I apologize for jumping into this thread and not being careful about what I
stated. I meant to state that when using 75 ohm coax (instead of a power
divider) to perform the impedance transformation, you need to use quarter wave
lines or odd multiples of quarter-wave lines to feed the antennas. To keep it
simple, use equal lengths. But, you may also, for instance, use a 3/4-wave line
to feed one yagi and a 5/4-wave line to feed the other. The 5/4-wave line is a
half-wave longer than the 3/4-wave line, so it presents a 180 degree phase
shift at the feedpoint as compared to the 1st line. In order to keep the
antennas in phase, you would then reverse the feed on one of the antennas to
cancel the 180 degree phase shift introduced by the longer coax line.
Again, I apologize for jumping in and creating confusion.
Paul, K7CW
________________________________
From: Paul Decker <kg7hf@comcast.net>
To: David McKenzie <k1fsy@vhfwiki.com>
Cc: vhfcontesting@contesting.com; Paul Kiesel <k7cw@yahoo.com>
Sent: Tue, April 13, 2010 11:06:34 AM
Subject: Re: [VHFcontesting] stacked yagi's
Thanks guys!
Just a recap, thinking outloud.
I think using the 50 Ohm power divider, any equal lenght of 50 Ohm coax can be
used.
When using the 75 Ohm version, equal odd quarter wave multiples should be used.
When stacking either vertically or horizontally, the driven portion of the
feedpoint should be oriented in the same dirction on both antennas. In my
case, I built them opposite of each other so the feedpoint connectors would
face each other.
Paul (KG7HF)
----- Original Message -----
From: "David McKenzie" <k1fsy@vhfwiki.com>
To: "Paul Kiesel" <k7cw@yahoo.com>
Cc: vhfcontesting@contesting.com
Sent: Tuesday, April 13, 2010 11:32:05 AM GMT -05:00 US/Canada Eastern
Subject: Re: [VHFcontesting] stacked yagi's
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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