All --
Just FYI, TAPR is working not only on the Reflock II, which can phase
lock virtually any oscillator with a DC control voltage to either
another frequency source, or to a 1pps from a GPS, but also an auxiliary
board specifically designed to work with the SDR1000. It will provide a
low-phse-noise 100MHz oscillator as well as an optional 10MHz TCXO to
serve as reference (if you have a 1pps source, or other frequency
standard, you can use that instead).
The Reflock II will be shipping within a few weeks (we hope to have them
for sale at the ARRL/TAPR Digital Communications Conference in Santa
Ana, CA on Sep. 23-25). The SDR-1000 accessory board is just going into
prototype but it's a pretty straightforward project so hopefully won't
take too long to get ready for production.
73,
John
----
Jim Lux wrote:
At 05:53 PM 9/6/2005, ecellison wrote:
Jim
I knew i could bait you! (smile). I am sort of 'gobbled up' by this
precision thing! I do have my GPS receiver and am ready for the 1 part
to the -13 (give or take a couple of exponents!). Can we take the 200
mhz standard out of the SDR 1000 as is? Actually I visit WWV
frequently with the phase display, from 20 meters, where I been
operating, and am actually pretty pleased with the long term accuracy
of the radio. Course I fall asleep and leave it on.
Eric
You can skin that cat a number of ways.
One way: pick off a sample of the 200 MHz and run it into a suitable
divider/counter widget (like the one Brooke Shera described a few years
back). Adjust in software
Second way: Get a 200 MHz source that has a "steering input" and use it,
instead of the 10 MHz source in a Z8301 type unit (or Brooke Shera's
board). You could drive a divide by 20 with the 200 MHz source and use
it in a system designed for 10 MHz unchanged.
Third way: Get a high quality 200 MHz phase locked source and lock it to
your 10 MHz source. ( you might be able to do this with an HP 8640..and
used 8640s are cheaper than brand new 200 MHz phase locked sources)
Fourth way: Measure the DDS output frequency against the 1pps or the 10
MHz, and calculate from there. You could either calculate a correction,
and retune the DDS (but that might screw up the spur minimization
techniques), or feed that into the IF processing in the software.
Fifth way: Generate a comb from your stable reference, making sure that
the comb spans the frequency bands you'll tune over. In software, find
the comb, subtract it out, and use it to calibrate the rest. This is
like using a crystal marker generator to calibrate your analog dial.
The latter is what I'm doing at work, and I'll have a publically
releasable descriptionof the details in a month or so. Suffice it to say
today that we calibrate an arbitrary number of free running SDR1Ks and
their PC sound cards to several ppb, including phase, especially if
temperatures are reasonably stable.
James Lux, P.E.
Spacecraft Radio Frequency Subsystems Group
Flight Communications Systems Section
Jet Propulsion Laboratory, Mail Stop 161-213
4800 Oak Grove Drive
Pasadena CA 91109
tel: (818)354-2075
fax: (818)393-6875
------------------------------------------------------------------------
_______________________________________________
FlexRadio mailing list
FlexRadio@flex-radio.biz
http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz