On Sun, 23 May 2010 07:01:52 -0700, Jim Thomson wrote:
>## OK, what abt #77 ferrite ??
>## the idea here is to supplement my existing type 43 bead baluns. The
existing type 43 bead baluns are 17" [24" long on 80m].. with a 7-16
>female din on the end. I could slide some type 31/77/43 beads
>over the 393 coax... before installing the male 7-16 din connector. Put
>some heat shrink over the beads, then plug the mess into the back end of
>the existing balun. That would make for a simple, clean install.
Yes, it's pretty, but it doesn't do much. Still low choking Z, and it's
inductive at HF.
>## Plan B is to wind 2-3 turns of 393 around 4-6 x stacked type 31
cores.... then install the 7-16 male Din connector.... then pug into the
>back end of existing bead balun..as above.
No problem with adding the wound chokes in series with other chokes. You'll
need more than 2-3 turns. See my Cookbook, which digests the measured data
into a simple form. Follow the recommendations for RG8/RG11 for each band.
>Type 31 ferrite comes in 2.4" OD x 1.4" ID... and also 4" OD x 3" ID x
>1" high .
I haven't seen or measured the 3-in ID toroids, but I would expect them to
behave like the 1.4-in ID toroids because the cross sectional area is the
same.
>I could also use type 43 toroids.... or type 77 toroids.
As noted in my Cookbook, #43 is slightly superior to #31 above 10 MHz, #31
is much superior to #43 below 5 MHz. #77 is not a good choice for HF.
>393 teflon coax is aprx .391" OD on the jacket. If toroids are used...
>coax wrapped 1st... THEN the 7-16 male din plug installed.
I can wind 5 turns of most RG8/RG11 (typically 0.405 in) through 1.4-in
toroids with a PL259 attached, 7 turns without the connector. This cable is
slightly smaller o.d., so you should be able to achieve that.
At HF, wound chokes are FAR superior to bead chokes. See the measured data.
I wouldn't expect to see any heating on an antenna that wasn't badly
broken, and the heating if there was any would be mostly in the coax, which
appears to be built to take it.
73,
Jim Brown K9YC
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