Re: SAQ Reception 2025-07-02

[Pete]

A line plot and a Spectrum Labs waterfall plot of the 09:00 UTC transmission. Using a mini whip active antenna at a height of 3 meters. The signal is feed into a UMU202HD sound card. The software is Spectrum Labs and Excel to process the data

[Dana Whitlow]

Hello,

I am seeking a digital recording of the received SAQ signal on 2July2025

for further analysis.  Basically I want to see if I can detect tiny speed

variations in the rotational rate of the Alexanderson machine going

from key-up to key-down, which should manifest itself as a very small

amount of "chirp" on the signal.  I would probably need fairly decent S/N

to get anywhere at all.  But if I had really good S/N, I might even be

able to detect the complementary chirp during key-up intervals.  I

suspect that the recording would need to be made within a few hundred

miles (at most) of the source to provide adequate S/N for this measurement.

So I am asking- has such a recording been made, and if so, could I

get a copy?  Even a few seconds should suffice for my purposes.

I had attempted to make recordings at my QTH, but was led astray

by an incorrect reporting of the broadcast time schedule.  At any

rate, it's extremely unlikely that the S/N at my QTH would have

been anywhere near sufficient for this purpose.

Thanks,

Dana    K8YUM (in limbo)

Kerrville, TX   (USA)

On Thu, Jul 3, 2025 at 5:21 AM 'Pete' via HamSCI <ham...@googlegroups.com> wrote:

A line plot and a Spectrum Labs waterfall plot of the 09:00 UTC transmission. Using a mini whip active antenna at a height of 3 meters. The signal is feed into a UMU202HD sound card. The software is Spectrum Labs and Excel to process the data

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[Dana Whitlow]

Pete,

A nice-looking plot indeed, but what I need to compute

is the phase versus time.  Does your SW provide for this?

Thanks,

Dana  (K8YUM)

On Thu, Jul 3, 2025 at 5:21 AM 'Pete' via HamSCI <ham...@googlegroups.com> wrote:

A line plot and a Spectrum Labs waterfall plot of the 09:00 UTC transmission. Using a mini whip active antenna at a height of 3 meters. The signal is feed into a UMU202HD sound card. The software is Spectrum Labs and Excel to process the data

--

[John Magliacane]

This is the best I could do from home in New Jersey, 6166 km from SAQ: A faint trace at the right place and at the right time, barely perceptible against a barrage of 60 Hz harmonics and static crashes from lightning.

Equipment consisted of a 40-turn, 6.7 mH, 5-meter circumference loop antenna brought to resonance at 17.2 kHz with parallel capacitance. The High-Z balanced feedpoint fed an AD620 Instrumentation Amplifier that drove a homebrew direct-conversion (image rejecting) receiver, providing an audio output of 800 Hz with an overall 3 dB bandwidth of about 150 Hz.

The audio was recorded using a 44100 Hz sampling rate, and plotted using Baudline software.

Dana: I recorded both SAQ transmissions through the WebSDR at Twente University in the Netherlands, if it might be of any value to you. I used that receiver to copy the CW message and to indicate when the transmission had ended.


73 de John, KD2BD

[Carl-Fredrik Enell]

For those interested, I was there and have shared a few of my photos and videos at 

https://cloud.i-kiruna.se/index.php/s/Fk7K9Y7jeHfFmgx

The 4K video files are best viewed by downloading them first

Best 73s Carl-Fredrik SM2YHP

[eric]

looks like you had a few 60 hz harmonics, but I guess that's to be
expected.   Congratulations!

I have three ELF coils just waiting to be put to use.

Eric

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[Dana Whitlow]

John,

Thanks much.  However, I'm thinking that the signal you recorded is probably too

weak and noisy.  

I see that you, too, are afflicted with powerline noise.  There seems to be a lot of

that going around these days  :-)  Mine runs anywhere from being moderately

annoying all the way up to (probably) enough to heat and cool the house.

My antenna is a 2m square, 12-turn loop made with 6-conductor rainbow ribbon

cable.  It has a center tap, which is grounded.  I also use an inamp, in my case

the AD8429, running into a Signal Hound SA44B spectrum analyzer running in

"Zero Span" mode.  In this mode it can record signals in IQ format, with considerable

flexibility, so that in most cases I can walk away from it for hours at a time.  i process

my data with "homebrew" SW written in 'C', and output graphs of this and that versus

time in CAD format for easy high-res plotting, measuring visually-selected phase

slopes, etc.  I've been developing this in little stages since early 2020.  With this

arrangement I can do my measurements at RF ranging from a few kHz to a few GHz,

in measurement bandwidths from fractional Hz up to a kHz or two.  

