The standard connection from the porcelain insulated connections to the
BC-939 is INDEED 50 ohm coaxial cable.
Those desiring to ELIMINATE TVI issues would NORMALLY install a Low-Pass
filter in-line between the BC-610 and the BC-939 which is already
internally wired with 50 ohm coaxial cable.
I also place the ME-165G in-line PRIOR to the BC-939 or the proper
dipole. My BC-610 location does not allow for a "wire" exiting from the
BC-939 to the outside. So it is coax to the outside.
I ALSO own a T-213, an overhauled BC-610 by depot, in August 1959. One
of the changes from BC-610 to T-213, was to remove the porcelain
insulators and replace ONE with an SO-239. I can find NO internal final
circuit mods other than this, and the schematics agree with this assessment.
As Geoff/W5MOR has indicated from his operations, I TOO have had ONE and
ONLY one gripe about getting into a CHEAP "portable" telephone since
2000. I provided the individual with the necessary information to
contact the phone company to have a filter put in place. He has NOT
returned or complained again.
There is NO question that the output of the BC-610 series, my first one
happens to be an (I) model, is indeed 50 ohms impedance. It is
unfortunate that some hams make the ASSUMPTION that since it has
porcelain insulators for the output, that it is a balanced output of
OTHER than 50 ohms.
I cannot stress the importance of obtaining the manual, carefully
studying it, and pay close attention to the details. The ME-165G is
unquestionably a 50 ohm input SWR/Wattmeter/dummy load. It comes with
"N" connectors for input and output.
Don is ABSOLUTELY correct!
The use of 44ft and 77ft "wires, AND the use of the "term" long wire, is
the military's AND the manufacturer's. If you are going to use a dipole
do NOT use the BC-939! It's intent was for the specified wire lengths
and/or the issued whip antenna.
Of course I have not pursued a whip installation. It would seem to be a
useless endeavor as the 160, 80, 40, and 20 meter bands are "normally"
of horizontal polarization. I see no logic in operating in cross
polarization, and making communications more difficult than necessary.
Bob - N0DGN
Donald Chester wrote:
The final is single-ended, but the plate tank circuit is balanced just
as in a pushpull amplifier. This is the classic plate-neutralised
triode final. The other half of the coil functions to generate the
out-of-phase rf voltage required to neutralise the circuit. True, the
tube works into only half the coil, but the circulating current of the
resonant tank circuit is present in the entire coil, which along with
the split-stator variable tank capacitor make up the tuned circuit.
The Q of the tank is determined by the LC ratio of the entire coil and
capaciter.
The circuit is inherently balanced. The flywheel effect of the tank
circuit takes care of the fact that the rf pulses are introduced on
only one end of the coil. The link output on the BC-610 came from the
factory balanced, with two ceramic insulators at the output. I have
seen many of these converted to an unbalance output by grounding one
side to the cabinet and using a SO-239. But the link in the middle of
the tank coil is inherently a balanced output.
Don K4KYV
--
Bob - NØDGN
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