[AMRadio] Re: Link coupling


rbethman rbethman at comcast.net
Wed Sep 5 20:22:24 EDT 2007


A.R.S. - WA5AM wrote:
> On 9/5/07, D. Chester <k4kyv at charter.net> wrote:
>   
>>> This brings up a thought I've had about link coupled tuners, of which I
>>> use.
>>>
>>> Of course I feed the 50 ohm coax to the link.  The center to one side
>>> of the link and the shield (ground) to the other.  What effect does
>>> the "link position" have on a tuner?  I suspect the link position
>>> (mine is rotatable) would affect the matching impedance to the coax?
>>>
>>> 73
>>> Brian / wa5am
>>>       
>>  If you have a variable link on the antenna tuner coil, there will be one
>> and only one critical degree of coupling that will give a perfect matching
>> impedance to the coax (assuming that impedance match is within the range of
>> the tuner).  Increasing the coupling will make the coax  see  too  low an
>> impedance, and decreasing the coupling will make the load impedance too
>> high.
>>
>>     
>
> Thanks Don, that's what I thought, and have indeed observed.
>
> 73, Brian
Yep!  That is "one" of the quirks with the BC-610 coil and link.

You can get yourself a pile of grief with these old girls!  They have 
some, shall we say "interesting" characteristics when you mess with the 
link coupling - AND - watch VSWR.

Then again, she'll get cranky dependent on the antenna system too!

I 'try' and stay away from the BC-939, and use tuned dipoles.  It gets 
out on the air better for me.  Some have great success with the "long 
wire" and BC-939.  I just do not have the house, property, and 
orientation, (N,S,E, & W), for that to do much good for me.

Bob - N0DGN


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