[amsat-bb] Re: Cushcraft 416-TB

[i8cvs]

Hi Howard ,VE4ISP

The Cushcraft 416 TB is a 2x8 elements crossed yagi for 70 cm with the
horizontal and vertical elements spaced 1/4 wave lenght in free space over
the boom.

The dipoles are feed using the T match system wich is a balanced system
and the balun is a 50 ohm coax line 1/2 electrical wavelengt used to
transform the 200 ohm balanced impedance of the dipole into 50 ohm
unbalanced impedance for the feed line.

To calculate the lenght of the balun you must multiply 1/2 wavelenght
into free space by the velocity factor of the coax cable used.

If you use RG-58/CU with velocity factor Vf = 0.66 then each balun
is long 22.7 cm or 8.9 " including the lug lenght.

The original phasing harness is 2 piece of 75 ohm coax cable wich is
an odd number of 1/4 electrical wavelenght and in your case the odd
number is 3 so that if you use RG-59/CU 75 ohm coax cable with
Vf = 0.66 then each 75 ohm line is 34 cm  or 13.4 " long including
the SO239 connector.

You can find all data to modify the above antenna in order to get four
polarizations H-V-RHCP-LHCP reading the instructions in the
following address.

http://www.pa3guo.com/cushcraft_416tb.html

73" de

i8CVS Domenico

----- Original Message -----
From: "Howard Kowall" <hkowall at shaw.ca>
To: "AMSAT BB" <amsat-bb at amsat.org>
Sent: Wednesday, March 23, 2011 2:28 PM
Subject: [amsat-bb] Cushcraft 416-TB


> Hello All
> I acquired a Cushcraft 416-Tb antenna,the so called phasing harness was in
bad shape,so I am going to make a new one for it.
> I could copy the original one,but yes I am making it hard on myself and
decide to calculate the proper cable type and length,and to do that I need
to know how the antenna actually works.Here is my problem ,the 2 driven
elements have a balun to each of the Tmatchs to make the impedance 50 ohms
on each driven element.The original phasing harness is 2 piece of 75 ohm
aprox 13" that goes to each driven element and the a so239 connector on the
other end of the harness is the 50 ohm feedline.I originally thought this
was a matching stub,but when I do the calculation for the matching
stub,should only be aprox 4" to each driven element.Am I missing something
here,how are they able to do this,does anyone know this antenna and how it
works.
> Thanks to all who read and respond in advance
> Howard VE4ISP
>
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