Topband: 160m noise

[Jeff Maass]

> -----Original Message-----
> From: Tom Rauch [mailto:w8ji at contesting.com]
> Sent: Wednesday, November 10, 2004 8:47 PM
> To: jmaass at columbus.rr.com; Larry Molitor; topband at contesting.com
> Subject: Re: Topband: 160m noise
> 
> >       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.

Tom:

That seems likely - same dimensions, same material.

I've gotta tell you, Amidon's numbering scheme seems to
make more semblance of sense. Actually *describing* the
item in some way that doesn't require a catalog to decipher
- imagine that!

> 
> 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.

I'm mailing one to you tomorrow morning to test and 
then to retain to use for ring toss, or napkin ring, or for
the central part of an Xmas wreath, or whatever.

In our case we (and I would guess most wanting to apply
chokes in receiving antenna applications) only care
about the effectiveness of the choke from 1.5 to 4 MHz.
Any best-guess of a more appropriate material and core
size?


> 
> 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.

Getting a good ground at both ends of a feedline (and 
along the run of the feedline) is not a problem in Ohio,
but its more of a fantasy on the dust, coral and hardpan
of Curacao.

A compromise is the best we can hope for, preferably with
a minimum of  requirement for network analyzers. We have
an MFJ 259, a good DVM, and lots of receivers!

Larry W7IUV pointed earlier to the use of an isolation 
transformer for the flag/pennant, and also pointed me to
your discussion of the subject. I have a bagload of Amidon
BN73-202 binocular cores (yes, I expect they are the same 
as the Fair-Rite 2873000202 you stack), and I'll replace 
the previously-used pennant transformer as a start to 
eliminate common-mode problems.


73,

Jeff Maass  K8ND