Signal Propagation

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Signal Propagation

Post by PanBiker » 25 Jan 2013, 18:45

Signal propagation is one of the areas of amateur radio that has always held a fascination for me. Propagation methods are many and varied depending on what frequencies you may be operating on. One of the largest influences on how radio signals behave on earth is the influence that our Sun exerts on Earth's geomagnetic field of and the various layers of the ionosphere that surround our planet and make up our atmosphere.

The Sun generates it's energy by nuclear fusion within it's core by the fusion of hydrogen nuclei into helium. This process generates huge magnetic forces that bind the gasses together. The magnetic forces are in constant flux as they churn around within the star. Some emerge at the surface to cause solar flares. Others emerge at one point on the surface disk and are then pulled back in at another adjacent point, this causes the surface to cool at those points and creates sunspots, sunspots are always in pairs as a result of this behaviour. Occasionally the internal forces can produce what is known as a CME or Coronal Mass Ejection, this is when internal magnetic forces burst out from the surface carrying with them billions of tons of plasma and gasses which are thrown out with the ejection.All of these natural events within the solar sphere create massive magnetic forces which can have varying degrees of effect on our planet including the way that electrical equipment operate and signal propagation behaves. CME's can cause Electro Magnet Pulses which can and do have a major effect on electrical equipment.

The largest ever recorded CME, known as the Carrington Event occurred in 1859 and caused major disruption to the telegraph system which was virtually the only electrical equipment that existed at the time. In 1989, a geomagnetic storm caused outages to portions of the National Electrical Grid in Canada which left over 6 million people in Quebec without power for over 9 hours. NASA and other agencies around the globe monitor the sun to try to predict when large potentially disruptive events on the sun are likely to happen. Early warning will allow time to shut down potentially sensitive equipment.

The level of geomagnetic forces generated by solar activy happens in peaks and troughs, each peak on an 11 year cycle, these peaks and troughs of activity are known as solar Maximum and Minimum. 2013 is due to be a Solar Maximum year although having said that the current space weather reports from NASA are saying that this particular Maximum may well be the weakest in the last 100 years. Nevertheless increased sunspot and flare activity will have a knock on effect on the way that signals are propagated.

This link from Space.com gives further details of Solar Cycle 24 and has links to related information.

Sun-Solar - Space Weather

In addition to geomagnetic activity from the sun many other factors can effect how radio signals are propagated around the earth.

The different propagation modes and their effect at various frequencies is shown in this Wikipedia article.

Wikipedia - Radio Propagation.

It's a lot easier following and predicting what may happen nowadays from when I was first licensed. The advent of the internet has put a wealth of information at everyone's fingertips. Dozens of applications have been created for collating propagation information and presenting it in various forms for amateur radio use. One such application is the desktop widget that I have found which presents current space weather and it's likely impact on the amateur bands. The widget can be downloaded for desktop use or the HTML code can be obtained for embedding the widget on web-pages. The widget gives a real time representation of how the various frequency bands are likely to perform, it auto refreshes from various data sources available on the internet. I have been looking at this for a couple of months now and one thing that I have noticed by using it is that the auroral latitude seems to be creeping south quite regularly between the hours of daylight and dark. The quiescent latitude under flat conditions is usually around 65°. I have seen it regularly creep near to 55° in the evenings and one short foray down to 53° This is likely to get even better as we progress further into 2013 and will have a direct effect on the propagation on various HF and VHF bands.

Propagation Widget

The widget is the one shown down the left hand side of the link screen. It gives information relevant to most propagation methods used on the HF and VHF bands and includes a current image of the solar disk. All the information is refreshed automatically from the internet once it is downloaded and installed. Full information on how to interpret the data shown is available on the site.
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Re: Signal Propagation

Post by Stanley » 26 Jan 2013, 04:21

All dutch to me but isn't it wonderful that we get expert contributions like this on the site! I remember in the early days looking at the barnoldswick.com site and being deeply distressed by the crap I found on it. This of course was what triggered Doc to start the original site in 1984.....
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Re: Signal Propagation

Post by PanBiker » 07 Feb 2013, 14:03

I'm no expert by any means Stanley but do enjoy trying to understand the hows and wherefores of what can be a very complex subject. The trick from a radio propagation point of view is how to interpret the bits of data you need to enhance your transmission or reception capabilities.

