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Old 27th Sep 2020, 9:56 pm   #21
SiriusHardware
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Default Re: Tropo lift weekend of 19-20th Sep (2020)

Not tropo assisted, but another interesting early evening contact from my occasional mobile operating spot (Danby Beacon, 988ft ASL) in north Yorkshire - A 2i0 station operating /P in the Mourne mountains, NI.

It's highly unusual for me to be able to work over to that direction from north Yorkshire due to the Lake District mountains and the Pennines both presenting formidable obstacles to that path, but he was up around 1700+ft ASL with a big mast so I think we made the contact purely by having height at both ends, especially where he was concerned obviously.

I got the impression that it was a regular Sunday teatime operation for him so it might be worth listening out for him on S17 / 145.425 at that time on a Sunday evening, around 1700-1900.
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Old 28th Sep 2020, 9:34 am   #22
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Default Re: Tropo lift weekend of 19-20th Sep (2020)

Hi SiriusHardware
Excuse this brief O/T swerve ... are there any remains of the WW2 Chain Home installation at Danby Beacon (happy to follow up by PM if mods prefer) - ?
Guy
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Old 28th Sep 2020, 9:43 am   #23
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Default Re: Tropo lift weekend of 19-20th Sep (2020)

Briefly OT - the outline of a rectangular brick foundation at the beacon itself, and distinct mounds where the foundations of the TX and RX masts and other principal buildings / blockhouses were.

Nothing much else.

A plaque on a boulder at the original site entrance commemorates the station's role in the interception and shooting down of the first WWII enemy aircraft brought down on British soil.
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Old 28th Sep 2020, 8:08 pm   #24
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Default Re: Tropo lift weekend of 19-20th Sep (2020)

Thanks
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Old 29th Sep 2020, 9:48 am   #25
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Default Re: Tropo lift weekend of 19-20th Sep (2020)

Interesting contact you describe. Was it, I wonder, important that you were at around 1000' asl, and the other station 1700' asl? If the signal is propagating at some high level in the atmosphere, it should not matter how many mountains are in the way, or how high the stations are at each end.

I note though that the Wikipedia page on tropospheric ducting says:

Quote:
High mountainous areas and undulating terrain between the transmitter and receiver can form an effective barrier to tropospheric signals. Ideally, a relatively flat land path between the transmitter and receiver is ideal for tropospheric ducting. Sea paths also tend to produce superior results.
I did a quick check to see what path you actually traced across the Lake District. Obviously I don't know where the NI station was exactly (do you?) - but when I assumed somewhere on a road in the Mountains of Mourne, I got a path across peak in the Lake District called "Water Crag", height 305m. So that's very close to your height, and a lot less than the NI station. So its possible you actually had a pretty clear path as far as mountains are concerned. Not all of the Lake District hills are 3000'+ peaks!

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Old 29th Sep 2020, 10:29 am   #26
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Default Re: Tropo lift weekend of 19-20th Sep (2020)

Very true, but a stroke of luck if so . There was no Tropo propagation on the night in question, as far as I know, so the contact was not assisted by that means (despite the thread title).

I missed the exact mountain he said he was on, Slieve ___?, but given that he had a huge mast (and was there at dusk) I think it probably had to be one you could drive up. Slieve Croob fits the bill as the altitude is about right, there are masts on top of it and a tarmac road going all the way to the top, although whether this is a road the public can use, I know not - it probably served a military lookout / listening post in recent times. A look on Google Earth shows several structures / compounds up there.
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Old 29th Sep 2020, 5:42 pm   #27
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Default Re: Tropo lift weekend of 19-20th Sep (2020)

OK, I ran the great circle map tool at GPS Visualiser again for Slieve Croob. That moves things slightly, so your path falls just south of Scafell, which is a pretty significant obstacle. Looks to me like its crossing the ridge between Scafell at Cross Pike at about the 800m level.

There's another ridge just east of that one, between Bowfell and Gunson Knott, where the path again crosses a ridge at about 770m. Probably more high points en route further east - haven't checked. At the NI end, looks like Slieve Croob is the first high point, and it has a clear run across a bit of land then across the Irish Sea.

Just wondering whether there's a tool that will give the ground profile between two points - which is what you really want to use to understand what's happening between two places for a VHF link. For that you would need a GIS with elevation data for both mainland UK and NI - I don't have one.

