There are far less expensive solutions for receive antennas. See the
applications note about this on my website. It will be in the next NCJ.
k9yc.com/publish.htm
73, Jim K9YC
On 2/19/2019 5:35 AM, N2TK, Tony wrote:
Jim,
Thanks for all of your help with this. You have significantly increased my
confidence that I will be setting up the feedlines correctly for my 80M 4-sq.
After I do this I need to wind 6 chokes for my 75 ohm fed receive antennas.
Tnx agn
N2TK, Tony
-----Original Message-----
From: RFI <rfi-bounces@contesting.com> On Behalf Of Jim Brown
Sent: Monday, February 18, 2019 7:14 PM
To: rfi@contesting.com
Cc: Ward Silver <hwardsil@gmail.com>
Subject: Re: [RFI] Common mode choke on 4 Square feedlines without skewing
phasing?
Tony,
Here are my recommendations for 75 ohm transmitting chokes wound with FEP or
PTFE mini-coax RG179 on 2.4-in o.d. #31 toroids. Turns are wound close-spaced
(touching on the inside diameter). As previously noted, this coax has fairly
high loss, so the choke should not see more than the approximately 360W it
would see when divided equally between four verticals, and even at that power
level, it MUST be exposed to air. Note that I am NOT saying that they CAN
handle this much power -- that's up to others to verify.
160M: 27 turns 12K Ohms Rs
80M: 24 turns 13.5K Ohms Rs
40M: 22 turns 10K Ohms Rs
To develop these recommendations, I wound Grant's coax on the same four cores
at the limits of recently purchased cores used for my recent RG400, THHN, and
Teflon pair 2018 Cookbook, tabulated the data, and chose worst case (lowest)
values for Rs on each band.
73, Jim K9YC
On 2/18/2019 1:15 PM, Jim Brown wrote:
On 2/18/2019 11:40 AM, tony.kaz@verizon.net wrote:
Thanks for the input. I use dumped power to check the bandwidth.
Okay, will
use RG400 for the chokes.
That's 50 ohm coax, so not ideal for your application. KZ1W sent me
some miniature TFE coax to measure, the size of RG179, which is 75
ohms with FEP jacket. That would be a better choice. Because it's so
small (0.1-in o.d.), dissipation is fairly high, so it will be
important that it be exposed to air. I'm currently developing winding
guidelines for it. Because it's so much smaller than RG400, they are
very different.
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