[VHFcontesting] stacked yagi's

Sun Apr 11 10:56:46 PDT 2010

If you use a power divider, use two equal lengths (it doesn't matter how long they are) of 50 ohm coax, from the power divider ports to each yagi. The impedance transformation is going on in the power divider, so  you already have 50 ohms available at each of the power divider's ports.

If you elect to use coax, use 75 ohm coax so you get the proper impedance transformation. You must use exact multiples of an electrical half wavelength. You will want to use as little coax as possible to reduce your losses in the coax, so if you elect to make both lengths of coax an EVEN number of half wavelengths long, then you will orient the feeds of the antennas so that they are both on the same side, symmetrical with each other, if you will. But, if you decide to have one length of coax be an EVEN number of half wavelengths long and the other length of coax an ODD number of half wavelengths long, then you will need to reverse the feed on the second yagi so that it is reverse from the first yagi. This is because the extra half wavelength of coax that you have going to one of the yagis will result in a 180 degree shift in phase. So, in order to get both antennas in phase with each other, you will need to reverse the feed on one of them by flipping the
 antenna upside-down or by mechanically re-arranging the feed.

73, 
Paul, K7CW

________________________________
From: Jon Casamajor <k6el at comcast.net>
To: vhfcontesting at contesting.com
Sent: Sat, April 10, 2010 2:09:05 PM
Subject: Re: [VHFcontesting] stacked yagi's

Hi Paul,

I am a little confused on what you are doing I guess.   I have two M²
420-50-11 Yagis stacked vertically, that is one above the other.  I am using
a standard M² splitter and stacking harness and the distance between the
Yagis is 28” and the phasing lines are identical in length however I’m not
entirely sure of their length as they are living at about 100’ now.  J

You said… “(note that I might switch units without warning)”, so I may not
be seeing something here.  If both phasing lines are the same length
wouldn’t they be fed in phase?  My little stack is on my QRZ page in case
I’ve confused you in return.  The little stack works quite well but I’m
planning to replace it soon with a 4329WL as the stack is a little sharp and
I need a bit more ERP.

73, Jon

K6EL

-----Original Message-----

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Message: 2

Date: Sat, 10 Apr 2010 03:07:25 +0000 (UTC)

From: Paul Decker <kg7hf at comcast.net>

Subject: [VHFcontesting] stacked yagi's

To: vhfcontesting at contesting.com

Message-ID:

<1210296233.8429611270868845217.JavaMail.root at sz0009a.westchester.pa.mail.co
mcast.net>

Content-Type: text/plain; charset=utf-8

Hey group, 

I'm in the process of stacking two 11 element 70cm yagi's.? I've modeled it
in eznec and I think the optimum distance is about 42".? (note that I might
switch units without warning). 

Once I have the two 50 yagi's stacked, my model says I need to have one 180
out of phase, does this seem right? 

If that is the case, then I need different lengths of coax to feed each
antenna. 

Should I use a 50 ohm power divider and feed each antenna with 1.25w and
1.75w 50 coax, or should I feed with 1.25 and 1.75 75 Ohm coax and simply
use a T connecter.? Is there an advantage of one over the other? 

thanks for any help, 73, 

Paul (KG7HF) 

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