Topband: half size flag antenna--NW6S

[w2pm at aol.com]

> In a message dated 3/9/2010 9:57:57 P.M. Eastern Standard Time,  
kingsburys at 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