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Do they still sell this kit? I bought one in a trip to USA in 1976!

Ignacio EB4APL


El 07/11/2020 a las 18:25, David Eckhardt escribió:

With a current balun or CM choke, it is the reactance (inductance) that

is

mostly responsible for the balun action. In the case of the choke balun,
beads installed along the coax at the feed with 31 or 43 material, they
form a reflective 'filter'. There is some absorption, but most of the
action is due to reflection from the inductive reactance they form
installed on a conductor. As such, they form a high-Z isolation point
between the feeder and the antenna center, assuming they are installed at
the feedpoint of the doublet. In the case of the CM choke, the common

mode

currents are reflected by the inductive reactance of the windings as with
the current balun and the balance of current between the two conductors

is

forced through induced opposing magnetic currents within the cone. This

is

the reason I prefer the CM choke for the purpose. In either case, the
common mode current is reflected to a large extent by the inductive
reactance back where it originated. Installation of a balun at the
feedpoint of a doublet does not make the CM currents go away, it just
establishes a 'fence' for those currents between non-antenna associated
currents (on the outside of the feedline) and the radiating structure.

I can assure you the core Amidon sells with their balun kit is a red

core,

Typie 2 material:
[image: image.png]

Ferrites designed to introduce loss or absorption are good EMC/RFI
suppression devices. In the case of these ferrites, current is induced
into the ferrite structure where resistive losses to the induced magnetic
currents turn that energy to heat. These ferrite structures become

rather

hot when used in the balun application for transmit energy.

If the balun action of the various cores were absorptive, they why are
'good' baluns specified as having , for example, 1000 ohms series
'resistance' at the lowest frequency of interest (or at least 5X the

system

impedance). This should be specified as +j1000 to be correct. It is the
reflection of the CM currents that this high-Z addresses, not the
absorption of CM energy. If absorption were the requirement, then why

the

higher +jX for better balun performance?

Dave - W?LEV

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