Hi Bob,
It can't hurt, but it's also unlikely to help unless your grounding and
bonding is poor.
It IS a good thing to add a second choke on feedlines for wires that are
long enough to interact with verticals in your antenna farm, and also to
reduce the common mode voltage, and thus the power-related stress, on
the choke at the feedpoint.
73, Jim K9YC
On Tue,4/19/2016 12:27 PM, Bob K6UJ wrote:
Jim,
I am using your choke design on both of my beams. With all this
discussion on chokes it got me to thinking.
My tower is only 10 feet away from the back of the house. I'm not
sure how much noise I have from the house so I am going to try adding
an additional choke on the lower end of the coax going in to the
shack. I hope I am pleasantly surprised and get a lower noise level.
Bob
K6UJ
On 4/19/16 10:06 AM, Jim Brown wrote:
There's something I don't understand here. In 2007, I published the
research upon which all of this is built, with measured data for a
broad range of chokes for the ham bands, and with full instructions
for buying the cores at very good prices, and a "cookbook" for the
various ham bands. Why in hell would you want to pay someone 3x the
cost of doing it yourself, when all you have to do to do it yourself
is wind turns of coax through ferrite cores?
AND -- l would not trust any published power ratings for ANY chokes
without understanding the common mode voltage that they will see in
any given installation. To do that, you've got to put them in an NEC
model that approximates YOUR installation. Simply putting one of
these chokes in a sealed enclosure greatly reduces its power handling
because it greatly reduces air flow around the choke.
73, Jim K9YC
On Tue,4/19/2016 3:30 AM, Jim Thomson wrote:
I just received a pair of CMC-230-5K common mode chokes...from
MyAntennas.com to experiment with.
They are configured as a line isolator, with silver-teflon
SO-239s on each side. They can also be configured as
a balun, with a pair of standoffs on the balanced ant side if you
like. Extremely well designed and built, better
than I expected.
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