Yep, I printed out your info to read tonight about receive antenna chokes and
use your advice.
N2TK, Tony
-----Original Message-----
From: Jim Brown <jim@audiosystemsgroup.com>
Sent: Tuesday, February 19, 2019 2:21 PM
To: N2TK, Tony <tony.kaz@verizon.net>; rfi@contesting.com
Cc: 'Ward Silver' <hwardsil@gmail.com>
Subject: Re: [RFI] Common mode choke on 4 Square feedlines without skewing
phasing?
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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