W.E. Sabin, W0IYH, did an extensive article on the 1:1 current choke in
the July, 1997, QEX. He found that 100 bead type 43 chokes could handle
more power than the traditional 50 bead type 77 chokes. Note the increase
in the number of beads, as well as the type change.
He did not experiment with mixed beads, but it would seem that the 2:1
ratio of type 43 to type 77 may be instructive. If using a mixed bead
choke, perhaps using twice as many 43s for each 77 replaced might be in
order.
Heat was not the only consideration. The choke impedance for the 50-bead
type 77 model was about 1400 ohms at 15 MHz and dropped to about 600 ohms
at 30 MHz. The 100-bead type 43-6301 choke remained just above 1000 ohms
from 15-30 MHz, while the 43-5622 choke ran from 1500 down to 1200 in the
15-30 MHz span. (Readings approximate from graphs.) The performance of a
100-bead type 77 choke is not shown. However, for good upper HF
performance (as defined by the 43-5622 standard), perhaps more beads are
in order. How many are actually needed to clean a given installation of
coax may be more a function of that installation, the variables of which
are not to my knowledge well developed.
Hope this material is useful.
-73-
LB, W4RNL
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