Hi Dave,
First, in my message below, I mis-stated about multiple half-wavelengths. I
meant to say multiple quarter-wavelengths. But, to answer your question:
Yes, use two equal lengths of 50 ohm coax. Make sure the yagis are both mounted
the same way.
73,
Paul, K7CW
________________________________
From: david vari <david_vari@yahoo.com>
To: Paul Kiesel <k7cw@yahoo.com>
Cc: vhfcontesting@contesting.com
Sent: Mon, April 12, 2010 4:08:33 PM
Subject: Re: [VHFcontesting] stacked yagi's
all replies have been interesting to read. but in my case i can not stack one
on top of the other my one 13b2 is just above the houses in my area and need to
go side by side. will i still need 2 equal lenghts of coax with my pd-2 power
divider?
dave-n2rhl
--- On Sun, 4/11/10, Paul Kiesel <k7cw@yahoo.com> wrote:
>From: Paul Kiesel <k7cw@yahoo.com>
>Subject: Re: [VHFcontesting] stacked yagi's
>To: vhfcontesting@contesting.com
>Date: Sunday, April 11, 2010, 1:56 PM
>
>
>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@comcast.net>
>To: vhfcontesting@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-----
>
>
>
>
>
>------------------------------
>
>
>
>Message:
> 2
>
>Date: Sat, 10 Apr 2010 03:07:25 +0000 (UTC)
>
>From: Paul Decker <kg7hf@comcast.net>
>
>Subject: [VHFcontesting] stacked yagi's
>
>To: vhfcontesting@contesting.com
>
>Message-ID:
>
>
><1210296233.8429611270868845217.JavaMail.root@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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>
>
>End of VHFcontesting Digest, Vol 88, Issue 9
>
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