Airdux is the stouter of the two - but still plastic - maybe a nylon or
delrin, but not polycarbonate like miniductor.
--
Neal, Nl7VL
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On Fri, 14 Jan 2011 13:43:49 -0500
"Rick - NJ0IP / DJ0IP" <Rick@DJ0IP.de> wrote:
> With those coil stock you have to be careful.
> B&W usually made two versions of coils, with the cheap one using
> plastic, which melts when it is hot.
> The more expensive ones used some kind of composite, which would take
> a lot more heat before melting.
>
> Maybe I'm being unfair, but I will assume the MFJ coils are the cheap
> plastic versions.
>
> 73
> Rick
>
> -----Original Message-----
> From: tentec-bounces@contesting.com
> [mailto:tentec-bounces@contesting.com] On Behalf Of Dr. Gerald N.
> Johnson Sent: Friday, January 14, 2011 11:28 AM
> To: tentec@contesting.com
> Subject: Re: [TenTec] ant
>
> I do have a small Johnson Matchbox, but it doesn't have the
> versatility needed for my wire antennas, so I've built my own tuners.
> My big tuner (built long before I owned an E. F. Johnson tuner) is
> overbuilt with a huge coil that's too long with a link in the center.
> I use a fixed link with a variable capacitor, probably 300 pf
> maximum, in series with the link. I use a pair of similar capacitors
> for the output side equipped with alligator clips so I can pick turns
> on the coil and capacitor connections either series for low impedance
> or parallel for high impedance. The link and the output coil do the
> balancing, I don't force balance by grounding the center of the
> output coil, though that often works.
>
> For 21 MHz and up, my tuners have been single band with a dual
> section capacitor that forces balance by grounding the frame of the
> capacitor. Then I tap the feed line to the turns where it matches.
> And use a variable link instead of the series capacitor on a fixed
> link.
>
> These tuner circuits are discussed in my 2002 ARRL Handbook long
> about figure 19-10. Construction is illustrated in the 17th ARRL
> Antenna Handbook on page 25-7. For the loads described they all work,
> some better for some loads than others.
>
> MFJ now makes coil stock, that we used to get from B&W. And variable
> capacitors. Mouser carries ceramic wafer rotary switches as does RF
> Parts. RF parts has them in PA sizes for good money. Not cheap.
>
> These circuits have been working for 70 or 80 years.
>
> Sometimes when a tuner doesn't have enough reactance or impedance
> range, we can adjust outside the tuner. Like adding more shunt C or a
> series coil on the LF end, changing the feed line length as much as
> an eighth of a wavelength, or for a very low impedance feed point
> using a ferrite core conventional transformer. These solutions will
> tend to be specific to one antenna on one band.
>
> I'm no fan of tuning a balanced line through a balun. I lost faith in
> that long ago when I tuned up on 10m and didn't hear signals, and
> when I unhooked the antenna the match into the tuner didn't change.
> I'd resonated the balun, not the antenna. A concept that I like
> better, but haven't done it yet is to float the tuner and feed the
> tuner through a balun so the balun always sees 50 ohms or 200 ohms
> depending on the tuner design and without significant reactance. I'm
> thinking the MFJ remote tuner that gets its power through the coax
> might be good for that, but I've not yet tried it.
>
> 73, Jerry, K0CQ
>
> On 1/14/2011 8:16 AM, Ed Purvis wrote:
> >
> > I need the definition and model number of a "good tuner".Hopefully,
> something without a balun. Maybe somethingalong the lines of the K1JJ
> homebrew tuner also??
> > tnx, Ed
> >
> > IF AT FIRST YOU DON'T SUCCEED, SKY DIVING'S NOT FOR YOU.
> >
> >
> > --- On Thu, 1/13/11, Dr. Gerald N. Johnson<geraldj@weather.net>
> > wrote:
> >
> > From: Dr. Gerald N. Johnson<geraldj@weather.net>
> > Subject: Re: [TenTec] ant
> > To: tentec@contesting.com
> > Date: Thursday, January 13, 2011, 4:41 PM
> >
> > And 6m and 2m quite well. And probably 160 with a good tuner.
> >
> > 73, Jerry, K0CQ
> >
> > On 1/13/2011 3:13 PM, ROD wrote:
> >> If you don't work 160 then a good ant. is the double extended
> >> zepp 83 ft
> on each side for a total 166 ft feed with 450 or 300 ohm ladder line.
> with a good tuner you can work 80 40 20 15 12 17 10 meters. the hams
> of yester year use this antenna. 73 Rod Dewald W3KRQ
> >> _______________________________________________
> >>
> > _______________________________________________
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> > TenTec@contesting.com
> > http://lists.contesting.com/mailman/listinfo/tentec
> >
> >
> >
> >
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