[amsat-bb] Re: 435 offset yagi phasing

[kc6uqh]

Andrew,
Yes that is correct with one exception that a 50 ohm, 1/2 wave section needs 
to be inserted for the opposite rotation in one antenna. This is switched in 
and out with a coax switch or relay. The 1/4 wave sections do the matching 
and both offer the same delay so there is no phase difference to the 
antennas. As the antennas are 1/4 wave offset one leads by 90 degrees. 
adding a 180 degree delay will cause that antenna to lag by 90 degrees and 
hence the opposite rotation.

Good luck with the project. Learning by doing is the best way!

Art,
KC6UQH
----- Original Message ----- 
From: "Andrew Rich" <vk4tec at people.net.au>
To: "Amsat-Bb at Amsat. Org" <amsat-bb at amsat.org>
Sent: Friday, December 28, 2007 3:25 AM
Subject: [amsat-bb] 435 offset yagi phasing


> Hi
>
> I have had good success with just one yagi of an offset crossed array I am
> building.
>
> http://wa5vjb.com/yagi-pdf/cheapyagi.pdf
>
> I will add the other elements shortly.
>
> I am not ready to tackle the phasing part.
>
> I hope I have this right.
>
> 1. The yagi's are offset, by 90 degrees so that is the offset already.
> 2. Both yagis's should then have the same length of coax coming from each
> one.
> 3. Both yagi's will require a 1/4 wavelength of 75 ohm coax for each feed.
> 4. Remebering that the velocity factor is 2/3 in coax cable, or the speed 
> of
> light 200 instead of 300.
> 5. Both 75 ohm feeds then join at a tee, the result of the 50 ohm antenna
> and 70 ohm feed giving around 120 ohm
> 6. By tee'ing the two together, this should present around 50 ohm, 
> required
> for the main feedline.
>
> Does that sound right ?
>
> ( 200/435 MHz ) /4 = 11.49 cm for each feed to the tee junction of 75 ohm
> cable.
>
>
> ----------------------------------------------------------------------------
> Andrew Rich VK4TEC
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