Hello Howard,

From the cable length that you measure it looks like 3/4 Lambda instead of 1/4 Lambda which is too short for convenience working. From the electrical point of view it is the same, assuming low loss coax.

David 4X1DG ----- Original Message ----- From: Howard Kowall To: AMSAT BB Sent: Wednesday, March 23, 2011 3:28 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

_______________________________________________ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb

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@shaw.ca To: "AMSAT BB" amsat-bb@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

---

Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb