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一个很小和天线计算程序

SUBJECT: UHF Rhombic

    In wire antennas part 5 we discussed the UHF Rhombic antenna. 
I have the plans for one here.  This antenna is called the Dual 
Hexamerous Rhombiod or DHR.  A stripline balun provides a 50 ohm 
output for interface with hardline or antenna switch.

    The antenna consists of two stacked six element rhomboids. 
Each six element rhomboid consists of six rhombics of which each
rhombic is 19 wave lengths and four sided.  Each rhombic is 
terminated at the 9.5 wave length mark with a *** 2w resistor.

    Each rhombic is geometrically interfaced to a wooden frame
with a common start and ending point.  Nineteen wave lengths was
choosen for gain and front to back ratio.

    The actual plans for this antenna are available via the 
snail mail through me.  Please include a legal size envelope and 
one stamp. The BALUN is the key to the antenna and I would 
recommend this for those who are into 23cm and have stripline 
experience.

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Folded Marconi

    This is an easy antenna to construct and I recommend this 
highly for those AROs who have limited room and desire an 
antenna that performs better than most wire antennas.

    The design is easy.  Cut a length of 300 ohm ribbon cable 
(TV line) using the following formula:

              246/fMHz

    ex:  At 7.15MHz the Folded marconi length would be 246/7.15 
or 34.4 feet.

    Cut back about 1/2 inch and expose the leads in the ribbon 
cable. Twist them together and solder.  Seal with RTV.  Punch a 
hole about one inch down from the soldered end and run a cable 
tie through the hole and save for later.

    At the other end, expose about 3/4 inch of lead and solder 
one lead to the center conductor of your coax.  The other lead 
is attached to a ground plane system or ... use the roof 
flashing on your house. You can ground the roof flashing and 
suspend the folded marconi over the house.  This is the setup 
I have used here at the QTH.  The antenna was suspended over 
the house from my tower to the Palm tree in the front yard.  
The vertical height was 25 feet and the rest was horizontal.  
With this antenna, the greater the vertical section the better.

    You will need a tuner with this antenna as the impedance 
is very low.



-WS