My SW still has plenty of rough edges, but that's life.  I went into it thinking that the

UI would probably account for most of the effort spent, but I keep having to re-define

"most" upwards.  I think it now sits at "well in excess of 99%".

Cheers,

Dana

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[John Magliacane]

On Thursday, July 3, 2025 at 12:37:15 PM EDT, eric <kl7...@gmail.com> wrote:

> looks like you had a few 60 hz harmonics, but I guess that's to be
> expected. Congratulations!

Thank you, Eric!

It's fascinating to me to see how certain power line harmonics became emphasized while others became attenuated at the same time during the 8 minute plot.

There was less power line interference during the earlier 0900 UTC (5:00 AM local time) transmission, but the "sferics" were significantly stronger at the time.

> I have three ELF coils just waiting to be put to use.

Good luck. Sounds like the makings of an interesting project! I used 40-conductor ribbon cable for my loop antenna. The same antenna (with less parallel capacitance) I use for 60 kHz WWVB reception.


73 de John, KD2BD

[John Magliacane]

Very good, Dana.

I think the frequency stability of SAQ has improved over time. I can remember hearing recordings in the past where it sounded very "musical" in nature.

Looking at the Netherlands WebSDR recording, I can see several Hz of wander and drift over the course of the transmission period. (See attached plot.) The SNR is high enough for "armchair copy" of the CW message, but not enough to measure the short-term drift characteristics you're looking to investigate. The gap visible towards the top of the plot is the brief off-air period between the ending of the machine sent test message (VVV DE SAQ), and the beginning of the actual, live, hand sent message at the top of the hour.

Even at its relatively close distance of 1125 km from SAQ, the Netherlands WebSDR waterfall showed SAQ being dwarfed by much stronger and much more distant VLF signals. From this side of the pond, SAQ reception is the VLF equivalent of EME. :-)

Thanks for pointing out the AD8429. For general reception with loop antennas at 100 kHz and above, I use a homebrew differential amplifier employing closely matched JFETs on the input terminals.

Good luck with the software projects. They tend to rise to completion, asymptotically.


73 de John, KD2BD

[Onno VK6FLAB]

I wonder if the WebSDR at Twente heard it and has a recording?

Another option is to check other WebSDR and KiwiSDR sites.

I am not sure what's around exactly, but there's plenty of people who have an SDR online.

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[Dana Whitlow]

John,

The frequency variations shown in the plot would clearly

make "my job" rather more difficult.  But the effect of time-

variable loading on the Alexanderson should be fairly

repeatable from dit to dit and from dah to dah.  As a

result, it might be practical to average the frequency

variations seen in a large number of dits, and in some

large number of dahs.  Worth trying, perhaps.  It's just

curiosity-driven, no practical point in it that I can see...

Dana

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[Jonathan]

Peter,

As always, excellent work on this!! I see the spikes you mentioned. Here in the US, it can be very difficult to copy during the summer with summer sferics, but I have found using vtblank increases the SNR quite a bit. 

Jonathan

On Thu, Jul 3, 2025 at 6:21 AM 'Pete' via HamSCI <ham...@googlegroups.com> wrote:

A line plot and a Spectrum Labs waterfall plot of the 09:00 UTC transmission. Using a mini whip active antenna at a height of 3 meters. The signal is feed into a UMU202HD sound card. The software is Spectrum Labs and Excel to process the data

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[Jonathan]

Dana,

Why do you need a phase vs time plot?

To try to see what you are looking for, you can run the carrier through vtfm of vlfrx-tools. It’s an fm demodulator and will show the frequency deviations. I do the same when I’m interested in the variation of 60 Hz and harmonics. Then, plot the output in gnuplot.

John,

Excellent capture! With power line harmonics that high, it may be best to locate the antenna as far away from any powerline source and isolate the signal using transformers. Much of power line interference is coupled into the antenna and electronics, so locating the antenna away from coupling paths then isolating to bring in the signal can often reduce mains harmonics.

