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Aurora - 20241010

We don't seem to get many auroras visible at our latitude in the UK (53N). Skyglow and just a bit too far south are the main culprits, but we did have a nice but localised (NW direction) display on 20241011. 

My image from the garden with a short telephoto lens makes it appear much grander than it was.

The tree and chimney pot belong to my neighbour who is also an astronomer.

The events leading up to this follow in the timeline.

2024-10-03

AR3842 (Active Region) unleashed a X9 flare, the strongest flare of the current solar cycle. This caused a Sudden Ionospheric Disturbance (SID), an enhancement to the Earths 'D' layer, causing a partial radio blackout at HF radio frequencies. At Very Low Radio frequencies (VLF), signals are enhanced.. The flare arrived at 1215 and by 1300, the ionosphere had returned to normal indicating the flare was finished. A Coronal Mass Ejection (CME) was detected pointing towards earth. These normally take about 3 days to arrive. The shockwave from the flare is relativistic, taking about 8 minutes. The SOHO coronagraph shows the CME emerging.

 

SOHO LASCO C3 image courtesy NASA

This chart shows the change in signal strength received from two VLF transmitters, DHO is located in Germany, GQD is located in Cumbria, UK.  The signal strength recorded (arbitrary units) is a combination of the received ground wave and received sky wave from each of the two transmitters.

The following chart shows the change in magnetic field strength measured in my back garden, well away from the road. Although it is scaled in nT (nanoTesla), the calibration is at best approximate. The magnetometer records changes in Bx (East-West orientated) and By (North-South orientated) magnetic fields.

You can see that at the same time as the Solar Flare arrival, there was also an unusual sharp disturbance in the Bx (E-W) trace on the magnetometer. The magnetometer detects disturbances in the Earth's magnetic field due to changes in the solar wind distorting the earth's magnetosphere. In this case, a shock wave associated with the flare comprising of X-Rays and intense UV. 

2024-10-06

At 2024-10-06, the CME glanced the Earth  resulting in an unsettled magnetic field  which persisted until 2024-10-08 before slowly settling back to normal. The Aurora Borealis was visible in Northern latitudes where the sky was clear. (It wasn't clear here!).

 

2024-10-08

While all this was going on, a second X class flare with CME was ejected from AR3848  at 01:56 on 2024-10-08

SOHO LASCO C3 image courtesy NASA

This also captured Comet Tsuchinshan-ATLAS (C/2023 A3) as it approached the sun. Fortunately, it appeared to miss the worst of the CME. 

VLF radio propagation is by the D (also known as the Daytime) layer. The D layer builds at Sunrise and dissipates at Sunset. My simple VLF receivers cannot detect SIDs that occur during night-time hours. 

There was no magnetic shockwave detected, however, this may well because the magnetosphere was still being affected by the CME from 2024-10-03.

So, we have a second major CME on a collision course with Earth in a matter of days.

In the meantime, the magnetometer records that the magnetosphere is settling down.

2024-10-09

The following day, the magnetosphere was continuing to settle down (although still rather noisy/unsettled) after the first CME impact.

2024-10-10

The second CME impacted far more directly than the first, with a pre-shock at approximately 08:45UTC with the initial main impact at 15:10 UTC. A CME may take several hours to engulf and then pass by the Earth, so at 19:00 a major shift in the Bx field (taking the Bx values off scale), followed by a further shock affecting By (N-S) at 23:30 UTC. Aurora Borealis was very visible across the UK and most Northern Latitudes around the world. (Where the sky was clear!)

2024-10-11

BY 16:00, the magnetometer By trace had returned to more or less normal. Bx was still very unsettled, but also starting to return to normal values. We were lucky, we caught the tail of the visible Aurora early evening and a partial display to the North West. The only clear evening here is South Cheshire that week.

Although Auroras are wonderful phenomena to observe, the associated energy involved following a major CME impact can damage satellites, interrupt satellite communications and also impact, indirectly, the grid lines carrying power.  This is one of the reasons why there are satellites (radiation hardened of course) in space that do nothing except monitor the weather on the Sun.

Links to other related articles here:

Magnetometer

VLF Receivers

 

 

Comet C/2023-A4 (Tsuchinshan–ATLAS)

I was in great hope that this would be a superb apparition. We followed the comet as it reached Solar perihelion, crossed fingers to make sure it didn't get fried and then waited for it to rise (in the UK) in the western sky. I had seen photographs taken from much more southerly latitudes showing a long tail and anti-tail clearly visible.

