I couldn't resist.
To make a 40-10m choke balun for 40-10m yagi's use type 43
beads [1" OD x .5" ID x 1" long] slid over RG-393 teflon
coax. The balun is 17" long when completed [16-17 beads.]
The Z at 7 mhz is 1350 ohms. On 10/12m... power rating is
8500 watts CCS dead cxr.
For 75m it has to be 24" long [1350 ohms Z.]
For 160m, it has to be 30" long [1350 ohms Z]
And no... 500 ohms Z is NOT enough... take ur ARRL ant
book ...and toss it !
10 turns of 10" diam 213 u won't work on 75m either.... too
low a Z. Coiled up coax in a solenoid is a huge windload...
and a pain to manhandle on a tower. When using [expensive new]
393 teflon high power coax... the last thing u need is a megabuck
worth of coax to make a solenoid.
Besides.. a real linear will cook 213 u on 75m.
Type 43 is bomb proof... and cheaper than the type 77 beads
[type 77 is shorter .81" long]
Type 43 beads are still $2.00 each.... the inferior type 77
are $3.00 each. They are cheaper still... in bulk from Amidon.
You can also get em pre-made from Ken Hirschberg at Cal-Av
labs..[and also from Jay Terleski at Array Solutions].. comes
with a 7-16 DIN... and teflon coated 10 ga wires. His are
pumped with silicone glop... under pressure.. then bubbles
removed in a vac chamber. All siver soldered to boot. The
teflon wires are unique. Each layer of fine wires is reversed
in twist cw.. ccw...cw...ccw etc.
End result is... when u form the 10 ga wire.. it stays put !!
Won't spring back....slick.
You can't blow these babies up if you tried. They won't heat up
either. Best Balun ever made... period. You can pump 15
kw into em all day long.
The boys on the contest reflector finally figured out the same
thing. The typ W2DU baluns using 303 teflon coax.. and the
tiny type 75 beads would heat up with just a 500 w dead cxr on
all bands from 1.8 to 30 mhz. They switched to type 43
small beads... and the same small 303 teflon coax.[slightly
longer.. more beads] They ran the exact same test as b4.....
except 2200 watts.... zero heat !
I use type 43 for all my bifilar rods as well. [for fils of
thoriated tungsten fils] .. but that will be another story.
Later.... Jim VE7RF
