The referenced Ameritron/MFJ part number is an 11 inch coil (aka BMW coil
stock of old), coil wound into 4 polystyrene rods. This one is 3 inches
diameter, four turns per inch, 10 AWG tinned bare solid copper.
This stuff is used in various Ameritron amps as part of the output Pi-L
networks. I have found that it's very touchy to cut sections for specific
lengths. The trick is before cutting anywhere on the 11 inches, across the
whole coil use a tiny drop of Krazy glue, or its equivalent, on both sides
of the wire at the points the wire is melted into the polystyrene rods.
This really stiffens up the "feel" of the coil. Then cut the wire first and
then the rods with a Dremel tool for specific needed lengths. I bought two
of the 11" lengths the last time, which should last me for a while.
Seems to me it was back-ordered for a couple months. They have to
manufacture a batch. And they are not going to undercut the coil on site
needed to manufacture their amps.
You can also get the edge-wound (flat) 1/4 inch by 1/16 inch coil that they
use in the ATR-30 rotary coil tuner. That's a killer piece of copper.
Good luck all.
73, Guy K2AV
Dunno what you guys do from across the pond to speed it up.
On Thu, Aug 30, 2018 at 5:55 PM Jim Thomson <jim.thom@telus.net> wrote:
> Date: Thu, 30 Aug 2018 07:44:04 +0100 (IST)
> From: MR TREVOR DUNNE <ei2glb@eircom.net>
> To: ''''''topband List' <topband@contesting.com>
> Subject: Topband: Air Wound Coil
>
> <Hi All
>
> I'm looking for an Air wondering coil like in this link,
>
> http://www.mfjenterprises.com/Product.php?productid=404-0669
>
> I've had one on order from MFJ via a UK company for 4 months now and no
> sign of it, I want to build a at matching network for my 160m inverted T
> using it or something similar,
>
> Can anyone tell me where I can get one of these or similar that is in
> stock today,
>
> I don't have access to the tools/parts to wind one my self,
>
> Thanks
> Trevor
> EI2GLB
>
>
> ### That mfj coil is listed as a whopping 79 uh ! I cant see having
> to use anywhere near that value for a simple 160m T ant.
> I calculated the value for a buddy a few yrs back, for his 160m T
> vertical, and it was no where near 79 uh...just a few uh. It was easy
> to wind by hand.
> The ant was resonated a bit on the high side, so the Xc of the ant + the
> coil formed a step up L network. No different than using a
> beta match or hairpin on any mono band yagi. Think we used 8 gauge
> wire.. which is .128 copper. It was freestanding, after being removed
> from the
> form used to initially wind it on. Coil was oriented vertically..and
> placed right across the feed point. Then the vert is also DC grounded.
>
> Jim VE7RF
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