Topband: 160m noise

[Pete Smith]

The common-mode choke arrangement described by ON4UN in his Low-Band DXing 
book (Third Edition, Fig. 7-19 and the text in section 9.2 on pages 
7-18/19) seems to meet Tom's specification -- high series impedance and 
low-impedance shunting to ground.

73, Pete N4ZR

At 08:47 PM 11/10/2004, Tom Rauch wrote:

> >       So, who has *practical* advice of how to apply a
>choke
> >       for flag/pennant antennas? I've been winding 15-20
>turns
> >       of RG8X in an FT240-77 core.
>
>Jeff,
>
>Amidon, being a distributor, makes up their own numbers.
>That part looks like it might be a Fair-rite 5977003801,
>which is a  2.4 od x1.4 id x .5 thick core.
>
>I'm not sure if that core is a good idea or not, especially
>with multiple turns. I see some people recommend that core
>in HF baluns with multiple turns, but I'd be a little
>cautious with that. 73 material rolls off sharply in
>impedance above 2MHz in a small core and isn't good at all
>at HF in large cores. 73 and 77 materials are similar.
>
>Just guessing, I suspect it isn't a good core above 1.8MHz
>as a choke. Of course I've never measured 77 material in a
>large multi-turn  core. Maybe someone else has. If I can get
>a sample, I'll measure one.
>
>In any event, no one is saying your cores won't work. What I
>am specifically saying is tossing a few beads on a hunk of
>coax is not all it is cracked up to be. The system needs a
>combination of impedance shunting to ground and series
>impedance. We are trying to build an attenuator pad, and
>without low impedance shunt elements adding a low to medium
>series impedance isn't going to exactly yank the cape off
>Superman.
>
>73 Tom
>
>
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