[TowerTalk] Coax Lengths for Stacked Yagis

[Grant Saviers]

Reminds me of the phasing box I was given that had the paralleled 3 
poles of open frame relay contacts evaporated.  I think he might have 
been using slightly more than QRO when it was hot switched. Although his 
200w output transceiver couldn't drive the amp to full output.

I built a 8' tall 4' x 6' doghouse at the tower base for my stacks 
phasing lines and coiled the lower antenna coax on removable 2x4 joists 
at 6.5' to not have any coax outside or on the tower. Phasing boxes are 
inside also.  I went with equal in length to the longer one as measured 
with a TDR. 10/15/20 2x 5L each feeds are 7/8" LDF5.  I wanted the amp 
to yagi coax losses <1db on these bands and that required 7/8 
hardline.   Considering what big yagis in a tall stack cost per db, big 
hardline dbs are really cheap (as are 7/16 DINs vs an N I had to replace 
at 120').

Grant KZ1W

On 5/3/2018 17:18 PM, Wayne Kline wrote:
> 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  � 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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