Electronics > RF, Microwave, Ham Radio

An interesting old antenna (10dBi at 17° TOA)


Just stumbled upon an antenna design from P.Carr (N4PC) dating back to 1995 and describing a simple, cheap wire antenna offering a gain of about 10dBi with a takeoff angle around 17° from horizon and a feedpoint impedance in the 50 Ohm range; being interested I decided to model the thing using NEC and the results confirmed what reported in the Carr article (see attached PDF) showing that the antenna should be a pretty good "DX gun" :)

On the "cons" side, given the dimensions, such an antenna isn't really suitable for the "top bands", yet, for the bands from 17m up to 6m and for the VHF it will be viable, the antenna in object is made by stacking two horizontally "squished" quad loop elements one above the other and the performance of such a simple design is quite impressive; for further informations and pointers about this antenna, please see https://sites.google.com/site/wvfisher/hdoublebay

As for the NEC model I used, it's pretty raw, but if someone wants to fiddle a bit and run some simulations, here it is

--- Code: ---
CM --------------------------------------------------------------------
CM H-DoubleBay https://sites.google.com/site/wvfisher/hdoublebay
CM Note: according to the informations found at the above site, the
CM optimal height for this antenna is the one which places the mid
CM junction at an height of about 1/2 lambda, also notice that the
CM characteristic impedance of this antenna is about 50 Ohm
CM --------------------------------------------------------------------

' calculated values
SY freq=29.000                ' calculation frequency
SY wire=0.00125               ' wire radius
SY conv=3.281                 ' feet-meters conversion factor
SY wave=(300/freq)            ' wavelength
SY spcr=(110/freq)/conv       ' horizontal elements
SY vert=(365/freq)/conv       ' vertical elements
SY hspc=(spcr/2)              ' half horizontal
SY hght=(wave*0.75)-vert      ' height of bottom from ground
SY base=hght                  ' lower point
SY midp=base+vert             ' mid point
SY uppr=midp+vert             ' upper point
SY segm=51                    ' vertical segments
SY segs=7                     ' horizontal segments

' vertical elements
GW  1 segm -hspc 0 base -hspc 0 midp wire
GW  2 segm -hspc 0 midp -hspc 0 uppr wire
GW  3 segm  hspc 0 base  hspc 0 midp wire
GW  4 segm  hspc 0 midp  hspc 0 uppr wire

' horizontal elements
GW  5 segs -hspc 0 uppr  hspc 0 uppr wire
GW  6 segs -hspc 0 midp  hspc 0 midp wire
GW  7 segs -hspc 0 base  hspc 0 base wire

' ground (real, standard)
GE -1
GN  2  0  0  0  13  0.005

' loading (copper=58000000, aluminium=37700000)
LD  5 0 0 0 58000000

' feedpoint
EX  0  7  (segs/2)  0  1.  0  0

' test frequency
FR  0  0  0  0  freq  0

' end of model

--- End code ---

as a note, an alternate way of building such an antenna (other than the one described in the PDF) is to use a pair of "squidpoles" to support the antenna vertical sections, with such an approach the squidpoles will be almost free to swing in the wind and the antenna should be able to support even strong winds, then, some "T" support at the bottom could allow to rotate the antenna and aim it as desired


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