On 09/09/2018 01:01 PM, Jim Brown wrote:
On 9/9/2018 12:39 PM, Bob McGraw K4TAX wrote:
How does one measure transmit antenna efficiency?
Not easily. :) B...
AND -- propagation reporting systems like WSPR and the Reverse Beacon
Network (RBN) can provide very good comparisons between antennas IF a
LOT of reports from a LOT of stations is averaged over a LOT of time.
Back in the late 1970s, when I worked at W1AW, a new 90-foot tower with
stacked monobanders for 20 meters was installed. We wanted to compare
the new antenna against the big rhombic that had been used for many
years for the 20 meter bulletin and code practice transmissions.
So, for a week or two, we did test transmissions after each scheduled
transmitting session. We would switch between antenna "A" and antenna
"B", send long dashes, and ask listeners to send in QSL reports. (Which
antenna was "A" and which was "B" varied randomly for each test.)
I collected the reports and plotted them on a map of the US. We found
that the rhombic was a little better directly on its boresight to the
west (toward southern California from Connecticut) but the stacked Yagis
had a much wider beamwidth so were better over the country as a whole.
By the way, you don't have to transmit to compare two antennas if your
receiver has an accurate S meter. Just switch between the antennas and
compare S meter readings.
Alan N1AL
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