[TowerTalk] Coax Lengths for Stacked Yagis

[Keith Dutson]

Nothing wrong with making the lines 1/4 wavelengths, except how is this done for a tri-bander?

73, Keith NM5G

-----Original Message-----
From: TowerTalk <towertalk-bounces at contesting.com> On Behalf Of Richard Smith
Sent: Thursday, May 3, 2018 8:09 PM
To: towertalk at contesting.com
Subject: Re: [TowerTalk] Coax Lengths for Stacked Yagis

Thanks for the feedback. There is a lot of great experience on this reflector.
Wayne,
What is the benefit of making the feedlines odd multiples of a quarter wavelength long?  I have heard this elsewhere, but have not yet figured out the benefit. Does it depend on the type of phase box - whether it is a simple relay switching box or a Stackmatch-type box with broadband transformers?
73, Rich, N6KT

      From: Wayne Kline <w3ea at hotmail.com>
 To: "john at kk9a.com" <john at kk9a.com>; "towertalk at contesting.com" <towertalk at contesting.com>
 Sent: Thursday, May 3, 2018 5:18 PM
 Subject: Re: [TowerTalk] Coax Lengths for Stacked Yagis
   
Rich,



I to am a supporter of having the phase box at the base of a tower. I am also subscribe to the notion of feed lines especially  after a switch box/phase box  be ODD multiples of  ¼ wave

Obviously taking the volicity factor  into account. There has been more then one occasion where a phase box got hot switched and had to be changed out in the DARK.



Wayne  W3EA



Sent from Mail<https://go.microsoft.com/fwlink/?LinkId=550986> for Windows 10



________________________________
From: TowerTalk <towertalk-bounces at contesting.com> on behalf of john at kk9a.com <john at kk9a.com>
Sent: Thursday, May 3, 2018 8:04:08 PM
To: towertalk at contesting.com
Subject: [TowerTalk] Coax Lengths for Stacked Yagis

I missed seeing your Bonaire tower construction project in March but I heard that you made positive construction progress with one tower. It's definitely not easy building a station away from home.

It is a wise choice to put the antenna relays at the base of the tower. It is really convenient when trouble shooting and relays are probably the most problematic electrical part of the antenna system.

My phasing relays are also at the tower bases. I run equal lengths of Heliax up the tower and coil the excess.  Shortening one coax 1/2 wl will give you a very high radiation angle.  Shortening a coax by one wavelength seems like it will give you the correct radiation pattern but is the one antenna a cycle off? Equal length feedlines is so easy.

John KK9A  (PJ4R in 2018 WPX Phone)




Richard Smith n6kt wrote:


I am part of a team that is building a station that will incorporate stacked yagis on 20 thru 10 meters. We plan to put all of the RF switching at the base of the towers, for ease of troubleshooting and maintenance. My question deals with the lengths of the coax runs between the yagis and the switching box at the base of each tower.

Example - 15 meter stack:

Upper Yagi at 150'Middle Yagi at 120'Lower Yagi at 90'
One option is to run equal lengths of coax from each yagi down to the switch box, and coil up the excess coax from the middle and lower yagis. But does it make more sense to use shorter runs of coax from the lower antennas to the switchbox? Specifically, if the coax runs from the lower yagis are shorter by multiples of one-half wavelength compared to the upper yagi (using the velocity factor of the coax in the calculation), would all of the yagis still be in phase?
Thanks in advance,
73, Rich, N6KT

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