Re: [RFI] Experience with RF-INQUIRY Hi-Q Chokes?

["Ian White, G3SEK" <G3SEK@ifwtech.co.uk>]

Tom Rauch wrote, in response to:
> > just came across an advertisement of a common-mode choke produced by
> > RF-inquiry of Japan. They claim to provide at least 50 dB of reduction of
> > common-mode-currents.
I agree with Tom's earlier post, that the 50dB target is hard to hit 
without accepting a reduced bandwidth.

Also, "at least 50dB" has to be at the top and bottom edges of the 
claimed bandwidth, so the mid-band performance would have to be better 
still.

Hmmm... we seem to be deep into the territory where "the more you claim 
to have achieved, the more you need to prove it."


Tom added:
> By the way, if the common mode source and load impedances are a fraction of
> an ohm it is easy to obtain -50dB. If the common mode source and load
> impedances (which have nothing much to do with line impedance) are 1000
> ohms, we would be lucky to see 10dB.
>
> It depends on how they measured.

The standard method is to measure between a 50-ohm source and load - the 
input being to the coax shield at one end, and the output from the 
shield at the opposite end.

The 50-ohm source and load may not represent any particular real-life 
application, but they do allow fair comparisons between competing 
products.


--
73 from Ian G3SEK         'In Practice' columnist for RadCom (RSGB)
                           Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek
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