QHY GPS Box
What many people know is that with the NAVSTAR GPS satellite system (and others such as GLONASS or Galileo), you can determine your geographical position worldwide in real time, within metres. What many may not know is that this requires highly accurate time information. Therefore, the GPS satellites have internal atomic clocks on board, which are synchronized between the satellites with high precision.
This time information is retrievable and decodable and can thus also be used in other technical applications. Together with the QHY GPS Box and some camera models a high-precision time correlation to the images is possible (start/end of exposure). The time allocation plays a major role in astronomical observations of objects that change their brightness during the observation period. For example, in the photometry of minor planets or variable stars, in the observation of star occultations and exo planetary transits too.
The GPS time base is much more accurate than the internal clocks of PCs and/or laptops, from which normally the time allocation of the camera shutter is read.
Technical description of the QHY GPS Box
The QHY GPS BOX is a compact camera accessory that provides high-precision GPS hardware time scales allowing some QHYCCD cameras to obtain accurate time information of the camera's exposure time.
In addition, this information is returned to the camera internally and added to the image data after the start of one frame of the image. GPS timing information and image information are therefore completely consistent. No confusion is created due to transmission, buffering or other reasons. It is very convenient to use and read.
The QHY GPS BOX has a built-in GNSS module and can currently provide both pure GPS operation and GPS/Beidou dual-mode operation. The latter can be set to work in GPS mode or Beidou mode through software.
The GPS BOX also contains a local 10MHz voltage-controlled crystal oscillator (VCXO) that provides an internal 0.1us resolution timing clock. At the same time, the timing clock is reset by the PPS model of the GNSS module. Therefore, the clock and the GNSS system's second start time are strictly aligned, and the error is within a range of 20ns to 100ns.
QHY GPS BOX and camera are connected by 6-type aviation plug. Contains the following signals:
Pin Function Description 1 Ground 2 Communication clock. Level 1.8V or 2.5V Output to GPS BOX by camera. Frequency <= 40MHz 3 Communication data. Level 1.8V or 2.5V Single-wire serial communication using synchronous feature head + data mode. 4 Configuration Data Level 1.8V or 2.5V Beidou / GPS selection 5 Measure the waveform Level 1.8V or 2.5V The camera measures the waveform based on the electronic shutter generated by the image sensor drive and outputs it to the GPS BOX 6 + 5 Volt Camera output power supply
Note that when choosing a camera, you must specify the special version with a GPS socket. The socket used in the standard version is a 5-core aviation socket. When the camera is working, an electronic shutter measurement waveform is generated every frame. The waveform is output to the GPS BOX. After the GPSBOX performs high-precision time measurement, it outputs a serial header data and sends it back to the camera. The camera records these data after the frame header of each frame (replacing some pixel values in the first few lines)
QHY GPS has a perfect fault tolerance mechanism. It can deal with the situation when the PPS signal is lost. If the PPS signal is lost, after 50.0us, an internal second step will be used. And this information will be recorded. For timing information without a PPS signal, a cumulative timing error of 50us per second will be generated.
When the PPS signal is restored, the PPS signal will be used again to reset the internal timer. Therefore, it has GPS timing accuracy after recovery and will not accumulate previous errors.
The QHY GPS will also output a GPS measurement value of an internal 10MHz clock every second. This measurement value can be used to accurately calibrate the frequency of the internal 10MHz crystal oscillator in later software to avoid an internal 10MHz crystal oscillator error and temperature drift
- QHY42-PRO und QHY163M have 6-Pin ports and support the QHY-GPSBOX without further modification.
In addition, the QHY6060, QHY4040, QHY2020 and QHY183M can be modified with the 6-Pin connector to be compatible with the QHY GPS BOX.
Remark about the QHY 600 EB: QHYCCD offers a special price for converting the accessory socket for existing EB owners if they want to upgrade to the PRO-L model first before upgrading to the full PRO version.
If you have any further questions, please send us an email to kontakt (at) baader-planetarium.de.