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@contesting.com> on behalf of john@kk9a.com
<john@kk9a.com>
Sent: Thursday, May 3, 2018 8:04:08 PM
To: towertalk@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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