RFI
[Top] [All Lists]

Re: [RFI] Common mode choke on 4 Square feedlines without skewing phasin

To: <jim@audiosystemsgroup.com>, <rfi@contesting.com>
Subject: Re: [RFI] Common mode choke on 4 Square feedlines without skewing phasing?
From: "N2TK, Tony" <tony.kaz@verizon.net>
Date: Tue, 19 Feb 2019 08:35:48 -0500
List-post: <mailto:rfi@contesting.com>
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.
_______________________________________________
RFI mailing list
RFI@contesting.com
http://lists.contesting.com/mailman/listinfo/rfi

_______________________________________________
RFI mailing list
RFI@contesting.com
http://lists.contesting.com/mailman/listinfo/rfi

<Prev in Thread] Current Thread [Next in Thread>