When the comet became visible in UK early evening skies, we were blessed(!) with poor weather and mainly cloudy skies. To cap it all, I was actually on holiday in York (city center) at the end of October with no telescope.

The one clear evening that I had that week (17th October, I had been in Whitby but managed to get back to the caravan site at Dusk.

I grabbed the only optical things that I had, a pair of 8x30 binoculars and tripod mounted Sony DSLR camera. Fortunately, adjacent to the caravan site there is a small park, with no distracting lights and better places with a clear view of the sky.

A quick peek through the binoculars had the comet located in twilight, no problem. I set the camera up and tried various combinations of shutter speed and ISO settings to try and get trail free but low noise images. Sadly, the images do not do it justice, especially as I have had to use jpeg format for the files which has lost some of the delicate definition of the tail.  However, if you squint carefully, you will see the tail goes right to the edge of the frame.

A few minutes later, with the stars annotated:

and again with a wider field if view:

The comet is rather lost in an image this wide.

Fairly quickly, clouds started to close in but I was quite surprised that the comet remained visible from behind the clouds.

The remainder of the week and following weekend, the weather remained cloudy.

The next glimpse of the comet was on 2024-10-25. Early evening the sky was clear but forecast clouds.

Using my 80mm F7 Refractor, the comet was spotted at 19:30UTC. Very much fainter than the previous observation with a much shorter tail. Located approximately 3 degrees below Alp Oph. My notes advised me that I was unable to image due to the onset of cloud, compounded with its disappearance behind my neighbour's trees. Ho hum..

 

Muon Counting - a brief update

I've just spent a couple of evenings reviewing the code that displays the Muon Counter detail. One of the problems of 'borrowing' other peoples code from the internet is that you may not fully understand it when you need to edit the code. My unhappiness stemmed from the fact that the graphs were not really showing me anything, I think this is because the sample window (was 1 minute) was losing valuable data in the general noise.

The display code has been re-written to sample at 1 second intervals, then amalgamated into a 10 second window. I can change this fairly easily in the future as I have actually commented my code.

The revised graphs are now very dense (8640 display points to the graph) and so I am not sure how this will work with a graph width of 1600 pixels.

I may need to rethink.

For information (if you are suffering from insomnia), the process is a broadly as follows:

1. I read a daily block of data from the Muon Counter Raspberry Pi.

It looks like this truncated file  from 2024-11-17:

Y,M,D,H,M,S,Event, Ardn_time[ms], ADC[0-1023], SiPM[mV], Deadtime[ms], Temp[C], Name
2024,11,17,00,00,11.869169,4959769, 1032619463, 453, 113.81, 845053568, 23.15,WOBO_MUON_1
2024,11,17,00,00,32.307766,4959770, 1032639923, 496, 144.49, 845057408, 23.15,WOBO_MUON_1
2024,11,17,00,00,33.598346,4959771, 1032641193, 377, 76.28, 845057600, 23.15,WOBO_MUON_1
2024,11,17,00,00,34.803068,4959772, 1032642419, 389, 81.58, 845057984, 23.15,WOBO_MUON_1
2024,11,17,00,00,44.020615,4959773, 1032651632, 415, 95.00, 845059712, 23.15,WOBO_MUON_1
2024,11,17,00,00,46.323831,4959774, 1032653933, 369, 73.42, 845060096, 23.15,WOBO_MUON_1
2024,11,17,00,00,53.045375,4959775, 1032660652, 425, 99.48, 845061440, 23.15,WOBO_MUON_1
2024,11,17,00,01,03.371836,4959776, 1032670971, 728, 431.28, 845063360, 23.15,WOBO_MUON_1
2024,11,17,00,01,15.304950,4959777, 1032682898, 472, 125.87, 845065664, 23.15,WOBO_MUON_1
2024,11,17,00,01,19.087461,4959778, 1032686678, 704, 326.52, 845066432, 23.15,WOBO_MUON_1
2024,11,17,00,01,24.596963,4959779, 1032692184, 450, 114.31, 845067392, 23.15,WOBO_MUON_1
2024,11,17,00,01,29.826490,4959780, 1032697220, 352, 66.89, 845068352, 23.15,WOBO_MUON_1

This is changed from the standard muon data file in that all the commas (its a comma separated file) are written at source. The commas delimit the tabular columns so that the individual data items can be easily separated for post processing.

 

To produce the graphs, the only data I need is the time (H,M,S) for each detection.

I then create a separate array and populate the first column of the table with the number of seconds in a day divided by the sample window, currently 10 seconds. 

