Greetings All,
For the Hi-Z arrays any additional common mode choking for most all
installations would not be needed. You are correct at K3LR there are added
common mode chokes in the element feedlines. I am fairly certain that adding
these helped more with interstation isolation. I have not heard for certain
that K3LR saw any noise reduction in that system due to the addition of chokes.
He has an 8 element version that already included combiner input common mode
isolation. Tim may want to comment on this. All my Hi-Z amps have had common
mode isolation in them since day one. So placing another choke at the Hi-Z amps
seems to be not necessary. In the older designs there was no common mode
isolation on the combiner inputs on the smaller arrays meaning the three
element and the 4 element. The 8 element arrays were designed with common mode
isolation at the combiner inputs making these systems completely isolated. In
the new redesigns I have added common mode isolation to the inputs of the new 4
e
lement array design just because I thought it certainly won't hurt anything
but possibly could help. The Three element array has so much less combiner loss
and its element feedlines are so short I have not added any common mode
isolation to its inputs. I have not seen any need here in many tests of that
array.
My take on the placement would be to put them closest to the controller for
the home brew W1FV array. From my older W1FV schematics his high impedance amps
have common mode isolation built in so placing added isolation would be better
at the combiner. Building your own high impedance amps would certainly need
common mode isolation.
You are correct Dennis as it depends on the overall system design.
Lee K7TJR
Hi-Z Antennas
-----Original Message-----
From: Topband <topband-bounces+k7tjr=msn.com@contesting.com> On Behalf Of
Dennis W0JX via Topband
Sent: Tuesday, November 30, 2021 9:48 AM
To: topband@contesting.com; John Kaufmann <john.kaufmann@verizon.net>
Subject: Topband: Feedline Choke Placement in RX systems
K9YC made an interesting comment in his post, saying that the feedline chokes
would be most effective if placed at the antenna end of the feedline.
W1FV's 9 circle YCCC array has them right at the controller.
The older K7TJR combiner utilized no feedline chokes. However, I believe that
Lee's new design has built in common mode protection on the combiner circuit
board.
So what is the best way? Is placement dependent upon the combiner design?
BTW, K3LR is using 2.4 in #31 toroids with at least 24 turns of RG-179 as
feedline chokes in his 8 circle HiZ array and I believe that there are chokes
on both ends of the antenna feedlines. Of course, K3LR operates in a high
intensity, multi-transmitter environment and may need all that choking.
73 Dennis W0JX
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