[CQ-Contest] Path Takeoff Angle analyzer

donovanf at erols.com donovanf at erols.com
Wed Dec 9 12:30:40 EST 2020

Hi Bill, 

Your email highlights exactly why the most effective contest stations 
have antennas at a variety of heights. We usually observe the elevation 
angles rise at the intensity of band openings improve. 

Often weak low angle signals -- especially just as a band begins to open -- 
can't be heard at all on low antennas. Then later in the opening 
-- when many signals are strong -- lower antennas often perform 
much better than the highest antennas. 

As sunspot activity increases over the next few years, contest stations 
without low antennas will be frequently beaten out in pileups my 
their neighbors with modest stations with low antennas. 

You can never have too many antennas -- but this is very important -- 
unless they interfere with each other as they very often do. 
It takes a huge piece of property to avoid antenna performance 
degradation caused by multiple antennas within a few wavelengths 
(or more) of each other. 


----- Original Message -----

From: "Bill Conwell" <bill at conwellpdx.com> 
To: contest-update at arrl.org 
Cc: "Ward Silver" <hwardsil at gmail.com>, "Frank Donovan, W3LPL" <donovanf at erols.com>, "Craig Thompson" <craig at thompsonet.com>, "Jari Perkiömäki" <jpe at kapsi.fi> 
Sent: Wednesday, December 9, 2020 4:50:12 PM 
Subject: Path Takeoff Angle analyzer 

Hi Brian, 

Jari, OH6BG, and team did a refresh of VOACAP.com a month or so ago - cleaning up code and using new maps, etc. 

More recently Jari has added a new beta feature - a path takeoff angle analyzer. Given both ends of a path, the code uses Voice of America software to figure out the statistical occurrence of different takeoff angles for available paths. 

Who knew, e.g., the path from Portland, OR to Washington DC on 40m most commonly uses a takeoff angle of around 5 degrees, whereas the longer path to Peru most commonly uses a takeoff angle of above 10 degrees. 

If I have a 40m sked with my cousin in Boise on 40m, I'll commonly be taking off at around 18 degrees. To chat with my son in Austin, Tx, on 15m, I should elevate my dipole to optimize a takeoff angle of about 5 degrees. 

Lower angles are much more prevalent than the antenna literature seems to commonly suggest. It's unusual to see predominant takeoff angles much above 15 degrees. 

(The take-off angle analysis covers all months from January to December, and assumes a fixed SSN. Naturally, condx vary month to month, and with changes in SSN.) 

Look for the "TO Angle" button at the bottom of https://www.voacap.com/hf/ : 



/Bill, K2PO 
Portland, OR 

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