> 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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