main battery is inserted and powered on. RTC calibration data is created as the TCXO warms up and increases RTC accuracy. So, I found that wasn't a dead BBRAM battery cause. The RTC accuracy is critical to compare to the GPS time data to determine distance ( time differentials). Until the RTC calibrations were completed, the GPS data produced errors that decrease as the RTC accuracy increases.
As far as predicting availability, the Almanac, when properly stored, along with the RTC offsets as the TCXO achieves max stability are much like using Kepelarian Elements to predict a satellite pass. I spent a good bit of time in the early 1990s learning how to communicate through low earth orbiters, the space shuttle packet robot and later the ISS APRS robot. Since they are all elliptical in orbit, there had to be a way to remove guesswork and point antennas to the right bird at the right time. I equate the Almanac and accurate time base to be the equivalent. It doesn't aim antennas, it just helps limit the focus to what should be visible at the time of flight. If the battery is dead, or charging to above minimum usable voltage, the GPS performance is slowed until this critical info is created RTC (calibrations) and downloaded ( almanac). On consecutive flights, it is retained ( thanks to Dadcat for getting that sorted out)
This could all be an absolute leap in the wrong direction, but it is what I gathered from what I knew and thought I knew. Since there is too much worry about being copied or revealing who was copied in these hobby applications, there is very little in the way of a manufacturers flow chart to base proper operation on. With that in mind, I fully accept that my understanding may change as more concrete data is found and shared.