[Elecraft] Follow-up: [Sorta OT]: Does terrain affect HF radiation patterns?

[Al Gulseth]

First, TNX for all the replies. You've given me a lot of information to wade 
through. In doing a quick browse about HFTA on the web I found a couple of 
presentations, which while being "apples and oranges" to my situation, 
nevertheless exhibited some of the same characteristics. It was really 
educational to see their graphs of what terrain can do to a signal's take-off 
angle and how the height of the antenna interacts with the terrain.

That being said, I'm wondering if this explains another phenomena I've 
observed. Another "beacon" system exists in the form of W1AW in that it gives 
a picture of closer in/domestic propagation on the various bands. In my 
experience their signal on 20M is surprisingly weak here most of the time, 
while 17M frequently shows full strength on the signal indicator during the 
periods when I'd expect that band to be open. I've also seen times when 17 
and 40M were both fairly strong, and it would seem logical that 20 should 
also be in the "sweet spot" at that moment, but it isn't. Is this possibly 
due to the terrain/antenna combination either on my end or W1AW's?

Again, TNX for the very informative comments.  73, Al
 
On Mon September 15 2014 8:54:38 pm Al Gulseth wrote:
> Greetings all,
>
> I've been following some of the antenna-related discussions here recently,
> and I've decided to see what the "gurus" here have to say about a question
> I have related to my QTH. As my post title indicates, what (if any) effect
> does nearby terrain have on HF radiation patterns? Is it along the lines of
> VHF?
>
> Without going into too much detail, my QTH is partway up what amounts to a
> long broad slope to the north. "Just for grins" I plugged my QTH
> coordinates and an arbitrary antenna at 50 feet AGL into the FCC's Height
> Above Average Terrain calculator. Here are the results, in meters of
> course, which shows what the surrounding terrain is like; the results seem
> realistic from what I know of the local area. I would also note that the
> area less than two miles away, which is not used in these calculations,
> would nevertheless correspond fairly closely slope-wise in my estimation.
> I'm aware that this calculation is intended for FM/TV broadcast: my
> question is whether it could be of use for hams on HF:
>
> Antenna Radiation Center Heights Above Individual Radials:
>
> 0.0°    	    -107.3 meters
> 45.0°    	    -37.4 meters
> 90.0°    	    39.6 meters
> 135.0°    	    100.3 meters
> 180.0°    	    92.9 meters
> 225.0°    	    86.6 meters
> 270.0°    	    -1.6 meters
> 315.0°    	    -40.0 meters
>
> Now, my observations: I've been using an inexpensive SW portable with its
> built-in whip to monitor some of the International Beacon Project and 10M
> beacon frequencies while I'm around the house. By using the portable, in my
> estimation I achieve two things: 1) it should "hear" a mostly
> omnidirectional pattern and 2) beacons heard under this circumstance should
> indicate the band would be usable to the area in the beacon's vicinity.
>
> That being said, I have found that other than 4U4UN, I'm most consistently
> hearing South American beacons, and at least some of them can usually be
> heard if I'm hearing anything at all. So, is the terrain around me
> affecting this, or if not, what might be happening?
>
> TNX/73, Al
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