[Antennas] dbi for horz bi-square

Thu Oct 4 18:59:13 EDT 2007

Sorry for the top posting, but I didn't want to insert things in your excellent 
reply. It really helped.
First the loop is 20' over average ground and fed at a corner, the NE corner of 
the loop. It lays on the roof of the building that is 28'x150'. The short sides 
(25 feet)run SE-NW and the long sides (90 feet) run NE-SW. Yes that a narrow 
rectangle. The feed line is RG-214 running from the NE corner towards the SW 10 
feet and then Down 15 feet and terminated at the tuner about 8 feet later.
If you go to the http://propnet.org/ site and click on the NA link (1hr, 4hr, or 
24hr) or even the animated one, you can get an idea of the stations that heard 
my 10w PSK signal into this antenna. Seems I was heard anywhere from 400mi out 
to as far as 1600mi. But I only heard one California station. Guess I need to go 
to plan B. (not sure what that is yet)
Not sure what take off angle equates to what states I am being heard by are 
broadside to my long sides (Cal, Co, Ut, Al, and Fl) as well as off the ends in 
the direction of the 90' runs (Mo, Md, Oh, and even into New England some.
Thanks again for your comments.
Terry Conboy wrote:
> At 03:51 PM 2007年10月03日, Sam Morgan KA5OAI wrote:
>> I'm trying to setup PropNetPSK in preparations for this weekend and 
>> one of the questions ask is the dbi of my antenna. It's a 190' 
>> horizontal loop at a height of 20' It resonates @ about 5.310mhz so If 
>> I'm running it on 30m it's a bi-square, I think? So what's it's dbi?
>> Sam,
>> Assuming it's fed at a corner and is over average ground, the maximum 
> gain should be about 5 dBi gain at a takeoff angle of 51 degrees in both 
> directions through the "side" corners (the corners 1/4 way around the 
> loop from the feedpoint). Since this may not be the most useful takeoff 
> angle for paths over 300 miles, it's worth looking at the pattern at 
> say, a 20 degree elevation, where the peak gain is about 0 dBi, also 
> bidirectional through the "side" corners. The gain at 20 degree 
> elevation on a line through the feedpoint corner and the opposite corner 
> is about -3 dBi. (At 10 degree elevation, those gains drop to about -6 
> dBi and -9 dBi.) Gain straight up is -1.7 dBi.
>> The two-wavelength resonance is about 10.65 MHz, where the impedance is 
> near 90 ohms (assuming #14 bare copper wire).
>> BTW, a bi-square is normally oriented with the plane of the antenna 
> vertical, but most importantly, the corner away from the feedpoint is an 
> open circuit. The pattern is totally different than a closed loop and 
> the feedpoint impedance is Hi-Z. If you opened the corner away from the 
> feedpoint, the gain is mostly straight up, where it is about 8.4 dBi. 
> At 20 degree elevation, the gain is about -3 dBi in the direction 
> opposite the feedpoint and -4.5 dBi toward the feedpoint. Off the sides 
> the gain is about -10.5 dBi at 20 degree elevation. The feedpoint 
> impedance is over 3000 ohms at 10.125 Mhz.
>
-- 
GB & 73's
KA5OAI
Sam Morgan