[time-nuts] precision frequency/time/amplitude reference
kb8tq at n1k.org
Tue Oct 10 11:27:38 EDT 2017
> On Oct 9, 2017, at 8:49 PM, jimlux <jimlux at earthlink.net> wrote:
> On 10/9/17 8:02 AM, Bob kb8tq wrote:
>> Pick a couple of local broadcast stations and record them. That will give you a baseline
>> for each of the parameters you are after in real time. They *will* drift.
>> Past that, I’d go with a sweep of each node before installation. That will give you the
>> frequency response and (to some degree) a guess for noise and spurs.
> The RTL-SDR has only about 2 MHz BW, so you'd have to be lucky to have a broadcast station in the band (and if I'm looking at trying to image Jupiter with an interferometer, at 20.1 MHz, I'm not sure that the SW broadcast bands cover within 2MHz - and you'd be subject to the vagaries of propagation.. low sunspots = low critical frequency = not much skywave propagation for WWV).
> So a local reference would be nice. Originally, I thought about just radiating a CW tone (perhaps modulated with timecode), but then, I realized I'd also like to calibrate the RF chain in the receiver, so feeding a calibrated pulse that has spurs (hey, a "marker beacon" in old school radios with a analog dial)
Monitor for 55 minutes and calibrate for 5 minutes. Do the calibration in maybe 10 second segments spread
out over the hour.
The gotcha with any “radiated” signal is finding a band you can legally transmit it in ….. For an array a few feet on a
side, not a big deal. For something a mile or two across, it begins to be an issue.
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