In the days before the advent of instant information via the internet, one form of tracking I used for Auroral propagation was to manually maintain a calendar. The sun has a rotation period of just over 27 days, therefore the surface of the solar disk facing the earth will repeat on this cycle. Sunspot activity has a direct effect on the solar wind and how this interacts with the earth's geomagnetic field which in turn is what triggers aurora at the poles. Depending on how intense sunspot activity is, the effects of any given sunspot field on the solar disk can last for more than one cycle of the disk. This is where the calendar comes in. When Auroral propagation was detected, (signified on VHF by Doppler shift on SSB signals). A record was made on the calendar and on any subsequent days that aurora occurred during the event. I used different coloured pens depending on the strength of the event. The calendar was arranged with 27 columns and enough rows to fill a page of A4. You could then transpose in pencil down the page and predict possible future events and the dates they were likely to occur. Really big events can have reoccurring effects over 3 or even 4 months

Massive increase in propagation distances can be achieved by reflecting signals off the ionised layers created by the excited plasma which shows as the visible auroral curtain. You do not have to be in range of a visible aurora, only aware that an event is happening and that the auroral latitude has come far enough South to be within range of your signals. As an example, at VHF frequencies under flat conditions, signal propagation will vary according to terrain and prevailing tropospheric conditions. Using the 2M band (144MHz) normal transmission distances are ground wave and will be anything up to 200 miles or so. There are a lot of variables to take into consideration such as location, antenna design, transmission power level and as mentioned before tropospheric conditions.
My best auroral contacts on 144Mhz from Barlick was into Siberia during strong auroral conditions, other contacts into what was Eastern Germany at the time and Poland. The angle at which signals are reflected from aurora will depend on where the auroral latitude is sitting at the time of the contact. The more obtuse an angle you can achieve between signals transmitted from your location to the curtain, the further your signals will reach. In all cases, directional antennas are pointed toward the aurora which will always occur between North and East from the UK. Maximum power used to make these contacts was 25W, that's a distance of roughly 3,000 miles into Siberia!
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Re: Signal Propagation

Post by PanBiker » 08 Feb 2013, 16:57

There is an Amber Alert from Lancaster University Aurora Watch, this was issued around mid day today and is still in force. My desktop widget that shows related information shows the auroral latitude to be at 56.7 degrees presently. The auroral flux index is at 8 where it is normally 1 -2. The geomagnetic field of the earth is shown as "Unsettled". These effects are likely to become more regular occurrences as we progress into Solar Maximum. I just wish I had my 144MHz beam antenna on the roof, it would be easy to confirm with the Doppler shift on SSB signals on the band.

Aurora Watch
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Re: Signal Propagation

Post by Stanley » 09 Feb 2013, 05:54

I read these posts and marvel, there is a whole world out there!
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Re: Signal Propagation

Post by PanBiker » 09 Feb 2013, 10:29

Yesterdays "event" subsided by 16.30. Strongest solar activity for a while though. I'm amazed at the predictive ability I have at my fingertips now all because of the internet. I can tweak the desktop widget to give me various filtered views of the solar disk. I can see it via infra red or see plasma emissions. There are about 20 different filters I can apply, it certainly beats my paper based calendar from 20 odd years ago, fascinating!
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Re: Signal Propagation

Post by PanBiker » 17 Mar 2013, 10:55

Looking at my propagation widget there appears to be a major geomagnetic event happening at the moment. The auroral latitude is shown to be at 51° which is classed as a Mid Latitude Aurora. Looking at the latest pass from the polar orbiting space weather satellite shows that the auroral disk is skewed and the 51° dip is over Canada and some northern states of North America. The aurora index reading is up at 10 which is the highest I have ever seen it. The knock on effect on the HF bands 1.8MHz - 30MHz is that they are suppressed and the desktop gadget shows them all as closed or poor propagation. I will go and have a listen on 14Mhz and 21Mhz to confirm. The radio amateurs in the Northern States and Canada should be having a field day!

[hr]
11.30 - 12.30
After a quick scan of the HF bands the widget is quite accurate. I can only hear a few EI and GI stations in the Republic and Northern Ireland working into mainland GB on 7MHz (40M Band). The higher bands just have a few near continentals audible above the noise on the bands. There has been a Russian contest on the HF bands this weekend, yesterday the bands were full of them and I worked quite a few to give some points away, only the guys with the biggest amplifiers and antennas are audible today and even they are way down in the noise!

We are being bombarded by solar radiation, tin foil hats on!
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Re: Signal Propagation

Post by Tizer » 20 Mar 2013, 09:29

Oh dear, I've only just read your post Panny so I'm 3 days too late with my foil hat. Perhaps that's why my tinnitus is playing up!

