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Re: [IRCA] 9/30/16 DU chase from IL



Merv posted details on the mwoffsets list Steve, but possibly more detailed than the IRCA list needs!

A quick precis from mwoffsets:

"Using winradio G31DDC as the receiver.
Have a signal generator locked to the 10MHz output of a GPS disciplined reference oscillator, Using spectrumlab to display the waterfall from the receiver with about a 5 ­ 10 Hz span"

The signal generator is used to update receiver calibration for simple offsets, but he calibrates Spectrumlab as well to get higher accuracy offsets using his own software.

Hope that helps.

best wishes,

Nick




For the quick method I inject a signal at the dial frequency of the receiver and use the â??calibrateâ?? facility on the G31DDC to align it exactly on the spectrumlab â??zeroâ?? display ... then simply read the unknown carrier from the spectrumlab display ... this will give one decimal place without any problems ... and once calibrated the G31DDC is generally good even when you change frequencies ... but can quickly check â??dial freqâ?? calibration at anytime by re-injecting a carrier at nominal.


For more accurate frequency readout I have a bit of software that uses an injected frequency (off nominal) to calibrate spectrumlab then interpolate that of the unknown ... it requires manually setting up the offset reference. Iâ??ve watched the 4QO/4QB TX pair on 855kHz (which use to be phase locked but recently it appears only one remains so) during ground wave propagation at midday track +/- 50 microhertz of true ... as we move away from midday you can see the variation from nominal change as the number of ionospheric reflections increase resulting in a perceived â??dopplerâ?? shift on the received signal because of multi-pathing.

I now have a LAN controllable, dual channel signal generator so I am in the process of writing the software to automate this process and use a second reference (one either side of the unknown) to make the measurement. The software talks to the receiver, spectrumlab and the signal generator.


At 00:56 07-10-16, you wrote:
Merv has a very professional approach to nailing these offsets down, so
I'd defer to him myself on this topic.

....would love to learn more about this if possible.

Steve




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Nick Hall-Patch
Victoria, BC
Canada
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