Re: NEC-LIST: Bazooka balun verification.

 Hi Tom,
         Thanks a lot for the detailed answer......really enjoyed it.
One point though......you had written........
"You can also tell a lot simply by noting
the feedpoint impedance for the excitation"

I dont have access to the excitation points of the balun which is why I cant verify the operation properly.Neither can I make an extension as the balun comes in an overmoulded assembly...

You are absolutely right regarding the impedance offered by the quarter wave section ...........its more like 500 ohm at 6oMhz.

Thanks for your comments ,
Regards,
George.

On Fri, 14 Mar 2003 10:07:03
 Tom Bruhns wrote:
>George,
>
>Consider what a balun is supposed to do. I assume you have access
>to both the input and output sides, just not the balun itself.
>So...if, at the frequency where the balun is supposed to do its job,
>you can make the extension beyond the balun resonant at the balun's
>operating frequency, and make the part below the balun (including
>also the outer surface of the balun outer conductor) also resonant,
>you can probe the current in each of those two resonant sections (by
>use of a toroid current transformer, for instance). Then you can
>excite the section beyond the balun, and see if the current in the
>other section is appropriately attenuated compared with the current
>in the excited section. You can also tell a lot simply by noting
>the feedpoint impedance for the excitation. Consider what it will
>be if the balun is working properly versus what it will be if the
>balun is not working.
>
>There are lots of other ways to get an idea of how well the balun is
>working, too. But in general, you'll be wanting to see, I suppose,
>if the balun chokes off a current which you excite on one side of
>it, and keeps that current from getting to the other side. Baluns
>are, generally, used to suppress antenna currents on conductors, no?
>
>By the way, I don't think a whole lot of that balun construction.
>Consider the impedance of the transmission line formed by the outer
>conductor and the middle conductor. I'll bet it's not very high.
>Considering the losses in that piece of line, what impedance does it
>reflect back to the open end? What value of resistance between the
>middle and outer at the point where they are supposed to be shorted
>together will cause the reflected impedance to drop below what you
>can tolerate?
>
>Cheers,
>Tom
>
>
>GEORGE VARGHESE wrote:
>>
>> Hi George,
>> Thats exactly what I cant do becos I dont have physical access to the balun.If I have access to the balun I have no problems at all........Is there a way by which I can probe and find the high impedance in a circuit without actual connection of the balun to the VNA?
>>
>> regards,
>> George
>> --
>>
>> On Thu, 13 Mar 2003 23:49:14
>> ghagn_at_erols.com wrote:
>> >I am not sure I totally understand your configuration, but you can try
>> >measuring the input impedance of the balun when the output is:
>> >
>> >a) Open circuited
>> >b) Short circuited
>> >c) Terminated with a 50-ohm resistor (non-inductive)
>> >
>> >This should give you some insight as to how the thing is working (or not
>> >working, whichever is the case).
>> >
>> >George
>> >
>> >P.S. If you get the same input impedance regardless of the termination of
>> >the balun, then it isnt working!
>> >
>> >Original Message:
>> >-----------------
>> >From: GEORGE VARGHESE rfengg_at_lycos.com
>> >Date: Wed, 12 Mar 2003 18:22:56 +1100
>> >To: nec-list_at_gweep.ca
>> >Subject: NEC-LIST: Bazooka balun verification.
>> >
>> >
>> >>
>> >> Hi All,
>> >> I need the Transmission line experts to pitch in with thier
>> >expertise
>> >> to my query..........
>> >>
>> >>
>> >> I want to fabricate a transmission line choke with the Belden 9222 triax
>> >> .The inner conductor and the inner shield layer of the 9222 will be used
>> >> for TEM wave propagation of the signal picked up by a transducer while
>> >the
>> >> outer most shield and the inner shield form a bazooka balun ( a quarter
>> >> wave length of line which is shorted at one end and open at the other).
>> >> When these are assembled with coax connectors and convoluted tubing, the
>> >> problem that I am facing is that, I dont have physical access to the
>> >outer
>> >> most shield layer as its not connected to any connector , and hence I am
>> >> not able to verify the operation of the bazooka balun as there are no
>> >> physical connections available to me where I can test after proper
>> >> assembly.
>> >> Do have any non destructive methodology by which I can verify the
>> >> performance of this unique balun without any physical access to the
>> >layers
>> >> forming the quarter wave choke?
>> >>
>> >> regards,
>> >> George.
>> >>
>> >>
>> >>
>> >>
>> >>
>> >
>> >
>> >_____________________________________________________________
>> >Get 25MB, POP3, Spam Filtering with LYCOS MAIL PLUS for $19.95/year.
>> >http://login.mail.lycos.com/brandPage.shtml?pageId=plus&ref=lmtplus
>> >--
>> >The NEC-List mailing list <nec-list_at_gweep.ca>
>> >http://www.gweep.ca/mailman/listinfo.cgi/nec-list
>> >
>> >--------------------------------------------------------------------
>> >mail2web - Check your email from the web at
>> >http://mail2web.com/ .
>> >
>> >
>> >
>>
>> _____________________________________________________________
>> Get 25MB, POP3, Spam Filtering with LYCOS MAIL PLUS for $19.95/year.
>> http://login.mail.lycos.com/brandPage.shtml?pageId=plus&ref=lmtplus
>> --
>> The NEC-List mailing list <nec-list_at_gweep.ca>
>> http://www.gweep.ca/mailman/listinfo.cgi/nec-list
>

_____________________________________________________________
Get 25MB, POP3, Spam Filtering with LYCOS MAIL PLUS for $19.95/year.
http://login.mail.lycos.com/brandPage.shtml?pageId=plus&ref=lmtplus

-- 
The NEC-List mailing list <nec-list_at_gweep.ca>
http://www.gweep.ca/mailman/listinfo.cgi/nec-list