n4kg@juno.com wrote:
> Winding the cable into a choke at the entrance to your house (and
> possibly at the base of the tower) 'helps' to mimimize current.
Had thought of that, tricky thing to do given the voltage slew rate
though since even a tiny bit of end-to-end capacitance would couple
the transient across.
Figuring all eight lines, for example, as a common mode source,
paralleling them in the network analysis allows for the design of a Q
of 1 second order current divider by putting a cap to ground on each
line to work against the common mode inductor in series to the
rotator controller in the shack. But this requires a known impedance
at that end in order to have a solution.
I was thinking of putting a connector on the ground window that would
short all the lines together and then to ground through a 47ohm 3W
ceramic resistor. Then the inductor back at the master ground bar
could be roughly 75uH, and each of the caps 3.9nF, which produces a
100KHz corner with a Q of about 1.
The caps would have to be high current, low inductance types, like
Panasonic M series polyester film and foil. The choke could be wound
as 8-in-hand of heavy build 30awg wire in a single layer on a 4"x0.5"
mat'l 33 ferrite rod for 38 turns. It would have to be oriented to
avoid coupling from the input terminal strip but with its ends away
from whatever can was used to hold the entire contraption. It would
also have about 0.5ohm winding resistance per wire, might not be a
good thing, I've no idea what kind of current flows in rotator wiring.
It'd also have to have mov and/or gas tubes across the lines as well
to protect the caps and limit the potential on the lines at the
entrance to the house but maybe that's overkill. If not, the trick's
sizing the @#$%@^& things so they don't explode but that requires
knowing the energy to be dissipated in a multi-strike event. Not an
easy task.
Is there a "standard" technique to applying a choke that isn't this
danged complicated that has met with success?
Thanks,
Pete, AD5HD
> Tom N4KG
> On Wed, 20 Mar 2002 21:31:11 -0600 Pete Goudreau <goudpj@mac.com>
> writes:
>> After some research, including towertalk archive searches, it looks
>> like the only protection units out there for control and rotator
>> cables are shunt types - Polyphaser and I.C.E. come to mind. While
>> researching the topic, there also seems to be a goodly number of
>> stories of lightning surges getting past exploding MOVs in said
>> protectors and blowing up most of the equipment in the shack.
>> Not being much of a fan of MOVs in the first place, I figured there
>> had to be some series type protectors out there somewhere but I'm
not
>> finding them at all. Design is relatively easy but extremely
>> difficult to test correctly.
>> Anybody have any suggestions as to the safest way to keep the lines
>> connected but well suppressed?
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