Jonathan

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[Dana Whitlow]

Hi Jonathan,

Well, I don't really "need" phase plots, but I find them

useful for understanding signals better.  For one thing,

the phase plot for a signal is typically much cleaner than

the corresponding frequency plot, meaning that useful

info and/or understanding can often be had with poorer

SNR.  Quite often a phase plot that is perfectly

understandable just looks like so much noise when

differentiated to get frequency.

And, if you can stand more, I would argue that phase is

the more fundamental item of interest, and that frequency

error is mainly useful as a specification of how rapidly the

phase goes awry.  Or differs from expectations, thereby

corrupting system operation.  If it weren't for that, I don't

believe that precision frequency measurement, or

frequency stability, would be of nearly so such interest.

My interest in all this was triggered by my being in an

Earthquake down in Puerto Rico around 2008 or so,

and it occurred to me that looking for phase variations

in a received signal originating from a stable source

would be a fun thing to try.  But I never got around to it

until after I retired from Arecibo and moved back to the

US in 2017.  One of my duties at Arecibo was keeping

our active H-maser on track and documenting its time

error (phase error) over time.  I wish I had an H-maser

now, instead of just a few old Rb standards.

The 'quake detection idea fell apart pretty quickly once

I got some equipment running- I had forgotten the

matter of Doppler-shifted reflections off moving aircraft.

It turns out that the resulting beat frequencies very often

fell in the band of interest for 'quake detection.  OTOH,

I did detect what I believe to be transmitting tower sway

from time to time.

Cheers,

Dana

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[John Magliacane]

> John,
>
> Excellent capture! With power line harmonics that high, it may be best to locate the antenna as far away from any powerline source and isolate the signal using transformers.
> Much of power line interference is coupled into the antenna and electronics, so locating the antenna away from coupling paths then isolating to bring in the signal can often reduce mains harmonics.
>
> Jonathan

Thank you, Jonathan.

My loop antenna is located in my attic. I'm fairly confident the source of my power line noise is external to my house. To combat this, I might try rotating the loop in azimuth to see if I can place the noise in one of the loop's two pattern nulls. Another option is to take the whole operation portable to the Atlantic Ocean front, which is less than 2 miles east of me. It hardly seems worth the effort, though, with such infrequent transmissions taking place, not to mention the suspicion I might arouse doing this in the wee hours of the morning. ;-)

For anyone interested, I've attached a short snippet of what SAQ sounded like at Twente University in the Netherlands during the start of the first message transmission on July 2, 2025. I selected this segment in particular because the frequency wandering is so plainly audible to the human ear.


73 de John, KD2BD

[Gwyn Griffiths]

Dana

I only have a wav file to attach I'm afraid, not phase, and from the 5 July 2020 transmission received here in Southampton UK. I lso attach a one-page summary of the observations. Two interesting points are that a) the antenna was an active short vertical dipole, a very early form of N6GN Glenn Elmore's SAS antenna and b) the KiwiSDR receiver was battery powered in a box at the top of the mast, connected to a WiFi router to a nearby shed. GPS antenna ground plane is the flat metal sheet at the top of the (deliberate) wooden mast.

73

Gwyn G3ZIL

[Terry Godley]

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[Dana Whitlow]

Gwynn,

Is this file the one you sent me?  See the attached

screenshot for the filename.

I certainly do hear a "warble", or something, but to tell

the truth my ear is not telling me whether this is in amplitude

or frequency.  So, I will attempt to extract actual waveform

data from the .wav file and then analyze it.

Thanks,

Dana

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[Jonathan]

John,

Even though the loop is in the attic, power line hum can still couple though from your house wiring, but identifying where it's coming in from and keeping it out can be a challenge.

Dana,

The warble you hear sounds like it's the background noise, including sferics, modulating the downconverted CW tone.

Gwyn,

I'm glad you made an observation of the SAQ transmission. This band can be quite fun and interesting!

Jonathan 

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[Gwyn Griffiths]

Dana

 Yes, that was the file I sent. I also have this wav file from the 24 October 2020 transmission, also received here at Southampton with the KiwiSDR. There's about 5 seconds of key down between 20 and 25 s.

Jonathan

I did indeed have some fun down at LF and VLF a few years ago - I had the early N6GN active dipole on a vertical plane rotator as I was interested in measuring wave tilt.

73

Gwyn G3ZIL