Very interesting Tim. Now I often work a few locals on HF, 30 or so km but the 10m challenge has been different. I don’t know if it’s the propagation on this band or the challenge driving people for QSOs.
I’ll believe groundwave for MM7MOX and probably GM4OIG but I really do not know what the real propagation method was for the others.
Call
Name
QTH
Distance
Mode
RST
MW0IDX/P
Roger
GW/NW-054
351km
CW
339-339
G4OOE/P
Nick
G/TW-004
311km
CW
339-339
G4OBK
Phil
Home
288km
CW
539-539
GM4OIG/P
Gerald
GM/CS-043
79km
CW
579-599
MM7MOX/P
Andy
GM/SS-176
21km
SSB
59-59
Fascinating stuff. Your contacts will have all been SSB which is even more remarkable.
Talking of propagation, I worked WB6POT and N6WT within minutes of each on CW. Both were easy copies when the shock/delight of someone in California calling you subsides. N6WT was a steady tone but WB6POT was fluttery. He didn’t sound multipath or have the classic 10/12m reverb or echoes. Polar Flutter maybe?
G4OBK always has flutter/echo with me on the higher bands. Not sure what mode of propagation that is but it doesn’t sound like a simple ionospheric refraction. Phil is technically in the same county as me.
I have also done a lot of groundwave QSOs on 10m… there are great propagation conditions… e.g. tropo, reflections,…
There are often QSBs with groundwave QSOs too.
Many QSOs that I assumed were groundwave QSOs were not actually groundwave QSOs - they were backscatter QSOs. This clearly showed the direction of the antenna of the other station or the shadowing by mountains.
Recently I have had a lot of QSOs with Mario @DJ2MX in Munich and he often told me in which direction he had the beam at the time.
EI7GL hypothesised that those 10m signals too far for ground wave and too close for ionospheric propagation could be caused by backscatter EI7GL - Backscatter on 28 MHz - 2nd Nov 2023
I too am fascinated by regional contacts (200-500km) on long-haul dx bands like 10m.
I agree with Andy @MM0FMF regarding what reasonably were groundwave contacts and what were due to some other form of propagation. With the curvature of the Earth – even with both stations on hills/mountains – the radio horizon is surprisingly limited, and that’s with no hills in between, e.g. the sea or a flat plain. E.g. with stations on 300m ASL hills, the horizon is about 60-70km.
At LW frequencies the wavelength is so big it diffracts a bit beyond the horizon which is why the BBC (R4 198kHz/1500m) and other EU LW broadcasters could reach most of Europe on groundwave albeit with huge power and giant antennas. But at 10m, the GW is pretty much LoS.
Ignoring the lovely contacts I got yesterday to N.America, Greece, etc, for the UK ones Colin M1BUU/P on G/NP-005 28km away from me on G/LD-058 was crashing my headphones with his 599 QRP CW on groundwave but I really struggled to copy the two more-distant UK stations, Kevin MW0KXN/P on GW/SW-025 and M0JSB in Surrey
By contrast the N/A stations - 1000’s of miles away - were much easier to hear, mainly 529 to 559 (with QSB in a few cases).
So, which propagation mode for the other inter-G contacts?
Too close for Sporadic-E? Too far for GW. Troposcatter is weak at 28MHz compared to VHF/UHF/SHF and with low-power, and without highly-directional antennas, the RF energy in the ‘shared volume’ must be tiny. Backscatter? It’s a mystery.
This topic came up before (I think, on the main 10m Challenge thread) and there’s an on-going investigation by the RSGB’s Propagation Studies Committee. Unless there are propagation experts on hand now, we will have to wait for the outcome.
I find ground wave to hard to believe for the the 300km contacts I had. They were weak in a CW BW, 250 or 300Hz but copyable with effort. A doc I was reading earlier suggests the 10m path loss for 300km is of the order of 220dB. I had 10W and 3dB antenna gain so 13dBWerp. A one way signal would be -207dB and my KX2 has an MDS of -106dBW (-136dBm 2.5kHz BW). Even allowing for an improvement dropping the bandwidth by a factor of 10, that’s not going to work!
Could be troposcatter. But when I was active on 2m SSB (30+ years) back, 8W into a 5ele beam (80W ERP) meant 150-200km QSOs were fairly repeatable. When I got a 9ele beam and 25W things were much better and 13ele and 150W (3kW ERP) meant working 400km QSOs were again a readily repeatable event. So 10W into a 3dB antenna (20W ERP) on a band were troposcatter is much weaker doesn’t sound right either.
