[TowerTalk] CMC-230-5K

[Jeff AC0C]

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 at 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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