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Re: Signal Propagation

Post by PanBiker » 25 Apr 2013, 08:16

Linking in with your post about Solar Storms in the station rebuild thread. There was a Mid Latitude aurora last night. The auroral disk made it down to 56 degrees and the flux index was up at 8. The surface of the visible solar disk looks like it had measles with the number of visible sunspots. It was not quite intense enough to affect the radio bands though, I had a listen but all seemed quiet but that could have been down to my currently inadequate VHF antenna setup.
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Re: Signal Propagation

Post by Tizer » 25 Apr 2013, 10:04

56 degrees, you had me digging out the Philips School Atlas to remind myself of where that line of latitude lies....through Edinburgh...not quite far enough south yet, even for you folk in the frozen north!

By the way, the `Philips Modern School Atlas' is probably still one of the best value-for-money purchases available unless they've hiked the price dramatically. It's time I bought a new one...my 1987 edition cost about £5 for 153 pages packed with maps, country data and all sorts of information. Every household should own one, every child should have access to one. In fact I've just a had a look and you can buy the latest edition for about £8 with free delivery, sold and delivered by Amazon:
LINK The Amazon web page allows you to `Look Inside' but unfortunately it doesn't show more than one map and is mostly gazeteer etc, so don't be misled - the atlas is mostly maps as you would expect!

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Re: Signal Propagation

Post by PanBiker » 25 Apr 2013, 13:53

Just a point Tiz. Any given aurora does not have to make it down to the latitude you live at to be workable as a reflector for radio signals. It's a combination of the latitude of the auroral disk from (in our case) the Northern Pole and the intensity of the sunspot activity that is driving it. The further South it comes the more likely you are to see a visible Aurora. From a propagation point of view you can reflect signals off the ionised auroral curtain even when it is at higher latitudes if the intensity is great enough.

It's back up at 60 degrees now but the intensity is still up at a 6.. This activity is a repeat of the last solar rotation period and we are now seeing the same active region of the disk. There was a similar event then when the flux index was up at 10 and the latitude down to 51 degrees. It looks like we are on the downward curve of this particular sunspot event. It may well repeat again next month at even less intensity.
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Re: Signal Propagation

Post by melteaser » 25 Apr 2013, 18:31

Imindoors has managed to acquire (for a good price) a second hand yaesu 817Nd. I'm baffled though. He's just been jumping for joy because he can get radio 4?! I did point out that radio 4 is easily available online, through the tv box thing and on the car wireless. Apparently I'm not quite getting it!

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Re: Signal Propagation

Post by PanBiker » 25 Apr 2013, 20:24

My new £42.00 dual band (2M and 70cm) handheld will get R4 also. From the 817 shack in a box point of view it just passes through the FM Broadcast Band between the 70 and 144MHz bands. Might just as well include it as not. I hope Imindoors likes menus as well as R4 Mel. :wink:
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Re: Signal Propagation

Post by Stanley » 26 Apr 2013, 03:33

Listening to you lot going on about esoteric kit reminds me of a point, when I was seriously building my shed up, when I had a crisis of conscience and began to wonder whether I was an engineer or a collector.... Not suggesting any of you aren't serious but I'll bet the thought occurs to you every now and again.
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Re: Signal Propagation

Post by melteaser » 26 Apr 2013, 06:37

Imindoors response, and I quote...
After a couple of hours with the manual and random button pressing it all does make sense. It's not so different from the FT60 handheld. Once most of it is set you don't need to go into those menus again.

I'm amazed he has actually RTFM! That's a first :wink:

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Re: Signal Propagation

Post by Tizer » 26 Apr 2013, 10:02

Ian thanks for the explanation about the aurora. One thing that surprised me on the Solar Max programme was learning that the solar storm affects the `night side' of the planet first - apparently it passes around Earth and bounces off the farther atmosphere and back inwards. So we get affected more during the night than the day. Have I got that right? They said this is why the effects are less - we get the biggest impact at night when the grid is under less load etc.

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Re: Signal Propagation

Post by PanBiker » 26 Apr 2013, 13:03

Most audible auroras seem to happen at night or in the late afternoon. Visible auroras are obviously best seen at night but can be seen in broad daylight under exceptionally high flux conditions. Day or night the effect is caused by ionisation of different gasses in the upper atmosphere which then turn to plasma and give us the multicoloured streaking curtain effect influenced by the magnetic poles when observed from the ground. The multi-colours come from the range of different gasses being excited. Aurora can also be seen from space, the crews on the ISS must have a fantastic view.
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Re: Signal Propagation

Post by Stanley » 27 Apr 2013, 04:38

That surprised me as well Tiz.
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Re: Signal Propagation

