What sort of scatter is this?

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Nick Gilly
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Location: Whitchurch, Hampshire, UK

What sort of scatter is this?

Post by Nick Gilly » 04 Nov 2014 20:50

Here is a clip of France Musique on 89.9 from Rennes, distance 330 km, recorded late yesterday evening:

https://app.box.com/s/33nk1ts7d43negefb3ue

As you can hear there are random fluctuations in signal strength, which don't sound like aircraft scatter but almost remind me of the type of fading that happens with E-skip (there is a slight amount of aircraft reflection briefly around 45-55 seconds). It's obviously tropospheric, but what sort of scatter produces reception like this? Is this pure troposcatter? It is very different from the choppy and fluttery reception I tend to get from transmitters with paths mostly over land such as Lille or Tournai.

Thanks for any help on this.
Good DX.

Nick, Whitchurch, Hampshire.

BW Broadcast RBRX Encore, Kenwood L-1000T, Yamaha T-2, Denon TU-800L, Kenwood KT-1100SD (modified), Yamaha T-85, Sony XDR-F1HD tuners, horizontal Körner 9.2 beam (Antennenland version), Yaesu G-450C rotator

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John Faulkner, Skegness
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Re: What sort of scatter is this?

Post by John Faulkner, Skegness » 05 Nov 2014 09:17

Hi Nick.

Definitely aircraft scatter in there and more than one plane too. If you saw aircraft scatter on a graph it would display very clearly as aircraft scatter. One of the confusing factors is the longer central peak of the scatter which, if it is above the noise, the signal appears to be stable, as if it were tropo.

As I understand it, and not wishing to cause confusion, troposcatter can sound very similar. I sometimes have continental stations suddenly fade in with a single sweep > peak > fade out again. No flutter or variation from that - just up and down once. I always assume this is troposcatter, but these things are probably never 100% certain. I tend to use the term "General Scatter" in my loggings as this covers everything, but I can guarantee that the vast majority of them, if not all, will be aircraft scatter.

We need some more volcanic activity to test out these propagation modes, though it's probably better if we don't ;)

Nick Gilly
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Re: What sort of scatter is this?

Post by Nick Gilly » 05 Nov 2014 18:15

Thanks John. It was the apparently random element to the fading that got me curious as it sounded different to the norm.

Funnily enough I was thinking exactly the same thing about the volcanic activity! :D
Good DX.

Nick, Whitchurch, Hampshire.

BW Broadcast RBRX Encore, Kenwood L-1000T, Yamaha T-2, Denon TU-800L, Kenwood KT-1100SD (modified), Yamaha T-85, Sony XDR-F1HD tuners, horizontal Körner 9.2 beam (Antennenland version), Yaesu G-450C rotator

daveB
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Re: What sort of scatter is this?

Post by daveB » 05 Nov 2014 21:42

Hi Nick,

I surely regret throwing out my 1969 RSGB handbook and 1974 ARRL VHF Handbook some years ago as they had had extensive chapters on VHF propagation and the current handbooks are so superficial in coverage - so I can only go by memory. But one thing that sticks on memory is the wide variation in strength that can occur randomly over short periods.

Apart from the bit of aircraft scatter it sounds like what JF would call 'general scatter' where the radio signals scattered by the troposphere are adding/subtracting randomly without any particular enhancement to the path. I'm currently getting very similar reception from Egem with signals ranging from down into the noise floor and up to noise free mono without any specific pattern. But now and then with the added "chuff-chuff" of aircraft scatter. And reception is coming in equally well on both the vertical and horizontal aerials.

The latter is an subject that warrants separate investigation - why do vertically polarised signals (apparently) 'suffer' from polarisation changes so much more so than horizontally polarised signals?

Rgds

David
Sittingbourne
SDRPlay, AirSpyMini, RTL dongles, SB920s, Yamaha TX930. 5 ele compact yagi on rotator at 18ft agl. FM5 facing east, FM5 facing south, FM3 facing NE, OIRT dipole, 3-ele Moxon vertical facing east.

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John Faulkner, Skegness
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Re: What sort of scatter is this?

Post by John Faulkner, Skegness » 06 Nov 2014 10:28

Perhaps I can tag another video to this thread.

I just recorded one of those odd single scatter peaks which I have always presumed were troposcatter. This one is so brief though it's got me curious. Usually this kind of single peak lasts three or four times this long.

http://youtu.be/tCxMwhDf6xA" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

There is a bit of aircraft scatter at the end which I don't think was anything to do with this and was just there underneath after the peak had passed. Any ideas please?

This one came about by accident while I was trying to grab a video to show a typical aircraft scatter peak. Today is not a good day to do this though because every time an aircraft scatter peak comes along it's been wiped out by meteor scatter.

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John Faulkner, Skegness
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Re: What sort of scatter is this?

Post by John Faulkner, Skegness » 06 Nov 2014 17:04

... and here's another mystery. While recording 97.3 overnight to monitor meteor scatter, this popped up. I'd say it is a UK station, probably LBC, or possibly something overseas(?), but the distance would be incredibly short if it was LBC. The furthest UK station from me would be Forth 1 from Craigkelly (Edinburgh) at 397km. The other three are in England, shorter distances and flea powered.

http://youtu.be/ubYIrsD_1eI" onclick="window.open(this.href);return false;

Nick Gilly
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Re: What sort of scatter is this?

Post by Nick Gilly » 06 Nov 2014 18:20

daveB wrote:Hi Nick,

I surely regret throwing out my 1969 RSGB handbook and 1974 ARRL VHF Handbook some years ago as they had had extensive chapters on VHF propagation and the current handbooks are so superficial in coverage - so I can only go by memory. But one thing that sticks on memory is the wide variation in strength that can occur randomly over short periods.

