Topband: best core material?

[Shoppa, Tim]

You'll notice in my original response I was trying to determine if this is only for receiving or if you were planning on transmitting with this transformer too :). FT-140 is pretty huge for a receive antenna transformer and winding just a few turns of skinny wire through it would look particularly odd.

Binocular cores will have better coupling and less leakage than toroidal cores. Toroidal cores might be preferable if you had to wind so many turns that it wouldn't be possible to fit through the binocular holes (admittedly the hole in a toroid is much bigger than the holes in a binocular core :)!)

Tim N3QE

From: James Rodenkirch [mailto:rodenkirch_llc at msn.com]
Sent: Monday, August 05, 2013 2:20 PM
To: Shoppa, Tim; BY THE LAKE; topband at contesting.com
Subject: RE: Topband: best core material?



 I wasn't going to use a binocular core, Tim - I was going to use the Amidon FT-140-43 OR the FT-140-77 IF it made any noticeable difference....is there some magical reason to use binocular vice standard "round"?


> From: tshoppa at wmata.com<mailto:tshoppa at wmata.com>
> To: rodenkirch_llc at msn.com<mailto:rodenkirch_llc at msn.com>; magoo at isp.ca<mailto:magoo at isp.ca>; topband at contesting.com<mailto:topband at contesting.com>
> Subject: RE: Topband: best core material?
> Date: Mon, 5 Aug 2013 18:12:48 +0000
>
> If receive only, you will do just fine using the 2873000202 binocular 73 material core that Tom mentions.
>
> I think this corresponds to Amidon part number BN-202-73. Newark stocks the part under the original Fair-Rite 2873000202 number.
>
> Tom shows 2:5 ratio but I've done other ratios just fine.
>
> I am very very impressed with the 2873000202 core, in fact I also use it in some DC-DC converters and the core just barely gets warm at the 10 watt level. Whenever I've accidentally transmitted into my receive antenna, the transformer survives just fine, it's the terminating resistor that goes up in smoke. I try not to make a habit of it :-)
>
> Tim N3QE
>
> -----Original Message-----
> From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of James Rodenkirch
> Sent: Monday, August 05, 2013 2:04 PM
> To: BY THE LAKE; topband at contesting.com<mailto:topband at contesting.com>
> Subject: Re: Topband: best core material?
>
> Sorry - didn't make it crystal clear that this is a Delta shaped variant of a EWE antenna!!!!
>
> My bad for not utilizing all of the necessary verbiage to make that clear....you see it in ON4UN's latest book on page 7-104.
>
>
>
>
> > From: magoo at isp.ca<mailto:magoo at isp.ca>
> > To: rodenkirch_llc at msn.com<mailto:rodenkirch_llc at msn.com>
> > Subject: Re: Topband: best core material?
> > Date: Mon, 5 Aug 2013 14:00:48 -0400
> >
> > A full-wave delta loop would have the transformation done with a 1/4
> > wave line of 75 ohm cable. This must be something other than a full-wave loop?
> >
> > Bill VE3NH
> > ----- Original Message -----
> > From: "James Rodenkirch" <rodenkirch_llc at msn.com<mailto:rodenkirch_llc at msn.com>>
> > To: <topband at contesting.com<mailto:topband at contesting.com>>
> > Sent: Monday, August 05, 2013 1:33 PM
> > Subject: Topband: best core material?
> >
> >
> > >
> > > I have a schematic for a delta shaped loop that shows I'll need an
> > > 18:1 transformer to transform the 950 ohms of the antenna to 50 ohms
> > > (feeding it with 50 ohm coax).
> > >
> > > One transformer diagram shows an FT-140-43 core being used.
> > >
> > > BUT, looking over some of Tom's, W8JI, write-ups, I see where he
> > > uses 73 material instead.
> > >
> > > I see where 77 material replaced 73 material so -- is an FT-140-77
> > > the mo betta way to go?
> > >
> > >
> > > Thanks, in advance, for any advice/info. Jim Rodenkirch K9JWV
> > >
> > >
> > >
> > > _________________
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