In my experience guys with antennas close to the house should do a RFI
generator "bug hunt" a couple of times a year. Pickup by the antenna from
the many directly radiated or re-radiated noise sources in the typical house
is certainly the first stop in finding the largest contributors to the
observed noise floor.
73/jeff/ac0c
www.ac0c.com
alpha-charlie-zero-charlie
-----Original Message-----
From: Jim Brown
Sent: Tuesday, April 19, 2016 3:02 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] CMC-230-5K
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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