Hi Grant,
What type of matching network are you using?
Does it have BOP mode and if so, is BOP achieved via inverting un-un or
external phase line?
Generally speaking, the distance from the match to the antennas makes no
difference other than acting as an extension of the feedline from the
transmitter to the match. Keep the feedlines the same length between each
antenna and the match or you won't achieve BIP.
Matt
KM5VI
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of Grant
Saviers
Sent: Saturday, February 07, 2015 8:48 PM
To: TowerTalk@contesting.com
Subject: [TowerTalk] Coax lengths for phasing a stack
I'm ruminating about what lengths I need for 5L over 5L stacks to equalize
the antenna feedpoint phase. The literature seems thin and the common
answer is "make the feed-lines the same length", which I am certain will
work.
However, when the stack separations are sufficient, there may be more than 1
wavelength of coax needed to equalize the lengths. e.g. 60'
separation on 20m at 0.89 vf (LDF5) is just about 1 wl. It seems to me
there is little downside with ham radio modulation systems to phase at 0
(equal lengths) or +/- n * 360 degrees (where n is 1 or 2). Perhaps some cw
waveshaped attack/decay envelopes will change a tiny bit, but that seems
like a slight downside.
So it may work out that no extra phasing line is needed for certain
separations. I am planning that all misc lengths of coax's and types are
the same for both antennas (rotator loops, boom and choke lengths).
Then there is the slightly counter-intuitive result that making the longer
(higher antenna) feedline a bit longer minimizes the coax used in the
phasing at some separations. And one more trick would be to reverse the
outputs of one side of the TLT matching transformer for BIP to eliminate 1/2
wl of phasing line. It wouldn't matter for Top or Bottom only use.
So, is this analysis correct? Any other options for using less coax?
Grant KZ1W
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|