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.
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
