Hi guys I'm planning to build a GPSDO to use as a frequency ref for my GHz ventures.
I've done research in what other people have built - but I have no experience working with long-term precision/stability products (nor do I have the equipment to do so -- I think). I'm using the Jupiter T (the one with the 10-pin header) GPS and its 10KHz output in an analog PLL that controls a 10MHz VCXO. It would be ideal for me that if I were to multiply the 10MHz output up to 10GHz, I would get about a few Hertz or so of inaccuracy. It would also be ideal if I can have a PLL lock time of a few minutes while maintaining accuracy. However, right now as I am trying to design my project, I can't find enough information on the web regarding the VCXO's (or the PLL oscillator, in this case) short term accuracy effect on output frequency. I know that its short term accuracy depends on the "response time" of the PLL, which also depends on the amount of jitter from the Jupiter-T's 10KHz output... I know that the longer the time constant for the PLL, the better accuracy, but I do not want to wait, literally, hours for it to lock... Also, what is the advantage of using a OCXO instead of a VCXO in terms of short-term accuracy? If the PLL time constant is only a few seconds, then a crystal shouldn't deviate in frequency by too much within a few seconds, assuming I'm using a crystal bought from a well-known manufacturer...or could it? I am inclined towards using oscillators that do not require any significant warm up time... For those who have experience using the Jupiter T GPS: I have bought this http://www.ebay.com/itm/Navman-jupiter-T-Tu60-GPS-Kit-1pps-10khz-GPS-Module-/260790984470but I could not get it to communicate via serial. So far, I do not have an antenna available and so the antenna port is just left disconnected. When I turn it on, there is a 1pps and 10KHz signal and the TX line is at logic high. However, I cannot get it to communicate to anything else, even a dumb terminal. It does not respond to when I send a message ID to it. (Because of computer difficulties, I am using the PicKit 2's UART tool). Is my device a dud or am I doing something wrong? Many inputs is highly appreciated. Thanks -- __________ 73, Ray Xu KF5LJO _______________________________________________ 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.