The array has bounds of 8640 rows x 2 columns.

I simply then parse through the imported csv file, calculate the time in seconds for each event, divide that by the sample window value and populate the array. In the sample above, the three highlighted entries would appear as a count of 3 for the sample window starting at 00:00:30 and ending at 00:00:39.

The array is then passed to a Python module (MatplotLib) to produce the graph.

One problem that I haven't as yet been able to solve is how to set the X axis values from a weird seconds /10 value to simple hours. 

 

Postscript:

After reviewing the following days results, I could see that many of the bars were not being plotted. 

The program was then modified to plot 8 x 3 hour windows which is much more of a handful but all the data is visible. I have also annotated the maximum daily count below the 'x' axis to help identify any interesting spikes.

 

A 1421MHz Interdigital Filter for H Line Receivers

This has been quite a long time coming. 

My Hydrogen line receiver design is described elsewhere.

The Interdigital filter is a metal item, no electronic components here..

Interdigital filters are extremely efficient and comprise of a number of tuned 'rods' that are resonant at the desired frequency. Each rod interacts with the adjacent rod, thus improving the rejection of unwanted signals. The result is a clean, flat passband with steep sides providing more and more attenuation.

Design

I can't claim any originality for the design, I used an online calculator that can be found here.

My requirements were for a 5 pole filter (the more poles the greater the rejection but also the greater the insertion loss), centred at 1420MHz. I specified 0db ripple as I wanted to make measurements within the passband and not have to worry about any ripple effects. 

After inputting the data into the on-line form, I was presented with the results:

Interdigital Bandpass Filter, based on work of Jerry Hinshaw, 
Shahrokh Monemzadeh (1985) and Dale Heatherington (1996).
www.changpuak.ch/electronics/interdigital_bandpass_filter_designer.php
Javascript Version : 09. Jan 2014
-------------------------------------------------------------------------
Design data for a 5 section interdigital bandpass filter.
Center Frequency          :    1420 MHz
Passband Ripple           :    0 dB
System Impedance          :    50 Ohm 
Cutoff Frequency          :    1415 MHz and 1425 MHz
Bandwidth (3dB)           :    10 MHz
Fractional Bandwidth      :    0.0070
Filter Q                  :    142
Estimated Qu              :    1961.04
Loss, based on this Qu    :    2.034 dB
Passband Delay            :    103.007 ns
-------------------------------------------------------------------------
Quarter Wavelength            :    52.78 mm or 2.078 inch
Length interior Element       :    47.54 mm or 1.872 inch
Length of end Element         :    48.37 mm or 1.904 inch
Ground plane space            :    19 mm or 0.748 inch
Rod Diameter                  :    6 mm or 0.236 inch
End plate to center of Rod    :    6 mm or 0.236 inch
Tap to shorted End            :    2.75 mm or 0.108 inch
Impedance end Rod             :    67.004 Ohm 
Impedance inner Rod           :    83.597 Ohm 
Impedance ext. line           :    50.000 Ohm 
-------------------------------------------------------------------------
                     **** Dimensions, mm (inch) ****
 #    End to Center      Center-Center        G[k]         Q/Coup
 0    0.00 (0.000)
 1    6.00 (0.236)      32.86 (1.294)        0.618        1.000
 2    38.86 (1.530)      37.08 (1.460)        1.618        0.556
 3    75.94 (2.990)      37.08 (1.460)        2.000        0.556
 4    113.02 (4.450)     32.86 (1.294)        1.618        1.000
 5    145.88 (5.743)     0.00 (0.000)         0.618        0.618
 6    151.88 (5.979)      

                      **** Box inside dimensions ****
Height : 52.78 mm or 2.078 inch
Length : 151.88 mm or 5.979 inch
Depth  : 19.00 mm or 0.748 inch

The program also predicts the performance of the filter:

So far, so good. All I had to do was to convert this design into metalwork and align it.

Construction

The filters are typically manufactured from brass or aluminium, with the brass parts optionally silver plated. 

Mine was built from 3/4" x1/4" brass strip for the walls, 6mm brass rod for the tuning elements and SMA connectors to interface to the outside world.

This is the type of SMA connector to use. It has an extended PTFE sheath that fits into a 4mm hole in the wall of a box, ensuring that the 50 ohm characteristic impedance is maintained.

Soft lead free solder was used to hold the rods in place, the rest was simply screwed together.

