Hi Wes,
The justification for 5K or greater common mode choke resistance
is to limit ferrite core heating for transmitting applications.
Although it can be done, IMHO there's no imperative for 5K choke
resistance for receiving applications.
Its also not apparent to me why a choke is needed at the transmitter
or transceiver end of a coaxial cable unless their shielding effectiveness
is very poor.
73
Frank
W3LPL
----- Original Message -----
From: "Wes Stewart via RFI" <rfi@contesting.com>
To: "rfi" <rfi@contesting.com>, "Martin Kratoska" <martin@ok1rr.com>
Sent: Tuesday, January 3, 2023 10:08:04 PM
Subject: Re: [RFI] Please comment this picture
Martin, you do say close to the antenna so that is good. You don't say what
kind of antenna, so that make a difference.
I'm not one of those guys who is adverse to using sleeve cores, if there are
enough of them. Looking at the Laird data, they show impedance v. frequency
without saying whether is predominately resistive or reactive. Because it's
pretty flat, I'm guessing resistive. In that case at HF, ten cores would give
600-800 ohm.
Many who subscribe to the idea that you need 5K or higher will disagree but I
think for the average beam or resonant dipole, that is enough. The only
problem I see is that the diameter is so small. I can't think of a cable I
would want to use that would fit through those cores.
Wes N7WS
On Tuesday, January 3, 2023 at 12:04:24 PM MST, Martin Kratoska
<martin@ok1rr.com> wrote:
The attached picture displays my proposed CM choking scheme around the
antenna switch. Take a look at this and comment, please - what is
insufficient, what is an overkill etc.
The pic is also here:
https://ok1rr.com/public/choking.png
73,
Martin, OK1RR
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