Regrettably, I can't attach an html file - invalid file type apparently - which is the output of the GPS Visualiser tool. There's a link to it here, but I think it will only be there temporarily while I am on that page. Here's a screen shot of the whole path from that tool, but you can't zoom in obviously:

Click image for larger version

Name:	2.JPG
Views:	25
Size:	92.8 KB
ID:	216675


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Old 29th Sep 2020, 6:37 pm   #28
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Default Re: Tropo lift weekend of 19-20th Sep (2020)

I'm sure there is a tool for showing the lie of the land between two points, for exactly the purpose we want it for, but I can't recall what it is or where to find it. Of course for that to be really useful we'd really need to know exactly where the other station was located but if you combine the first part of the location ('Slieve') with the height which I remember was 1700 (and something) feet, that narrows it down quite a bit, especially if we go with the assumption that there is good / easy access to the summit.

I had already realised that the path was more or less east-west but your line shows the path heading down the line of the pass over which the A66 runs, although even there the summit of the pass (Stainmore) is at 1300+ feet. That may explain why the Pennines aren't the great obstacle I assumed they would be.

If this is a regular 'spot' for this station I may have other opportunities to hear him, if not work him, on forthcoming weekends, and if I do I'll try to listen more carefully for where he says he is.

Problem was he was running it like a local (to him) net so every time he invited another call he was naturally answered by someone elsewhere in NI or the Republic with a much stronger signal than mine. I only finally got in when he was just about to wind down. If he would ask, every now and again, for calls only from Southern EI / From GM / From GW / From GD / From G, I think he would be surprised to find how far his signal is actually going.

P.S> you can attach almost any type of file if you put it into a .zip file, as long as the .zip file does not exceed the maximum allowed size for a .zip file.
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Old 29th Sep 2020, 6:56 pm   #29
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Default Re: Tropo lift weekend of 19-20th Sep (2020)

Yes, of course the path appears curved on a standard flat 2-D map, but its a great circle path due to the curvature of the earth. That tool - GPS Visualiser - does a great job there. All you need is the lat/long of each end of the path, and I used the "Calculate the great circle distance between two points" tool on that page.

Its quite surprising how far signals will go on VHF, when both ends are high up, and have masts, etc, plus presumably plenty of transmit power. 332km apparently in this case. Do you know the details of each station? Transmit power, antenna gain (including feeder loss), etc?

Interestingly, the "radio horizon" for your NI station was about 95km from him. Your radio horizon was at 72km. Those distances are where a straight path leaves your antenna and hits the horizon - only for radio waves at VHF its 4/3 times the optical path length. So you had a "line of sight" low loss path for about 167km - about half way. I suspect, given the hills and the extra diffraction loss they would cause, that you possibly did have some help from tropo.

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Old 29th Sep 2020, 7:03 pm   #30
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Default Re: Tropo lift weekend of 19-20th Sep (2020)

I might add that I did quite a lot of VHF propagation study work, about ten years ago, when I was studying the first VHF network (as far as I know) built in the UK. That was during WWII, and it was on 45 - 65Mc/s roughly, and was built for the Special Duties Section of the Auxiliary Units - a sort of stay-behind unit, which supposedly was going to make life tough for the Germans had they invaded.

I think the tool I was using then was "Radio Mobile" - a free but pretty comprehensive tool, and I see still available at: http://radiomobile.pe1mew.nl/?Welcome...

That would certainly give a path elevation profile - not sure whether it has NI data though. If it can manage NI, then it would doubtless tell you whether ordinary VHF propagation would work for that long path.

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Old 29th Sep 2020, 7:16 pm   #31
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Default Re: Tropo lift weekend of 19-20th Sep (2020)

I guess the only way to prove whether tropo was involved is to try to catch him again. The Hepburn Tropo forecast (linked to in the first post of this thread) had the tropo conditions over the UK on Sunday not actually at zero, but quite subdued. Maybe even that was enough.

I know he was using 25W (FM), his aerial / feeder type I did not hear mentioned but was probably a vertical omni and on a high mast, 50ft I thought I heard him say.

At my end, 20W to a typical dual-band mobile aerial appx. 5ft long magmounted on the car roof. Signal reports exchanged were about 5-1, 5-3. He was suffering local interference, possibly just other amateurs on the same frequency or possibly due to the presence of the nearby masts if indeed he was on Slieve Croob. I also had low level traffic (audible, no signal strength) at my end and I was dreading the arrival of strong local stations on the frequency before I got a chance to work him. Fortunately that didn't happen.
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Old 29th Sep 2020, 11:02 pm   #32
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Default Re: Tropo lift weekend of 19-20th Sep (2020)

I've just managed to trawl this out of an online file of DX spots.

