[Boatanchors] Ferrite Choke

[Geoff]

As Im sure Gary is aware there is a lot more to creating a good common mode 
choke than just winging it without understanding what is involved.

Ive had good results with a HP-4815A Vector-Impedance meter. By good I mean 
acceptable to my needs realizing the possible measurement errors from 
strays.

Here is a good paper on the subject that goes into a lot of detail. There 
are errors in his measurements that have been covered elsewhere and the 
number of the large ferrite toriods can be substantially reduced.

http://www.yccc.org/Articles/W1HIS/CommonModeChokesW1HIS2006Apr06.pdf
----- Original Message ----- 
From: "mac" <w7qho at aol.com>
To: <garyschafer at comcast.net>
Cc: <boatanchors at mailman.qth.net>
Sent: Monday, July 16, 2012 12:03 AM
Subject: Re: [Boatanchors] Ferrite Choke


> Hi Gary, it's ben a while....
>
> Yep, I know all that.  Special considerations concerning radiation
> pattern,noise or
> RF feedback existing or anticipated then OK.  For normal Ham
> installations, though, just give it a
> simple first try and maybe save yourself some effort and expense.  In
> my personal experience
> baluns, ferrite beads and tubes, etc. at wire antenna feed points or
> not never made
> a significant difference in what I could hear and who I could work.
>
> In the game since 1951
>
> Dennis D.  W7QHO
> Glendale, CA
>
> ***************
> On Jul 15, 2012, at 6:05 PM, Gary Schafer wrote:
>
>>
>>
>>> -----Original Message-----
>>> From: boatanchors-bounces at mailman.qth.net [mailto:boatanchors-
>>> bounces at mailman.qth.net] On Behalf Of Ron Youvan
>>> Sent: Sunday, July 15, 2012 8:30 PM
>>> To: boatanchors at mailman.qth.net
>>> Subject: Re: [Boatanchors] Ferrite Choke
>>>
>>>   Dennis D.  W7QHO  mac wrote:
>>>
>>>> Might be interesting to put the antenna up without any choke or
>>>> ferrite and see how it works out......
>>>
>>>
>>>   That is all that existed B 4 antenna baluns were created.
>>> The advantage of any kind of balun at the feed point of a dipole is
>>> to
>>> prevent a nearby object to
>>> one half of a dipole from unbalancing the antenna.  If it is equal
>>> lengths and really in the free
>>> and clear it does nothing of any great use.  Baluns can be made with
>>> powered iron also cores.
>>> --
>>>    73 Ron KA4INM
>>
>> Consider that a coax cable feeding an antenna is actually 3 wires.
>> Two inner conductors (center wire and the inside of the shield) and
>> the
>> third conductor is the outside of the coax shield.
>>
>> When connected to a balanced antenna, the center conductor is
>> connected to
>> one side of the antenna and the other side of the antenna is
>> connected to
>> the inner shield and the outer shield.
>> That makes the antenna have one leg on one side and two legs on the
>> other
>> side, one being vertical (the coax).
>>
>> This unbalances the antenna and causes current to flow on the outer
>> shield
>> of the coax which acts as part of the antenna.
>>
>> It may work very well in this configuration as many have for lots of
>> years.
>> The disadvantage is the vertical part can pick up more noise and put
>> RF back
>> into the shack on transmit. It disrupts the dipole pattern if you
>> care about
>> that.
>>
>> The commonly used balun acts as a choke to isolate the outer coax
>> shield
>> from the leg of the antenna that is connected to the shield.
>>
>> 73
>> Gary  K4FMX
>>
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