> In a message dated 3/9/2010 9:57:57 P.M. Eastern Standard Time,
kingsburys@bellsouth.net N6WS writes:
>>I am interested in building a half size flag antenna (15 ft by 7 ft) to
work on 80, 40 30, & 20meters.
Hello Jim,
I'm a pretty new user of antenna modeling software, but let me take a
crack at answering your question and lets see how it corresponds to other
responses you get.
I analyzed your desired dimensions using a frequency of 3.5 MHZ.
Looks like a termination resistance of approximately 986 ohms is a good
starting point, as this is the value that provides approximately zero
reactance at the feedpoint and it provides good null off the back side when
looking at the elevation plot.
You will need a transformer at the feedpoint of the antenna for matching to
your feedline, and you will also need a preamp.
Lets see what other answers you get to see how far off I am.
73's
Don (wd8dsb)
Don - Regarding Half Flags there are also Half Pennants which in some cases are
easier to install and deal with than Flags. With Pennants, the resistance
should be 740 ohms - large or half size. Same with Flags - half size use same
resistance as full ~ 970 ohms. In all cases the rear null can be shifted and
deepened by a change in that resistor but I've found it's not worth the effort
and the standard values produce classic cardiod patterns.
In fact, K6SE conceived the Mini Terminated Loop which is a very small square
flag - 5 ft each side. That also produces the great cardiod pattern of the
others with, of course, much lower sensitivity - in the area of - 55db. That
version is far more useful than a Magnetic Loop of the same size and is
broadband.
73 Pete W2PM
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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