Everything I've read about phasing two 50 ohm yagis with 75 ohm cable
stipulates equal, odd multiples of a quarter wavelength at the desired
frequency. Both feed points should face the same direction; if you are
stacking vertically, then both are on the bottom; horizontally, both on the
left. I have two 2M9FMs horizontally stacked using 9/4 wavelengths of RG59
coax to achieve the proper match and make the distance to the mast in the
center.
When stacking with 50 ohm coax I have seen even half-wave multiples used.
http://www.scribd.com/doc/8511618/Building-Phasing-Harnesses
.
On Sun, Apr 11, 2010 at 1:56 PM, Paul Kiesel <k7cw@yahoo.com> wrote:
> 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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