Topband: Feedline Choke Placement in RX systems

[Lee STRAHAN]

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 element 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 at contesting.com> On Behalf Of Dennis W0JX via Topband
Sent: Tuesday, November 30, 2021 9:48 AM
To: topband at contesting.com; John Kaufmann <john.kaufmann at 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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