If 10m propagation worked reliably at the distance here with 10W and a relatively simple area then someone would have come up with a nice digital mode with lots of FEC and be using it commercially. It’s not happening, so it’s reasonable to assume it’s some kind of scatter from SpE or F2 clouds.
Could be Andrew. Me and my contest mob use it a lot for 70&23cm when contesting. I might push the times into flight radar sites to see what was about yesterday.
Over many years I’ve had aircraft flutter on many 2m QSOs but didn’t consider the rapid QSB an enhancement or something exploitable (due to its unpredictable occurrence).
A much more frequent aircraft interaction I have operating regularly in G/LD land are military jets. The inhabitants of the Lake District get used to them flying low over us. They come usually in 2’s or 3’s in single file on training flights screaming loudly (100dB?) as they fly low in the valleys below my summit activation. Their combined noise makes listening to my rig impossible for about 40 seconds. I cannot even hear my CW sidetone to warn chasers to standby.
Note to self:
As I rarely use the 3 text messages feature of the KX2, I should set one to something like “qrx qrx = pse standby 40s = loud jets loud jets = cannot hear de g8cpz/p”.
Anyone else have novel uses of text messages?
Oh indeed, definitely explore the potential for a rapid S9 signal peak over 500 km. Where the aircraft route or flight path aligns with the RF path between two summits or two stations you can expect a midpoint reflection (737 at 10km altitude) lasting approximately five minutes, depending on the aircraft speed.
A widebody A-380 will enhance the signal strength but only for the same 5 minute window.
During an AE contact the characteristic flutter is a sign of mulipathing associated with the reflection off a moving object, in this case a large aircraft.
An aircraft crossing the RF path at a midpoint location will offer the potential for a very short enhancement window, say one minute.
The more aircraft en route will likely increase the opportunity for an AE contact.
Try experimenting with two summits around 400 km apart and under a known commercial flight path, or aligned to a busy flight path. Of course coordination with another SOTA activator is critical to the success of a AE S2S. Flightradar24 will reveal the commercial flight paths.
The stations I worked were all line of sight, ignoring the curvature of the earth. I checked this on SoTLAS.
Looking at this, I was not able to work other G station stuck behind mountains, despite trying a few. Why could I not hear @MM0FMF when he spotted SSB ?
If this was Troposcatter or aircraft, one should hypothesise that I should be able to work stations hidden from line of sight?
This was also consistent - there were several s2s contacts I had beyond 200km+
I’ve also had plently of 200-300km QSOs on 2m VHF without sporadic activity ?
Tim, are you saying the SoTLAS calculator ignores curvature of the earth or you do? Either way, you won’t be (literally) line of sight if the stations are more than a certain distance apart no matter if you are both on huge mountains.The straight line (signal path) will ‘hit’ the ground somewhere in the middle. That’s not to say some of the RF won’t get through via reflections or other propagation modes.
Interesting factoids: The longest theoretical line of sight on Earth is from Mt. Dankova in Kyrgyzstan to Hindu Tagh in China, a horizontal distance of 538km The longest line of sight in the British Isles is from Snowdon to Merrick – 232km
Unfortunately you cannot ignore it. EM waves (RF and /or light) act a bit like Newton’s 1st law (“keep moving in a straight line at constant speed unless it is acted upon by a force”).
RF does the same, travels in a straight line till something “bends” it. i.e. refraction, reflection or diffraction.
You can work out your radio horizon in km as approx 3.6 * sqrt(height) (height in metre). For the signal to travel further it has to be reflected, refracted or diffracted.
For your non sporadic 200-300km QSOs on 2m you are experiencing tropo scatter from microscopic dust/dirt/water molecules a few km above the earth.
However, for tropo scatter to work, both you and your radio partner’s antennas must be able to see and illuminate a common scattering volume. The signals are weak so you normally need beams and watts to make it work. The strength of the signals can be significant or weak and fluttery. If you both can’t see a suitable common volume of the right type then you wont get a non-LOS path to work.
The three aircraft departing Melbourne, when they are midway between Melbourne and my QTH in Canberra, which is Albury, I should be able to work a station aligned to the flight path.
I not trying to be a closet flat earther . I do agree, that is no line of sight.
But to my point, shove a mountain or two in the way and there is no QSO. To me this means is not propagation via troposphere or aircraft backscatter, these are far too high and should allow communication behind a hill or two!
Nice to get you on 2 bands and 2 summits Tim
. I do agree, that is no line of sight.