[Elecraft] Common mode chokes
Ian White
gm3sek at ifwtech.co.uk
Tue Aug 9 17:41:16 EDT 2016
>
>Add another winding to a choke and it magically becomes a transformer!
>
Unfortunately that doesn't work for RF current measurement. The
objective for a choke is to create a high series impedance, but the
objective for an RF current transformer is exactly the opposite: to
avoid disturbing the situation that is being measured, the impedance
inserted into the main line must be as low as possible.
To achieve a low impedance in the main line, an RF current transformer
requires *ONE* pass of the primary winding (feedline) through the core
and typically about 10 turns on the secondary. The secondary must also
be terminated in a low load resistance, typically about 50 ohms. With a
1:10 turns ratio the series impedance inserted into the main line is
then about 0.5 ohms.
That is why a common-mode choke and a common-mode current transformer
are two completely different creatures. Don't confuse them.
73 from Ian GM3SEK
>-----Original Message-----
>From: Elecraft [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of
>Josh Fiden
>Sent: 09 August 2016 22:16
>To: elecraft at mailman.qth.net
>Subject: Re: [Elecraft] Common mode chokes
>
>Add another winding to a choke and it magically becomes a transformer!
>
>73,
>Josh W6XU
>
>On 8/9/2016 1:56 PM, MaverickNH wrote:
>> Just wondering - short of +/- RF Burns and Audible Noice, can one
readily
>> detect/measure Common Mode Current on a coax antenna feedline?
>>
>>
>>
>> --
>> View this message in context:
>http://elecraft.365791.n2.nabble.com/Common-mode-chokes-
>tp7621305p7621430.html
>> Sent from the Elecraft mailing list archive at Nabble.com.
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