Quote:
2I0VOF/P,On Slieve Croob Co. Down,
145.425,2020-09-27 T 16:50:35,
Northern Ireland,54.73,6.68,54.73,6.68
So there you have it, unless he managed to get from one high mountain top to another about the the same height in just over two hours, that's where he was.
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Old 30th Sep 2020, 8:33 pm   #33
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Default Re: Tropo lift weekend of 19-20th Sep (2020)

Yes, its possible to do a fairly back-of-an-envelope calculation to get a rough idea of the path loss over this path, to see whether ordinary propagation is possible, given the antennas and power you were running. I have used the ITU-R paper "Propagation by diffraction" because we think there are some significant mountains on the path in the Lake District.

I will take the path from your transmitter to his location on Slieve Croob, since you say you had to the lower transmit power. So here the link parameters:

Frequency: 145.425MHz

Wavelength: 2.06m

Transmit power: +33dBm (20W)

Transmit antenna gain: 5db (I note you have one 5' long)

Transmit antenna height: 301m asl


Receive antenna gain: 5dB (guesstimate)

Receive antenna height: 530m asl (including mast at 50' agl)

Feeder loss: 2dB

Receiver sensitivity: 0.12uV across 50 ohms = -125dBm

Transmit location: 54.473573,-0.865698 (lat/long)

Receiver location: 54.340088,-5.973671

Path length: 332km (great circle)



The first step is to calculate the free space path loss over this path length. Using an online calculator I get 118dB. This is the total loss from the output of your transmitter to the input of his receiver, including antenna gains, and cable losses if both stations were in outer space, transmitting with nothing in the way at all.

The maximum path loss you can stand while still communicating = 33 + 5 + 5 -2 - - 125 = 166dB, so at the moment we have plenty of signal in hand, on this theoretical free space path. And this is our worst case link budget.

Now we add in the extra loss due to the curvature of the earth, and the fact this path is beyond the radio horizon. This makes adjustments for the distance of the link, and the heights of the two antennas above the earth plane.

Using Fig.3 in the ITU-R paper I get another 145dB of loss due to the distance. We then need to offset this by looking up the height gains of the two antennas

Transmit antenna height gain = 19dB

Receive antenna height gain = 34dB

So our total excess loss for over the horizon operation = 145 19 -34 = 92dB

The path loss due to free space loss, plus the earth curvature loss = 118 + 92 = 210dB.

This loss is far higher than our link budget of 166dB, so we can say the path is not viable for ordinary across the earth propagation. And in fact the total losses are even higher than this, because we have not yet added the excess loss due to the mountains en route.

I conclude you must have had help from some tropo conditions, which effectively allowed the signal to bend way over the horizon, and skip the mountains too.


Richard
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Old 30th Sep 2020, 8:53 pm   #34
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Default Re: Tropo lift weekend of 19-20th Sep (2020)

Thanks for taking the time to make such a thorough analysis - it seems this is going to have been a rare or one-off event for me after all.

If that gentleman toils up Slieve Croob every Sunday teatime as he seems to have been doing for quite a while I would imagine he can be heard all along the Irish sea coasts and some way inland under flat conditions, but you would have to be listening on S17 / 145.425MHz as that seems to be where he operates.

Whether he'll continue to do this as winter draws in, I don't know. As an experienced fell walker, I know how much worse the weather can be, and how much colder, at that sort of altitude than at ground level.
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Old 30th Sep 2020, 10:10 pm   #35
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Default Re: Tropo lift weekend of 19-20th Sep (2020)

Yes, if it seems to be good to be true......then it probably is! And I think its instructive to get some feel for what works in the ordinary way. And for VHF, line of sight links are dead easy, but they aren't easily arranged over long distances on earth. And once you get a few obstructions, the losses mount up rather quickly. The radio horizon really is like a sort of blackout curtain - most of the time.

You needed another 44dB to deal with that earth curvature. If you had both been running 400W, that would have added 26dB. You could have used 12dB yagis at each end - that would give you another 14dB. Still another 4dB to go......and options then are running out.....perhaps a high mast your end would have swung it, but I still haven't allowed for those Lake District mountains!