Post by PanBiker » 01 May 2013, 20:16

There is another Mid Latitude Auroral event happening at the moment. It has been active for most of the day with the Index nailed as far as it will go at 10. The auroral disk from the Northern pole is skewed to 51 degrees Latitude angled again towards North America and is down as far as the Great Lakes in the USA. If it was the same in the UK (which it isn't) the disk would be down as far as London. Lancaster University with its detectors at Crooktree are correctly reporting "No significant activity".
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Re: Signal Propagation

Post by PanBiker » 23 Mar 2014, 17:40

Lancaster University Aurora Watch issued and amber alert for visible aurora in the UK. The index hit amber status at 1300 for 3 hours to 1600. We are nearly 27 days from the last major event for the UK so the next few days, if we get clear skies may very well be worth having a look to the N - NE. The Suns sidereal rotation will present the same active region towards earth that caused visible aurora in the UK last month.

Aurora Watch

Space Weather - Northern Hemisphere Auroral Disk
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Re: Signal Propagation

Post by PanBiker » 23 Mar 2014, 18:44

Just looked at the Aurora Watch Facebook Site which says that the alert between 1300 and 1600 was caused by maintenance on the magnetometer which is situated at Crooktree in Aberdeenshire.

Aurora Watch Facebook Page

The current real status is Yellow although we are still approaching the 27 day rotational period mentioned above. Well worth keeping an eye on the links over the next few days.
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Re: Signal Propagation

Post by PanBiker » 07 Apr 2014, 21:09

KP index up and an amber alert from Aurorawatch today between 3pm and 6pm. Back down to green now. This is the second time in the last few days that that it has reached amber.
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Re: Amateur Radio Homebrew (Shack Culture)

Post by Stanley » 29 Jan 2015, 06:22

Ian, forgive me for barging in on what is obviously your topic but I couldn't think of a better place for this. I stumbled across the town Schenectady in NY State last night and it reminded me that this was one of the radio stations on the large dial on our old 8 valve Superhet Ekco radio when I was a lad. Even during the war we could tune into places like Hilversum, Vilnius, Droitwich, Rome and even German stations. I think they were on short wave mainly.
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Re: Signal Propagation

Post by PanBiker » 29 Jan 2015, 11:47

First of all, no problem Stanley. As you can see I have moved your post here into the propagation thread, probably better in here as its related. We can bash it about a bit if you want to know more.

On domestic receivers the radio spectrum was generally referred to as a series of bands rather than direct frequencies which would be a lot harder to remember. Each band of course represents a range of frequencies within the radio spectrum. Long Wave, Medium Wave and Short Wave bands. Some receivers split the Short Wave band into more than one, SW1,SW2 etc.

The normal AM broadcast bands, LW and MW cover frequencies from 30KHz to around about 1600 -1700 KHz. On domestic receivers all frequencies above MW are referred to as the Short Wave bands. On the better domestic receivers frequency coverage would extend up to about 30MHz which is where the VHF bands start. Your Ecko 8 valve would probably be attached to a wire antenna strung across the street which is all you really need to receive that portion of the spectrum. Broadcast stations run thousands of watts to cater for inefficient receiver systems so with a few tens of feet of wire strung between the terrace's and a reasonable receiver you could listen to stations from all around the world.

The Schenectady radio station in NY State that you mention, transmitted on various frequencies but settled on the 31 Meter Band (9,550KHz (9.5MHz) - 9,900kHz (9.9MHz) from the mid 1920's. Station power eventually reached 50kW.

WGY (AM)

The amateur radio HF band allocations are in the same portion of that spectrum, adjacent to various broadcast sections but not overlapping. 1.8MHz (160M) band is just above MW, 28MHz (10M) is just below the VHF bands.

To guard against interference and to protect various sections of spectrum for specialist use, all allocations are agreed by international treaty. Each country has its own authority managing their sections of the spectrum, ours is currently managed by Ofcom. In turn these organisations meet to agree international allocations of spectrum.

From a radio amateur point of view, the Radio Society of Great Britain (RSGB) represents radio amateurs interests in the UK with Ofcom.

Radio Society of Great Britain (RSGB)

I have recently received notification from Ofcom detailing the latest proposed changes to the amateur radio band plan. Ofcom are obliged in law to notify licence holders prior to implementing any changes. There are changes to wording in various sections of the licence and some changes to frequency allocations.

Radio amateurs have allocations in many areas of the spectrum from VLF to UUHF. Our current band plan, before any of the proposals is appended here;
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Re: Signal Propagation

Post by Stanley » 30 Jan 2015, 05:08

No problem about the move, it fits better here. I used to spend hours on the floor in front of that old free-standing radio. We had a good aerial and I marvelled at the fact that despite the war we were still getting transmissions from places I knew were in enemy territory.
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