Apart from the bit of aircraft scatter it sounds like what JF would call 'general scatter' where the radio signals scattered by the troposphere are adding/subtracting randomly without any particular enhancement to the path. I'm currently getting very similar reception from Egem with signals ranging from down into the noise floor and up to noise free mono without any specific pattern. But now and then with the added "chuff-chuff" of aircraft scatter. And reception is coming in equally well on both the vertical and horizontal aerials.

The latter is an subject that warrants separate investigation - why do vertically polarised signals (apparently) 'suffer' from polarisation changes so much more so than horizontally polarised signals?

Rgds

David
Sittingbourne

Hi Dave. This is the definition of troposcatter as far as I know, and it agrees with the Wikipedia article on the subject:

http://en.wikipedia.org/wiki/Tropospheric_scatter

That article also says that up to 99.98% efficiency can be achieved using TS, which suggests that it is there all the time.

As for my recording, I could have filled up an entire CD (80 minutes) of 89.9 behaving like that. So I think this was troposcatter, not aircraft scatter. I can't see aircraft supporting reflections constantly, particularly at that time of night. During the day, the effects of AS are more obvious, including interruptions from co-channel Wenvoe.

As for your transient fleeting reception John, 103.7 must have been reflecting off something, maybe a flock of birds (these can show up on radar) and 97.3 could have been a burst from Forth 1 as you suggested.
Good DX.

Nick, Whitchurch, Hampshire.

BW Broadcast RBRX Encore, Kenwood L-1000T, Yamaha T-2, Denon TU-800L, Kenwood KT-1100SD (modified), Yamaha T-85, Sony XDR-F1HD tuners, horizontal Körner 9.2 beam (Antennenland version), Yaesu G-450C rotator

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John Faulkner, Skegness
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Re: What sort of scatter is this?

Post by John Faulkner, Skegness » 07 Nov 2014 21:03

I call it "general scatter" as a kind of catch-all, just in case it's not clear what the mode is.

So what I have been assuming is troposcatter, probably isn't. Hmm. Back to school for me. So my single fade-in/fade-out over several second signals may be bird scatter? This makes sense, though I still cannot be 100% sure. We have HUGE flocks of birds flying around The Wash at this time of year. You can easily see why so many of them can show up on radar.

The flocks tend to swoop around in all kinds of patterns though, so I would expect the signals to fade up and down accordingly instead of just one single fade-in.

The thing about aircraft scatter is that there is a very definite pattern when you observe it on a graph.

Here are other examples of long fade-ins https://www.youtube.com/watch?v=zUnLr5IGf0U" onclick="window.open(this.href);return false; and go to 1'28". See how Slam FM fades in, stabilises and then fades out. Maybe it's just very brief tropo.

France Inter from Villers-Cotterets comes up shorlty after this at 2'38".

An example of aircraft scatter can be seen on this video https://www.youtube.com/watch?v=qpNh5AFKJf8" onclick="window.open(this.href);return false;. If you scroll four seconds in and pause you can see the centre of the peak in the middle of the display. It's not a bad example but this effect is often clearer on transmitters such as Lille or Wenvoe, for instance.

I'll see if I can grab some better examples, unless somebody else has something clearer they can post.

daveB
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Joined: 07 Oct 2014 16:49

Re: What sort of scatter is this?

Post by daveB » 08 Nov 2014 12:30

I've been browsing the Internet for the last couple of days trying to refresh my memory on troposcatter. Still can't find the path-loss charts that were in the old books - which basically showed that beyond the horizon the path loss flattened out and stayed almost constant for 'hundreds"? of km before going back to the usual increase with distance.
Anyway - there is lots of info about long distance military and commercial scatter links including the NATO ACE High system which had a station at the top of Detling hill Maidstone with 65 ft parabolic dishes a landmark for many years.
I've found reference to the phenomenen where a signal will "fade up from nothing for a minute or two and then disappear never to be heard again" - the writer putting it down to aircraft scatter. (Really?)

But then searching on 'aircraft scatter' there is a whole load of info that looks to be quite exciting - there is a software program available that allows realtime plotting of aircraft flights and predicts when an airecraft will provide a VHF path between two stations. Apparently on the 23 cm band radio amateurs are making use of aircraft scatter to achieve QSOs over hundreds of km. If I read it correctly you enter your own location and the location of the station you want to receive and it will show you when an aircraft is in the right position! I can't see why it can't apply to Band 2. Could be a nice project for the dull winter months.

Website is http://www.dj5ar.de" onclick="window.open(this.href);return false;

ADD: The website thst has the aircraft scatter prediction software: http://www.airscout.eu" onclick="window.open(this.href);return false;

Rgds

David
Sittingbourne
SDRPlay, AirSpyMini, RTL dongles, SB920s, Yamaha TX930. 5 ele compact yagi on rotator at 18ft agl. FM5 facing east, FM5 facing south, FM3 facing NE, OIRT dipole, 3-ele Moxon vertical facing east.

MarkdxAnglesey
Posts: 115
Joined: 31 Mar 2015 15:38

Re: What sort of scatter is this?

Post by MarkdxAnglesey » 07 Apr 2016 20:45

Hi everyone

Has anyone managed to download this and get it to work...is it any good?

Cant get it to install here

D: The website thst has the aircraft scatter prediction software: http://www.airscout.eu



Mark
Mark Davies
Isle of Anglesey
Elad FDM S2
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