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Having had some success now via Sporadic E to VK4 and tropo to VK3, I decided to do a more in depth evaluation of my take off angles and ability to work tropo outside of VK7. This was spurred on by tropo conditions from VK3 to VK6 across the Bight. I live in a valley, mostly surrounded by mountains and hills.
The website HeyWhatsThat provides a good means of evaluating local elevation profiles in relation to a station. This is my profile.
This may not mean much to the reader, but it will as I compare paths to the various call areas.
Above is an overall view of local terrain. Purple is horizon marking. We want this out as far as possible to avoid local obstructions. Red is line of sight. As can be seen from the above photos, the path toward NE is quite favourable. Obstructions are "set back" a lot further.
I also decided to evaluate my 2m yagi's performance using MMANA. I don't think I have documented this on the blog. I use a EF0211 of YU7EF design. This has a forward gain of 12.98dBd and a F/B ratio of 20.2dB in free space. My antenna is at the top of the tower, so about 9 metres above ground.
Gain increases due to the ground to 20.92dBi. What is of more interest is the elevation lobes of the antenna now. We now have two major lobes, one at 3.3 degrees elevation where a majority of our gain is now focused. The next lobe up is at 10 degrees (19.9dBi). Another lobe is observed at 17 degrees but our Gmax minus Ga has fallen below 3dB (HPBW).
The horizontal HPBW of this antenna is +-17 degrees, or 34 degrees total. How does all of this help? The horizontal beamwidth is handy to know. If I beam directly say at 280 degrees (VK6), I have a margin of +-17 degrees in the azimuth plane to maybe get a signal past a hill, valley, cutting in the terrain etc to get my signal to water, and hopefully, into a duct. Further below my terrain elevation plots are done directly.
Onto elevation.... It's probably easier to categorize these into target areas, or call areas azimuths from my location.
Below is the elevation plot to VK1 and 2. The elevation alt is 4.36 degrees, and the nearest obstruction is around 13km away. This is above our main lobe of 3.3 degrees, but the elevation lobe's 3dB HPBW according to MMANA is around +-1.5 degrees, so it's a pretty good result really.
Toward VK3 is a different story. Our elevation increases to 8.31 degrees as a local hill only 1.3km away starts to obstruct my horizon. That said, the second lobe may still clear the hill.
VK5 is probably the worst. Elevation is nearly up to 10 degrees, and the hill is directly in the way now.
Toward VK6 it starts to improve. Elevation is back downto 5.3 degrees with the only local obstruction 6km away. Interesting to note that beaming at 270 (still within our 3dB HPBW) the elevation drops down to 2 degrees and the obstructions move out to 12km. A surprising result.
Below is ZL. Again, about the same as the path to VK2 elevation wise.
Now, digging a bit deeper. I've assumed that effectively to evaluate performance, I also have to look at the terrain between the coast and my station as I assume I have the best chance of getting into a duct over water.
Below is the path toward VK6 to water from Google Earth. Surprisingly its not as far as I thought, only 138km. If local over land tropo conditions are right, it could be possible. There is two main "peaks" in the way as can be seen over 1000m, but a majority of the path averages between 250m and 500m.
A good comparison now is with the path to VK3WE. As can be seen, it's a lot worse and further than the path to the coast toward VK6. I also just skim the Central Highlands plateau. However there is still a few mountains over 1000m. The last 100km of the path is excellent, over flat terrain (apart from a hilly range to the east of Launceston).
A lot of stations on the WSPR map are in and around Melbourne. So I decided to check my path toward that way. As can be seen, it is substantially worse. Almost the whole of the Central Highlands is in the way, and the path to the water is 216km. Average terrain is over 1000m. A very high level duct may be able to make this path, or AE.
I didn't even bother with VK5. The close in hill coupled with a similar path to VK3 means it will probably only be possible on Sporadic E. Interestingly despite this path, my 6m Sporadic E paths to VK5 are still quite good. I quickly modeled my 6m yagi (a YU7EF EF0606). The main lobe is at 11 degrees with the 3dB point at 18 degrees elevation which probably explains how my signal is getting into the E clouds.
Just out of pure interest I changed the "Up in the Air" value on my elevation profile in HeyWhatsThat to 110km or the nominal height of a E layer cloud. From this I can roughly gauge where I can expect my Sporadic E cloud position paths to extend to. Too bad nothing is South!
Below is the elevation path to ZL and is by far the best. Only 76km to clear water toward ZL and only one major hill in the way at only 700m. The rest of the path is pretty much water.
