sensors-21-02210.pdfsensors-21-02210.pdfGoal is to determine short term fluctuations in effective optical path from WWV and other beacons (NYC) through ionosphere.
One method is to measure phase fluctuations of a CW carrier on short time scales. This can be done with an SDR that is tuned near zero beat, so that lower mixing product phase reflects carrier phase.
GPS-disciplined receiver can be used to determine stability of local oscillator in SDR.
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ISM bands, can broadcast 1 W!
WWV: Minuts 8 from WWV and minute 48 from WWVH send out ionosphere diagnostic signals. See https://www.nist.gov/pml/time-and-frequency-division/time-services/wwvwwvh-scientific-modulation-working-group
These each last 45 seconds.
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Transmitter RWM in Moscow transmits a CW waveform for around 8 minutes on the half hour, at frequencies that are close to WWV, namely (see https://en.wikipedia.org/wiki/RWM) 4.996 MHz with 5 kW and on 9.996 and 14.996 MHz with 8 kW
So at 15 MHz that's a wavelength of 20m. Should be workable at 2000 UT which is afternoon (4 to 5 pm). VOCAP above is for 8 kW transmit power.
Web SDrs
MA http://sigmasdr.ddns.net:8073/
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| item | part number | vendor | price | notes | references | status |
|---|---|---|---|---|---|---|
| magnetic loop antenna | DXE-RF-PRO-1B | DX engineering | 675 | have one, need one | ordered 8/3/2023 Order #4433160 | |
preamp | DXE-RPA-2 | 250 ea | BNC 12-18 V dc power at 150 mA | dxe-rpa-2.pdf | ordered | |
linear DC power supply for preamps | Tekpower TP3005T Variable Linear DC Power Supply, 0-30V @ 0-5A | amazon.com | 80 | provides clean regulated power to preamps | ordered | |
| delay line for phase slip | DB64 | SRS | 695 | BNC | asked Helen on Aug 3 | |
| 50 ohm signal combiner | ZMSC-2-6+ | minicircuits | 74 | BNC | ZMSC-2-2.pdf | ordered 8/3/2023 Fed Ex ground order # M189BDEC83C0. |
| low pass 30 MHz | BLP-30+ | minicircuits | 50 | BNC place this after the preamp | ordered 8/3/2023 Fed Ex ground | |
| high pass at 2.6MHz | amazon | SMA, note there will be phase slips at WWV freq of 2.5MHz if this is used. Place it between antenna and preamp | https://www.amazon.com/gp/product/B01N9SHS7P/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1 | |||
| SDR radio | Airspy HF+ Discovery | Airspy | 184 | SMA | ordered 8/3/2023 | |
| GPS-disciplined osc. | GPSCSG V2.0 GPS Disciplined Oscillator GPSDO GPS Signal Generator Dual Output | ebay | 112 | SMA Adjustable frequency: 10KHz-220MHz - Frequency accuracy: ±0.2Hz - Output level: 12dBm±2dB (can be customized to any value from -10dBm to 10dBm; amplitude can be calibrated) - Frequency synthesizer crystal oscillator: TCXO - Phase noise: -132dBc at 10KHz - Output type: square wave - Harmonic rejection: even harmonics are better than -50dBc and odd harmonics are better than -10dBc Do we need a low pass filter on this? If so needs SMA connectors | can't find an online manual | ordered 8/1/2023 for mid-Aug delivery |
| Red Pitaya SDR + Linux computer | dual channel SDR with external clock input. | RedPitaya | 700 | SMA inputs but 0.1 header for clock input. | documentation on beacon monitoring at | ordered 8/8/2023 |
Fast storage scope option:
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one scope option: https://www.rigolna.com/products/digital-oscilloscopes/dho4000/
Bandwidths
If we're looking for variation in phase of the received signal on some timescale tau, we'll need a bandwidth of 1/tau. For millisec time scales this is 1 kHz. For microsecond time scales it's a whole MHz. SNR is going to be a major challenge! It's like the low pass filter on the output of a phase-locked loop.
Six-band beacon
https://turnislandsystems.com/meet-the-beaconblaster-6/
A First attempt:
an initial experiment, Aug 4 2023
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https://hamsci.org/cw-reverse-beacon-network-how-guide
One potentially interesting experiment:
Ham radio beacon freq is 28.22 MHz. ISM unregulated band is 27.18 MHz. We could set up an automated transmitter with coherent CW transmission on both of those bands. Doppler shift is proportional to frequency so fractional difference in Doppler is one part in 20, high freq gets bigger Doppler shift. For an achromatic change in optical path length the time delay change is a constant. and we get a phase shift that is proportional to frequency.
We could try this out with Russian RWM station at multiple frequencies at same time.
references
Operational HF DF systems employing real time superresolution processing.pdf
sensors-21-02210.pdfsensors-21-02210.pdf