[TowerTalk] Which better: TOP of hill or SIDE of hill?

Wed Dec 29 01:43:02 EST 2004

Hello Guy (and all),

I have spent the majority of the past week playing with HFTA. I found the 
process of acquiring my USGS data from the web and preparing it with 
MicroDEM to be quite challenging..... UNTIL I READ THE HFTA INSTRUCTIONS, at 
which point it became a piece of cake!  (Just because one works with 
computers doesn't mean every single application is intuitive....<gulp>  By 
following the directions in the Help file to the letter, it worked perfectly 
right away - except the URL for TIGER data didn't work, but I didn't care 
about that anyway.)

I second what Guy advises - if you don't have the ARRL Antenna Book and 
HFTA, and you use or plan to use a dipole or beam antenna, you need to get 
it!  The software is quite amazing, and yes, it shows that antenna 
performance does indeed change (slightly but noticeably) when you move a 
tower back 50' or 100' from a ledge, etc.  I have found it very helpful, and 
have heard great things about it from others, so I will be relying heavily 
on it while planning and building my new station.

In my particular situation, however, I was wanting the software to do 
something it cannot do. It is unable to take into account the terrain that 
is BEHIND the beam. I wanted to find out whether I would do better to Europe 
by placing a beam as much as 70' below the top of a northeast facing slope, 
rather than placing it at the top of the slope.  The "TA" software (which is 
not available) can apparently model this, but HFTA cannot. (You can't put 
elevations that are "negative" distances from the tower into your PROfile.)  
  I don't mind moving the tower down 70' if it will improve things, because 
I am at 600', and the NE property line is down at 450', still only half way 
down a 300' dropoff.

I spoke at length with N6BV about this, and he advised me to put the towers 
on the high point of the property. (A plus is that I will only need half as 
many towers that way, because I won't need separate west towers. But then 
again, I will have only half as many towers! =)

Dean said that placing the antenna down the slope would improve apparent F/B 
by knocking down the signals off the back, but would not improve absolute 
forward gain. I will definitely buy that.

My next question is: will moving the antenna down the slope also increase 
the level of super-high angle (approaching 90 degrees) stuff, which is more 
likely to be atmospheric than radio signals, except perhaps on certain bands 
in the middle of the day when you wouldn't likely be on them anyway, other 
than perhaps the Sunday doldrums period of my favorite November contests....

I don't have the answer to that question, so I conceived of very structured 
experiment to perform this spring. It uses five identical and parallel 
dipoles (40M or 20M, any suggestions?), all installed at the same height 
above ground, each 200' apart, one in the middle of a large flat area, one 
each on the precipice (ledge) of an eastern and a western slope, and one 
each about 70' below the top of each slope on the slope-face. I will examine 
what happens to low angle and high angle received and transmitted signals at 
different times of day and year. The big questions will be: how much do I 
reduce the signals off the back when I move down the slope, do I introduce 
more noise, and do I see any difference in signal strength at all when 
switching between the flat-area dipole, and the ledge-top and slope-face 
dipoles on the favored side, and if so, for what angle signals.  (Any 
difference should be more pronounced on low angle stuff, I would think.)
I will report back in the late spring with results, assuming I am successful 
at obtaining town permits and I go ahead and buy this property.  I will have 
a space 1,000' by 1,000' for antenna experimentation, including a large flat 
area and nice slopes down to the east, west and north. The south slope down 
is 900 feet away, at the bottom of the neighbor's property. Always wanted to 
have my own hilltop. For now, I'm going to have to share one.  :-)   Should 
be enough to keep me busy for a while at any rate...

Cheers and Happy New Year all,

John
WA2GO

>From: "Guy Olinger, K2AV" <olinger at bellsouth.net>
>To: "John WA2GO" <xnewyorka at hotmail.com>,<towertalk at contesting.com>
>Subject: Re: [TowerTalk] Which better: TOP of hill or SIDE of hill?
>Date: Tue, 28 Dec 2004 23:44:08 -0500
>
>This will not be a question with a simple answer.
>
>You need to obtain a terrain analysis program, such as HFTA, which comes 
>with the ARRL Antenna Book.
>
>Both optimum placement of the antenna relative to the slope, and optimum 
>tower height can be COUNTER-INTUITIVE, and are remarkably variable 
>depending on the specifics of the foreground terrain.
>
>With the program in hand, you can try various placements and heights and 
>see the results. I believe that HFTA can use USGS terrain files and give 
>you very specific data for your situation.
>
>HFTA will take your entire situation into consideration.
>
>I would not under any circumstances commit yourself to any configuration 
>until you have done a very careful HFTA analysis of your situation.
>
>73, Guy.
>
>
>
>----- Original Message ----- From: "John WA2GO" <xnewyorka at hotmail.com>
>To: <towertalk at contesting.com>
>Sent: Monday, December 27, 2004 10:02 AM
>Subject: [TowerTalk] Which better: TOP of hill or SIDE of hill?
>
>
>>My new qth-to-be has a north-south ridgeline running through the center of 
>>the property.
>>I can put towers right on the ridgeline at 600' ASL, or I can put towers 
>>down the sides of each hill. In the latter case, I would have an 
>>Europe/Africa/S. America at 550' with 50' of hill rising behind it, and a 
>>US/Asia/Oceania/S. America tower at 530' on the West side, with 70' of 
>>hill rising behind it.
>>(This setup also puts the East and West towers 700' apart!)
>>
>>Question is: Which is best?
>>  a) being on the hilltop,
>>  b) being on the precipice of the drop-off, or
>>  c) being partway down a 250' slope, with 50' - 70' of hill sloping up 
>>behind the tower.
>>
>>(Yes, it slopes down 250' to both East and West, as well as North!!)
>>
>>I would experiment with dipoles, but I can't really experiment now, 
>>because I don't own the property yet.  Also, I imagine the answer might be 
>>different for 40M vs. 10M.  I can have a single tower for each band if 
>>necessary/best.
>>
>>I am in the permitting process, and I want to apply for what I really need 
>>in order to maximize my chances for approval.
>>
>>Is there modeling software I can use that takes into account the terrain 
>>BEHIND the beam?  If so, which one?  Anybody out there already done this 
>>modeling, or better yet, already done real-world experimentation?   
>>Intuition says having slope up behind beam is good, but that's only 
>>intuition. Wondering if it is, how much slope is needed in order to be 
>>worthwhile, on each band.
>>
>>Thanks!
>>
>>John
>>WA2GO
>>
>>
>>_______________________________________________
>>
>>See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless 
>>Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with 
>>any questions and ask for Sherman, W2FLA.
>>
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>>
>