I'll risk exposing my ignorance to the list.... (i.e. open my mouth and prove it...)
I seem to recall a comment on the LOWFER list recently about the data decodes being much worse the previous night and a reply saying it was probably due to storms moving into the area between the LOWFER beacon and the receiving station. And in general the LOWFER activity tends to die off in the summer months due to thunder storm activity making it more difficult to hear anything at all. If we apply the same comments to WWVB, it is likely that the past few winter months are the prime time for relatively undisturbed WWVB reception and the coming summer months will be more difficult and a better measure of how good the receiver design might be. And IIRC, the best technique for use of LORAN was to make your readings at about the same time of the morning every day, preferably before sun-rise and the morning path disturbances took place. And I seem to recall a discussion on this list recently about using the time stamp info to verify which second you are measuring so you could lock an oscillator against a signal that wasn't always available. You had to keep a time stamp of the oscillator you are disciplining so you could compare it to WWVB or GPS time stamps after a long outage and verify you were measuring the same second and how far you had drifted. By extending that idea you could compare time stamps, measure the WWVB 1PPS differences for an hour or two to verify the standard deviation and average (median?) error and maybe watch the RF signal levels. This might help to identify disturbed conditions that might be causing errors in the received signal decode and timing. If the signal variations or SD indicate conditions are disturbed, continue hold-over of the oscillator, no adjustment. If signals are good, you have enough long(ish) term data to make an adjustment to the oscillator and go back to hold over until the next test period is complete. I'm assuming there is nothing new in this procedure since it is basically what was done manually with LORAN or WWVB. I would expect that somebody has already done a study to identify the best time of day and methods to use with WWVB for precision timing but I haven't done a search to find it. There are probably quite a few people on this reflector who would have the equipment and software to capture this sort of data and collect it centrally for further examination. It could be interesting if it hasn't been done already. Finally, I expect that using DSP for recovering the WWVB carrier information below the noise would be fairly successful. I seem to recall that knowing the expected phase and frequency of the signal is a primary advantage for using DSP to dig way under the noise. I would expect good DSP to add 20dB to the margin of any simple analog WWVB receiver. I wonder if this might be an application for crossed loops and stereo sound card with 96KHz sample rate. Could leak a bit of 50KHz from your 10MHz oscillator so the software has a known signal for comparison if needed. You could at least extract a lot of signal quality info with the DSP and processing available in the computer. I'm glad that someone else is working on this (not me) and I'll be very happy to read your results when done. Now I think I'll go back to hiding in the weeds..... 73, Doug. ==================================== Date: Sat, 26 Mar 2011 18:53:30 -0700 (PDT) From: "J. Forster" <[email protected]> To: "Discussion of precise time and frequency measurement" <[email protected]> Subject: Re: [time-nuts] WWVB Measurements Paul, I did that years ago in a qualitative way. I used a local reference of an HP 105B and the 117A w/ HP loop. I synced a Tek 7854 to the local standard and watched and averaged the recovered 60 KHz. I no longer remember the results well, but sometimes the "seeing" was <1uS P-P and on other days it was at least 10s of uS to hundreds of uS. This may be hard for some to believe, but the seeing seemed to depend on weather. A big front coming east would make the "seeing" much worse. This was just a casual observation. I never spent much time studying it. If I saw the seeing was horrid, I just left the stuff running and went away. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
