[TenTec] [Sorta OT]: Does terrain affect HF radiation patterns?

[Al Gulseth]

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