Further support for Petit Chordal Hop Es propagation Part 1
On 30 December 2009, Richard VK2SWL2, of Numeralla NSW, posted a report on a Forum here about the reception of TNQ7 Townsville. You can read it here: ttp://www.vklogger.com/forum/viewtopic.php?f=2&t=8940
. Scroll down the page to where Richard posted a Brisbane ionogram.
Richard recently confirmed by email to me that the vision carrier of TNQ7 Townsville, on 182.25 MHz
, was received briefly by him at Numeralla - first at 0041 UT on 30 December 2009, at S6, then peaking again at 0050 UT at S2. Reception was made on a TV Band II dipole antenna.
In response to Richard's posting, Peter VK3QI reported:
FWIW, at the time you mentioned, there were very strong signals on 6 mx between VK3 (Melbourne) and VK4 (Brisbane).
I have analysed these reports and the associated propagation paths. A map of the situation is below (Fig. A), and below it (Fig. B), the 0040 UT Brisbane ionogram Richard put in his Forum posting:
The Townsville-Numeralla path is 1982 km long, while the Brisbane-Melbourne path is around 1365 km.
The path mid-point for Townsville-Numeralla is about 520 km WNW of the Brisbane ionosonde. That's too far from the Brisbane ionosonde for the 0040 UT ionogram to be relevant. However, sporadic E cloud systems in this region are known to often travel in a generally westward to WNW direction, driven by the background wind at the relevant heights in the E-region at speeds ranging from 40 metres/second up to 100 metres/second [1,2].
To get a better idea of what the ionosphere was doing at the Townsville-Numeralla mid-point at 0040 UT, we could look at what was happening at Brisbane earlier because what happened there then may have blown across the path mid-point around the time TNQ7 was received in Numeralla. I decided on four likely background wind speeds because they're in the range likely to cause turbulence to Es layers, creating spread Es on ionograms.1/
At 85 m/s - that's 306 km/h - it would take 1 hr 42 min for an Es cloud to travel from Brisbane to the path mid-point.2/
At 80 m/s (288 km/h), it would take 1 hr 48 min.3/
At 75 m/s (270 km/h), it would take 1 hr 56 min.4/
At 70 m/s (252 km/h), it would take 2 hr 5 min.
So. I looked up the nearest-time ionograms for (1/) 0040 UT minus 1 hr 42 min = 2300 UT 29/12/09; (2/) for 0040 minus 1 hr 50 min = 2250 UT 29/12/09; (3/) for 0040 minus 1 hr 55 min = 2245 UT 29/12/09; and (4/) for 2 hr 5 min = 2235 UT 29/12/09.Case 1/
The 2300 UT 29/12/09 ionogram shows spread Es with the following characteristics: h'Es 96 km.
ftEs 16.1 MHz, foEs
= 16.1 - 0.7 = 15.4 MHz.
(Refer to Part 4, earlier. The gyrofrequency, fH, at Brisbane is 1.4 MHz).
As the path distance (D) is 1982 km, angle of elevation (e) is 1 deg. and angle of incidence (i
) at the Es is 80.0654 deg., making angle (b) 9.9346 deg. The raypath would need to find an Es tilt angle (t) at the path midpoint of half that, making angle (c) 4.9673 deg. (See Fig.9 in Part 5).
The M factor, 1/sin(c), is 11.549. Thus, the MUF in this case would have been at least 177.8 MHz.
A tad too low, unfortunately.Case 2/
The 2250 UT 29/12/09 ionogram shows spread Es with these characteristics: h'Es 96 km.
ftEs 17 MHz, and thus foEs = 16.3 MHz.
Angles (e), (i
), (b) and (c) are as for Case 1. With an M factor of 11.549, the MUF would have been at least 188.2 MHz. Clearly, this could have been the scenario at the time Richard VK2SWL2 heard TNQ7.
However, the two other cases could also have been equally likely.Case 3/
The 2245 UT ionogram shows spread Es at 96 km and a derived foEs of 18.8 MHz.
With all the angles as before, the MUF would have been 217.1 MHz.Case 4/
The 2235 UT ionogram shows spread Es, still at 96 km, with ftEs off-scale at 20 MHz ! The MUF would have been at least equal to, or greater than, 222.8 MHz !!
These results are summarised in Table A, below.
On to Part 2 of this update.73, Roger Harrison VK2ZRH
 From, W.R., and J.D. Whitehead 1986, “Es structure using an HF radar”, Radio Science, Vol. 21, No. 3, pp 309-312.
 Whitehead, J.D. 1997, “Sporadic E – A Mystery Solved?”, QST, October and November.