sensors-21-02210.pdf sensors-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.

GPS receiver from ebay:

https://www.ebay.com/itm/285244181517?_trkparms=amclksrc%3DITM%26aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D252416%26meid%3D31841f706dd0486e93412310b010fbed%26pid%3D101195%26rk%3D1%26rkt%3D12%26sd%3D266216859978%26itm%3D285244181517%26pmt%3D1%26noa%3D0%26pg%3D2047675%26algv%3DSimplAMLv11WebTrimmedV3MskuWithLambda85KnnRecallV1V2V4ItemNrtInQueryAndCassiniVisualRankerAndBertRecallWithVMEV3%26brand%3DUnbranded&_trksid=p2047675.c101195.m1851&amdata=cksum%3A28524418151731841f706dd0486e93412310b010fbed%7Cenc%3AAQAIAAABUPqB0EgCndAssfMWNy0AT0GytGzF9%252By0G%252BlcW69DgBK3Qlz4BjwJQqPkN4K8I7qz9GoVciN1QNWqyS8EeqYS8rZRsDvyvw34m3N%252FyJKokwCTIIc3RNym2SNW8ARudP72DyiwgIY0dfUnIr5%252BMZDTaou%252Bf97VLmKujF1xnn1EGWjrUHEUvXp7yNeBStCBICkUQbXxs%252F%252F2Sf7JAexI%252FSgpIFon6HI%252FgG%252BMiLi0wE2k9ZIqwzTOEquDl7yGaTqTFVzuDy5bliq5xWSQv7fl%252FBPS1ZY92UcLW4TFdEqvypNOeft7%252B8VFhsqVDjrkpAaecey6XVnO%252Fovg0bOAEGjFA0c75R1m3bvn3v9wRf799CHiQf9gEcR3bBsSrJzWytza%252FAb8V8rezUqaMg9KZFxaS4alKttj6vW%252BYsX54AkrJl5y656EeF5bbGdEAp65B4CrgYzbWA%253D%253D%7Campid%3APL_CLK%7Cclp%3A2047675

SDR code:

https://github.com/f4exb/sdrangel/wiki/Compile-in-MacOS

OSX shell script audio recording:

https://apple.stackexchange.com/questions/326388/terminal-command-to-record-audio-through-macbook-microphone

HUIT-FAS-MacBook-Stubbs:proposals cstubbs$ ffmpeg -f avfoundation -list_devices true -i "" -hide_banner

[AVFoundation indev @ 0x7f7f8d824c80] AVFoundation video devices:

[AVFoundation indev @ 0x7f7f8d824c80] [0] FaceTime HD Camera (Built-in)

[AVFoundation indev @ 0x7f7f8d824c80] [1] Capture screen 0

[AVFoundation indev @ 0x7f7f8d824c80] AVFoundation audio devices:

[AVFoundation indev @ 0x7f7f8d824c80] [0] ZoomAudioDevice

[AVFoundation indev @ 0x7f7f8d824c80] [1] MacBook Pro Microphone

: Input/output error

from GPT-4, time-tagged shell script

---------------------------------

#!/bin/bash

# Identify the external microphone device using its name or index
MIC_INPUT="Microphone Name or Index" # You may need to replace this with the correct name or index

# Directory to save the audio files
OUTPUT_DIR="/path/to/your/directory"

# Ensure the output directory exists
mkdir -p "$OUTPUT_DIR"

while true; do
# Get the current minute
current_minute=$(date +"%M")

# Check if it's 7 minutes past the hour
if [ "$current_minute" -eq "07" ]; then
# Get the current time for time-tagging
timestamp=$(date +"%Y%m%d%H%M%S")

# Capture the audio stream using ffmpeg
ffmpeg -f avfoundation -i ":$MIC_INPUT" -t 3600 "$OUTPUT_DIR/audio_$timestamp.wav"

# Sleep for the remaining of the hour to prevent capturing multiple times
sleep 53m
fi

# Sleep for a minute before checking again
sleep 1m
done

----------------------------

To rotate polarization basis with 90 degree phase slip, we need a time delay of one quarter of a period.

WWV frequencies are 2.5, 5, 10, 15, 20 MHz.

freq MHz	period (ns)	period/4 for 90 deg (ns)
2.5	400	100
5	200	50
10	100	25
15	66.667	16.6667
20	50	12.5
25	40	10

NIST broadcast format: https://www.nist.gov/time-distribution/radio-station-wwv/wwv-and-wwvh-digital-time-code-and-broadcast-format

This box is useful:

Configurations:

Two magloops: one in horizontal plane, one in vertical plane. Vertical one in plane that points towards CO
Take output of one of them and feed into delay line.
Run A and (B-delayed) into signal combiner, which sums them. That picks out circular polarization
setting on delay line determines polarization we are monitoring

combination	polarization of E-field
vert coil only	horiz E field
horiz coil only	vert E field
combine with 0 delay	45 degree linear polarization
combine with 180 delay	-45 linear polarization
combine with 90 delay on A	circular 1
combine with 90 delay on B	circular 2

Note that we could inject a GPS-disciplined oscillator that is offset in frequency but within the SDR capture bandwidth as a phase reference, making the system immune to LO fluctuations with abiliity to measure Doppler.
Also inject GPS signal directly to measure LO systematics on SDR.

WWV signals

f	lambda
2.5 MHz	120 m
5	60 m
10	30 m
15	20 m
20	15 m
25	12 m

CO to MA propagation estimates:

Signals:

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.

Reverse Beacon network is another source, see: https://www.ncdxf.org/beacon/ and https://www.reversebeacon.net/main.php?rows=10&max_age=10,hours&hide=distance_km

Pirate beacons: https://www.hfunderground.com/wiki/High_Frequency_Beacon

RWM from Russia transmits CW dashes, see https://www.sigidwiki.com/wiki/RWM. Did an initial experiment with that. See linked page below. Can we 'see' that from Boston? Sorta:

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.

SDR with detuning option:

Selection of SDR that allows for MAC scripting, 14 or 16 bit digization.

dual-receiver SDR but only runs on windows machines: https://www.sdrplay.com/rspduo/

wiki page with summary of SDRs: https://en.wikipedia.org/wiki/List_of_software-defined_radios#cite_note-Lunaris_SDR-64

Airspy HF+ Discovery looks promising- mac SW at https://groups.io/g/airspy/topic/using_airspy_devices_on_macos/88509576?p=

Parts list:

item	part number	vendor	price	notes	references	status
magnetic loop antenna	DXE-RF-PRO-1B	DX engineering	675	have one, need one	dxe-rf-pro-1b_vw.pdf http://w6si.com/MagLoop/MagLoop-001-Intro.html	ordered 8/3/2023 Order #4433160
preamp 0.2 - 30 MHz 16 dB gain, 50 ohm	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 https://www.ebay.com/itm/285200853562	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 https://content.redpitaya.com/blog/using-the-red-pitaya-sdrlab-on-the-reverse-beacon-network-part-1	ordered 8/8/2023

Fast storage scope option:

We could just run the amplified signals from the two magloops straight into a fast digitizing scope. For the 10 MHz WWV station, let's imagine we digitize at 100 Msamples/sec.
A pretty cheap 8 bit A/D scope can capture 14Mpoints, so around 7 Mpoints per channel per sample. That is 7/100 seconds or 70 msec of data, which is 7e5 cycles. Plenty!
External trigger input would allow us to lock onto GPS-disciplined oscillator. It can produce 200 MHz square wave that could trigger the scope.

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

HAMSCI resources:

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.pdf sensors-21-02210.pdf

19042702.pdf

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