[TowerTalk] choke / balun design needed

[Joe Subich, W4TV]

On 2015-04-27 1:02 PM, TexasRF--- via TowerTalk wrote:
> So, is there ANY solution to providing a feedline choke for an OCF
> dipole used with high power?

Gerald, they typical solution is to cascade a 4:1 current balun *and*
a high choking impedance common mode choke.  The problem is maintaining
the high impedance across the entire operating range of the antenna.
By the time one has the 4:1 current balun (two cores) plus a pair of
high impedance chokes in series (one for 20-10, the other for 80-30)
that is a substantial amount of bulk *and weight* at the feedpoint.

It is somewhat practical for low power (< 250W) installations but gets
difficult for "legal limit" applications.

73,

    ... Joe, W4TV


On 2015-04-27 1:02 PM, TexasRF--- via TowerTalk wrote:
>
>
> In a message dated 4/27/2015 11:41:23 A.M. Central Daylight Time,
> jim at audiosystemsgroup.com writes:
>
> On  Mon,4/27/2015 6:50 AM, Alex Malyava wrote:
>> What would be the bestest  design for choke or balun to be used with
> dipole
>> or OCF  dipole?
>> Like what type of core, number of turns or number of  beads?
>
> k9yc.com/RFI-Ham.pdf
>
> See the Choke Cookbook and text that  precedes it.
>
> An off-center fed antenna is inherently poorly balanced,  so it puts a
> high common mode current on the feedline, which in turn  places a high
> common mode voltage across any choke. It is well known that  even very
> good common mode chokes are likely to fry (fail destructively)  when used
> with even moderate power levels. You MIGHT get away with it at  100W, but
> at some higher power level it WILL break.
>
> 73, Jim  K9YC
>
> So, is there ANY solution to providing a feedline choke for an OCF dipole
> used with high power?
>
> 73,
> Gerald K5GW
>
>
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