[time-nuts] Building a GPSDO & trouble using Jupiter-T
ernieperes at aol.com
Sun Jan 29 02:01:14 EST 2012
please find on this link the info what you are looking for.
From: Ray Xu <rayxu123 at gmail.com>
To: time-nuts <time-nuts at febo.com>
Sent: Sun, Jan 29, 2012 7:51 am
Subject: [time-nuts] Building a GPSDO & trouble using Jupiter-T
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
xperience working with long-term precision/stability products (nor do I
ave the equipment to do so -- I think).
I'm using the Jupiter T (the one with the 10-pin header) GPS and its 10KHz
utput in an analog PLL that controls a 10MHz VCXO. It would be ideal for
e that if I were to multiply the 10MHz output up to 10GHz, I would get
bout a few Hertz or so of inaccuracy. It would also be ideal if I can
ave 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
nformation on the web regarding the VCXO's (or the PLL oscillator, in this
ase) short term accuracy effect on output frequency. I know that its
hort term accuracy depends on the "response time" of the PLL, which also
epends on the amount of jitter from the Jupiter-T's 10KHz output... I
now that the longer the time constant for the PLL, the better accuracy,
ut 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
hort-term accuracy? If the PLL time constant is only a few seconds, then
crystal shouldn't deviate in frequency by too much within a few seconds,
ssuming I'm using a crystal bought from a well-known manufacturer...or
ould it? I am inclined towards using oscillators that do not require any
ignificant warm up time...
For those who have experience using the Jupiter T GPS:
have bought this
could not get it to communicate via serial. So far, I do not have
ntenna available and so the antenna port is just left disconnected. When
turn it on, there is a 1pps and 10KHz signal and the TX line is at logic
igh. However, I cannot get it to communicate to anything else, even a
umb 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).
s my device a dud or am I doing something wrong?
Many inputs is highly appreciated. Thanks
3, Ray Xu
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