10 months later, I made a start. Much of the delay was due to other activities, but the nagging worry was the alignment. Aligning Interdigital filters (or any filter for that matter) is tricky without the correct tools.  To meet the alignment requirement, I acquired a NanoVNA SAA2 which has a 3GHz upper frequency limit and also a copy of the excellent "NanoVNAs Explained" book, authored by Mike Richards G4WNC and available from the RSGB.

The metal was sourced from a Model Engineering shop, Macc Models in Macclesfield (UK). SMA connectors came from stock.

The tools required in addition to normal hand tools were:

  • Pillar Drill with Machine Vice
  • 6mm, 4mm, 3.5mm and 2.5mm SHARP drill bits
  • Blowtorch
  • M5, M3 Taps
  • Digital Vernier Calliper

Manufacturing steps are broadly as follows:

  • Cut the strip bars to length (151.88mm) as accurately as possible. The lop and bottom bars are most critical, cut oversize and fille down to the correct size, making sure that the ends are square.
  • Cut the side bars to length adding 0.5" as these will overlap the top and bottom bars..
  • Using a metal scribe, mark out the positions of the rods in the top and bottom bars. This will mean 5 holes cut in the long sides.
  • Clamp to the two long strip bars together and drill through both using a 4mm drill. (Ideally a 4.2mm drill).
  • On one of the sides, open out the holes in the 2 outer and centre to 6 mm. Tap the remaining two holes to M5.
  • On the second side, do the opposite Tap the two outer and centre hole to M5, drill the remaining two holes to 6mm
  • Cut and fit the resonator rods. 
  • Solder the resonator rods in place. Before soldering, use the Vernier Calliper to set the exact internal length. Note that the inner 3 resonator rods are a different length to the outer pair. Use a blowtorch to heat the assembly, fitting and soldering one resonator rod at a time. You may need to use additional electronic quality flux (not plumbers flux) to ensure that the solder flows freely. Use minimal lead free solder, it is very lossy at these frequencies. File off all traces of solder that may have strayed.

  • Mark and drill the side  pieces  - 4mm for the SMA connector and 2 x 3.5mm clearance at each end for a single M3 screw used  to attach the side bars to the top and bottom bars.
  • Solder the SMA socket into the end pieces, avoiding heating the connector directly with a flame.
  • Align the end bar with the top and bottom and trim the SMA connector pin so that it just touches the first tuning element. 
  • Mark the position of the end securing screw and drill the lower bar with a M2.5 drill 12mm deep and then tap to M3.
  • Repeat for the other end.
  • Secure the end pieces with a single M3 screw
  • Position the top bar and adjust the width to 52.78mm. Mark the top screw hole and drill through to the tune screw hole with an M2.5 drill. Tap to M3
  • Repeat for the other end
  • Fit short screws to secure the top bar to the side bars.
  • Solder the SMA connector pin to the end resonator rods. Avoid getting the blowtorch flame on the SMA connector. Remove any surplus solder.
  • Mark and drill (M3.5) the side plate screw holes in the completed frame. 2 holes at each end and 4 holes in the long bars.

 

  • Using thin brass sheet (thickness not critical, I used 0.032"), cut the sides to the correct size. Clamp in place and drill through the frame through the side plates.
  • Secure the side plates with 12 x 25mm M3 cap bolts and nuts.
  • Fit the M5 Tuning Screws with locknuts.

Alignment

Without any alignment tools, this is very tricky. However, the availability of very affordable nanoVNAs have brought complex alignment tasks within reach of the average amateur constructor.

This is not intended to be a tutorial on using a nanoVNA, they are all slightly different. 

The Interdigital Filter is a 2 port symmetrical device, either end can be defined as input or output. The nanoVNA has an output port, (port 1), and an input port, (port 2).

We will measure 2 characteristics of the filter, S11 configured as VSWR and S21, configured as through.

Calibrate your nanoVNA as per the setup instructions

Set the Start and Stop frequencies to 1401MHz and 1441MHz respectively with a marker set to 1421MHz.

Adjust the Tuning Screw nearest the input port (Port1) until the VSWR suddenly drops.

Swap the cables round and repeat for the opposite end Tuning Screw.

Slowly screw the 3 inner tuning screws until the S21 trace resembles the passband illustrated above.

Tweak for a nice flat passband response from 1415MHz to 1425MHz and a flat VSWR response.

The blue trace shows VSWR. It looks horrendous but actually only varies between 1.8:1 and 2.2:1. Not ideal but should be acceptable.

200MHz Span. After further tweaking, I managed to get the insertion loss down to 5dB and the VSWR less than 2:1

2024-11-09

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