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.
73
Frank
W3LPL
----- Original Message -----
From: "Bill Conwell" <bill@conwellpdx.com>
To: contest-update@arrl.org
Cc: "Ward Silver" <hwardsil@gmail.com>, "Frank Donovan, W3LPL"
<donovanf@erols.com>, "Craig Thompson" <craig@thompsonet.com>, "Jari
Perkiömäki" <jpe@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/ :
image.png
73,
/Bill, K2PO
Portland, OR
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