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Old 1st Oct 2020, 5:38 pm   #36
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Default Re: Tropo lift weekend of 19-20th Sep (2020)

All of the above proves why AMATEUR radio is FUN

You can never be sure, despite all theory, if something will work or not and you often get pleasant surprises

Professional radio links with >99.999% reliabilty are a different case and important when someone's life may depend on it

I have done both!

73 Fred
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Old 1st Oct 2020, 6:18 pm   #37
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Default Re: Tropo lift weekend of 19-20th Sep (2020)

Propagation is an inexact 'science'. That's what makes it fun!

At the start of WWII, Dr. R.V. Jones was leading a team investigating the German 'Knickebein' beam-navigation system and used a scientific paper published by one of the other team-members - the Marconi company's VHF propagation-expert - which predicted that a transmitter on 30MHz, located in Germany, would be receiveable over much of the UK. To prove this, Jones scheduled a test-flight over the UK of an aircraft fitted with a Hallicrafters S27 receiver which covered the predicted German beam-frequencies.

The day before the proposed flight, Marconi's propagation-expert basically withdrew the predictions in his paper, saying something along the lines of "That was only a prediction - I don't believe it would actually work in real-life", and saying that the test-flight was therefore a total waste-of-time.

Jones had however been at a meeting with Churchill earlier in the day and replied to the effect that "I heard the P.M. give authority for the flight and if it doesn't go ahead I will maked damned sure that he gets to know who it was that cancelled it!".

The test duly went ahead, and the interlocking dot-dash pattern of the German Knickebein beams were detected.
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Old 1st Oct 2020, 6:22 pm   #38
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Default Re: Tropo lift weekend of 19-20th Sep (2020)

I'm actually relatively inactive these days so the past three weeks or so have been a reminder of how much I used to love the hobby when I was 'keen', with two recent very long range contacts not only just from a handheld but on 70cms, and then this, as it turns out, highly improbable east-west /M 2m band contact reaching all the way from N.I. almost to the North Sea near Whitby. I have to admit I've been enjoying myself.

Edit: For more on the exploits of the redoubtable R.V Jones one can do no better than to read his 'Most Secret War', one of the best books concerning the 'Wizard War' as Churchill termed it, and no wonder: Jones was right at the heart of it all.

Last edited by SiriusHardware; 1st Oct 2020 at 6:27 pm.
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Old 1st Oct 2020, 7:13 pm   #39
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Default Re: Tropo lift weekend of 19-20th Sep (2020)

Quote:
Originally Posted by G6Tanuki View Post
Propagation is an inexact 'science'. That's what makes it fun!
That depends what you mean by "inexact". If you mean that the calculation I gave above could be out by 10dB either way - or even 20dB either way - I would say "sure". That's particularly true for non-line-of-sight paths at VHF, where diffraction is involved - and that's definitely the case once you are beyond the radio horizon. And I didn't even bother to add in the further diffraction loss over the Cumbrian hills, because at 44dB over the link budget, anything further would be a waste of effort.

However, mobile telephone networks are highly predictable now, and a huge effort is made to model the network before any mast sites are bought, and anything constructed. When I was involved in that 20 years ago, access to software for just one engineer was costing 100k p.a. No idea whether its more or less now - software does tend to get cheaper so maybe that huge cost has come down somewhat. The skill level needed to drive the software and understand the results is high - so the cost of paying someone to do the job is also high. However the job is do-able, which is just as well when the difficulty and cost of acquiring mast sites is considered - and the time delay of course in planning, which means while you are waiting you are not earning revenue from your kit.

Your story about R.V. Jones and the assertion that the Knickebein beams would bend around the curvature of the earth shows just how much propagation theory has moved on since WW2. I haven't seen the detail of the Eckersley paper (I think he was the Marconi expert your referred to), but I assume it was to do with the idea that radio waves would go beyond the optical horizon. Its now well known that that there is a "radio horizon" beyond the optical one, which is roughly equivalent to the earth having a notional radius 4/3 of its actual physical radius. That 4/3 factor does vary by location somewhat, but that's good enough for most practical purposes.

Richard
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Old 2nd Oct 2020, 2:48 pm   #40
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Default Re: Tropo lift weekend of 19-20th Sep (2020)

Hi All,
You may find the path profiling software by Mike Willis M0MJW useful. It is on his web site as "path profile" in the software section. it uses terrain data downloaded from somewhere else and so I think can cover UK and NI.

http://www.mike-willis.com/software.html

Be ready for some big files when downloading terrain data!
cheers
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